CAN THE PINION ANGLE CHANGE ?

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cawley

cawley

383 Bcuda
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Can the pinion angle change from one car to another ? We took the 8 3/4 rear out of my dads 67 gtx & put it in his 62 polara. We drove the gtx & it ran fine no vibrations. Now in the 62 polara there is a vibration. Got the drive shaft balanced. Took the wheels off. Checked every thing. I was told it might be the pinion angle.
 
cawley said:
Can the pinion angle change from one car to another ? We took the 8 3/4 rear out of my dads 67 gtx & put it in his 62 polara. We drove the gtx & it ran fine no vibrations. Now in the 62 polara there is a vibration. Got the drive shaft balanced. Took the wheels off. Checked every thing. I was told it might be the pinion angle.
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Yes especially if someone has played around with the spring perch mounts.
 
cawley said:
Can the pinion angle change from one car to another ? We took the 8 3/4 rear out of my dads 67 gtx & put it in his 62 polara. We drove the gtx & it ran fine no vibrations. Now in the 62 polara there is a vibration. Got the drive shaft balanced. Took the wheels off. Checked every thing. I was told it might be the pinion angle.
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Also, you might check those axles in the 62, there is a year or two where the 8.75 had axles that were longer inside the carrier than the later 8.75s. I don't recall the exact year though
 
What I forgot to tell ya is when my dad bought his gtx it had an 8 3/4 in it & the 62 polara had a dana in it. He swapped the rears. Spring perches were never touched.
 
Not just yeah, but hell yeah. What if the car you swap the rear axle into has a different ride height in the rear? There's your pinion angle change.
 
You're saying that you took the 8.75 out of a 67 GTX (B body) and put into a 62 polara (also B body)? Pretty sure the 62 stock is narrower than a 67 8.75, what I'm drawing a blank on is whether the perches are also narrower or not.
 
dukeboy_318 said:
You're saying that you took the 8.75 out of a 67 GTX (B body) and put into a 62 polara (also B body)? Pretty sure the 62 stock is narrower than a 67 8.75, what I'm drawing a blank on is whether the perches are also narrower or not.
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No we checked before we swapped them. The distance between the perches are the same between the two rears. The Dana was not original to the 62 polara. The car was raced by the owner my dad bought it from. As for the 8 3/4 that was not original from the 67 GTX. The only reason my dad swapped them because the 67 GTX came originally with a Dana. My dad knows that because he bought the 67 GTX new.
 
If the cars have different amounts of arch, and arch in different parts of the spring, or longer / shorter shackles the pinion angle will absolutely be different.

Air shocks (which should never be used), or shocks with springs on them (same goes..... they are a band aid for bad springs) will also twist the pinion upwards.

Be aware as well that the retainer straps for 7260 and 7290 u joints can be mixed up, but are dimensionally different and could also contribute to a vibration if used in the wrong application.
 
pinion length is different [axle centerline to center of U-joint] Dana has a longer pinion. About an inch. could be compensated for with the right parts. [special yoke etc.]
 
So, the Dana wasn't original to the car it was in, and the 8 3/4 wasn't original to the car it was in, and someone else did all that work before you got them.

So really, you have no way of knowing if either of those rear axles are originally B-body axles, or if the perch angles are the same on both axles, or if the perch angles on either rear axle were correct for a B-body to begin with.

That's before we address different springs, ride heights, driveshaft lengths, etc.
 
72bluNblu said:
So, the Dana wasn't original to the car it was in, and the 8 3/4 wasn't original to the car it was in, and someone else did all that work before you got them.

So really, you have no way of knowing if either of those rear axles are originally B-body axles, or if the perch angles are the same on both axles, or if the perch angles on either rear axle were correct for a B-body to begin with.

That's before we address different springs, ride heights, driveshaft lengths, etc.
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That was exactly what I was thinking
 
When my dad bought the 67 GTX (new) it was a 4spd w/ a Dana. When he bought it back someone put an 8 3/4 in it. Instead of buying a Dana for it he just used the rear that was in the 62 poloara. Now I have done many rear swapped, narrowing, leaf spring relocations. We did our home work before the swap. The perches were never moved. The leaf springs are the same distance apart. I drove the 67 GTX since the swap & that drives fine, smooth.
 
