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69f bird · 10-22-2004, 05:46 PM

I have busted 2 rear u-joints in my '69 Firebird since installing the new rear end and suspect a pinion angle problem. Could the new springs be an issue? Would a Camaro 12 bolt have the perches in a different angle than a Pontiac 10 bolt?

The first joint was provided by Hauser with the new 12 bolt rear, Pontiac shaft to Chevy 12 bolt type...it was a heavy duty unit. It snapped at E-Town in the spring...only about 100 miles on it (many of you may remember). The second was a heavy duty Spicer that came installed with the new drive shaft which used Chevy style all around (pictured below and at the attached link). Both times the bearings seemed to fail. The ends that are bad are the rear pinion side, not the drive shaft side. What would cause wear like this? The bearings were powdered!

u-joint pictures

69f bird · 10-22-2004, 05:46 PM

I have busted 2 rear u-joints in my '69 Firebird since installing the new rear end and suspect a pinion angle problem. Could the new springs be an issue? Would a Camaro 12 bolt have the perches in a different angle than a Pontiac 10 bolt?

The first joint was provided by Hauser with the new 12 bolt rear, Pontiac shaft to Chevy 12 bolt type...it was a heavy duty unit. It snapped at E-Town in the spring...only about 100 miles on it (many of you may remember). The second was a heavy duty Spicer that came installed with the new drive shaft which used Chevy style all around (pictured below and at the attached link). Both times the bearings seemed to fail. The ends that are bad are the rear pinion side, not the drive shaft side. What would cause wear like this? The bearings were powdered!

u-joint pictures

crossbreed455 · 10-22-2004, 05:53 PM

do you have any lapper bar on it? it may be going to a bigger pos angle on load putting more stress on the u-joint and breaking the u-joint.

mike m.

69f bird · 10-22-2004, 05:58 PM

no I do not.

DOC · 10-22-2004, 06:17 PM

Does the entire u-jont bearing cap sit entirely in the rear diff yoke? If the rear diff yoke is wider that the width of the u-joint it may expalin why the ends are broken off.

PMDRACER · 10-22-2004, 06:43 PM

Holy crap!

You've got a serious binding problem.

What is the angle of the pinion? What is the angle of the trans tailshaft? Are you sure the rear end is centered in the car correctly, as is the engine and trans?

I'd have that rear end double checked too. Check the mountings and the internals.

On first look I'm wondering if the rear is going completely negative on pinion angle (down below level) under power.

455firebird1969 · 10-22-2004, 06:51 PM

69f bird,

I run a chevy 12-bolt in my 69 bird, it has not given me any problems. I broke an axle in my origional 8.2 this past spring, but the u-joints and drive shaft have held up. I had to install the two sized u-joint to mate the chevy yoke to my Pontac driveshaft. I also use the Moroso aluminium caps, instead of the strap style method. You can get heavy duty joints that are pre-greased, they do not have a hole for the zerk fitting, which makes them stronger. Also make sure when you install a joint with a zerk fitting, install it so as to stretch the zerk fitting, not compress it.

crossbreed455 · 10-22-2004, 07:20 PM

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by PMDRACER:

What is the angle of the pinion? What is the angle of the trans tailshaft? Are you sure the rear end is centered in the car correctly, as is the engine and trans?

I'd have that rear end double checked too. Check the mountings and the internals.

On first look I'm wondering if the rear is going completely negative on pinion angle (down below level) under power. <HR></BLOCKQUOTE>

Checking the angle now will not do him any good now, it looks like he is breaking them from the load and the rear-end twisting too far. Or the driveshaft to long. If the rear-end was off too one side it would have at least scored the other ends of the u-joint. What do the other caps look like?

mike m.

mike

russ467 · 10-22-2004, 07:21 PM

Could your drive shaft be too long? If you installed/measured it with the rear tires off the ground, your suspension drops, therefore making the driveshaft easy to install. But when the suspension is under load and squating, it is making the distance from the rear yoke to the tailshaft housing on the tranny shorter.
If you reused the same driveshaft from the old rear end, the pinion snout is probably longer, therefore making the distance again shorter than before.

