is this the correct method and interpretation for checking pinion angle?

1, put the car up on blocks, to have enough room to work under it and have the car's weight on the suspension

2, removed drive shaft

3, set an angle finder on the tranny out put shaft, stacked a magnet and a washer together to make up for the output seal over hang,, the needle was to the left of the 90 by 3 marks, I make that to be tranny end down by 3 degrees

4, set a second angle finder on the flat of the yoke flange, the needle was again to the left of the 90 by 3 marks,but because the diff is pointing in the opposite direction, I took that to be the diff pinion was up by 3 degrees.

photos of the set up

https://www.flickr.com/photos/13718356@ ... 9710840322

I am thinking the -3 of the tranny is cancelled by the + 3 of the diff and everything is good,,

is that right??

thanks

Sounds right to me. If you have no vibration, then that is the biggest indicator you are good. Some folks set up a 2 deg net down angle on the pinion, but for a low HP application this is not needed.

Lou

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Home of Slant6-powered fun machines since 1988

you ideally want the trans and diff angle to be the same under normal driving conditions . the faster you drive, the more the pinion rises . since your angles are the same at a static position, they will not be the same as you cruise down the highway . if you have some vibration, that would be one place to consider changing . i typically set the pinion up so it is around 1 degree lower than the trans . at low speed it does not rise much but you wont notice vibration from the mismatch in angles because of the low speed . at higher speed, the pinion will rise and be closer to the angle of the trans then your current setup which will reduce the potential for vibrations to happen.

You have it right John.

You need a little angle on both ends and your 3 degrees is perfect.

Of course the pinion does not rise the faster you go,,,,but it will rise on hard acceleration. In your application that rise need not be compensated for.

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Yeah....Im the one who destroyed this rare, vintage automobile.....

The pinion certainly does rise a little more the faster you go. It has also been proven with video cameras mounted to the bottom of the car.

...that sure is a purdy '68 cuda...

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https://tinyurl.com/yynpj4v2

Interesting topic.

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Yeah....Im the one who destroyed this rare, vintage automobile.....

Barnett; The other replys aren't trying to discredit you, or call you a liar. They are trying to dispense accurate info, as well as correct what you're trying to dispense. You are partially correct. The pinion does rise, but not as speed increases. It rises as torque increases. At initial launch, whether it's a gentle motoring away from a stop, or a drag-race launch with all the car can muster, the rear tires dig in, causing the axle assembly to attempt to rotate the opposite direction, thus elevating the pinion angle. As the applied torque fades away, then the pinion angle rotates back to, (or close to), the at-rest angle. There are some variations while driving, due to road surface, but that's small.

You are not required to believe what I've just told you, but I recommend this; Check out what I've said with an independent source. What you claimed above is wrong, and apparently someone taught you incorrectly.

Roger

Barnett and Dart 270....you are most definitely correct from my experience...of course the pinion rises as speed increases. Yes it's a torque reaction,no doubt about that and the most reaction would be on a launch or during hard acceleration,but that's not the time the driveshaft is operating at high rpm and vibration issues typically aren't present at this time,and it's the high driveshaft speeds that will usually show if you have alignment or phasing issues,and unless you can overcome the immense drag the typical Mopar aerodynamic brick creates at speed the engine needs to develop more power to propel the vehicle at high speeds resulting in a minor pinion rise. To allow for this about a 1 or 2 degree difference is usually the end result to give vibration free high speed operation,this is for the usual old buggy spring design and will vary slightly with different springs of course,4 links are obviously a different set up. Remember your taking these measurements with zero forces on the drivetrain of course,it's obvious that some deflection or pinion rise must take place during operation to propel the vehicle.... This is what you are catering for in any specific vehicle in order to create a zero degree difference in uni joints DURING OPERATION...If in doubt mount a go pro and watch for yourself....sure you may get away with a zero stationary difference,especially on a hard sprung vehicle like a truck,lets face it,slants aren't exactly powerhouses or high speed weapons,but the 1 or 2 degree difference is pretty typical of a reasonable power output vehicle with buggy springs. At the end of the day if it doesn't vibrate your on a winner. People get all carried away with pinion angles,fair enough,but there is also the need to have both Uni joints parallel on both the longitudinal and lateral axis...ie,when they weld the yokes in the distance between the centres of the front and rear bearing cups must be equal on each side,plus inline with each other. I've had shafts done that have been out like this and created problems.

nope....GTS 225 has it right

If the pinion rose 2 degrees on a hard launch in low gear at max torque it would rise far less at the same torque applied in high gear,
That is because the appled torque is not multiplied in high gear nearly as much as in low gear. Lets not even get into tire growth.....

If the slant in question develops 300ft/lbs of torque x a 3.5 first gear ratio the applied torque on the springs is 1050 ft/lbs

In high gear its 300 ft /lbs x1 = 300lbs applied to the springs.

Launch the car in high gear and see how much the pinion rises.

Typically on our cars the downforce and lift at speed are about equal.

Luckily our original poster has a good understanding and has his angles within range and will be fine.

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Yeah....Im the one who destroyed this rare, vintage automobile.....

Only use jack stands!!!! Blocks are in no way safe.
Will

Thanks for that, Will.

Roger

it is my understanding that the weight of the vehicle needs to be loaded on the suspension, when measuring pinion angle

I agree that jack stands under the rear axle tubes would accomplish that,
don't know how jack stands could be used to load the front torsion bars.. ?

Front end is irrelevant.

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Official Cookie and Mater Tormentor.

I agree the most accurate measurement will have the car with weight on all 4 wheels and car level as it will sit on the road. For example, if you put stands under the front frame rails behind the wheels, then you will unload the rear springs some and change the angles. As one example, if you put stands under the ends of the LCAs and the rear axle tube, then you should be fine. Or, put the front tires on ramps - might be easier and safer. You could also put tall stands under the fronts of the front frame rails and that should be fine.

Lou

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