camar0corey

iTrader: (22)

Well I put a 12 bolt under the car and the back end of the car seems shaky now around 65+ mph. Like I look at the review mirror and it is useless.

I made sure when I installed the drive shaft that it sat down in those cups evenly and I got the bolts on the u clamp as tight as I could. Could it possibly be loose though or something?

The other thing is pinion angle or driveline angle or whatever people want to argue about. Is it pinion subtract driveshaft or driveshaft subtract pinion?

I am looking from the driver side, rear wheels on ramps. Driveshaft looks like +2 and pinion looks like +4. So one way it would be +2 and one way would be -2. So you can see where I am confused.

I have also been trying to adjust it, because in my head I think it is pinion minus driveshaft. Only problem is I can't get the nut on the adjustable torque arm to break loose. The one furthest forward that jams up against the body of the torque arm? I can get the one to break loose on the part you want to twist to adjust it, but the other one won't come loose. Sorry if this isn't clear. Why won't it break loose?

MeentSS02

iTrader: (11)

Unless I've got it completely *** backwards, a negative pinion angle will point the schnoz of the rear end towards the ground compared to the driveshaft.

As for why the other nut won't loosen, I'm guessing it is because it is a right-hand threaded jam nut - try turning it clockwise to loosen it.

camar0corey

iTrader: (22)

So even though they are on the same piece of metal it could be threaded the other way? I'll try to hulk it the other way tomorrow then, I've already put the car back on the ground.
I also think it is pinion minus driveshaft then, because the pinion looks more up then down at the moment.

Other annoying sound is it sounds like the driver side brake is rubbing on occasion? This is driving me nuts, I know the axle shouldn't be moving in and out so I don't get why it rubs. On that side though when I put the axle in it pushed back at me about a 1/4 inch. Why would it have been doing that? The splines def. engaged in the differential fine but it would come back on me. I ended up more or less bolting down the backing plate to get it to stay, but nothing was in its way so it doesn't make any sense.

MeentSS02

iTrader: (11)

What 12-bolt do you have? I'm assuming it has c-clip eliminators like most do, which should keep the axle from moving in and out at all.

As for having both right and left hand threads on either side of the adjuster, it is very common.

camar0corey

iTrader: (22)

Thanks for the heads up on the right hand thread, I'll check that out tomorrow.
Its a Moser 12 bolt, yep c-clip eliminators. I'm thinking clearance maybe is just tight or something so the brake randomly rubs. Or maybe my wheels aren't centered, would that possibly cause brake rubbing and my vibration?

I see the wheels don't sit tight on the axle like they did on the 10 bolt, so I don't know if I should get different kind of lug nuts for the back or something?

MeentSS02

iTrader: (11)

I'd make sure the lug nuts are seating on the wheel like they should...if they are coming up even a little short (which would be caused by longer wheel studs), that could cause some big issues. I guess if that was suspected, just using open ended lug nuts would be a quick way to verify that everything was seating as it should be.

Beyond that, I'm not sure where I'd look next...but the wheel should sit as tight against the rotor as it did with your 10-bolt.

Bob@BruteSpeed

iTrader: (16)

The 1/8" shims are for using LT1 brakes, if you didn't use them then that could be your problem.

The front of your rear-end should be angled down 2 degrees, as under power it will rotate up. Below is info from BMR's website. Bob

Set the pinion angle using the following method:

Load the rear axle by either setting the car on the ground or letting the car rest on jack stands positioned under the rear axle.

Place the angle finder on the driveshaft and record the angle. The driveshaft angle is negative if it slopes downward towards the rear of the car. The driveshaft angle is positive if it slopes upward towards the rear of the car.

Now place the angle finder on the rear end torque arm mounting plate and record the angle. The rear end angle is negative if it slopes downward towards the front of the car. The rear end angle is positive if it slopes upward towards the front of the car.

Add the two measurements. This is your pinion angle. (Example: -2 rear end angle plus -1 driveshaft angle = -3 degrees)

Turn adjuster to achieve the desired angle.

As a starting point, most F-Bodies seem to like the following initial settings: Automatics: 1-2 degrees negative Manuals: 2-3 degrees negative

Please refer to www.bmrfabrication.com to view the video for setting the pinion angle.

Once pinion angle has been set, tighten all jam nuts. Verify that torque arm mounting bolts are tight and tighten the rear cross bolts attaching the rod-ends to the torque arm mounting bracket.

camar0corey

iTrader: (22)

I am using open lugs, the wheels do go tight against the rotor.

Thanks for the post Bob! I def. did not use shims. This is most likely why I get rotor rub? Or does it also have to do my vibration issues?

Bummer, its always something!

Bob@BruteSpeed

iTrader: (16)

You're welcome. That would be the cause of the rotor rub. Check your pinion angle with the instructions I provided, that is most likely the cause of your vibration. Bob

camar0corey

iTrader: (22)

Yeah the vibration has me scratching my head. I look at the angle finder from the driver side as my exhaust is in the way on the passenger side. The needle points towards the rear of the car, approx. at the 4 position on the driveshaft and the 3 position on the torque arm mount. It appears the pinion is pointed down. But according to these instructions I would be at negative 7 or positive 7? That doesn't seem right, or does it not matter if the needle points towards the rear of the car or the front? My brain wants to say if it would be positive or negative if it pointed on one side or the other of the zero, but I could be wrong?

