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8.75 clutch type power lock rear end pinion angle

Posted By: tee-john

8.75 clutch type power lock rear end pinion angle - 03/20/11 01:33 PM

I purchased a rebuilt 8.75 clutch type power lock rear end to install on my 68' Barracuda. I knew that I would have to get the drive shaft shortened. I noticed that the pinion has a downward angle. If I put the mounting holes for the u-bolts straight up and down there is about 3/4" difference from center to center when I pull a measurement from the slip yoke. Is this ok and will I need a pinion snubber,and if so how close should it be from the bottom of the car? Thanks
Posted By: RapidRobert

Re: 8.75 clutch type power lock rear end pinion angle - 03/20/11 03:27 PM

w flat seal, 3/4" from full forward to back seated in the cups is perfect. How much power/what app for the snubber Q (if needed). Not sure on it's clearance EDIT missed the mounting holes straight up part
Posted By: JohnRR

Re: 8.75 clutch type power lock rear end pinion angle - 03/20/11 03:44 PM

I'm lost , if your car had an 8 3/4 in it and all you did was change the chuck nothing should have changed ?
Posted By: ahy

Re: 8.75 clutch type power lock rear end pinion angle - 03/20/11 04:27 PM

I've used the instructions from the MP Chassis Manual to check/set pinion angle... its hard to explain the steps in a post. If fine adjustment is required wedge shaped shims under axle mounting pads are normally used to adjust the angle. The chassis manual and shims are available from Mancini Racing.

I've got the same question John had... did you change rear end sizes (say from 7 1/4" to 8.75)? A pic would help showing rear and driveshaft in rough mounting position.
Posted By: DoctorDiff

Re: 8.75 clutch type power lock rear end pinion angle - 03/20/11 06:20 PM

Pinion angle is the relationship between the transmission centerline and the pinion centerline, not to the ground and not to the driveshaft. Ideally, you want the pinion to become parallel to the transmission when the vehicle is under power and the pinion torques upward.

Make the pinion parallel to the transmission as a baseline, then pivot the pinion downward 2 degrees for a street car. This is referred to as a 2 degreee negative pinion angle.
Posted By: Yancy Derringer

Re: 8.75 clutch type power lock rear end pinion angle - 03/20/11 08:21 PM

Quote:

Pinion angle is the relationship between the transmission centerline and the pinion centerline, not to the ground and not to the driveshaft. Ideally, you want the pinion to become parallel to the transmission when the vehicle is under power and the pinion torques upward.

Make the pinion parallel to the transmission as a baseline, then pivot the pinion downward 2 degrees for a street car. This is referred to as a 2 degreee negative pinion angle.




THE ABOVE IS ONE OF MOST CONCISE, SIMPLY PUT, and IMPORTANT concepts I've ever read on here VERY well put.
Posted By: JohnRR

Re: 8.75 clutch type power lock rear end pinion angle - 03/20/11 08:32 PM

Quote:

I purchased a rebuilt 8.75 clutch type power lock rear end to install on my 68' Barracuda. I knew that I would have to get the drive shaft shortened. I noticed that the pinion has a downward angle. If I put the mounting holes for the u-bolts straight up and down there is about 3/4" difference from center to center when I pull a measurement from the slip yoke. Is this ok and will I need a pinion snubber,and if so how close should it be from the bottom of the car? Thanks



The OP Pm'd me and said he did a rear end swap, with what dr. diff said you should see a slight downward angle at rest , especially if you have the rear up off the ground so you can get under it . As far as a pinion snubber , do you alredady have one and are asking if you need an adjustable unit ? You should have one anyway or else the yoke can contact the floor under full suspension compression.
Posted By: JonC

Re: 8.75 clutch type power lock rear end pinion angle - 03/11/12 11:00 PM

Quote:

Pinion angle is the relationship between the transmission centerline and the pinion centerline, not to the ground and not to the driveshaft. Ideally, you want the pinion to become parallel to the transmission when the vehicle is under power and the pinion torques upward.

Make the pinion parallel to the transmission as a baseline, then pivot the pinion downward 2 degrees for a street car. This is referred to as a 2 degreee negative pinion angle.



Will raising the transmission up 2° give the same effect?
Posted By: Junky

Re: 8.75 clutch type power lock rear end pinion angle - 03/11/12 11:20 PM

Quote:

Quote:

Pinion angle is the relationship between the transmission centerline and the pinion centerline, not to the ground and not to the driveshaft. Ideally, you want the pinion to become parallel to the transmission when the vehicle is under power and the pinion torques upward.

Make the pinion parallel to the transmission as a baseline, then pivot the pinion downward 2 degrees for a street car. This is referred to as a 2 degreee negative pinion angle.



Will raising the transmission up 2° give the same effect?

Yes, if the pinion angle is still parallel to the transmission. No matter if the transmission is up (positive) or down (negative) set the pinion angle parallel to it, either up or down, then take away 2° down (negative). So in theory the two will be parallel to each other under power.

