Rear axle flange run out question.

Ken47

Ken47

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Supporting Member
On my 47 Ford I’m using a 68 camaro differential with leaf springs. I have a vibration in the drive train. I thought it was the engine but now I’m reasonably sure it’s from the drive train. I have been adjusting pinion angles to try to sort out the vibration problem. I have tried 1,2,3,4,5 and 6 degrees of caster shims in but it hasn’t solved the problem. So now I’m looking at the wheels and axles. So my question is; what would the allowable run out be on the rear axle flange. I have measured it at .020 axially (wobble). The run out at the wheel rim is .025” or there abouts. Is this enough to cause a noticeable vibration? The tires are new and balanced. The vibration starts at 90 - 100 kmh
 
Not sure if this is going to help but my drive shaft had 15 thou. run out and it came in around 80 to 100 k. Had to replace the driveshaft so I’m thinking you have quite a bit of run out. Probably enough to case a issue. Pinion angle is a biggy also. Doesn’t take much to start a vibration. Has to be pretty close to the motor angle from what I experienced.
 
Hi. My drive shaft was bent and out of balance. it was new too😩. I had it straightened and balanced so I’m pretty sure that’s not it. I agree about the pinion angle and when I put it in as you describe the vibrations are much worse. Right now I have the angles at: trans 3.8 deg down drive shaft 1.9 deg down and the pinion .7 deg up. According the the online drive line calculators (TREMEC Tool box) and spicer that should work ok. At this set up it seems ok but the vibration seems to be wheel related. I’m running with the wheels off the ground so it likely isn’t a fair test.
 
I learned that running the car on the stands gave me a vibration no matter what I did. Wasn’t until I put it in the ground and drove it after every adjustment that I figured what was working and what wasn’t...
 
If you could figure out a way to keep the car on the stands and take off the drive shaft and spin the rear up to a decent speed. That would take the motor and tranny and driveshaft out of the equation. if it vibrates you are correct and its in the rear or the wheels. If it's good it's in the rest of the drive train. I have no idea how to acheive this...just throwing ideas against the wall...
 
Thanks for all the replies so far. I’m at a loss as to what to do next. I’m thinking about taking it to a shop that has a dyno that could run it and try to figure where the vibration is coming from. My big concern is that it would be like writing them a blank check. But I’m hooped, I have done everything I know of and what has been suggested to me. I though maybe the diff was not square in the car but after carefully measuring it, it’s only out 3/32” which I think is irrelevant. Anyway, eventually I will get it running good. Right now Up to 90 kmh it’s perfect lol.
 
I'm still thinking your issue is not a wheel or rear wobble. If it was a tires of rear axle issue I think you would feel it at any speed. If it's a motor ,tranny or drive shaft issue you won't feel it until the u joints can't handle it no more and then you get a vibration. Anyways good luck and hopefully the dyno people won't empty your pocket book...
 
Thanks Johnny. I agree with you. I do think it’s drive a shaft angles issue but am at a loss to figure out the solution. The engine and differential are kind of fixed in their location as that’s how they fit in the car. To change any of them requires major surgery to the car. I’m wondering about a double cardan (CV) drive shaft. Typically they are for extreme drive shaft angles but it may be my solution even though the angles aren’t too extreme. I may need to cut the spring saddles off the axle tubes and reposition them once the angles are figured out but that’s not too bad cost wise. I just need to be sure it’s the drive train to focus on. I’ll let you know how I make out 😄
 
Update: the driveline vibrations have been solved. Changed the shims to adjust the pinion angle to get angles within spec. Also changed the U joints to better quality ones and straightened and balanced the driveshaft. It’s nice and smooth now. Now I’m back to the the engine/torque converter vibration potential cause 😀. I’m trying to eliminate every possible vibration source before I have to bite the bullet and pull the engine out😄
 
Hey glad you got it...those pinion angles are very important...and not the easiest to figure out.
 
Driveline vibrations can be tough to locate. On my 36 ford pickup, for twenty years I chased a vibration in the steering wheel, right at 60 mph, I changed every part in the front end, two sets of wheels, 4 sets of tires, couldn't find it. Driveline specialties built the driveshaft, it was never removed in the twenty years, and one day last spring, under the truck with it idling in gear, my friend thought he noticed the driveshaft move very slightly out of round. Out came a pencil and a block of wood, and.....you guessed it, bent driveshaft. Right in the center, very slightly, but enough. $500 later, new driveshaft, and a twenty year old problem solved, truck is smooth as glass now.
 
Ha...your not alone..several of us here have chased a drivetrain vibration that led to a new drive shaft... Glad you tamed your demon...
 
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