Darth_V8r

iTrader: (4)

For about two years I've dealt with that annoying vibration between 70-90 mph. I have the poly trans mount and a stock 10- bolt with a stock torque arm.

I kept thinking wheels and tires. Then I thought wheel bearings. I thought a dead cylinder, motor mounts. Like always, I threw parts at it without really understanding it. Then I finally put together that it was related only to vehicle speed. 3-6 gear made no difference, neither did gas pedal position. Started reading some threads hereabout pinion angles so I checked mine. The hardest one to get is the angle between the transmission output shaft and the driveshaft.

Then, I had a sudden realization. I don't need the driveshaft angles at all. If the transmission output shaft is parallel to the input shaft to the rear axle, then the angles at both u joints are identical, which should cancel out the vibrations. In theory.


I put 180 pounds in the driver seat and 120 in the passenger seat to load the car, raised it, and checked angles.

I had 6 degrees incline rear to front on the transmission shaft and 3 degrees incline rear to front on the rear axle shaft. I used someone in here's trick to put a socket on that cap to get the angle finder on it. I measured the transmission angle off the crank pulley - again, someone else on here's idea.

So, I loosened the transmission from the crossmember and shimmed the rear of the transmission up, reducing the angle from 6 degrees to 3.5 degrees, which also increased the rear axle angle to 3.5 degrees by lifting the nose of the torque arm. Basically I kept adding shims until the angles matched up, meaning the two shafts were parallel. Then, used a longer bolt to hold it together.

No vibrations at all from 0 to 100 mph! Full throttle, light throttle, or any gear 3-6. The passenger seat doesn't even rattle like it used to when unoccupied.

In case anyone else is struggling with this, thought I'd try to help. May or May not apply to aftermarket rear ends. It worked with the stock 10- bolt

01ssreda4

iTrader: (96)

And that my friends, is cutting through the bullshit. Learning who and who not to listen to on this vast internet is far more important then the what/why of what you're actually hearing. Congrats on solving your issue, I know vibrations are one of my pet peeves and annoy the crap out of me. I too have faced and conquered them.....for the most part

babyd

OP took your advice did the same thing and got my driveline ironed out. It's funny how crazy you can make yourself reading these forums sometimes.

kingtal0n

iTrader: (1)

So you added shims to the transmission crossmember between the top of the member and the trans to raise the output shaft of the trans? Do we get a picture?

Do you think the OEM unit just eventually sags (started out correct but gradually sagged) and what do you think actually sagged, the car itself changed or the crossmember actually got bent?

Darth_V8r

iTrader: (4)

wow, 2.5 years. Time is fun when you're having flies! Glad it worked for you.

Talon, in my case it was from installing poly motor mounts. Raised front of engine a scoshe.

bigsticksupra

iTrader: (3)

i think the poly trans mount gets blamed for horrendous vibration a lot of times. if people would take the time like you did and correct the angle after the mounts, they'd probably have no problems

what did you use to shim the trans mount?

i suggest all people suffering from vibration after a poly trans mount installation to try your tutorial.

Darth_V8r

iTrader: (4)

Thanks!!!

I can't link, because Lowe's isn't a sponsor, but basically, I used a combination of steel fender washers and rubber fender washers from Lowes with a hole big enough for the trans mount to cross member bolt. The rubber to absorb some vibration and keep the steel washers isolated so they don't rattle.

I do think you're right. I think that the poly mounts change the trans angle, and cause vibrations. Just part of modding cars

kinglt-1

iTrader: (26)

Good ****! I will keep it in mind if I ever replace my motor mounts.

user 4737373

deleted- wrong thread.