I had a post on this very subject a couple of weeks ago. Do a search for it.
Posted By: Clayton

Re: 8.75 clutch type power lock rear end pinion angle - 03/14/12 06:09 AM

I just swapped the the 7 1/4 in my 67 barracuda for an 8 3/4 and according to the book it said 5 down from level for auto car and 6 down for 4 speed
Posted By: 72Swinger

Re: 8.75 clutch type power lock rear end pinion angle - 05/12/12 04:23 AM

Doesnt U-joint angle come into play? If any of those settings gives you 0 U-joint angle then what? The reason I say is with my setup right now is gonna be tough it has 2 dgrees down at the trans and with the U-joint angle at 5 degrees down at the pinion for U-joint angle per Mopar Chassis book im still 1/2 degree negative U-joint angle at the trans. So as it sits the driveshaft comes out of the trans and angles upward.
Posted By: Evil Spirit

Re: 8.75 clutch type power lock rear end pinion angle - 05/12/12 02:03 PM

Quote:

Quote:

Pinion angle is the relationship between the transmission centerline and the pinion centerline, not to the ground and not to the driveshaft. Ideally, you want the pinion to become parallel to the transmission when the vehicle is under power and the pinion torques upward.

Make the pinion parallel to the transmission as a baseline, then pivot the pinion downward 2 degrees for a street car. This is referred to as a 2 degreee negative pinion angle.




THE ABOVE IS ONE OF MOST CONCISE, SIMPLY PUT, and IMPORTANT concepts I've ever read on here VERY well put.



Yet it leaves out one of the most important pieces of info - rear axle must be supporting the weight of rear of the car, as in not having the body of the car on stands with the axle hanging down.
Posted By: DoctorDiff

Re: 8.75 clutch type power lock rear end pinion angle - 05/12/12 02:32 PM

Common sense suggests if the pinion becomes "parallel to the transmission when the vehicle is under power and the pinion torques upward", the angle is set with the vehicle's weight resting on its suspension.
Posted By: Evil Spirit

Re: 8.75 clutch type power lock rear end pinion angle - 05/12/12 03:32 PM

Quote:

Common sense suggests if the pinion becomes " parallel to the transmission when the vehicle is under power and the pinion torques upward ", the angle is set with the vehicle's weight resting on its suspension.



That is the end result of setting the angle, not how to check it.

And if people had all this common sense that you speak of, after the 1000's of posts on this, would there still be so much confusion on it?
Posted By: Rick_Ehrenberg

Re: 8.75 clutch type power lock rear end pinion angle - 05/12/12 07:17 PM

Quote:

Pinion angle is the relationship between the transmission centerline and the pinion centerline, not to the ground and not to the driveshaft. Ideally, you want the pinion to become parallel to the transmission when the vehicle is under power and the pinion torques upward.

Make the pinion parallel to the transmission as a baseline, then pivot the pinion downward 2 degrees for a street car. This is referred to as a 2 degreee negative pinion angle.



Picture this scenario: The rear springs have a foot or two of arch -- the car is, as we used to say, "jacked up". It would be possible to shim the axle hosing (or re-weld the perches) so that the pinion was perfectly parallel to the trans's mainshaft, but U-joint angles would be through the roof!



Cruising on the highway, you'd like front and rear u-joint angles to be complimentary, and very low (but not zero). For drag racing, you need some pinion nose-down (in relation to the propshaft) so the angles remain opposite at all times. How much of an angle? A serious drag car with only leaf springs might need as much as 4 or 5 deg., which a car with better axle windup control (pinion snubber, 4-link, quadrashocks, Caltracs, etc.) would require much less. With real street tires, there's rarely a need for more than 1 to 1.5 deg.

Rick
Posted By: DoctorDiff

Re: 8.75 clutch type power lock rear end pinion angle - 05/12/12 07:51 PM

A 2 joint driveshaft is designed to OPERATE with the pinion relatively parallel to the transmission, regardless of the application.

If a car (or truck) is "jacked up" beyond the operating range of the U-joints, you must drop the transmission tailhousing a few degrees, then re-set the pinion angle using the same procedure I posted earlier in this thread.

If this is not possible, you must point the pinion directly toward the transmission and install a CV joint off the transmission. This is why 4 x 4 trucks run CV joints on the transfer case end of their short, steep front driveshafts.
Posted By: Rick_Ehrenberg

Re: 8.75 clutch type power lock rear end pinion angle - 05/12/12 07:59 PM

I've been wanting to try a CV from an Imperial for years...never got around to it.

Rick
Posted By: 72Swinger

Re: 8.75 clutch type power lock rear end pinion angle - 05/12/12 09:05 PM

So what I need to do is compromise and set mine so that U-joint angles are at a minimum (1-3degree max) under power and with weight as it would be and call it good even though the trans will be nose down and the pinion nose up in that scenario? My ride height is pretty low and im running a Viper 6spd. I have always pictured it like the Chassis manual diagram but that is only possible with Super Stock springs. Have also read that the 2 U-joint angles need to be within 1 degree of each other for vibration harmonics. I understand the 2 degrees nose down from parallel at the pinion part but even after that im gonna be nose up in relation to the driveshaft.
Posted By: DoctorDiff

Re: 8.75 clutch type power lock rear end pinion angle - 05/12/12 11:21 PM

This is a good example of why you can't follow the Mopar Chassis manual to set pinion angle. It is just a re-print of a shop manual where all specs of a particular drivetrain combination are known.

Don't worry about if the driveshaft slopes up or down relative to the ground. Make the pinion parallel to the transmission as a base-line, then roll the pinion downward 2 degrees and weld your perches.
Posted By: 72Swinger

Re: 8.75 clutch type power lock rear end pinion angle - 05/13/12 12:35 AM

Ok I will Cass! Was just worried about U-joint operating angle. Shouldnt we stay between 1 and 3 degrees if possible?
Posted By: DoctorDiff

Re: 8.75 clutch type power lock rear end pinion angle - 05/13/12 01:07 AM

I don't think you will have a problem with operating angle unless the tail housing is almost touching the ground.
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