Quick question - I know I read this in someone's post, but now it's not coming in a search. Do I want the more compliant rubber on the leading or trailing side of the frame mount?

TIA

 

Poly in front rubber on the rear.

Click on images from this Google search.

https://www.google.com/search?q=poly+and+rubber+t%2Fc+rod+classiczcars.com+&client=ms-android-americamovil-us-revc&source=android-home&source=hp&ei=SQVZZNyGMMHKkPIPjdm46A8&oq=poly+and+rubber+t%2Fc+rod+classiczcars.com+&gs_lcp=ChFtb2JpbGUtZ3dzLXdpei1ocBADMgUIIRCgATIFCCEQoAEyBQghEKABOhEILhCABBCxAxCDARDHARDRAzoLCC4QigUQsQMQgwE6CwgAEIAEELEDEIMBOgUIABCABDoLCC4QgAQQsQMQgwE6DgguEIAEELEDEMcBENEDOg4ILhCABBCxAxDHARCvAToICAAQgAQQsQM6FAguEIAEELEDEIMBEMcBENEDENQCOggILhCABBCxAzoRCC4QigUQsQMQgwEQxwEQ0QM6CAgAEBYQHhAPOgYIABAWEB46CAgAEBYQHhAKOgUIIRCrAjoICCEQFhAeEB1Q0Q9Y-akBYMe2AWgBcAB4AIABywGIAeIhkgEGMC4yNi4xmAEAoAEBsAEA&sclient=mobile-gws-wiz-hp

Well here’s my thinking. The rod is under compression as long as the car is moving forward, I’d put the compliant material in front.

I’ve noticed in actual practice, just putting new rubber on both sides with proper torque gives you wonderful ride and handling.  Having poly on either side, front especially makes for more road shock feel and noise in the wheel when you hit a pothole. 

Unless you’re racing and trying to keep very very tight suspension geometry in spec I can’t imagine why you’d put poly on either side of the TC rod mount. Like putting poly on the transmission mount. You want to hear your gears why? 

The poly in front will stop the control arm from moving backward on braking.  It gives more precision to the steering.  That's its only real purpose.  It started as a racing thing, people saw a market, and started making poly parts for anything that was rubber.

If you put poly in the back it puts side force on the tip of the rod as the suspension moves.  The rod actually changes its angle through that mount as the suspension moves.  You can move it by hand and see what happens.  Since yours is apart you could assemble the rod and mimic it.  Eventually the metal will fatigue and it will break off.  It will also creak and moan when you go over bumps.  It happened on my 76.  That was with old rubber in the control arm bushings.

Some people have said that they put poly everywhere and did not have any problems.  So it might be that the mix of poly and old rubber creates a problem.

And, finally, some people have drilled holes in the poly to reduce its overall stiffness.  But, of course, that just makes it more like rubber.

Ok many thanks for all the responses. Sounds to me like all rubber or poly on the front side is the way to go. I don't want to damage the rod by making the outer length unable to pivot through the travel range. 

On older Volvos that use caster rods, they have a large bushing on the body side to allow for rotational flex over suspension travel, and the resistance bushings are set into an ear in the control arm. X1/9's are setup like the Z, with a rigid mount at the control arm and the resistance bushings at the frame, just forward of the control arm instead of aft. Those wear the bushings rapidly, in the scheme of things 

Edited May 8, 20231 yr by HusseinHolland

I have poly on both sides and the extra stiffening didn’t have any adverse affects. 
maybe the later, heavier cars have more stress and need one side rubber. 

Two guys whom I know in the UK had their compression rods snap with a big BANG due to poly on both sides, so beware! This was not an isolated incident either. Fortunately both those guys were moving slowly and one of them had his go while going over a speed bump at an appropriate speed.

Poly on both sides makes it too stiff under it’s normal operation on a public road without billiard table smooth surfaces!

Imagine a paper clip being held in a vice and bent back and forth constantly - that’s basically what is happening.

I bought the special kit from MSA to replace my poly ones with and not only did it sharpen the steering but it got rid of the wandering under braking where the toe angles were changing.

https://www.thezstore.com/product/6551/tension-rod-tc-kit-70-887-zzx

In summary - Always rubber at the rear side.

Truly unfortunate that the suspension aftermarket suppliers are so biased toward 'performance' in their choice of the urethane grade they use for these bushings.  I suppose it makes sense for a 3000 lb + American muscle car or for competition use, but it's way too stiff for a small coupe of sportscar being used on the street and highway.