59 tbird pinion angle

[StealthSRT10]

Hello all,

Ready to pull out my hair at this point.

I have taken measurements

4 degrees nose up at yolk.
Driveshaft angle 5 degrees.

What is my pinion angle and is it correct.
Changed out some items and just trying to narrow down issue. Vibration was present at about 60 mph before new leaf springs and now its alot worse and at 30 to 40 mph. Btw new leaf lowered car an inch in rear and they are still super squishy. but thats a different problem. Wasnt happy about that.

[Tbird1044]

Wow, I installed a new set of leaf springs and it raised my rear bumper by about 1 1/2". The springs I removed had been rebuilt and re-arched years ago. You probably already checked your U joints so I wonder if the driveshaft could have a balance problem.
Nyles

[StealthSRT10]

The origionals were 6 leaf and new ones are 5. didnt show that when i got them. and cost to renturn them means i would only get 100 bucks back so gonna keep them i guess. but the pinion angle is what im looking into now.

Wow, I installed a new set of leaf springs and it raised my rear bumper by about 1 1/2". The springs I removed had been rebuilt and re-arched years ago. You probably already checked your U joints so I wonder if the driveshaft could have a balance problem.
Nyles

[simplyconnected]

I'm with Nyles. New springs raised my car and now it doesn't scrape in driveway aprons any more.

To answer your question directly, in a perfect world, your pinion angle should match your engine/trans angle. Having said that, the rear end moves up and down all the time and your number of passengers and different weight in your trunk will change the squat.

As you consider the variables, the angle can live in a wide variety of angles. 'U' joints are notorious for vibrations but so are tire imbalances. So are wheel and tire combinations that are 'out of round'. So many times, I felt vibrations in cars with new tires that went away when different new tires were installed. - Dave

[DKheld]

The "heavy duty" replacement rear shocks for Land Rovers that Dave found really helped the stability and ride on the rear of my car and I mean a HUGE difference.

Maybe that would be something you could try and will improve the rear end "squishyness".

Although a pain in the rump maybe re-install the OEM springs?

Mine has a vibration at about 60 also. Was smooth as silk on the interstate at any speed before I replaced my engine. Weird thing is if the car is sitting still and you run the new engine to any RPM and hold it there you never feel any vibration. Tried matching the RPM I would be running at on the interstate with the car sitting in the garage - no vibration. I put it up on jack stands and ran it up to 60 but was so scared it was going to fall off and crash through the wall I couldn't really tell if there was a vibration. I just figured - however unlikely - that something else went bad about the same time I replaced the engine.

So.....

I replaced the rear shocks with the heavy duty Land Rover shocks - great improvement in ride and about a 50% improvement in the vibration but it was still there.

Replaced the rear wheel bearings - no change.

Had the drive shaft balanced - no change.

Replaced the universal joints - no change.

Lived with it for a few months and the tires went bad so replaced all the tires - no change in the vibration - maybe a very slight reduction.

Even though you can't feel any vibration in the engine when the car is sitting still I decided to pull it loose from the transmission and rotate the flywheel 45 deg and see if that helped. I had marked it all when removing and re-used the original flywheel on the new engine so 100% certain I put it back like it came out but figured I had tried most everything else - unfortunately - no change.

My original harmonic balancer went bad. Ordered a new one and while I was waiting on it to arrive I was thinking - wow - bet that's what the problem was all along - NOPE - no change.

Beginning to think it's the rear bushing on the transmission but will just live with it until the transmission dies. Tired of seeing the original engine sitting in the shop taking up room and I know I'll never get rid if it so figure I'll just rebuild and re-install - maybe this summer or next. Curious to see if that makes any difference.

Sorry about the long winded post - hope you find your vibration ........

Eric

[simplyconnected]

In my youth, Dad purchased a new Pontiac Safari (wagon) for our family of 7. It came with a nasty vibration.

The dealership was stumped. We live close to Pontiac, Michigan and Dad was one of their vendors. The engineers at Pontiac went through the car.

The engine was a 389 cubic inch with a Turbo Hydromantic trans. Pretty much standard fare back in 1961.

What did they find??? After hours of testing they found nothing until the car was on the road. They determined, the muffler pipe was hitting the body. Why the dealership couldn't fix it, we will never know. A slight muffler system adjustment and all was right. Who would have thought...

Eric, Good job on those shocks. I'm using the same type on our '59 Galaxie. I love the ride. - Dave

[pbf777]

What is my pinion angle and is it correct.

The "pinion angle" is determined by establishing the differential angle of the output shaft of the transmission and the input shaft/pinion shaft of the differential. The as measured angle of the driveshaft is irrelevant in this definition.

Normally, one is expecting a somewhat downward angle (negative angle), as the differential (pinion) is expected to rotate upward, canceling this negative value as torque is applied, due to motion permitted in its' mountings. Speaking in round numbers, leaf spring cars generally exhibit valves of -4° to -6°, control arm vehicles with the differential somewhat more positively located generally a lesser value is realized.

The U-joint manufacturers generally recommend a minimum of 3° differential angle for best life of the joint; although a zero degree differential is perceived as ideal in high load racing applications for survival.

Also, check for excessive "end-play" in the U-joint trunnions as this will cause drive-line vibrations.

Scott.

[StealthSRT10]

well i flipped the shackles back to normal and that fixed the low speed vibrations. but im back to dragging the exhaust again.

[StealthSRT10]

Problem fixed. Apparently one of the u joint caps was "almost" all the way in. now i have a press and its in all the way no issues at any speed.

[Tbird1044]

Glad you found the fix. Always a good feeling.
Nyles