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Transmission, Rear End... Talk & Q&A! Tranny, rear end, drivetrain related stuff... shift it... grind it... pop da clutch!

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Old 11-26-2021, 08:50 PM
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Default Tail Shaft, Pinion, Drive Shaft Angles

Thought I'd put this here instead of my build thread. I've been messing with this Trimec Drive Line Angle program on the wife's smart phone and can not dial the numbers in. Seems that this phone app does not work right...no matter where I place the numbers I can't get a green light.

I lowered my motor mounts by 1.750 to get my rear pinion / tail shaft heights closer....it was a 4.5 difference now it's 3". It may not have been needed, but I'll do better in the way of body roll and it does have a better look. The bottom of oil pan is 2" above the axle.

I just used the Spicer Calculator online.. my kid told me to plug in parallel numbers. Tail shaft 3 degrees down and pinion 3 degrees up. My drive shaft angle (piece of tubing right now) is 4 degrees. These numbers seem to work and give me operating angles of 1.5 which is a green light

So the question is....does 3 degrees down on the tail shaft / 3 degrees up on the pinion make sense? I wasted a good part of the day trying to work around what I read about the pinion should be facing down.... ARRG

Maybe I eat too much turkey (

Last edited by Couper; 11-26-2021 at 09:43 PM.
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Old 11-26-2021, 10:34 PM
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Your kid was right, the transmission output shaft has to be parallel to the pinion shaft, and that's what you have now. Good show.
A side note is, make sure the shafts are parallel side to side also.
There are some good U-tube videos showing why you get vibrations with bad angles in your driveline. When you transit power through a bent U-joint the driveshaft changes rotational speed twice per revolution. If your driveshaft is in phase and has an equal and opposite angle at the other end, the speed changing is negated and the pinion shaft is driven at a constant speed.
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Old 11-26-2021, 11:05 PM
kenny c kenny c is offline
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Quote:
Originally Posted by MercuryMac View Post
Your kid was right, the transmission output shaft has to be parallel to the pinion shaft, and that's what you have now. Good show.
A side note is, make sure the shafts are parallel side to side also.
There are some good U-tube videos showing why you get vibrations with bad angles in your driveline. When you transit power through a bent U-joint the driveshaft changes rotational speed twice per revolution. If your driveshaft is in phase and has an equal and opposite angle at the other end, the speed changing is negated and the pinion shaft is driven at a constant speed.
Best way of explaining it I've heard. Mac, you're a word smith.
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Old 11-27-2021, 09:59 AM
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Thanks Merc...

Been researching all morn and I think the reason why it wasn't coming out in the calculator was my "ups and downs" where confused.

The definition from the spicer site is:

Up: Rises from front to rear of vehicle
Down: Descends from front to rear

Trans shaft.... simple = angled down towards rear

Drive shaft..... simple = angled down towards rear

Rear pinion (you'd think proper term is angled up cause the end facing the motor is up to the sky) It's not, it's down because per the description - Down: Descends from front to rear

1) Very simple video by Spicer. Around 4.30 they show you how to do the math.....simple.

Video here: https://spicerparts.com/videos/measu...erating-angles

If interested in seeing the calculator its here:

https://spicerparts.com/calculators/...alculator#more

Maybe this info will help someone who coms along who doesn't understand it.

The only thing that doesn't make sense to me is why the trimec smart phone app keeps coming up red.
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Old 11-27-2021, 10:45 AM
bob w bob w is offline
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I use "equal and opposite" angles. However the included angle in a given u-joint should not exceed a certain number, which I can't remember. (maybe 5 degrees from straight through???)
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Old 11-27-2021, 11:18 AM
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I've always used 3 degrees down on the engine/tranny & 3 degrees up on the rear end... never a problem!

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Old 11-27-2021, 11:50 AM
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Thanks Bob & Tripper!
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Old 11-27-2021, 04:05 PM
bob w bob w is offline
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Quote:
Originally Posted by Tripper View Post
I've always used 3 degrees down on the engine/tranny & 3 degrees up on the rear end... never a problem!

BoB
And I generally use level engine and level pinion. Depends on the build. If the elevation difference between the engine and rear end is too great (That included angle again) then I start tilting stuff.
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Old 11-27-2021, 04:41 PM
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This stuff is confusing as hell..... Somewhere I read 3 degrees on the motor. But also level carbs. How in the hell do you get both??????

It seems that all will be driven off driveshaft angle which I can't change.....or only change slightly with tail shaft / pinion angles.

Once I have the drive shaft I'll adjust to get that 1.5 operating angle.

My biggest dilemia was not understanding pinion pointing up is really front to back DOWN.
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Old 11-27-2021, 06:34 PM
bob w bob w is offline
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Somebody will correct me if I'm wrong. I believe some Chevy engines were installed from the factory angled to the rear. The intake manifolds were designed with the carb mount level with the engine slanted to the rear. Using these manifolds on a level engine would result in the carb tilted forward 3 degrees.

It's common in the hot rod world to install the engine slanted 3 degrees to the rear and the pinion pointed up 3 degrees.

To add to the confusion, in drag racing the pinion is frequently pointed as much as 6 degrees down regardless of the engine angle. This allows for rear end "wrap up" under hard acceleration.
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