Hello - looking for information on the insights in replacing the dog bone bushings. Have an 89 coupe, was bone original, i am 2nd owner. 50K.

Replaced sway bar bushings and now looking to replace the rear end OEM bushings with urethane. Have not done rear carrier bushings yet.

Any tricks on taking out original dog bone rubber bushings and replacing urethane bushings? Other considerations?

Appreciate any information.

 

You don't really want to use a poly bushing in the dog bone as it will cause binding. That being said to remove the original bushings, a simple hydraulic press will work just fine. If you don't have one I'm sure a local shop would be able to press them out. Iirc there are a couple videos on YouTube for going through the suspension bushings on these cars to give an idea.

 

^^^ Agreed. The Super Pro bushings are a softer, more compliant urethane that should work well. Stay away from the normal hard urethane like Energy Suspension in the rear of a C4, though.

 

Once again, the forum prevails. Thanks for the info.

I am curious on the dynamics of bushings. What i glean from the caution on urethane is the bushing are too stiff to allow the suspension to absorb the transfer of energy....and the harder bushings will cause other pieces to fail due their (bushings) rigidity. Is this interpretation close?

Thanks to all. My 89 coupe has orginal bushings...i suspect they are tired and the rubber used in the OEM applications should be replaced or upgraded. The car seemed to be cared for and i am the 2nd owner...49K in miles when i bought it. Thoughts?

 

Not really. Imagine just one dogbone on the car for a moment. It has a urethane bushing and is bolted to the frame bracket in the normal way. the other end (knuckle end) easily swings up and down as the dogbone pivots around the bushing bolt at the frame. As it does so, the knuckle end actually moves in an arc rather than just up/down in a straight line, right? So the end is moving up/down plus backward and forward as it goes through that arc, effectively shortening the wheelbase when it's not parallel. So far, so good. But if you try to pull the knuckle end of the dogbone left or right, it will resist doing so quite a lot, right? Because the bushing only freely allows one axis of rotation.

Now consider the lateral camber rod. It also swings around an axial bushing at the diff, but its arc is in a plane 90-degrees to the dogbone's arc. When the knuckle end of the camber rod moves up and down, it also moves left and right instead of the backward and forward. So it's effectively shortening the track width of the car when it's not parallel. If you try to pull the knuckle end of the camber rod toward the front or rear of the car, it will resist moving that way, right?

So the problem is that camber rod is trying to move the knuckle end of the dogbones left and right when the suspension moves, and the dogbones are trying to move the knuckle end of the camber rod forward and backward. And in both cases, the very stiff poly bushing is resisting that off-axis movement with a lot of force. That extra force required to overcome this resistance adds to the spring rate in a rising-rate fashion. That's bind. Roll resistance and pitch/heave resistance in a suspension are supposed to only come from the spring and swaybar. But now the force required to overcome the bind is adding to it, progressively, that means your car gets more and more tail-happy the more it leans or brakes - exactly what you don't want. Snap oversteer is the result.

This is why all the bushing kits made from Delrin aren't even offered for the rear suspension. Delrin is even harder than poly. But poly is hard enough to cause evil handling. Stock rubber bushings are compliant enough to minimize such bind cheaply. Probably the Super Pro ones are, too. Rod ends are ideal because they offer free movement in all planes around a single point (up to their limits of travel), but they aren't always the ideal solution for several reasons.

 

Just to sum up what Matthew said in my own dumb manner (how I justified superpro to myself), traditional poly only allows rotation around the sleeves axis, which is why you can torque a polyurethane suspension unloaded. The rear on these move in several planes and the poly being harder doesn't allow for that lateral movement. Now the superpro parts are egg shaped around the outer part that resided in the suspension components shell... so the bushing itself can rotate against the sleeves axis of rotation, kind of like a pseudo spherical bearing or heim joint.

I can say so far I love the superpro and that the suspension is actually more compliant that it was stock. (Predictable, less jerkey, tracks the road better and joints and ruts are less jarring.) Also, no suspension squeaks unlike other vehicles I've had that have poly components.

 

I've purchased a few sets of dogbones with fresher rubber bushings... one solution to consider, and there seem to be reproductions which I've found a while back but never ordered (one of the Corvette Catalogs) .... after that I installed Super Pro bushings on one end (chassis) and pressed in a monoball on the other (upright). I think Super pro on both ends is fine, the QA1 Monoball I suspect would wear out fairly soon, but i never had the chance to find out. Superpro grease is real slick unlike the very sticky urethane versions which have no place on the dogbones of course.

I wanted clearance for 12" wheels and as they would hit the dogbones, went to a aurora/heim joint rod end setup to allow for more clearance. Problem with Heim is that the arms are constantly moving quite a bit as we drive, under load, so they can wear out VERY quickly. Medium quality ones ($40) seem to last a 1,000 miles at best before it starts to develop excessive play (easy to check rotating the uprights for and aft with spring loosened up, Aurora CB/CM series for example). For a little bit better results, get the higher quality and expensive ones such as Aurora AM10 AB10 (with inserts/spacers added to the fronts) and they will last maybe a few years ($800 worth to keep in mind what we're talking about). Need about 15+ degrees of misalignment capability or they will have a short life and loosen up the threaded rods, check at full droop.

 

All, thanks for the education. The explanation is fairly straight forward, and while i am under the car it will help to see the connections and linkages and the movements.

No autocross, racing, just a DD that i want to tinker and improve aspects each year and keep it in the best shape i can. Again, appreciate the explanations. Thank you.

 

On the rear, it's pretty easy to remove the nuts from one end of the spring. Then you can use a small jack to run that corner of the suspension through it's entire range of motion and see what's going on.

For that use, I would say either use the SuperPro bushings or new OE dogbones with rubber bushings. Either should work well. Beware that all the stock dogbones I've seen out there from the usual Corvette parts places actually have black urethane bushings, not rubber. So be sure before you buy anything.

 

Good point, i see that most if not all replacement dog bones come with black urethane. I am a gluten for punishment and will likely replace the old bushings on the ones i take out with SuperPro products.

I see there are replacement upper and lower arms that have adjustable "heim" type ends with urethane bushings as well. These parts would yield the same "binding" issues - correct....to be clear?

Thanks again for the insights!

Best,
Warbear.

 

Are we still talking about rear suspension links? I'm guessing you're looking at the Van Steel strut rods with poly axial bushings but threaded length adjusters with jam nuts? If so, then any "axial" bushing (a single plane of rotation, like around a bolt) will cause bind, even if it's just at one end of the link. For the front suspension, the upper and lower controls only move in one plane, so poly or even Delrin bushings there are just fine.

 

Yes, rear control arms (dog bones).

Got it on the loading on single or multiple axis.

Great discussion. Thank you!

 

Banski still make rearend suspension pieces for our C4. It would put you more in an extreme change, but I have heard nothing but great things when people installed them.
This talks a little about the binding, first blue link..
https://www.banskimotorsports.com/c4-irs.html

 

Do the 1996 Composite Dog Bones have any advantage over the Aluminum ones ? I see my 1990 project car has them on one side along with a small fiberglass repair to one of the storage compartments. Makes me wonder if they were sold across the parts counter as a service replacement. So I am now "Upgrading" the other side to Composite. What was the General thinking when they made this design change when they knew the C5 was late and they were going to make C4s in 1996 after all.

 

Contract ended so they found someone quick to make them? Wanted to test composite for the future? It was cheaper? I don't think I've ever really seen or read of a real explanation from the source as to why the composite parts exist. I don't seem to recall there being a real reported issue of strength in them on normal driven vehicles either. Though I do recall an older thread where it did break. Granted it was at the strip...