lowering and bump stop rubber question

[Martin71RS]

I installed Hotchkis leafs and QA1 coilovers on my 71 Camaro... today I put it back on it's wheels after a loooong time :bananna2:

I still need to finish the car and determine the ride height but it is pretty low.

What I would like to know if anyone modified (cut) the bumpstop rubber on the lower A-arm to allow the car to go lower. (and are there things I should know/think about?).

Thanks,
Martin

[MrQuick]

You have to or it will ride on the stops. Sometimes cutting will not do it cause there is a steel insert and rubber will not support well after a certain thickness.

In these cases I've used modified Energy suspension traction bar bump cushions. You can cut to fit. The same applies to the mid rear end cushion. On the outers you can either raise them or trim to fit.

[Martin71RS]

Thanks Vince.... I kinda thought so.....

(next on the list is new wheels with more BS)
Martin

[Marcus SC&C]

As usual there`s a LOT more to this than meets the eye. The LCA bumpstops are an integral part of the suspension and they have rate,just like a spring. They are in fact elastomer springs. Their rate is progressive,that`s why they`re usually conical. Cut the top off and the rate becomes much less progressive and the ride much more harsh when you contact them. The more you lower a car the more critical the LCA stops become,especially with the QA1 "coil overs". We get a lot of calls on those having coil bind issues at low ride heights. Removing the LCA bumpstops or trimming them way back is just asking for trouble with them. It should also be pointed out that since most of us on PT.com are more concerned with performance than "laying frame" and such nonsense that it`s quite possible to lower the car too much and ruin it`s performnce. One pretty good rule of thumb based on basic front end geometry is that you never want the pivot axis of the lower ball joints higher than the inboard pivot axis of the lower control arms. I didn`t say the arms have to be level. It doesn`t matter what angle the arms look like they`re at,the pivot/pickup points dictate the suspension`s geometry not the arms. Go past this point and the geometry goes wacky and the roll center starts to dart all over the place. Also bear in mind that the front end will dive under heavy braking so give yourself a little extra height to compensate for this,the last thing you need is your roll center going haywire when you`re hammering the brakes and throwing the car hard into a corner. If you can`t lower the car to your liking with the QA1s before you cross that point drop spindles or tall lower ball joints are possible solutions but neither are generally a great alternative on a `71 F body.
Modern progressive rate jounce bumpers can be a great tuning aid. GM spent millions to tune them for use on lowered applications like the S10 ZQ8 but we can buy them for $10 ea. :) They`re actually intended to contact the frame much of the time and have a much more progressive rate than old school rubber snubbers. Consider them before you cut the stock rubber snubbers up or replace the them with short poly ones which give you even less control over what precious little bump travel is left on a lowered car. Mark SC&C

[Martin71RS]

WOW, this is some good info Mark :cool: !
I will have to see the exact ride height (and balljoint height compared to pivot point) when I finish the car and will take your comments into account.
Thanks,
Martin

[MrQuick]

Good stuff. I always tried to get the bumpers to NOT touch the frame unless in an extreme jounce. Never thought it could be a factor in chassis tuning.

Good info as always.

You wouldn't have the gm PN's for said jounce bumpers would you?

[Apogee]

I got these numbers from another thread Marcus posted in a while back...just got my new ones from GM today for about $9.00 each. The first part number is firmer than the second, but I can't say by how much. I figured I'd start stiff and maybe try the softer ones later if they feel too harsh.

BUMPER, JOUNCE, FIRM, GM #15956547
BUMPER, JOUNCE, SOFT, GM #15989674

[MrQuick]

Thank you. How high do they sit from the LCA surface?

[Chevy350]

The bumpstops are quite popular over by the Impala SS crowd as well, works well with their lowered cars (suspension similar to the 2.gen F-body).

Picture of one here:
https://static1.pt-content.com/images/noimg.gif
The threads on the bottom are 3/8" UNC (9/16" nut), use as reference.

[TnBlkC230WZ]

Will these work on 3rd gen Nova's/1st gen Camaro's as well? I'm installing Hotchkis springs with a 2 inch drop. Would you recommend the soft for firm?

Glad I saw this or I might have bought those expensive, less than optimal urethane bumpers.

[PT Goat]

Just a quick note on the later style round (#15956547) bumpstops - I installed them on my '65 GTO last night and they contact both the spring and the tie rod, due to their shape. From the pics I have seen, the earlier style (#15989674) are rectangular, like the factory bumpstops. I'm going to try a set of those today and see if they clear.