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R320: Why Buy a Mercedes?

This AWD minivan is our new efficient family hauler.

This AWD minivan is our new efficient family hauler.

I know, I know, it sounds crazy that the guy who used to be so practical-minded would buy a Mercedes, of all things. Please allow me to explain!

First, the Suburban was requiring too much attention. The diesel conversion in a vehicle that complex required constant attention. Further, being that the vehicle was an aging, poorly-designed K1500 model, I was never happy with the handling or the brakes (yes, these are common complaints with the stock vehicle, so my conversion wasn’t the culprit). My wife was never comfortable driving it, either. When one of the rod bearings started making banging noises, I already had my eyes on a somewhat smaller vehicle as a replacement, one that would achieve 90% of what the Suburban did in a ready-made, well-integrated package. I don’t think that doing the conversion was a mistake, and I learned a lot that can be applied to future vehicles, but I definitely want to stick to simpler, lighter-weight vehicles where such a conversion can really shine. Perhaps something like a diesel sandrail or one of those common VW-TDI-into-Suzuki-Samurai swaps. We’ll see where I go in the future on this front, but I really want to pursue something where the swap results in an improvement over stock performance and things are kept simple and inexpensive. The Suburban cost me about $16k to build, and with all the systems I needed to integrate to make everything functional, it took about 18 months of my “free time.”

For those who are new to this blog, I currently own four turbo diesel vehicles. Call me strange, but I love torque and I demand good efficiency in my vehicles. The result is that diesels make a lot of sense. People will point out a higher initial cost of these vehicles, but I never buy new vehicles and when you look at used machines the cost of a diesel, typically, is not much higher. Especially not when you take the longevity of these machines into account. Maintenance may be more expensive, but I do my own maintenance. My vehicles are my #1 hobby, so I enjoy maintaining them and I absolutely refuse to go into debt to buy a vehicle.

R320 Rear View

There are some cosmetic imperfections, but this vehicle is mechanically solid and has a lot of potential.

This post wouldn’t be complete without bringing up the current car market. Are you looking for a new car? I’m writing this in May of 2017, and Peter Schiff’s latest update included information about manufacturers seeing worse-than-expected demand for their new vehicles. This is especially notable when they were already expecting declining year-over-year sales figures. So, the decline is worse than they thought. Don’t let Janet Yellen or her minions at the Fed fool you: this economy is on the precipice and we are seeing cracks in our biggest three economic bubbles in the United States (homes, autos, and education). These guys are playing a con-game with our economy and their “data-driven” approach to managing the economy (something which Austrian Economics shows can’t be done) is creating a mess. Without going further into detail on Austrian Economics (see Mises.org, or Contra Krugman, if you’d like to learn more), the bottom line is that lots of dealers have inventory sitting on their lots and now is a great time to find a deal. Further, that fact also affects the used car market and many used cars are ridiculously inexpensive right now. Given that I’m a person who prefers to stay 100% debt-free (yeah, I have a mortgage, but I’m working on that), this makes the capability that can be found in a used car a completely amazing bang-to-buck ratio!

So, still, the question is why I would buy a Mercedes. The answer is in the specs for this Mercedes minivan:

  • Spacious room for six, even the third row will comfortably fit somebody over 6 feet tall (though nobody in my family comes anywhere close to 6′).
  • The same 3.0 OM642 V6 turbo diesel that is used in the Sprinters and a slew of other Mercedes-Benz vehicles. A common engine means that its strengths and shortcomings are well-known and parts won’t be too terribly rare.
  • More on the engine: 398 lb-ft of torque!
  • 4-matic. How many minivans have all-wheel drive systems?
  • Combining this with the same seven-speed automatic and transfer case that are used in a number of other models, including the R63 500+hp fire-breathing R-class, the drivetrain ought to be bulletproof.
  • The machine is EPA rated at 28 mpg highway.
  • Depending on where you can find the information, the towing capacity is between 3500 and 4600 lb.

