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Pinion angle question...

DougG69

DougG69

Member
I've got to set my pinion angle (have a little vibration at cruise).

It's my understanding that for a street car, you want the pinion angled upward to the same degree that the transmission tailshaft points downward (parallel).

With leaf springs & a manual transmission, how much - if any - degrees leeway should I leave for spring wrap?
 
Slight vibration at highway speed is now more pronounced at low speed. Parked it until we can get it on a lift Thursday. Rear u-joint looks like it's been ejecting grease due to centrifugal force.
 
3 up 3 down is the rule of thumb.

Spring wrap should only be an issue when accelerating and braking.
 
The max difference should be 3deg. When I did my T56 swap the trans pointed down at 2.5deg and the pinion measured level. Sounds like you have other issues besides a driveline angle
 
"buening" said:
The max difference should be 3deg. When I did my T56 swap the trans pointed down at 2.5deg and the pinion measured level. Sounds like you have other issues besides a driveline angle
Click to expand...

I have no doubt there's something else going on.

I shimmed the pinion so that it's parallel to the transmission tail shaft, and it helped some, but did not eliminate the vibration. I don't feel it in the steering wheel, to me it seems to come from the back. We have rotated tires front to back with no difference, so I think we can rule out tires/rims. Had the car on a lift recently & did not see anything obvious with the car in gear. Driveshaft is new, balanced.

Part of the reason I started this thread is that the rear end is the only part of the driveline that hasn't been rebuilt or replaced. Upgrading from the stock open diff. is something that I want to do anyway, & I'm hoping with a new 3rd member, axles, etc., I might fix the vibration in the process.
 
Is it speed related with the transmission in neutral? While cruising down the highway in gear note the vibration and then pop it into neutral and see if the vibration is still there. This will tell you if it is in the driveshaft/rear end/wheels, or if it is in the drivetrain. If your u-joints are spitting grease then they may be bad, which can cause a vibration. I'd opt for a sealed spicer unit if it were me.
 
I swapped driveshafts with the clone and my vibration went away. I noticed when I put the new rear u-joint in that the rear yoke seemed kinda tight and the clips had to be coaxed into place.

I think that is causing a bind in the rear joint and vibrating the driveline. I'm going to send it out and have it fixed or have a new one made.
 
"Sluggo" said:
3 up 3 down is the rule of thumb.
Click to expand...

to also add, it's highly dependent on the max driveshaft RPM.

the angle is the working angle of the u-joint. some seem to confuse it with the angle of the engine and pinion by themselves.
 
"buening" said:
Is it speed related with the transmission in neutral? While cruising down the highway in gear note the vibration and then pop it into neutral and see if the vibration is still there.
Click to expand...

Just got a chance to try this this evening... makes no difference if the transmission is in neutral or drive.

I should probably get the wheels/tires balanced again just to make sure it's not something simple. There's a place not too far away that does lug-centric.

Wonder if one or more of the tires could have developed a problem from the car sitting too long in one spot?
 
Yeah check the balance and make sure there aren't any knots on the tires where a belt may have broke. If they check out, you may have an issues with your rear diff assuming you got your u-joint issue figured out.

Did this issue just show up all of a sudden? Did it pop up after sitting awhile? Have you check your tranny fluid just to be safe?
 
"buening" said:
Yeah check the balance and make sure there aren't any knots on the tires where a belt may have broke.
Click to expand...

We checked the tires when we rotated front to back, didn't notice anything. I'll have the guys at the tire shop go over them again when I go in for the balance job.

"buening" said:
If they check out, you may have an issues with your rear diff assuming you got your u-joint issue figured out.
Click to expand...

I have replacement u-joints on hand which I'll try to get put in over the next couple of days. For today I just wanted to get the longer leaf-spring center pins in (necessitated by the axle shims) & try the old "rotate the driveshaft 180 degrees" trick to see if it helped any. Which it didn't.

"buening" said:
Did this issue just show up all of a sudden? Did it pop up after sitting awhile?
Click to expand...

The slight vibration at highway speed has been there since I got the car on the road. Probably only have about 350 miles on it, mostly back & forth to the shop or paint, or little shakeout runs close to home until recently. The new element I just noticed is kind of a 'rumble' at lower speeds. So I'm thinking I may have a couple of things going on here.

"buening" said:
Have you check your tranny fluid just to be safe?
Click to expand...

Not yet, but it sounds like a good idea. It's a Tremec, filled with the recommended GM Synchromesh at installation. It's a hydraulic clutch setup, I'll have to crawl under there & double-check the adjustment on that too.
 
Ok, quick update on the vibration issue (still working on it).

  • Replaced the rear u-joint. Front was inspected for any binding or slop & looked good.
  • Still need to get the wheels balanced. Shop was closed early yesterday.
  • Took a brief run in the car today, found a pretty smooth back road where I could run the car up to where it's vibrating & put it in N & cut the engine. No change at all, with clutch in or out.

So I'm assuming it's safe to eliminate anything from the engine/flywheel/clutch/pressure plate, which is a relief.
 
Ok, some more info to add today.

Got the rear end up on jack stands, rear wheels off the ground.

Engine revs smooth when not in gear, rear tires not turning.

Run it up through the gears to where the speedo shows 50-55 mph, the vibration is there immediately, and increases with the speedo.

Shut the engine off, can hear something in the rear end/axle/wheel area until the tire comes to a stop. Not too loud, a kind of grinding/scraping noise. Could be a brake pad just brushing the drum? The sound seems to oscillate just a bit, and the tire/wheel look like they are just barely doing the same on the driver's side.

Maybe the axle or wheel bearing?

If so, I'll find out in the next week or so... I already have new axles/bearings for an upgrade to 31 splines & some kind of non-open differential.
 
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