Pinion Angle

[my79monza]

Since I'm using a 2004R the stock torque arm needs modified which I can do.
What is the correct pinion angle?
The tranny is pointed down 3 degrees does the pinion then go up 3 degrees?
Merle

[cjbiagi]

This is one of the more simpler and clearer links to pinion angle. The simple answer is the engine and rear should be parallel to each other so your initial statement is true.
http://jniolon.clubfte.com/drivelinepha ... asing.html
http://www.hotrodders.com/forum/how-det ... 76780.html

[chevyart]

merle you would be right if the rear had no upward motion, but it does.. pinion angle is based on engine angle(which does not move) and how much the rear pinion shaft moves up under load, to give final angle(always preferably parallel),, or maybe one degreee less on the rear side.i know how much ladder bars move(aprox 1 degree up) 4 link 0-1 degreee up) leaf spring cars 5-7 degrees up) and factory 4 links(4-5 degrees up.). i have no idea how much a torque arm gives up in upward motion,. if there is any flexibility built into it(rubber bushings etc) ,then i would guess maybe it would give up 2-3 degrees) and with no bushings in the arm itself, i would think it may give up 1-2 degrees, as there are still rubber bushings in the lowers, which may allow a little give.. if it was my car i would start with a dead level pinion shaft angle, working against your 3 degree down tranny tail shaft angle, and with a little up motion, you would be darn close to parallel under load.. most of the sites that explain pinion angle always fail to add in the most important part of the equation(the up movement of pinion shaft under load.) PS how do you get to adjust the pinion angle of the rear housing on your car with the torque arms.i am a vega dude, with the 4 factory control arms. art

[cjbiagi]

A torque arm rear is pretty much going to set itself once you attach the front of the torque arm. There is incredible leverage at the front of the torque arm to rotate the rearend. Once you attach the arm to the trans it rotates the rear to where it wants to be (factory angle) The only way to change the pinion angle is to start modifying the torque arm mount at the trans. If you are using a torque arm just bolt it on and you should be very close to factory specs. If you feel the need to change the angle then we can discuss that.

[Monza Harry]

Merle you are building a mostly street car No? With an occasional trip to the track? If that is the case you should stay closer to stock than the race set up Art is discussing as if you decide to take part in some "Real Street" race the high way drive with the drive line vibe from being out of alignment will drive you crazy and may eventually take out the u-joints. The pinion angle change with a torque arm should be quite minimal. 3/8 of an inch over 4ft is 1.5* so at best. (50% deflection over approximate length of the arm) I would only adjust the pinion down 3/4* if you plan to spend lots of time at the track and only the occasional high way jaunt. I hope this opinion of mine is helpful Harry

[chevyart]

harry, what i was talking about was pinion angle in general.. when i was saying what each type of suspension gives up(upward pinion shaft movement), that is just showing how racing suspensions dont allow all the unwanted movement upwards that stock suspensions give up. that is why we have to allow a certain amount of pinion angle down(less than engine angle) to compensate for the upward rotation and come out so the engine centerline and rear end centerline is parallell or (pretty close)( rear could maybe be 1 degrees less than the engine angle).. harry says the torque arm gives up around 1 1/2 to 2 degrees of upward movement(i think that is what he said), so. then i wuold set the rear end pinion shaft angle level at dead rest, and. with the upward swing of 1-2 degrees, that would put you within 1 degree of being parallel with the engine angle),9 which is 3 degrees down). my calculation is based on what harry has said about the torque arm deflection BEING 1-2 DEGREES UPWARD). between all of us, i think we can get our monza friend pretty close to being right with his setup. keep us posted art

[my79monza]

Well since I am using a 2004R it throws everything out of kilter.
car was a 4cyl with a TM200 now its a smallblock with the 2004R and neither the driveshaft or a V/8 torque arm come close to fitting as they are both too long.
I tried to cut the torque arm and overlap it to shorten it but then the tranny end bolt that passes thru the rubber mount hits the tunnel.
So I am going to offset splice the torque arm making the front lower to line up with my tranny mount.
When I was messing with it I found that when it lined up where it would have been with a tm200 I had right on 3 degree up on the pinon so that is what I am shooting for when finished.
The car is on stands so I jacked up the rear axle until I could wiggle the stands so the axle should be at normal riding height.
As i see it the torque arm will not vary any more than what the rubber mount will compress which is very little at most.
Hell with street tires they will go up in smoke before the torque arm gets that much stress.
Merle