Does that sound good enough? How about this: I found one with somewhat high mileage (145,000) for less than $7k. It has its scuffs, dings, and a number of issues that need attention, but this is an amazingly capable vehicle for the price. With classic Mercedes vehicles going 500,000 miles, I expect that this machine will also achieve a long life with some minor adjustments and modifications, along with proper maintenance.

That leaves one more question: What about maintenance? Given the time and capability I’ve shown in doing the Suburban modification, I believe I can do what’s needed on this vehicle, too. Further, I’ve already purchased a knock-off SD Connect multiplexer and software, giving me the code scanning, reset, and recoding capabilities that the dealers have. Perhaps more, as the system I have includes Xentry with development mode and something called Vediamo, which is a development suite.

So, that gives you a quick background on my latest project machine. I’ll follow this with posts about some of the work I’ve been doing.

Meanwhile: may the Lord bless you and keep you running on all cylinders!

Suburban for Sale

Everybody, it’s been a long time since I’ve posted on here and I need to let you know that I’m making some changes in my life. Because I’m the father of two homeschoolers who are in their last couple years of high school, I can’t put the effort into the automotive hobby that I have in the past.

Yes, you haven’t seen much on here, because I wind up “just doing it,” and don’t have the time to take snapshots or even write blog posts about what I’m doing. I’d like to change that in the future, but that’s where I stand today.

I recently did a valve job on the Suburban’s 4BD1T with new valves, rebuilt rockers, and had everything professionally machined. I got it all back together, but now it sounds like something went in the bottom end of the engine. This really drove it home how much time I’m spending out in the workshop and I really need my 4×4 ready for winter. So, I’ve decided to sell it: http://indianapolis.craigslist.org/cto/5913573016.html

Meanwhile, I found a screaming deal on a Mercedes R320 CDI. This vehicle is basically an all-wheel-drive minivan with a 3.0 turbodiesel under the hood. These get 29 mpg on the highway and the engine has 400 ft-lb of torque at 1700 rpm. At the low price I paid, it’s no surprise that it needs a bit of work, but the drivetrain is solid and it’s driveable right now.

I intend to post information on the work I do to this vehicle and our other turbo diesels, but I’m really under the gun right now. Also, I need to roll up my sleeves on some political actions, and I intend to start sharing that again, too.

Free Book Until This Sunday!

The Kindle e-version of my book The Art of Diesel: Building an Efficient Family Hauler is free until this Sunday, the 12th of July 2015.

This book is primarily about why and how I put an Isuzu turbo diesel into a Suburban. The result is a large, capable, four-wheel-drive vehicle that is fun to drive and achieves 25+ mpg on the highway. Preppers might like that this vehicle has 1,000 miles of range and looks like any other 1999 Suburban on the road.

I manage to sneak a fair amount of libertarianism into the book, and I do my part to promote the concept of unfettered free markets. A couple readers complained about my politics, but the book still manages to get 4.7 stars out of 5 — so it stands on its own as a how-to/hobbyist/automotive book.

 

Diesel Suburban: New Leaf Springs

Leaf Spring Comparison

The new leaf spring assemblies (5+1) are much beefier than the ones they will replace (4+1).

The Diesel Suburban just got a new set of leaf springs.  I’ve been messing around with the suspension since the diesel was installed and running.  The vehicle has seriously handled like a pig — and it’s not just because of its size.  I’ve driven large vehicles that handled better than this one.

  • My first shot at improving handling was to replace all of my bushings with polyurethane.  It didn’t help.
  • I realized that because I’m using the Isuzu 4BD1T’s power steering pump, I no longer had speed-sensitive steering, so I increased caster to get more “feel.”  No improvement.  I may still consider a non-speed-sensitive steering box at another time.
  • I swapped torsion bars in the front end for a set that were a bit stiffer, and got some improvement.
  • I swapped tires, and got no improvement, except that the newer ones don’t follow grooves in concrete as much.
  • I put a larger rear sway bar in, but it didn’t help.
  • I put some air-pressurized shocks in the rear to stiffen things up, but I suspect that spring wrap was still occurring.
Spring Overlap

The new springs feature more overlap between the leaves, which will further stiffen the system.

