Guys with poly bushings in both their upper and lower control arms in here please

[JD]

For those of you that have them installed, has anyone had trouble with having a lot of vibration at higher speeds? I installed poly-bushed boxed uppers and lowers and a new solid rear swaybar and I'm getting a lot more vibration.

I had to make a run to Jax last night, and as soon as I get above 70 mph it starts to get very pronounced. When I got off I-10 after coming back this morning, I heard the throwout bearing doing a lot more squeaking that it used to. Perhaps the vibration has worsened the condition of the TO bearing, but I don't think that's the cause of the vibe. I'm going to try re-indexing the driveshaft after work today to see what improvement can be had there.

I just had the rear rebuilt in December with all new bearings, races, and seals (except for the axle bearings, but those usually emit a "dragging" sound not unlike worn out brake pads on rotors and I'm not hearing that)
I'm well aware of the increased NVH of poly, but this seems excessive. I don't think that it's vibration from the driveshaft or U-joints since I have a new aluminum D/S. The lower control arms are boxed stockers (non-adjustable) with poly bushings installed, so I think I can rule out a bad pinion angle due to incorrect CA length. Car handles well, though. Any idears?

[hobbstc]

Glad to hear you made it to Jax. I was waiting for a call to come get you off the side of the road after the LCAs fell out or the swaybar split. Even with the MM arms with spherical bushings I never had vibrations at speed. See how the re-indexing works out. Maybe the poly lowers are fighting with those uppers. Or maybe it's the lack of quads on there.

[JD]

Glad to hear you made it to Jax. I was waiting for a call to come get you off the side of the road after the LCAs fell out or the swaybar split. Even with the MM arms with spherical bushings I never had vibrations at speed. See how the re-indexing works out. Maybe the poly lowers are fighting with those uppers. Or maybe it's the lack of quads on there.

You've got to trust your own skills to participate in this hobby.

I dont think that the CA's are fighting each other, although I'll be glad to ditch the uppers once the TA/PB setup is on there. Perhaps it's the DS, but I kinda doubt it since it didn't vibrate during the 6 weeks I drove it with the alum D/S and the old lowers.

The quads don't really do much other than dampen the left-to-right rotation during launch, so I doubt that's it but anything's possible.

[hobbstc]

Ok, let's try this idea. It could be the rear swaybar. IIRC, it's physically rubbing on the arms. Not that you really want to take it off again, but maybe it's inducing vibration. Only other thing I can think of. Or the bolts we used on the arms.

[93zm6tally]

JD,

I run poly bushings in my front end, motor mounts, and rear. Never experienced additonal vibrations from any of these. I don't see how poly bushings could cause vibration at all. Are you maybe confusing increased "feedback" from the highway as vibration. Did you have the front end aligned after replacing these bushings, if you did the control arm bushings you need too. My car actually got smoother after replacing worn out bushings. I've got plenty of vibration now, but that's more from the rear end and spherical TA bushings than from the front end. Is it possible you lost the weight off of the driveshaft. Or more likely that you haven't had the car on that stretch of the road in a while and are "hyper sensitive" to the feel of the car after modifying it.

Mark.

[JD]

The changes made to the car since the last time it drove smoothly at speed (Friday) are:

Rear LCA's with poly at both ends
Rear swaybar
Rear springs with poly isolators top and bottom.

There's no vibration at all around town. It's only above 65-70 that it happens.
The old rubber spring isolators couldn't have been dampening vibration because they were almost falling apart. The old LCAs were 19 years old and the rubber couldn't have been helping in the handling department, but they could have been dampening some of the vibe.

I looked at it last night and saw that the new aluminum driveshaft has a white paint daub that isn't lined up with the white paint daub on the pinion flange (NO, I didn't install it the last time and somebody was a little careless). Perhaps lining them up or indexing it to a better point on the pinion flange will decrease or eliminate this. I'll keep you guys posted.

[JD]

Well, I went over to Paul's and had him re-clock the driveshaft so that the white paint daubs on the pinion flange and DS are lined up (well sort of, since the DS is a Ford Racing aluminum unit that didn't come stock on the '96 Cobras). Anyway, they were 45* off of one another. Now that they are as close as they can be, the vibration seems to be substantially diminished.

I don't know if there is a better clocking to use, but this one feels pretty good. The vibe is still there but it's much better. There are a bunch of other things that could be causing it, so they are my next mods:

Clutch - I've been putting this off for over a year. I've had the clutch sitting in my closet since last winter

Tranny- Needs freshening. Slight whine and I have to be careful shifting because of synchros that need to be replaced. I'm looking at my alternatives. The tranny and clutch are my priorities and will be addressed soon- very soon,

Axle bearings- Need to be replaced, and I may just jump to 31 spline and be done with it.

Rear tires- Chewed from when I had the softy springs in.

The poly bushings are probably transmitting all of the previously existing driveline vibrations much more clearly now than with the old rubber stuff. My next big mod will eliminate some of this. After that, who knows what I'll do. :wicked:

[93zm6tally]

The poly bushings are probably transmitting all of the previously existing driveline vibrations much more clearly now than with the old rubber stuff. My next big mod will eliminate some of this. After that, who knows what I'll do. :wicked:

Probably upgrade to a fast car, like a Chevy. :kinson: