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Formerly known as jbj302
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Discussion Starter #1
Not sure what’s causing this, although I see it’s a widespread issue. The vibration will start around 70mph and up. Pushing the clutch doesn’t change anything.

I’ve swapped the driveshaft and nothing changed. Transmission(3550) has been fully rebuilt by promotion.

Any ideas?


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I have a 3550 in my 1990 LX convertible and experienced vibration issues. However, my vibration was more rpm/load dependent but would seem to change depending on certain factors (weight in car, weight in trunk) which told me it must be pinion angle.
The 3550 sits lower at the rear unless you use spacers at the mount but in my situation, because the tunnel is tight I could only raise it so far. The solution is to lower the pinion angle at the rear end to be within .5 degree of the angle at the transmission (U shaped driveline). It helped my situation tremendously however I am still chasing a slight vibration.

This is a great reference below on how to set it up, and also explains U vs Z drivelines.

https://forums.corral.net/forums/general-mustang-tech/1917082-driveline-pinion-angle-configuration-lowered-cars.html

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Formerly known as jbj302
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Discussion Starter #3
I have a 3550 in my 1990 LX convertible and experienced vibration issues. However, my vibration was more rpm/load dependent but would seem to change depending on certain factors (weight in car, weight in trunk) which told me it must be pinion angle.

The 3550 sits lower at the rear unless you use spacers at the mount but in my situation, because the tunnel is tight I could only raise it so far. The solution is to lower the pinion angle at the rear end to be within .5 degree of the angle at the transmission (U shaped driveline). It helped my situation tremendously however I am still chasing a slight vibration.



This is a great reference below on how to set it up, and also explains U vs Z drivelines.



https://forums.corral.net/forums/general-mustang-tech/1917082-driveline-pinion-angle-configuration-lowered-cars.html



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Thanks. That’s good information. I’ll give it a try. So what’s your pinion angle? Mine is at -2°. I have solid upper CA and poly/solid lower


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Thanks. That’s good information. I’ll give it a try. So what’s your pinion angle? Mine is at -2°. I have solid upper CA and poly/solid lower


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I can't remember where I had it set at the moment, but I did not have my car sitting level when I checked it. It is not so much what the pinion angle is (unless it is extreme) but the difference between the angles at the trans and the rear end.

Did you use any spacers at the trans mount?

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Formerly known as jbj302
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Discussion Starter #5
I can't remember where I had it set at the moment, but I did not have my car sitting level when I checked it. It is not so much what the pinion angle is (unless it is extreme) but the difference between the angles at the trans and the rear end.



Did you use any spacers at the trans mount?



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I did not. It’s been a while since I put the transmission back in, but I do not remember adding any spacers for any reason


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I did not. It’s been a while since I put the transmission back in, but I do not remember adding any spacers for any reason


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They maybe your issue, I know in both my 88 hatch and my 93 coupe I had to use a stack of washers to space the trans up enough to cut down the difference in angle
 

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Formerly known as jbj302
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Discussion Starter #7
They maybe your issue, I know in both my 88 hatch and my 93 coupe I had to use a stack of washers to space the trans up enough to cut down the difference in angle


So what does this do to your pinion angle. I ask this because having a bad pinion angle is what caused me to damage my main shaft


Also, do you guys have aftermarket transmission mounts?


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Formerly known as jbj302
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Discussion Starter #8
Well i took a look today and it appears I had a bad angle at the tranny that would lead me to believe it needed to be shimmed up. So I have probably shimmed it up approx. 1/4”. It may need a little more. It got dark on me


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So what does this do to your pinion angle. I ask this because having a bad pinion angle is what caused me to damage my main shaft


Also, do you guys have aftermarket transmission mounts?


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It creates more of an angle which in my daily driven 88 hatch seemed to cause a vibration. I eventually noticed the angle was a little extreme so I stacked washers to shim it up and problem went away. With that I knew with the 93 I would have to do the same. Both factory crossmembers with prothane poly mounts
 

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Formerly known as jbj302
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Discussion Starter #10
Guys, I’m back and I’ve tried it all. Raising the tranny, adjusting the pinion angle, and etc... any other ideas? I’m going to remove the tranny and replace the rear main seal. Any ideas of what I could try while I’m in there? I do have a blow proof bellhousing if I haven’t mentioned that already. I can’t remember what name brand it is. I do remember it’s gold and it’s huge. I’ve read something about it having the possibility to be dial indicated maybe?

If all else fails, I’m going to at least try the old aluminum bellhousing to see if that helps.


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If you push in the clutch and the vibration is still there then you have eliminated EVERYTHING from the transmission (except the rear bushing) to the motor. No need to mess with the bell housing.

Now think of ANYTHING that is rotating as the tires turn and the engine is not running.

Now, what does this leave? Do not assume it's only in the rear of the car. Generally anything wrong in the frontend can be felt in the steering wheel but not always so don't assume this.

Front end parts: Front wheels, tires, bent rotors, loose ball joints, tie rods, etc. One of the engineers I work with had a vibration that started after about 20 minutes of driving. He found out that one of the front brake pads was dragging just enough that it heated up the rotor and caused it to warp enough to cause a vibration. Once it cooled down the vibration was gone. This can also be the rear rotors dragging and causing the same issue.

Rearend:
Bent rear yoke which happens a lot, rear tires, rear wheels, tires out of balance (no more than 2oz of weight!), bent axle, bent axle tubes, bad shock, bad control arm bushings, brake pad dragging and warping rotor, etc, etc..

Remember: anything that is still moving at highway speed.

ks
 

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Formerly known as jbj302
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Discussion Starter #12
Understood and will consider it all. I see you mentioned the pilot bushing/bearing. We were discussing it. I plan on replacing it as well when I replace the rear main seal.

I don’t know if I mentioned this but before I broke the tranny it didn’t have this vibration with the old aluminum bell housing. Besides the clutch that’s the only thing that was changed


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In addition to what Kevin said.

Put the rear axle up on jack stands. Remove rear wheels and tires. Install 1/2"-20 nuts on all five wheel studs. Run the cat up to 100mph this way. It will eliminate the tires and wheels as problems.
 

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Formerly known as jbj302
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Discussion Starter #14
In addition to what Kevin said.



Put the rear axle up on jack stands. Remove rear wheels and tires. Install 1/2"-13 nuts on all five wheel studs. Run the cat up to 100mph this way. It will eliminate the tires and wheels as problems.


I was planning on doing this with and without wheels once I got it up on jack stands. Was trying to see if I could do this with the driveshaft removed as well. I have a plug for the tranny but not sure if it would stay in


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Discussion Starter #15
Update. Went thru eliminating the wheels then the drive shaft, and with the driveshaft removed it’s smooth as silk. Waiting on a friend of mine to see if he has an extra Drive shaft that I can try and hope that’s the issue. I still need to pull the tranny to replace the rear main seal but trying to narrow down the vibration before i do that




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Both times I had vibration issues it was the rims. Not sure if you eliminated that (apologies if so) but something to consider.

Scott
 

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Formerly known as jbj302
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Discussion Starter #18
I think we have it figured out. My exhaust somehow moved and got against my rear end, plus i swapped in a fairly new aluminum ford Motorsport driveshaft.

I pulled the tranny and all to fix the leaking rear main seal




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