As mentioned in the last item, I found out that some other large SUVs had problems from the factory, because they were shipped with light rear springs that allowed some rear steer which is caused by spring wrap.  These vehicles were fixed by adding radius arms, but they could have also been fixed with beefier springs.

Nobody complains about Suburban handling from the factory, except when they’ve run into issues with the speed-sensitive steering being out-of-whack.  Many bypass the feature to get predictable behavior.  A suburban with 170,000 miles and over 14 years on the road may have weak rear leaf springs and start behaving in a similar fashion.

I called around, and found Warner Spring in Indianapolis had the best deal on a pair of OEM-style leaf springs.  Some online locations might have saved me $20, after shipping costs were included, but the headaches of online returns when dealing with 200 lbs worth of springs helped me to go with a local shop.

Overload Leaf Comparison

The overload leaf on the new spring shown here is much beefier and longer than the other. This will allow more load-carrying capacity.

Though the springs from Warner were supposed to be a direct replacement, they are 5+1 springs, rather than the 4+1 springs my K1500 Suburban came with.  That’s OK, as I wanted them to be stiffer, and certainly feel that this Suburban was too lightly sprung from the factory.

When I got the springs home and removed the original springs from the Suburban, I set them down side-by-side and took a few photos.  The differences include:

  • A 5+1 setup, meaning that there are five primary leaves, plus a single overload leaf.  This overload leaf doesn’t engage until heavier-than-normal loads are placed in the rear of the vehicle.
  • Heavier leaf overlap.  The leaves on the original springs didn’t overlaps as much, meaning that there was a lot less spring at the ends.  The overlap on the new springs will add to the stiffness of the system.
  • Beefier overload spring.  The overload leaf on the new assemblies is much longer and thicker than on the originals.  This means that it will provide more load-carrying capacity for heavy loads.
New Leaf Springs Installed

The new leaf springs are installed. I still need to get the vehicle up to highway speeds to know if I’ve improved the handling.

I got everything installed on Saturday morning, but I haven’t had a chance to get the Suburban up to highway speeds.  I have some errands to run and a meeting to attend this evening, so I will report back on whether this finally fixes my handling problems.  I did notice that this lifted the rear end of the Suburban noticeably, and I may look at ways to counter that; including lowering shackles and cranking up the torsion bars a bit.

–Still learning things the hard way!

Diesel Tweaks: Performance and Fuel Economy

With a few inches of snow last night and crews that don’t seem too interested in actually cleaning road surfaces, the Suburban was in its element today.  It was very slippery early this morning, and it wasn’t much better when I came home late in the day.

I decided that if I’m going to be driving this machine, I should take some time to make a couple quick adjustments.  I decided to adjust the injection timing to tune for better fuel economy and to adjust the wastegate pushrod for more boost.

Injection Timing Markings

The marks show how the injection pump has been moved relative to the engine block.

When I bought this engine, the injection timing was set at approximately 8 degrees before top dead center.  To find this out, I disconnected the output connection for the #1 cylinder on the injection pump, primed the system, and slowly rotated the engine while looking for the point where the fuel would be released from the #1 port.  The 8 degree timing was an indication that this engine was originally retarded from the normal Isuzu specification of 13 degrees in order to meet California emissions standards.  Of course, I fixed that.  In the attached photo, you’ll see a row of three punch marks I made on the pump on the left side of the vertical joint shown.  On the right side, you’ll see a row of three marks which were in alignment with the three marks on the pump when it was still retarded.  When I set the timing to the normal Isuzu specification, I made a single new marking in that location.

In the photo, you’ll note that the pump has been rotated even further recently.  I thought I’d see if further advancement of the timing would help the engine’s fuel economy.  Given that that two marks on the right are about 5 degrees apart, I believe I advanced the timing another 4 degrees; taking the engine to approximately 17 degrees BTDC. It actually hurt the fuel economy by several miles per gallon, so I pulled all but about one degree of this additional advance out.  I’ll top off the tank, again, and watch my fuel economy for a few weeks, again, under a variety of conditions.

