Can I get lowering advice using shims?

[BlueCorvette]

I have a 1985 with the Z51 option. I have the suspension disassembled and was thinking of changing the shim position to lower the car about 3/4".

The rear seems simple, just move the shims from top to bottom and you're done.

I read that you can just remove the front shims. Does anyone here have experience with that?

Looking at the rubber shim assembly on the front leaf, it doesn't look like it was designed to be messed with or disassembled. It looks like it was put on the leaf as one unit, sliding from the end and then stuck in place.

Also, doesn't the spring need room to flex up and down in the crossmember. Would taking out the top shims affect that?

Thanks

 

[BlueCorvette]

I found some info on this. I was mistaken, you can't just take out the front shims, you have to replace them with thinner ones.

They have an explanation here if you are curious:
1984-1996 Suspension Lowering Kit, 12 Piece Car Set From Mid America Motorworks

The ad says you can lower up to an inch, but it doesn't look like there are an inch of parts stacked on the front leaf shim assembly.

 

[BlueCorvette]

It turns out that for some reason my car does not have the long bar shims that sit above the rubber assembly. The link above was for lowering the front further than just taking those shims out.

 

[aboatguy]

I lowered mine back in 2005 and I used the wedges, and moved all the shims from the top of the spring to the bottom (sounds wrong but it lowers the car by making top of spring closer to the crossmember, I also cut the pads off the end of the springs which probably added at least a 1/2' to the drop. I have been daily driving my vette since 2004 and I have never regretted the drop. Here's an old thread on how low my car is


http://www.corvetteactioncenter.com/forums/archive/index.php/t-120065.html

 

[Hib Halverson]

I found some info on this. I was mistaken, you can't just take out the front shims, you have to replace them with thinner ones.

They have an explanation here if you are curious:
1984-1996 Suspension Lowering Kit, 12 Piece Car Set From Mid America Motorworks

The ad says you can lower up to an inch, but it doesn't look like there are an inch of parts stacked on the front leaf shim assembly.

The explanation of Mid America's kit is mostly BS.

Here's the straight story.

The amount of factory shims was to compensate for differences in spring rate consistency. Back then, the makers of the leaf springs could not be as consistent as was necessary to have consistent ride heights so GM developed this shim system for C4. The springs which were a little under the specified spring rate got shimmed a lot. The ones which were right on got shimmed a little and the ones which were a bit high got no shims.

In the front, you can remove all of the long aluminum shims. In fact, from the factory, there will be either no shims, one shim or two shims per side. In the rear, you can move all the shims on each spring mount from the top to the bottom of the spring but all the shims must remain. Do that and your car will be as low as the factory would build them.

As for lowering the car more than just removing shims, in the front, you can do that with the wedges most of those kits include. And in the rear you can do it with the longer spring bolts.

But...regardless of what ads for suspension products say, for a street driven C4, any lowering beyond the removing (front) or changing location of (rear) shims will excessively decrease ride travel. With a base car this can have the suspension hitting the bump stops in normal driving situations, especially if you have two people in the car. That decreases ride quality, obviously. As for the "improvment" in handing because you lower the CG, in theory that's true, but in practice on a street car, especially a car with base suspension, the actual improvement in handing will be small and difficult to perceive.

Now, on a car with Z51, because of that car's stiffer springs, you may not be on the bump stops as much, but, again, when you decrease ride travel an inch, you risk hitting bump stops more often, espeically in the rear.

For racing or very aggresive street driving on smoother surfaces, lowering a car with Z51 or Z07, along with suspension alignment for track use will usually make an improvement in at-limit handing.

I realize that one of the big reasons for lowering a car is appearance and not ride or handing and, for that purpose, those lowering kits sold by Mid America and others, are good choices. If you install them...just remember when you give up ride travel, the suspension will hit the bumps stops more often and when that happens ride and handling are degraded.

Lastly, when you lower the car, regardless of why your doing it, you must get the suspension realigned.

 

[BlueCorvette]

Thanks, that's great info.

I ordered and installed the replacement retaining brackets, and the wedges for the front spring. I also moved one of the rear fat shims from the top to the bottom and installed the longer bolts in the rear.

I have the engine out , so I can't really tell what kind of lowering will occur yet. An inch would be what I'd like, but with the stiffer Z51 suspension, it might end up less. I had no front shims at all when I removed the front spring. I rebuilt the suspension and put in new Z51 spec bilsteins, so hopefully that will control the wheel travel.

Do you know what limits front suspension travel? Is it just the shocks?

I started down this path because the replacement rear polyurethane bushings plus washers on the spring ends were fatter than the old rubber bushings. Combined with the increased rear spring rate of the Z51, the suspension seemed much higher than stock when I reinstalled the stock bolts.

 

[spro2395]

Could the shims be moved to the bottom of the front spring and trim most of the rubber off the top to lower instead of adding the wedges ?

 

[BlueCorvette]

Could the shims be moved to the bottom of the front spring and trim most of the rubber off the top to lower instead of adding the wedges ?

In short, no.

You need the wedges to protect the spring from damage as it flexes against the crossmember. The wedges replace the stock pivots, and should lower the car slightly.

If you install the wedges, then you have to remove the slack that creates in the retainers by shortening the retainers. If you have the old style stamped steel retainers you have to swap them with the new aluminum ones and trim to fit.

 

[spro2395]

In short, no.

You need the wedges to protect the spring from damage as it flexes against the crossmember. The wedges replace the stock pivots, and should lower the car slightly.

If you install the wedges, then you have to remove the slack that creates in the retainers by shortening the retainers. If you have the old style stamped steel retainers you have to swap them with the new aluminum ones and trim to fit.

Wouldn't trimming off let's say 3/4s of the stock rubber accomplish the thing? I do have the steel clamps on mine so who's a good vendor to source aluminum ones from?

 

[BlueCorvette]

What you are talking about is not rubber, it is a alloy and plastic pivot that sits in a rubber holder on the top of the front spring. So you can't trim it down. You remove the pivot, and slice off the rubber. Then you sand the 2mm rubber top stub that is left to get a good surface to glue the wedges onto.

mamotorworks has a clamp replacement kit for $80. Only one I have seen oline.