455firebird1969 · 10-22-2004, 07:32 PM

Russ,

Good point, my shaft is borderline too long when I compare the two rearends, the 12-bolt is closer to the tranny slightly...

wrench · 10-22-2004, 07:40 PM

Are you using the u-bolt style clamp to secure the joint to the pinion yoke? If so, I have seen them overtightend enough to cause that problem in the past.

wrench · 10-22-2004, 08:18 PM

I got this quote from Denny's Driveshaft website.

"Why does my rear u-joint wear out so often?
This is usually the case when a u-bolt style pinion yoke is used. The pinion yoke is not the problem the overtightening of the u-bolt is the cause of the failure. You may find that every time you change the damaged rear u-joint you will find that one or both of the journals or caps that are under the u-bolts are destroyed and the ones that are pressed into the shaft are still in good shape. You did it to yourself! 17 ft/lbs for 1310 & 1330 series and 20 ft/lbs on the 1350 series."

Brian Baker · 10-22-2004, 08:25 PM

It's binding...notice the bluing? That's from heat.

When you get on the throttle, the pinion rises. This will push the driveshaft forward into the transmission if you have the pinion angle set negative at rest. The first two things I would check would be pinion angle, and driveshaft length. If you have, say...2 to 4 degrees of negative pinion angle, and the driveshaft is too long (ie - slid too far into the tranny), the front of the shaft could be bottoming out inside the tranny causing the U-joint to bind (which can also crack the tailshaft housing on the tranny).

It's also important to make sure (this is very important) on U-joints with grease fittings, that the grease fitting is under compression when the driveshaft rotates in a forward gear.

69f bird · 10-22-2004, 08:45 PM

I was using the U styled straps. I may have overtightened them. I have to get back to the garage to measure the pinion angle. I did check the driveshaft length with the car on jackstands originally, not with the axle loaded...DOH! I'll check that as well. Thanks for all the great suggestions...keep them coming please.

tininjun67 · 10-22-2004, 11:01 PM

I'd go with the overtight u-joint bolts. The distance from yoke to tailshaft actually gets longer when the car is on the ground and shorter when the axle drops out of the car. You wouldn't think by looking, but the angle of the suspension link (in this case the spring) pulls the rearend forward as it drops. Learned this the hard way installing a too long driveshaft and had to jack the rearend back up to stock position to get the shaft in. duplicating pinion angles while under the car is esy enough with a floor jack under the pinion of the diff, then you can see if the shaft is bottoming in the trans. support the car properly of course.

russ467 · 10-23-2004, 04:54 AM

I disagree Tininjun. At least on my firebird, my driveshaft will not go in my tranny enough to clear my pinion yoke when the suspension is loaded to install my driveshaft. I have to unload the suspension to get clearance.

Brian '74 · 10-23-2004, 06:58 AM

Shelly,
Do you still have the 10 bolt? The 12 bolt will be at least 1/2" longer at the pinion yoke compared to the 10 bolt. How much play does the yoke have going into the trans? They do sell shorter trans yokes.

69f bird · 10-26-2004, 04:50 PM

OK, here are the measurements. The driveshaft has 3/4 inch of play into the trans. The car is supported by all 4 wheels under load.

The trans is -3 degrees measured on the pan (front lower then rear)
the yolk is 0 degrees (measured on the u-joint cap when vertical)
the driveshaft side of the front u-joint is -2 degrees (front lower than rear, measured on the u-joint cap when vertical)
the driveshaft side of the rear u-joint is 0 degrees (level, measured on the u-joint cap when vertical)
the pinion side of the rear u-joint is 0 degrees (level, measured on the u-joint cap when vertical)
the rear 0 degrees

[email protected] · 05-31-2005, 09:40 AM

69 fbird,
did you ever figure out what was breaking your joints? I just did a similar swap with a corporate 10 bolt into my 68 bird. It seems ok, but I want to make sure that I"m not going ot break anything. Thanks
Bob

69f bird · 05-31-2005, 06:01 PM

Bob,
When I swapped out the rear, I installed a set of replacement springs. Turns out they were much weaker than the springs I removed. That plus the rear was at zero pinion angle. On launch, the springs were wrapping up so the pinion was up several degrees overstressing the u-joints. This was actually the second u-joint blown in a month. I had the pinion yolk replaced in the rear, put back in the stiffer springs and used a 2 degree wedge to adjust the pinion angle down a bit. Problems have disappeared!

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