17mm Gear Wrench with Flex

This 17mm Gear Wrench with a flex joint near the end allows me to reach the top injection pump mounting bolt between the pump and the engine block.

When viewed from the front, rotating the pump counter-clockwise advances the timing, while moving it clockwise retards it.  The injection pump is mounted with four nuts on studs that have to be loosened to rotate the pump relative to the engine case.  These nuts aren’t easy to reach, especially the bolt at the top of the pump between the pump and the engine block.  To reach this, I use a 17mm Gear Wrench with a flex end.  When I get the flex angle just right I can use it to loosen and tighten that bolt.  I should find a ratcheting wrench with a smaller angle between clicks, because it’s so tight in this area that I can only get 1-2 clicks of ratchet between tightening or loosening movements.

I’ve been reading Dougal Hiscock’s thread on turbo sizing and performance predictions on the 4BTswaps website.  Dougal also provided performance predictions that made it into my newly-released e-book The Art of Diesel.  Looking at these, Dougal predicts that the maximum horsepower can be extracted from these engines by allowing the turbo to produce around 26 psi of boost.  Because I once experimented with disconnecting my wastegate, I know that

Threaded Wastegate Actuator Rod

The rod on the wastegate was cut and threaded. With this threaded coupler installed, I can now adjust the length to tweak my maximum boost setting.

my GT2259 will produces approximately 25 psi of boost measured at the manifold, after an intercooler that has about a 1 psi pressure drop (based on further experimentation).  When I previously tried increasing the boost above the wastegate’s 15 psi setting, I didn’t actually increase the performance, but I hadn’t backed out the fueling screw or removed the aneroid pushrod.  I have more fueling available, now, so perhaps the additional boost would be put to good use.  This shouldn’t hurt normal fuel economy, as 15 psi is rarely seen and the wastegate isn’t exercised that often.

I’ve threaded my wastegate’s arm and installed a sleeve nut to make the length adjustable.  Tonight I considerably shortened the length, and tomorrow I’ll see how much boost the turbo will provide.  Soon I should have some butt-dyno and mpg results to report.  I’ll get back on this soon!

Diesel Suburban Update: New YouTube Video

I had been asked by a few people how the Suburban was doing, so I thought I’d provide a video update. I asked my son for some help, and he brought out his video camera to take this footage. I know the audio is patchy, because that camera’s microphone is pretty sensitive to airflow — whether it’s wind or the Suburban’s vents. Oh, well, this at least gives you a feel for the “final product.”

Jetta TDI: A Quarter Million Miles and Counting!

Jetta: A Quarter Million Miles!

My Jetta TDI has reached a quarter million miles!

I have to share this! My 2001 Jetta TDI just reached a quarter million miles on the way home from work yesterday.  From the photo, it can be seen that I had over 500 miles on the tank and it was getting to be time to fill up, again.  I filled it up today, and calculated 45.5 mpg on this tank — that little turbo diesel keeps working like it’s new!

It’s a little funny, because I just realized that my lowest-mileage vehicle is the Liberty CRD with 138,000 miles on the clock.  Is it time to buy a newer vehicle?  Nope!  That’s why I own diesels:  Torque, longevity, and efficiency!  Who needs debt, anyway?

I should probably put some time into refreshing the Jetta.  Indiana backroads are a little rough on the exterior.  I see some strategically-applied bedliner and some fresh paint in its near future.  Perhaps I should also look at a top-mounted intercooler and some improved air delivery.

–Never enough time!

Diesel Suburban: Air Conditioning Version 2.0

When I build the Suburban and got it on the road last summer, I managed to maintain the deluxe system that the vehicle came with — though some modifications were required.

