odd drivetrain vibration - 86 mustang

gxnos

gxnos

Forum Member
I have an odd drivetrain vibration on my 86 GT and I can't quite narrow it down. It was all original, all stock and it would vibrate above 70mph (only speed related, not RPM). I checked out the driveshaft and the U joints had some free play, so I thought I figured it out. Recently I did some work to the car including a new motorsport clutch and flywheel, new world class T5, and a new ford racing alum driveshaft.

The vibration was a bit better, but it was still there. Very recently, I installed a 3.73 gear and the vibration is much worse. It starts to show up at about 45-50mph and gets really bad at higher speeds. This tells me that it is definitely related to the driveshaft, due to it spinning at higher speeds, but I have no idea why.

Does anybody have any ideas? TIA
 
I talked to a few people and they say it has to be the driveshaft or the pinion angle. Maybe its a coincidence that the U joints were bad on the 1st one and the new one is out of balance... I dont know. Im checking the run out later.
 
i checked the run out on the driveshaft, and it was almost .25"! what the hell, brand new out of the box ford racing driveshaft has a ton of run out.
 
gxnos said:
i checked the run out on the driveshaft, and it was almost .25"! what the hell, brand new out of the box ford racing driveshaft has a ton of run out.
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pull it, take it to a driveshaft shop, have them make it good, they will balance it at the very least
 
QuickLX said:
Make sure the pinion flange is not bent.
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how does a pinion flange get bent? that would be crazy... but ill check it.

got my driveshaft back yesterday. they fixed the runout and balance. I'll put it on today to see if its fixed.
 
got back the driveshaft from dynotech - smooth as silk, even at high speeds. POS FRPP driveshaft.
 
Eric, something I noticed and forgot to mention on you mustang, Your exhaust system dumps out right on the axle tube. This will over heat your rear axle fluid, and eventually damage rear axle components. You either need to finish off the exhaust or install a down spout for it that directs it away from the axle tube. Glad to hear your driveshaft is finally corrected.
 
Detroit Gearbox said:
Eric, something I noticed and forgot to mention on you mustang, Your exhaust system dumps out right on the axle tube. This will over heat your rear axle fluid, and eventually damage rear axle components. You either need to finish off the exhaust or install a down spout for it that directs it away from the axle tube. Glad to hear your driveshaft is finally corrected.
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yeah, one of your techs mentioned that to me as I was leaving. I knew about the exhaust. I actually plan on putting the tail pipes on today. I just wanted it to sound cool for a while :)
 
gxnos said:
i checked the run out on the driveshaft, and it was almost .25"! what the hell, brand new out of the box ford racing driveshaft has a ton of run out.
Click to expand...

I had the same thing with the ford aluminum driveshaft. The place i took the driveshaft to have it redone said they had to do them all the time.
 
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