Weird drivetrain vibration at 70mph in Ď88 Coupe - Ford Mustang Forums : Corral.net Mustang Forum
 
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post #1 of 9 Old 06-10-2019, 02:42 PM Thread Starter
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Weird drivetrain vibration at 70mph in Ď88 Coupe

Not sure whatís causing this, although I see itís a widespread issue. The vibration will start around 70mph and up. Pushing the clutch doesnít change anything.

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

Any ideas?


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post #2 of 9 Old 06-10-2019, 06:31 PM
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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/gen...ered-cars.html

.



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1990 Light Crystal Blue LX Convertible, TW170, Lunati 20350711, TMOSS GT40 Tubular, 3550 5-speed, 3.55 Gears
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post #3 of 9 Old 06-10-2019, 07:17 PM Thread Starter
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Quote:
Originally Posted by ragtop50 View Post
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/gen...ered-cars.html



.


Thanks. Thatís good information. Iíll give it a try. So whatís your pinion angle? Mine is at -2į. I have solid upper CA and poly/solid lower


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post #4 of 9 Old 06-11-2019, 08:08 AM
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Thanks. Thatís good information. Iíll give it a try. So whatís your pinion angle? Mine is at -2į. 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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1990 Light Crystal Blue LX Convertible, TW170, Lunati 20350711, TMOSS GT40 Tubular, 3550 5-speed, 3.55 Gears
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post #5 of 9 Old 06-11-2019, 09:36 AM Thread Starter
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Originally Posted by ragtop50 View Post
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?



.


I did not. Itís 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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post #6 of 9 Old 06-11-2019, 12:14 PM
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I did not. Itís 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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I spec'd my whole build to fit a cold air intake I had
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post #7 of 9 Old 06-11-2019, 11:45 PM Thread Starter
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Weird drivetrain vibration at 70mph in Ď88 Coupe

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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


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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post #8 of 9 Old 06-12-2019, 10:23 PM Thread Starter
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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. 1/4Ē. It may need a little more. It got dark on me


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post #9 of 9 Old 06-13-2019, 08:55 AM
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Originally Posted by NotoriousNotch View Post
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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I spec'd my whole build to fit a cold air intake I had
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