It has front and rear A/C units and they are both run by a single good-sized compressor under the hood.  On the Chevy 5.7, this compressor was mounted on the front-left side of the engine and used a serpentine belt.  Through experimentation, I realized that the existing lines could be used to mount the compressor on the right side of the engine.  I switched to the Sanden compressor I’m currently using because these are modular in design and I could swap the block on the back for one with different connections if I had to improvise.  More importantly, it allowed me to use a double v-belt pulley available, and I didn’t want to improvise a serpentine system.

Broken Tubes

Vibrations from the diesel engine destroyed these tubes on the A/C compressor.

Hot, humid summers are the norm in Indiana, and I got the A/C functioning right away on this machine.  I replaced the expansion valve in the rear unit, the orifice tube for the front one, and the accumulator/dryer.  After that, I added the right amount of oil, and charged it up with R-134a.  I got 40 degree air, and life was good.  It worked for a few months through the summer, and I didn’t have any issues until we were on our trip to Colorado last October.  That’s when one of the cantilevered tubes connected to the compressor broke.  I covered the pipe ends with some balloons to keep moisture out of the system, and we continued on our way to Colorado.  Thankfully, temperatures dropped for the rest of that trip, and we haven’t needed air conditioning again until recently.

Hose Assembly Attachment to Compressor

This is part of the new A/C line assembly. It attaches to the compressor using the bolt hole in the center of the block between the LOW and HIGH valves.  Note how much aluminmum tubing is held cantilevered — making this assembly quite fragile.

Recently, as things have been warming up, I decided it was time to fix the air conditioning.  I had been planning on this, and it was in my budget.  I ordered another hose assembly online for $90.  It’s important to note how the IN and OUT lines both attach at a single point, and that the aluminum tubes extend a long distance from these points cantilevered.  I don’t recall if they were supported on the Chevy 5.7, but I knew that these would break again if I didn’t support them.

So, I temporarily installed the new lines on the compressor, and started working with some angle iron I had laying around.  I ran one from the left-rear mount on the compressor to the lower bolt where the hose adapter attaches to the intake manifold.  I ran another across the two mounting points on the compressor’s right side.  I ran a piece of angle iron between these two, making a rounded cut in it to cradle the cylinder in the line.  I built a small outrigger for the right-side bracket to support the other cylinder.  I put notches in the appropriate locations for some hose clamps I had laying around.

Brackets Supporting A/C Tubing

It’s not easy to see in this photo, but the tubes are now supported by angle iron brackets and hose clamps. Further protection from vibration is offered by the EPDM rubber strips between the hose clamps and the cylinders.

The lines and the angle iron brackets were installed, marked, uninstalled, reinstalled, etc. until I thought everything was right.  Then I painted the angle iron components black.  When the paint was (mostly) dry, I did my final installation.  I put the brackets in, tightened the bolts, then put the lines on.  I didn’t want metal hose clamps scuffing or creating any pinch points on those aluminum cylinders, so I used some EPDM sheet to help spread the loads.  I tightened the clamps to make things snug, but didn’t overtighten them.

Since then, we went to a John Birch Society event in Columbus, Ohio.  On the way back we checked the fuel economy and found that we were getting 26 mpg on the freeway.  The engine is running smooth, the A/C is operating great, blowing 40 degree air, and life is good, again!

Aneroid Pushrod Removal

Aneroid on the back of my fuel injection pump.

This is the aneroid that I chose to disable.

A few days ago I removed the aneroid pushrod from my injection pump.  The 4BD1T in my Suburban is a direct, mechanically-injected system that requires no electronics.  Combined with the NV4500 5-speed manual transmission, this makes for a drivetrain that requires no electronics to function.  In an encounter with an electromagnetic pulse (EMP) or high power microwaves (HPM), most vehicles will be completely unusable.  The Suburban might lose the dash instrumentation, the radio, and the ability to shift in/out of 4wd because all of these things use solid state electronics, but it would still be drivable.  Chances are that this will never matter.  The real benefit of mechanical injection is that it’s simple and somewhat adjustable without expensive tuning equipment or programs.

