[11craig11]

At around 70 there is a vibration and if i get off the throttle it gets worse till about 55. The problem is not there if i take out the driveshaft and put a yoke in and bring it up to 70. So far i have new motor and transmission mounts, harmonic balancer, b&m flywheel, new transmission and torque converter from monster transmission, brand new front and rear u-joints, new driveshaft, all my wheels were balanced last week, just tried putting a new 8 inch center section in the rear, and made sure my axles were straight on a lathe with a dial indicator, and new wheel bearings, and i have air shocks and tried many different heights to make up different pinion angles. Anyone have any suggestions that i have not tried yet.

[05horse]

turn the drive shaft 90º and try then if not 90 more ect ect till u get one turn i know that can help some times

[ITLRUN]

If that doesn't help, your driveshaft is out of balance. Or something in the driveline definetly, when you get to 70mph then get off the throttle and it gets worse. You definetly have something, in the driveline out of balance, Mike. SCT Tuner.

[rocky289]

Can you similate the problem with rear of the car on some axle stands?
What do you mean by: (The problem is not there if i take out the driveshaft and put a yoke in and bring it up to 70)

[11craig11]

if i put the car on jack stands and then put a yoke in the tailshaft of the transmission there is no vibration, but everything from the flywheel back is new.

[Gstang71]

Just be careful on the highway now!
I had the same situation happen to me, and I floored it and my transmission literally blew up in 3 peices.

[rocky289]

I know you guys in the US use different terminology to us Kiwis, but what is it you are calling a yoke?
I'm curious because I have a similar problem in my car.

[11craig11]

well i swapped driveshafts out and it still didn't help so i started shimming the leaf spring perches and the vibration is not so bad so i have to readjust the pinion angle and hopefully that does it.

[rocky289]

Ok now I'm with you.
You are effectively altering the axis line of the pinion shaft.
In theory the input & output angles of the driveshaft should be parallel, but not necessarily on the same plane.

[racin_ryan]

Driveshaft slip yoke is the piece that attaches to the front u-joint and slides into the tranny. Looks like a "U" on top of a splined post.

[rocky289]

Originally Posted by racin_ryan

Driveshaft slip yoke is the piece that attaches to the front u-joint and slides into the tranny. Looks like a "U" on top of a splined post.

Yep that's what I thought.

[daw00l]

what about the tires? I have heard that if they are old, even if they arent too worn, they start making the car vibrate, then they just fall apart soon.

[rj8806]

Originally Posted by 11craig11

well i swapped driveshafts out and it still didn't help so i started shimming the leaf spring perches and the vibration is not so bad so i have to readjust the pinion angle and hopefully that does it.

I started to post about it not being the driveshaft but you just found that out .
Driveshaft vibrations can be identified quickly by dertermining if the vibration is speed related or rpm related. In other words, if you have a vibration at 70mph in 5th, run the car at 70mph in 4th. If the vibration is NOT there in 4th at the same speed, it is not a driveshaft. The driveshaft turns the same rpm(speed) no matter what gear you're in. Example, at 70mph in 5th, the driveshaft turns 7000rpm. At 70mph in 4th, the driveshaft is still turning 7000rpms.

A driveline angle problem, is not speed related, but it is rpm related. If your vibration comes in a 3000rpm in 4th it will be there at 3000 rpm in any gear.
In your first post, you mentioned that the vibration got worse when you let off the gas....this is classic driveline angle symptom.

Driveline angles are not too tough if you take your time and understand what the angles are telling you. General rule of thumb is you need an angle of between 2* and 3* on a passenger car.
The easiest way to check the angles is to have the car at ride height, zero out the gauge on the frame and then take a couple of angle readings.

First, get an angle reading off of the bottom of the tail housing near the end of the case itself, we'll call this one " A ". Next, get a 2nd angle from the middle of the driveshaft tube, we'll call this " B " and finally, with the pinion yoke turned vertically, use a socket the same diameter as the u-joint cap and get a reading off of the socket as it is placed on the u-joint cap itself. We'll call this " C ".

Now take A - B = Front u-joint working angle. Then take C - B = rear u-joint working angle. It is these 2 working angles that are critical. They should be equal but opposite and cannot vary by more than 1/2*. In other words, a +2* and -2* or a +3* and a -3*. You need at least 1/2* of angle present for the u-joint to work properly. Also, none of your readings (or the working angles) can exceed 5*.
You want the tailhousing and the pinion yoke at the same angle but in opposite planes. In other words, if you could draw a line from the front of the crank, thru the transmission and out the output shaft going towards the rear bumper and then draw another line from the center of the pinion yoke going up towards the front of the car. these lines should be the same angle but in different planes. Ideally, on a leaf spring car, you want the pinion yoke angled slightly downward, usually in the 2* or 3* range. Going along with that, you would want the transmission tail pointed slightly upward, in the 2* or 3* range.

Hopefully this wasn't too confusing, if so, feel free to PM me and I'll be glad to elaborate on it more.





Richard
Tech Support
Tremec TKO, T45 & T56 Transmission Systems