Pinion angle

Questions about all other brand differentials.
billytbass26
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Pinion angle

Postby billytbass26 » Wed Mar 06, 2013 6:37 pm

Wondering if my pinion angle has been changed on my 79 hbody. While putting on traction/lift bars I noticed they were too tight for the snubbers. Only have about an inch of space. Just thought about the pinion angle due to having a fabricated trans crossmber. If the tail of the trans is slightly higher would that necessarily cause a higher pinion angle on the differential and cause the traction bar clearance issue? Could this be harmful to any of the drivetrain? Also is there different height trans mounts so I could lower it slightly?

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monzaz
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Re: Pinion angle

Postby monzaz » Wed Mar 06, 2013 11:30 pm

Pinion angle on the rear is solely controlled buy the control arm mounts and or control arm length.

drive line pinion running angle (which can cause drive line harmonics and vibrations ) will be controlled by the differences in the transmission tail shaft angle and the pinion angle.

these to angle are totally different from each other but will affect each other in driving the car and keeping the drive line harmonic in check.

pinion angle on most cars is 4 degrees positive

drive line angle from trans u-joint to pinion u-joint is -4 degrees.

Now if you do not understand what i am talking about you need to google drive line running angles as they can explain it all better than I can with me not having the proper pictures and such as we do not deal with that angle because it is more chassis oriented work. We only set the pinion angle with the brackets on the rear with stock parts.

IF you have modified engine and suspension you need to readjust all the points that will affect the running drive line angle so the two u-joint create the -4 degree running angle.

This can be done by lowering or increasing the tail shaft height or shortening or lengthening the control arms lower or upper.

Tail shaft mount. GM does have 2 different thicknesses of mounts for the trannies. Best to get some steel shim and work with that as in a h-body there is not much room to work.


IF your motor mounts are custome you might want to check there forst if you have a bad drive line angle. Jim
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billytbass26
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Re: Pinion angle

Postby billytbass26 » Thu Mar 07, 2013 7:03 am

Thanks Jim,

Yeah this is something I wont mess with for obvious reasons. lol.( limited knowledge)
I just purchased some tiny snubbers to place on the bars for now. There appears to be no issues with harmonics or vibration so I'll leave that alone.

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monzaz
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Re: Pinion angle

Postby monzaz » Thu Mar 07, 2013 8:20 am

Yah - even when it comes to chassis work you really have to be really in the now as it get really messy.
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Bobman58
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Re: Pinion angle

Postby Bobman58 » Mon Sep 30, 2013 11:45 pm

So you say -4deg. I've seen it written that the tail shaft and the pinion angle should be the same only on a different plane. Is this running angles or at rest angle? My traction bars have 1/2" clearance to the snubber so they don't allow much axle wrap before they cantact. I assume the trans and pinion angles should be set to running specs(under full power).

Robert

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monzaz
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Re: Pinion angle

Postby monzaz » Sun Oct 06, 2013 12:09 pm

-4 is rest angle not in motion with the suspension loaded.

with full torque applied it should go to 0 degrees then as torque is unloaded down the road or track it will progressively relax down to between 0 and -4 for the correct angles where hopefully harmonics will not happen. THIS again are measurements taken for the trans engine center line to the pinion center line differences. NOT the pinion angle to the bracket mounts on the rear WHICH is where I work on and they are usually +4 degrees... See how confusing this can all be ... :) Jim
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