After I replaced the stock turbo with a Garrett GT2259, the engine can produce much more boost than the fueling justifies.  Recall that, on a diesel, fueling dictates power while boost keeps the exhaust gas temperatures in check.  So, a turbo is a safety feature to protect the engine from high-temperature damage.  So, with the wastegate set the way it was for a Hino truck, I get a maximum of 14 psi and I get it by around 1800 rpm.  I have an EGT gauge on the A-pillar, and I know that my temperatures are never at dangerous levels.  So, I know I can get away with more fueling without damaging anything.  Provided that my foot isn’t heavy all the time, it shouldn’t hurt my fuel economy in normal driving, either.

Many who have transplanted the 4BD1T into other vehicles have pursued larger injectors and a modified injection pump to increase their fueling.  Reworking the injectors could easily cost $500 and the injection pump modifications start at twice as much.  I’m not ready to pay for these increases, but I would like a little more fueling for better performance and driveability.

Removing the aneroid

I removed the aneroid with a 27mm wrench.

The aneroid is a barrel shaped device with a nipple on the back of it hanging on my injection pump.  This device contains a diaphragm that senses ambient air pressure and adjusts fueling appropriately.  At high altitude, this limits fueling to ensure that the engine won’t be hurt by high EGTs.  This pump doesn’t have a boost compensator that would increase fueling when boost pressures increases, so this injection pump has no clue that this engine has a lot more turbo than it originally had.  Stock fueling curves — even with the fueling screw backed out all the way — is a little weak.

Because this device limits fueling, it turns out that it may even be limiting fueling at sea level.  Several people on the 4BTswaps boards have said they got better performance with the aneroid pushrod removed.  I’ve been meaning to do this for awhile, but I finally had a chance to do it.

aneroid removed

This is the aneroid removed from the injection pump.

I got out my 27mm wrench and loosened the locknut on the aneroid.  Then, I was able to twist the aneroid to unscrew it from the back of the injection pump.  When it was out, I mistakenly thought that the the pushrod to be removed was the one that extends from the inside end of the device.  After starting disassembly of the aneroid, I realized that there wasn’t an easy way to get rid of it, though I could take the caps and locknut off the outside end and adjust the aneroid to back it out as much as possible.  Removing the pushrod was still the objective — in order to assure that this device doesn’t limit my fueling.  After doing some more reading, I realized that the pushrod others have removed must still be in the injection pump.

pushrod & aneroid

Here’s a shot of the pushrod laying next to a partially-disassembled aneroid.

I put my finger into the cavity where the aneroid attaches and found a button that felt like there was a spring on the other side of it when I applied pressure.  I realized that this must be the pushrod, but I couldn’t get my fingers onto it to pull it out, so I withdrew it with a magnet.  I reassembled the aneroid and reinstalled it in the back of the injection pump.  I set the pushrod aside in case I decide to reinstall it at a later date.

I drove the Suburban to work on Friday morning and noticed faster rises in turbo pressure and a little more responsive torque from the additional fueling.  Exhaust gas temperatures are still extremely safe, so I’m not worried about damaging the engine with this modification.  I can certainly do more to increase fueling, but this sure was a cheap and easy way to get a noticeable difference!

–Putting the “engine” back in engineering!

Cruise Control: Finally!

I was hoping to get cruise control installed before our trip to Colorado in October.  It wasn’t strictly necessary, however, and I was still addressing a number of other handling-related issues.  After driving 1200 miles each way without it, I kept it on my TO DO list as a priority.

Today I finally got around to it.  I had purchased a replacement connector, thinking that I had cut it off by accident, and did the same thing I did with most of the fuel-injection related components.  For all the connectors I didn’t need, I cut them off and simply to taped the wires up, tucking them away in case I had a need for the circuits later.  It pays, before cutting off a connector, to ensure that you know what it’s for, first!

