Vibration right off idle

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Has this engine ever run before? Or is this a 100% new build?

All the trans recommendations make sense, but don't forget the basics. Verify your firing order? We all screw it up at least once and it can cause some odd issues with the right cyls switched.

The engine, while relatively new has been run with the 904 behind it for a very short time. This can't be. Misfire. I can feel it in my seat.
 
The engine, while relatively new has been run with the 904 behind it for a very short time. This can't be. Misfire. I can feel it in my seat.

OK if you can feel it in your seat, that is telling you that the transmission is making contact with the tunnel and transfering the vibration through the floor up to your seat.

Yes, scratch the misfire then.
 
Ok, so I think I got the vibration off idle, fixed. I looked all around the trans and all was good, but I noticed that my driver's header was touching the torsion bar. So I used a pry bar and put a wood shim in there and tested it on stands and it appears that noise vibration is gone. So I need to fix that. While doing so I noticed that I have two different motor mounts (rubber) so I need to fix that and level the engine and retest. Ugh... I created a new thread in the SB engine section seeking help to confirm what I need.
 
I'm gonna put it up high on stands tonight after work and check it out.
While you are under there, if possible, take the torque convertor bolts out rotate the convertor 180 degrees and reapply the bolts.
See if that changes your vibration
 
Not yet..I'm waiting for you to turn that converter 180 degrees..lol..or should that be haha?
Dont laugh to hard partner.
I personnel saw rotating the convertor cure a vibration on a $120K street rod.
I know theoretically it should not work, but, it does not cost any $ to give it a try.
 
Ok then, I'll hold my breath starting right now...lmk when you get those last two bolts to go in..
Well you may be right.
I know on my 727 there is one offset hole.
Not sure what they do on the OP's setup
The street Rod had a GM system
 
Ok then, I'll hold my breath starting right now...lmk when you get those last two bolts to go in..

I gotcha now. I can't remember if the A500 had an offset hole or not. It's the same plate as the 904.

I have to sort out my motor mount situation and go from there.
 
Ok, so I got new biscuit rubber mounts and the motor is sitting level side to side and so is the trans.

I wanted to get your guys opinion on where to measure for pinion angle? For the transmission, I've measured on the pan rail and the end of the tail shaft and I get two different angles. Same goes for the pinon, I measured on the bottom flat, and also the flat of the yoke. Once again two different angles.

If I go by the trans tail shaft I get DOWN 2.5* and the flat bottom of the pinion is DOWN 3.9* I used the Tremec App and it will only go green if the pinion is at a max of 3* DOWN.

What I don't understand, is all I read is that the pinon needs to be parallel with the trans under load. To be parallel wouldn't the pinon need to be at 2.5* Up under load?
 
Ok, so I got new biscuit rubber mounts and the motor is sitting level side to side and so is the trans.

I wanted to get your guys opinion on where to measure for pinion angle? For the transmission, I've measured on the pan rail and the end of the tail shaft and I get two different angles. Same goes for the pinon, I measured on the bottom flat, and also the flat of the yoke. Once again two different angles.

If I go by the trans tail shaft I get DOWN 2.5* and the flat bottom of the pinion is DOWN 3.9* I used the Tremec App and it will only go green if the pinion is at a max of 3* DOWN.

What I don't understand, is all I read is that the pinon needs to be parallel with the trans under load. To be parallel wouldn't the pinon need to be at 2.5* Up under load?
Then only place to measure the tranny angle is the tail shaft. Likewise the only place is the pinion yoke for the rearend.
You are correct the trans must be tipped up (positive), rearend tipped down (negative).
I set mine so they are as close to same angel (-/+) so the tranny and the rearend are parallel.
Sounds like you have a bum transmissiom mount.
I had to shim both to get it correct.
 
Then only place to measure the tranny angle is the tail shaft. Likewise the only place is the pinion yoke for the rearend.
You are correct the trans must be tipped up (positive), rearend tipped down (negative).
I set mine so they are as close to same angel (-/+) so the tranny and the rearend are parallel.
Sounds like you have a bum transmissiom mount.
I had to shim both to get it correct.

Thank you. I'll re measure at the pinion yoke tonight, to confirm measurements. I have an A500 so it's not stock, but the mount is new.

I'll see if I can shim the trans up. When you say you had both angles the same +/- (trans up, pinion down) was that at rest or calculating the pinion rising x degrees under load?
 
3° down at the rear end pinion angle as compared to the tailshaft angle sounds correct if memory serves me.

3° down under load comes up to 0° when you put the power too it and get on it.

Bump stop above the rear yoke is a safety stop to keep the rear angle from twisting up to high under load and taking the rear u-joint out.

Been a long time ago in the 80s when we were setting up new length drive shafts for extending frames and sleepers for semi-tractors, those were set at 1.5° down.

In my opinion, double check some more info and or call a driveshaft shop.

Good Luck

You don't want those driveshaft angles fighting each other. Kind of like some old PTO driven farm machinery when you turn too tight, the u-joints start rattling to beat heck, and is extremely hard on the u-joints.
 
Thank you. I'll re measure at the pinion yoke tonight, to confirm measurements. I have an A500 so it's not stock, but the mount is new.

I'll see if I can shim the trans up. When you say you had both angles the same +/- (trans up, pinion down) was that at rest or calculating the pinion rising x degrees under load?
At rest on my 4 post lift with the weight of the car on all 4 tires.
Try to keep the angles between 2-2.5 degrees and you should be good to go.
 
At rest on my 4 post lift with the weight of the car on all 4 tires.
Try to keep the angles between 2-2.5 degrees and you should be good to go.

Yes ^^^^^ with the weight of the car on the 4 tires, not free hanging rear end in the air.
 
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