Horrible vibrations after switching rear to coilovers

[Crashburndie]

Hey everyone,

I just took the car (MK 1) around the block before the snow comes in the morning and it started vibrated violently from the rear end. This is the first time I've had it out since I've changed it from the 4 strut rear (2 vertical 2 horizontal) to the VPM Coilovers. So I'm guessing this might be the issue but I wanted to run it by you guys first but at the same time I have read on several different places on here that once you put coilovers on the rear you can get rid of the horizontal struts. I didn't change anything else, the only other thing I can think of is that the rear sits lower and thats changing the angle of the trans/rearend. What would you guys suggest to track down the cause of this?


Thanks
CBD

[jlfernan]

Not an expert,but if the rear is sitting lower, you need to reset the pinion angle. The driveshaft is probably binding. Fix it before you break it.


http://img193.imageshack.us/img193/2561/jorgec.jpg (http://thefactoryfiveforum.com/private.php?do=newpm&u=111)

[Jeff Kleiner]

Yep, pinion angle.

Jeff

[Crashburndie]

I believe its the 4-link stock setup. Here is what it looked like under there before I changed to the coilovers

http://i1117.photobucket.com/albums/k588/parksrm/Cobra/DSC00537.jpg

http://i1117.photobucket.com/albums/k588/parksrm/Cobra/DSC00546.jpg

http://i1117.photobucket.com/albums/k588/parksrm/Cobra/DSC00543.jpg

[Crashburndie]

[QUOTE=Wantin2b;48902]Does the above post mean that you changed from Mustang shocks & cut Mustang springs to the VPM coilovers?

I used the springs that came with the coilovers. here's the link. http://www.vintageperformancemotorcars.com/carrera_coil.htm

[Crashburndie]

so I used my iPhone App to measure angle degrees it said neg 5.6 degrees and from what I read it needs to be closer to neg 3 deg. here is a picture of where I measured at.
http://i1117.photobucket.com/albums/k588/parksrm/Cobra/photo.jpg

now to figure out how to adjust the angle...

[Jeff Kleiner]

so I used my iPhone App to measure angle degrees it said neg 5.6 degrees and from what I read it needs to be closer to neg 3 deg. here is a picture of where I measured at.
http://i1117.photobucket.com/albums/k588/parksrm/Cobra/photo.jpg

That is not your pinion angle, it is driveshaft angle. When we speak of pinion angle we are referring to the pinion shaft relative to the transmission's output shaft in their horizontal axis.
My method for ease of measurement:
Set ride height then put the car on jackstands so that the axle is loaded. We don't care if the frame is dead nuts level; we're only going to look at the difference between output shaft & pinion. We know that the crankshaft and trans output shaft are parallel therefore the face of the damper/ crank pulley is perpendicular to the output. We also know that the pinion flange face is perpendicular to the pinion. See where I'm heading? For me it is easier to get a good measurement with the magnetic angle finder by reading vertically on the crank pulley/ damper and pinion flange rather than trying to work with the horizontal shafts themselves. Once you can see the two angles you can then calculate the difference. Generally with these cars we want the pinion down ~1-2 degrees (meaning the input is pointing down). Reason being is so that when the axle tries to rotate it's input upward under accelleration the pinion angle becomes less. This rotation is especially more pronounced on a 4 link car using the soft rubber bushings in OEM Mustang arms vs. a 4 link car with poly bushings or a 3 link with polys in the lowers and the solid upper link.


now to figure out how to adjust the angle...

Three link is easy; simply alter the length of the upper link however with a 4 link using non-adjustable upper arms you can not change the angle of the rearend. If you raise the rear of the transmission though it has the same effect as tipping the front af the rear axle down (making the pinion angle less, or more negative). Lowering the rear of the trans has the opposite effect.

That explains pinion angle but doesn't answer why you developed a vibration. If you returned the car to the same ride height the spring change should not have introduced it. Did you make a significant change to the rear ride height? Got any shiny spots showing in the driveshaft yokes indicating that they have bound? Have you checked your u-joints for wear?

Sorry, that's all I've got right now.

Good luck,
Jeff

[oldguy668]

He has a four-link, not a 3-link, so he can not adjust the pinion angle. Having him going crazy measuring it solves nothing. He said in his first post that the ride height was lower than before, so the solution is to adjust the ride height back to the original setting.