I asked about drive shaft length because, if you pull the shaft too far out of the back bushing, then the yoke sometimes starts whipping around not on the trans centerline.If this is allowed to continue, it wears the bushing tapered.
But before you drive yourself crazy, be sure you have isolated the vibration to not being in the wheels or tires,etc. I know you said it was fine until the swap,..............but

You didn't by any chance swap pinion yokes?
 
cawley said:
When my dad bought the 67 GTX (new) it was a 4spd w/ a Dana. When he bought it back someone put an 8 3/4 in it. Instead of buying a Dana for it he just used the rear that was in the 62 poloara. Now I have done many rear swapped, narrowing, leaf spring relocations. We did our home work before the swap. The perches were never moved. The leaf springs are the same distance apart. I drove the 67 GTX since the swap & that drives fine, smooth.
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Ok, sure then. You’re absolutely positive that two rear axles you have zero history on are both completely unaltered, factory original B body rear axles despite the fact that neither was original to the car they came to you in. I sure wouldn’t assume that at this point, but if you’re positive that’s great.

So why don’t you just measure the pinion angle in the Polara? You’ve moved perches so you’ve set pinion angles before, check the pinion angle and see if it’s within spec. If it is, your vibration is elsewhere. Simple.
 
I don't have much time today but I did get the time so far to take the drive shaft out. I started it up & brought the rpms up a little & no vibration.
 
Ok so now put the D-shaft back on with the correct straps and in the right sized yokes with a tightened to spec pinion nut. Make sure the shaft is not too short. It should be set about all the way into the tail and then back-out 1inch as a working length. You should have to push it back into the tail to fit it to the rear yoke, and then pull it into the saddles. Make sure the U-joints swivel freely, and smoothly.Finally,grab the D-shaft at the front U-joint and push it up,down, and sideways. I don't have a spec for how much is too much, but I suspect .080 at the U-joint cups is too much.
Then verify the vibration is still there. Then jack the car up, and onto axle stands. And retest. If vibration persists, remove the wheels and tires and retest. If it persists remove the drums . Do not hit brake the brakes with the drums off.
At this point you're down to axles, and pinion angle. So first check/adjust the axle endplay, and retest. Axles are seldom bent and you said it was fine in the other car.
So that leaves the pinion angle.
The driveshaft has to run at a non-zero angle at both ends to keep the needles from pounding into the crosspin.This also keeps the grease moving around. Usually the shaft goes down to the diff from the trans and back up to the diff at the other end, this is called nose-down at the back.The angles at each end should be equal and opposite in direction, when under full power, but not less than zero at the back, that is to say not nose-up relative to the driveshaft..
To achieve this, the pinion angle gas to be adjusted to compensate for the engines ability to torque the rear end up. A big powerful engine and a very big starter gear (like 10/11 or more) will need more compensation than a little engine, an automatic and 2.76s,say. Also in the mix are the rear springs; the softer they are, the more compensation will be required.
For street suspension and a stock 360 with about a 3.55, a 2250 TC, and a 2.45 low, perhaps 4 degrees is enough with SS springs. But perhaps 7* with the factory springs.
By 400 hp and a 3000TC and 3.91s, and SS springs, she might need 7* compensation.
This means that when the power is off,and she's just cruising, there WILL be vibration, that's just the way it is.
To help you get started, have a helper get in the driver's seat, lock the brakes, put it in low.You, meanwhile, go get eyes on the pinion nose. At your command have the helper slowly apply power,with the brakes locked. You watch the pinion climb. You will have to compensate for that climb,and more, cuz the brakes are gonna fail to hold at about 2000 to 2400 rpm, but full torque may not be reached until 3800rpm or more depending on the build spec.
Happy compensating.
 
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The rear yoke has the right u joint. The front is the bolt on type. No yoke
 
cawley said:
The rear yoke has the right u joint. The front is the bolt on type. No yoke
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In that case, you still need to check the tail bushing, and the the guts in the B&T still need to be position in a suitable place, not in a worn out area on the slideways and not too far back, same as the slip-yoke kind.
 
72bluNblu said:
Ok, sure then. You’re absolutely positive that two rear axles you have zero history on are both completely unaltered, factory original B body rear axles despite the fact that neither was original to the car they came to you in. I sure wouldn’t assume that at this point, but if you’re positive that’s great.

So why don’t you just measure the pinion angle in the Polara? You’ve moved perches so you’ve set pinion angles before, check the pinion angle and see if it’s within spec. If it is, your vibration is elsewhere. Simple.
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100 % sure I will measure pinion angle.
 
cawley said:
100 % sure I will measure pinion angle.
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This is the driveshaft You had re-balanced recently? With the rear end up high, the B&T angles more and takes up more room in the housing, that restricts the already
minimal amount of travel available from that joint. The length on that shaft's gotta be almost spot-on to come up roses............................
P.S. IIRC Mine has 1.25" of plunge total, and that's w/-0- deg angle.................
 
Havent had much time to look at it but this what I have so fare. Drive shaft length is-54 1/4 With the rear end loaded ( on the wheels) from the trany to the rear yoke is - 55 3/16
 
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