I spent a few hours yesterday digging into my wiring harnesses looking for a set of nine wires that would be connected to this ten-pin connector.  The first wire, and the easiest to identify, is the gray one that turns the power steering unit on.  Whenever I thought I had found it, I hooked up a voltmeter, flipped on my ignition switch, and toggled the cruise control on and off using the controls on the stalk.  After about three hours of looking, I gave it up last night.

With a fresh mind on my afternoon off today, I spent some time looking at a harness that goes back behind the engine, thinking it might be buried back there.  It was a painful process and I scratched up my arm on some sharp edges, but I didn’t find it.  Not all pain is gain!

Cruise Control Module

The Suburban’s original cruise control module was reinstalled.

I decided to start at the steering column and trace where these wires wend.  I could tell that the bundle was passing through the firewall on the vehicle’s left side by the convenience center.  I looked at the bundles on the outside of the firewall, identifying where each one went, knowing that I had missed something.  When looking at a few bundles going under the fuse/relay center, I found one that didn’t seem to be attached.  I pulled on it and found myself staring at the connector I thought I’d cut off!

So, I reinstalled the Suburban’s original electronic cruise control module on the firewall.  I chose to see if the original cable could be modified to work with the 4BD1T, rather than trying to build an entirely new one.  Recalling some aftermarket cruise control installations I’ve done in the past, I picked up some pull chain components from Rural King.  I also salvaged a part that attaches a pull chain to a bolt that

Pull-Chain and Cable Stops

Pull-Chain and cable stops were used to connect the cruise control linkage to the throttle. Note the angle-aluminum bracket used to hold the sleeve.

was still attached to the lower side of the bellcrank in the throttle linkage.  By flattening one side of a coupler and drilling a small hole in it, I was able to slip it over the stock cable and keep it from sliding off with a cable stop.  I used the bolt-to-chain coupler on the other end, using the cable stop that grabs the throttle linkage cable.  The pull-chain is a great idea, as it ensures that the cruise control system can only pull on the throttle lever, and cannot keep the driver from applying throttle when needed.

I also cut a piece of angle aluminum and made a square (12mm x 12mm) hole in it so that the cable sheath could snap in place.  When I got this together, I checked to see that the pull chain wasn’t long enough to droop and touch the glow plug rail.  I’d hate to have a short here!

This morning, when I was still at work I realized that I really needed to add a switch to this system.  Because the Suburban was originally equipped with an automatic transmission, I needed a switch that would sense when the clutch was being used and cancel the cruise control.  The brake pedal has two inputs to the cruise control system.  One is normally open, and the other is normally closed.  Either one will cancel when switched from the normal condition.  The normally closed one is what got my attention.  By running this through a second normally-closed switch, either switch will cancel the cruise control.

Clutch Switch

This is a clutch switch that matches the 2000 K2500 pickup clutch assembly I used. It snapped in place perfectly and provided normally-open and normally-closed connections.

My clutch assembly is from a 2000 K2500 pickup, so I looked for an appropriate switch and picked up this odd-looking device on my way home.  The white plastic piece pops off, and this switch snaps onto the clutch pushrod.  The white part snaps back into place to lock it on.  When I got under my dash with it, it was obvious how it would fit and it was a perfect match.  Connections on the end provide normally-open and normally-closed connections.

I spent a fair amount of time looking for the appropriate purple wire under the dash.  When I thought I had it (several times), I used a test light with a needle point that can dig through the wire’s insulation and a ground clip to check.  I was looking for a wire that would give +12V with the ignition on, but would shut off when I touched the brake pedal.  When I found it, I cut the wire, added some extending leads, and put the normally-closed portion of this switch in series with the brake switch.  Now touching either the brake or the clutch will result in an interruption of this signal, canceling the cruise control.

With these components installed, I went for a short test drive.  I got the Suburban above 30 mph, turned the cruise on, and hit the set button.  At first I thought it wasn’t working, but then I started climbing a hill and the vehicle maintained speed.  Clutch use canceled operation, brake use canceled operation, coast and accel/resume functions were working.  Mission accomplished!

-Time for some holiday travels to try it out!