I know it tilted the pinion downward yesterday when I adjusted it though, the top of the girdle cover had been touching the upper panhard rod mount, as I adjusted it I could see it tilt towards the front of the car and clear the panhard mount.

Also with the u clamps retaining the driveshaft, there is currently a lock washer and then a nut. With this setup the u clamp is just barely flush with the nut. With it like this you can move the u clamp just a little bit. Could this lend to a vibration problem? Would I be better off with a regular washer and red loctite so I could clamp that down tighter?

How much are the shims? I didn't see them under 12 bolt parts for 93-97 fbodies. I'm kinda torn, might order bearings also, when I traded rears with 383LQ4SS well the bearing didn't press off the axle in one piece when we were trying to get the backing plates swapped.

Also I have the lower control arms in the lower of the two holes. Car is at stock height, can this cause issues? I had heard it should help with traction, but figure I should mention it in case it is a variable in my issues.

Torque arm is a full length adjustable Spohn. Which seems to be making contact with the undercarriage of the car. Do people usually remove that little plate that is welded to the body? Looks like it was for the rear seatbelt receptacle maybe? That is where the torque arm is touching the car. At least while it is on ramps. I have the rear wheels on ramps when I am doing all this.

Sorry for the long post!

Bob@BruteSpeed

iTrader: (16)

As long as the front of the rear is slightly tilting downward when you're adjusting the pinion angle, you're thinking correctly on the angles.

Your U Clamps should not be able to move when they are tightened down. This could indeed lead to your drivetrain vibration. I'd switch to locknuts, and ditch the lock washers. Just make sure you don't tighten the clamps down so tight that you distort the caps, as you'll wipe out the bearings.

I've never sold just the shims so I'm not sure on their cost. Mosers number is 260 726-6689 and they can send them out to you. You're going to need to replace the wheel bearings.

The lower holes are where I would have the lower control arms installed at too.

You don't want anything on the chassis touching the main part of the torque arm, as it could limit it's travel and could be the cause of a lot of noise. Bob

camar0corey

iTrader: (22)

Ok so I finally have the pinion angle dialed in to around -1.5-2. Also the lock nuts did make it more secure and I made sure not to crush them down, just made them tight til I couldn't wiggle the u-clamp anymore.

Bob I have a question. I just ordered the shims from Moser. They are quoting $65 for axle bearings. What do you get for a pair of axle bearings? I didn't see them under 12 bolt parts. I'm hoping these will press off, but after seeing what the last ones did I should probably have a pair on standby.

Bob@BruteSpeed

iTrader: (16)

Their price isn't bad at all, you can pick them up at your local Napa. Here is the pn #. Thanks. Bob

Napa Replacement part numbers for 12 bolt wheel bearings: Bearing: 9508b

driveshaftshop

If you give me a call later today i can help you with this there a few reasons this would vibrate. If you changed the rear gear to a higher numeric ratio and used the same shaft it could be the problem (especially if its steel) It could also be a harmonic coning from the trailing arm (also worse with Steel shafts) the pinion angle could do it but normally U-joint angles show up in lower speed ranges and are torque (or gas pedal) sensitive. give me the angles like this diagram and ill hep out

Frank

Supers

This is why i hate u-bolts....

The u-bolts should not be more than 22 ft lbs....

Making them as tight as possible, you crush the caps and the joint can not oscillate correctly, you should 1st try making them 20 ft lbs and see what happens..

Why everyone thinks to just tighten the u-bolts till they can't be turned anymore is beyond me.

This kills the cap and joint and makes vibrations

Driveshaft Shop

If your more inclined to doing things your self, click the link below to our site. it has allot of information about this sort of thing.


Angle calibration

Real speed 9500Rpm balancing

new products and things were doing

camar0corey

iTrader: (22)

Well I didn't crush the caps down. With the lock washers in there you couldn't even get it tight enough to take the slack out of the u bolt. I didn't really squash it with the lock nuts either. I got it tight enough I couldn't move the ubolts side to side anymore and went another half turn.

I still have some vibration. Hopefully this weekend I can take care of the whole torque arm touching the body issue and if I still have some vibration maybe I need the driveshaft balanced.

It is a Denny's Nitrous Ready Driveshaft, it came with the 12 bolt.

The vibration seems to occur more the faster I go, starts to show up around 60ish minor, its fairly rough at around 80, like I slow back down to 70.

Thanks for all the help so far everyone!

Driveshaft Shop

Dennys is a good builder, give him a chance to check it out if you dont get anywhere and your looking to have a expert high speed balance done let us know. we have taken delivery of a new custom made balancer that enables us to be able to spin a shaft like that to 9500rpm.

for more info click here.

camar0corey

iTrader: (22)

I called up NAPA with that part number, it wasn't in their system and they said it didn't cross check with anything?