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!

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