[lbperry]

CBD;
It might help to have some pics of what everything looks like now after the mods. Something may jump out at us that looks out of whack.
Good Luck,

[AJ Roadster NJ]

Several comments;


CBD, can you confirm for us that when you referred to "struts" that you meant the shocks, as opposed to control arms? All four control arms, of course, need to stay regardless. (Sorry if I'm stating the obvious but sometimes you'd be surprised what we see here.) So in your first pic, the blue quadshock (horizontal) goes away, the white shock gets replaced with the coilover, and the two control arms on each side (black) remain in place.
All coilovers allow rideheight adjustment. I concur with others that getting that set correctly is probably going to solve your problem. I use about 4.75" to the bottom of the framerail.
Regarding pinion angle, the only way to adjust that on your car is by shimming the trans mount (or by removing shims if they are already there). For reference, with my Tremec 3550 and the normal Ford 8.8" rear end, I used .50" of shim between the frame and the trans mount to get my pinion angle. Don't putz with this AT ALL until you get your ride height correct, and see if it still makes noise.



HTH.

AJ

[Crashburndie]

AJ,

Yes I meant shocks, I left both the upper and lower control arms in place, removed the blue shocks and replaced the white shocks with the VPM coilovers. I will try changing the ride height and see if that takes care of it. Thanks for all the replies.

[Crashburndie]

I think I have figured it out, when installing the new coilovers I followed the instructions sent to me word for word. No where in there did it say anything about removing the original spring perch for the quad-shock system. I read on another thread that they are not needed now. I'll report after I take them out, thanks again forum

[first time builder]

I assume you took out the old springs. How long was the car sitting since you last drove it, total prior to and after the modification? I know if my car sits in one spot for a long time, the tires tend to get a flat spot (especially in cold weather) . When I take the next drive, I get a bad vibration untill the tires warm up.
Just a thought !!

Kenny

[Crashburndie]

found out that it was the driveshaft that was binding, once I removed the spring perch and spring that allowed the angle of the u-joints to change thus no more vibration/knocking.

[first time builder]

Originally , when you installed the coil overs ,you didnt remove the old springs ?

Kenny

[Crashburndie]

Originally , when you installed the coil overs ,you didnt remove the old springs ?

Kenny

Correct, I wasn't aware that the needed to be removed. Once I removed them both, the driveshaft binding stopped occurring.

[AJ Roadster NJ]

Yikes. May I suggest that you post pics now, with the old springs removed, so we can do a rough review of the installation for you? I would be particularly interested in both the lower and upper coilover mounts, the coil placement over the shock, and the restraining cables. Think of us as friendly quality control helpers to make sure it's all good. Even when everything is perfect, these cars have an evil streak in them, and you don't need anything to be out of whack.

AJ

[AJ Roadster NJ]

When you say you removed the "perch", what does that mean? The top perch for the stock spring is a spiral thingy welded into the frame by FFR. The lower perch is part of the lower control arm, and must stay in place even when the spring is removed.

The one and only piece to come out of each side should have been the spring itself, nothing else. Can you confirm that only the springs came out? Just trying to keep you safe man.

AJ

[Crashburndie]

Here are some pictures of what it looks like under there before I removed the quad-shock springs. Yes only the spring itself was removed, the spring perch is welding in place and I didn't feel like cutting it out.


http://i1117.photobucket.com/albums/k588/parksrm/Cobra/DSC_0133-1.jpg

http://i1117.photobucket.com/albums/k588/parksrm/Cobra/DSC_0132-1.jpg

http://i1117.photobucket.com/albums/k588/parksrm/Cobra/DSC_0131-1.jpg

http://i1117.photobucket.com/albums/k588/parksrm/Cobra/DSC_0130-1.jpg

[Crashburndie]

Here is a picture of the driveshaft binding that was occurring. I didn't take a picture of it before I removed the spring, sorry about that.

http://i1117.photobucket.com/albums/k588/parksrm/Cobra/DSC_0190.jpg

[Crashburndie]

Something else I'll add - Also when the quad-shock spring was still installed and all the wheels were on the ground, the coilover springs weren't' compressed which I thought was weird. Now the the spring is removed the coilover springs are compressing properly.