New guy to boards needs help with rear end

[groupbmonster]

Whats up guys, this is my first post but i have been lurking for some time now just soakin up info. This is my second fox, its an 89 gt with 3.73s, bbk equal length shorties, bassani catted x pipe, flowtech warlock mufflers, and an mgw shifter.

Now here is my problem, im getting vibrations through the shifter as my speed increases, the vibration is bad enough that around 90 ish i can no longer hold the shift knob because it vibrates too much, and the vibration translates through the cross member and exhaust and is loosening my header bolts. yeah crazy. I have recently had new gears installed with a new trac-lok and bearings, new tires, balanced driveshaft, new u-joints, and new motor and trans mounts. I bought new axles and bearings today which will be installed soon. I just checked all bushings and suspension components and find nothin visibly wrong. What else could it be? Could the axles and bearings be the culprit of my problem?

Ive also read that some people have had this problem after a different ratio gear install and have cured it with an aluminum driveshaft. Also was curious if it could be maybe a shock thats dead or a quad shock? at this point im open to any suggestions Thanx in advance.

 

[89streetbeast]

had that same problem when mine was a 5 speed. lasted maybe a couple years that way and popped. broke the shift fork for 1st and second. dont know if that might be your exact problem but its worth a guess

 

[jrichker]

The driveshaft is out of balance, or installed with the alignment marks out of alignment. Yellow paint is used to mark the alignment of the driveshaft to rear axle flange. The two paint marks must line up. When the marks are lined up & you still have problems, the balance is off. The problem becomes more evident with new gears because the driveshaft spins faster for the same road speed. Instead of turning 1700 RPM in 5th for 65 MPH with 2.73 gears, you are turnning 2200 RPM with 3.73 gears. That makes the out of balance condition more noticeable. The stock driveshaft can be rebalanced for $40-$75 if you can find a shop to do it. The aluminum driveshaft is also a fix, Summit has them for $235. See http://store.summitracing.com/egnse...veshaft&searchinresults=false&N=+115&y=8&x=24

 

[fiveoh]

One additional thought to jrichker's post: before you remove the drive shaft to see if it is balanced, check to make sure the drive shaft is securely bolted to the pinion flange. If those four bolts are loose, that will cause a bad vibration throughout the drivetrain.

 

[groupbmonster]

Just checked all bolts last night to see if they are tight, which they are. I had the driveshaft balanced not too long ago but didnt know about the marks to clock it right on the pinion flange. i'll check that when i get home, hopefully its that easy. Thanx guys.

 

[89streetbeast]

just another suggestion to look at. bad harmonic balancers are known to cause bad vibration in the drivetrain. might want to check and see if its wobbling more than it should. my 84 wobbled so bad you couldnt get the rpm's past 3500 and the speed past 75. thought it was the tranny so i replaced it and found it was the balancer.

 

[dragnazz5.0]

if there are no visible marks left on the pinion flange and driveshaft try removing the driveshaft and rotating it 180 degrees and see what happens. if it gets worse than put it back if it gets better than youre all set but if it stays the same than turn it 90 degrees and see what happens

 

[groupbmonster]

Yeah the weight on the rear end is still there. the rpm of the engine doesnt affect the vibration, which led me to believe it wasnt the engine but from the transmission back. when i installed the driveshaft i dont remember there being any marks on the pinion flange, but who knows i probably missed em . so i guess ill play with it when i get home and go from there.

 

[groupbmonster]

yeah the u-joints were replaced when the driveshaft was balanced.

just got back from the test drive........ its still there just not so pronuounced

while re-clocking it on the pinion flange i think i found the factory setting, which was hidden under a coat of paint that was convieniently taken off by my penetrating oil. is the factory marking a white stripe kinda thing? well after trying the other setting i set it to that and still no avail.

so maybe i will try the band clamp idea to see if the guy that "balanced" my driveshaft actually did the work. it seems like this is the most logical fix to my problem.......... i had heard that an aluminum driveshaft might cure my problem and can get a decent price on them from my work, anybody know about this as a fix??????? thanx

 

[jrichker]

yeah the u-joints were replaced when the driveshaft was balanced.

just got back from the test drive........ its still there just not so pronuounced

while re-clocking it on the pinion flange i think i found the factory setting, which was hidden under a coat of paint that was convieniently taken off by my penetrating oil. is the factory marking a white stripe kinda thing? well after trying the other setting i set it to that and still no avail.

so maybe i will try the band clamp idea to see if the guy that "balanced" my driveshaft actually did the work. it seems like this is the most logical fix to my problem.......... i had heard that an aluminum driveshaft might cure my problem and can get a decent price on them from my work, anybody know about this as a fix??????? thanx

The FMS aluminum driveshafts are a good fix for the vibration problem. The price has dropped recently, so they may be manufactured in China now. That may raise some questions about the overall quality. The Cobra intake manifolds are now Chinese made and show a lower quality level from the original American made ones. Look for the "Made in USA on the box".

 

[bennettracing]

You said you got new mounts in the original post, are either the motor or the trans mounts solid perhaps? This would certainly amplify any vibrations. Also one solid and one regular mount would cause something nasty to happen I'm sure...

Just a thought,

-KB