[Monza Harry]

Yes Art what you are saying is correct, but that is to have the pinion parallel under full throttle ie: Max horsepower lets say 300 to 400HP, a really healthy street going H-body so at a peak horse power of 350 at or near 5250 rpm the torque is equal at that rpm (33000ft/lbs. divided by 2pi [6.28] =5250) so lets guesstimate 400ft/lbs. @ peak so 400x2.86x4.11/4' will equal 1175.5 lbs. of lift on the bushing at the tranny that would compress that bushing to about 1/2 it is about 3/4" /side as I recall. 400 is the torque 2.86 is first gear in a 2004R and I gave Merle a zoomie gear of 4.11 (I will probably go with a 3.90 in my car trying to make a cruise RPM that my cam will deal with (0.67 OD x3.90 Rear = 2.67 overall) and 4ft. is a (short I bet) torque arm length estimate. So that would be a LOOSE converter and trans brake launch. Purely an estimate for a starting point. So with your racing No's that would work out. But in contrast at 55mi/hr. the Chevy Citation needed 16 HP. to cruise (sorry I never heard Monza No's but I would think similar with less frontal area and some things the OEM's started to do to lower Coefficient of drag No's on the 80's cars beyond the shape) I am thinking the H and X body would be similar HP needs. So if we compare to the first calculation that would mean at Hwy. speed we lose the first gear multiplication and lose more torque on the arm as OD is lessening the torque (to boost drive shaft speed) and at 16>20HP the torque is much less than @ peak (2000 Rpm 53ft/lbs. =20HP) so if we take that x 0.67 (OD) x4.11 rear gears that gives us 36.5 lbs. of lift at 4' that would equal zero bushing deflection, so for a street driven car I would just use the stock setup as GM already did this math and tried it out. I am just trying to make the point that end use is a major part of the math and ultimately the chassis tuning/setup. If you are using a stock rear(7.5") and arm adjusting it to a set number would be a major pain as in how much would you move the upper torque arm holes forward to change the pinion angle down 3/4* (or whatever angle you think you want for your setup) remember you would be redrilling weld on the back side of the hole and 1/2 of the old hole on the front not easy in the driveway (or anywhere else). Or make a different mount to lower the front down which ever you think will be easier of better. I hope this helps out Harry Edit I guess I have to learn how to use the trig functions on my computer as that angle wasn't sitting well with me so rechecked on my old trusty calc. and the angle is 0.448* less than 1/2* Sorry for the less than perfect info myself

[Fasterthansome]

Equal and opposite to the trans.

[chevyart]

wow harry. really dont understand the engineering skills you have, but im sure it works out.knowing what we have all put together(info wise) merle can start with whatever setup is built, into the factory brackets, with one extra adjustment(if there is room). he can always shim the tranny-engine angle up towards a 0(level) position, if he needs to adjust angle some in that direction to get the proper angle at dead rest., art

[cjbiagi]

Harry, your math is giving me a headache

[Monza Harry]

Sorry guy's "Math is my Friend" Just trying to show that the pinion wrap that everybody* thinks they need to account for in their build is really only going to last for the first 10+/- seconds the next four hours on the highway the pinion will be out of alignment for a street car. If you are building a street car go stock a race car build in some nosedown attitude into your pinion. In between adjust accordingly. Merle are you going to make it through all of our CR P? We are all trying to help (in ten directions at once Sorry 'bout that) If you need an aspirin on of Us will help out. Harry P.S. Clyde I left out the torque convertor multiplication because I have never read any two things that came to anywhere near the same conclusions on that subject. So if you'd like we can start over! Do we need homework class because Clyde wasn't paying attention. * just a figure of speech (a bad one I know) I promise to do my homework on that right now!