Thread: Pinion Angle

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I have had trouble with vibration for a while now an could'n find the problem. I took my car to a older gentleman who kinda dose his owne thing tends to his business. I talked to him about my trouble he said I'll find the problem so I left it.In a few day he called me back said your ready to go. Now my trans angle is down an the rearend is angled down to but not on the same angle it's smooth as silk and no vibration. That's right the opposite of what I have been reading so can someone please explaine

sounds like you were binding the U joints, by changing the angles it let them move freely. Both down doesn't sound right but you didn't say what they were before. Rear up trans down is what works best.

Down and down doesn't sound right to me. Tranny down and pinion up on equal angles is the traditional "right" layout - http://www.iedls.com/asp/admin/getFi...&TID=28&FN=PDF

I just read a great piece on this on HotRodHotline.com ... In short the trans needs to be 3 deg. down and the rear pinion needs to be up the same amount the trans in down but no more than 1 deg. off...

Down and down has worked great for me for years...Still keeps both U-Joints at any angle.... A "pinion up" angle never made any sense to me on any car.. I've always viewed all the articles on "How to Build It" as just another guy expressing his opinion, some are good, some aren't.

Thanks for the reply, it's good to hear Dave has been doing this for years.

I'm glad that the down & down has worked for you, but the setup recommendations I posted are from Greg Frick of Inland Empire Driveline Service, not "just another guy" in my opinion. Down and Up doesn't take away the working angle of the u-joints, they are both still going through their gyrations but with the angles equal and opposite the harmonics in that motion cancel out. The problem with a mis-match is that the forces developed during rotation can compliment each other, adding together instead of cancelling each other out which leads to vibration you can feel, and increased wear.

There's a huge difference in setting up the driveline for a highway cruiser compared to a quarter mile warrior where it's common, accepted and correct to account for the wrap of the rear suspension during launch and max acceleration. Equal and opposite puts the u-joints in a bind in that situation, and with the high power, torque and bite leads to broken parts. If it were me I'd go back to that "older gentleman" and pick his brain a bit about exactly what he did, and the rationale behind it but if it's working it's working, right?

Plot out the suspension angles when the car is in motion.... Not at some 7" travel thing like a lot of these theories are working under, but the usual 1 1/2" ti 3" of travel from center, then plot in some squish and the pinion's natural tendency to climb up the ring gear...I've guessed at 1 degree with heim ends and as much as 3 degrees with poly ends on the rear arms.... All the "equal and opposite" stuff works good on paper, but for some reason I've always had the best luck just setting the top of the engine level at the intake, and somewhere between 1 1/2 to 4 degrees of pinion down.... I don't claim to have all the scientific data as to why this setup works, but it's worked for me with no driveline issues (other the too much power combined with too much bite and a few broken parts from that) on drag cars and street cars for years.... I think a lot of it is people looking at these angles in static, no load conditions and not taking into account just how much things back there move around! I think this equal and opposite thing works great, but most people don't have the application down right. Found over the years it also has a lot to do with tire flex (on acceleration and over bumps), most of this stuff (as well as suspension settings) are done in a "no load" condition, ie the car sitting on jack stands and no account is taken for the weight of the liquids carried in the car, driver and passenger weight, and a host of other things. Companies like Inland Empire do a good job, but you've also got to remember that their recommendations (much like OEM specs) are "generic" in nature, allowing for wheelbases from 95" to 115", and not necessarily ideal for a short wheelbase car with 400+ horsepower being applied by a drivetrain that actually works, not the OEM crap of eating up 20% of the power produced in parasitic loss..... Think about how much all these static changes changes by the time you're on the road with two adults, a trunk full of junk, improperly inflated tires, and 15 gallons of 92 octane. I'm not an ME, I just do what works based on trial and error over the years.

Also, I've always wondered just how much of this written stuff from the experts in whatever subject is just some guy with little or no practical experience expressing something on paper that is meant to either justify his existence or sell whatever product he is pedaling???? The one absolute I have found to be unfailing in building Hot Rods and Race Cars, is that there are no absolutes!

Where to start??????????


OK--its a commonly accepted assumptionthat the theory of the presumed conditions where maybe written out by an graduate engineer with a law degree so the detailed suggested guidelines would answer the political corrected papers that have been exchange bewtween the gov dept of trans and the justice department tp arrive at a threshold of general public searching the internet could then post repeatedly in threads plus have back up (in theory) on small business ads that pop up on a google search------------


A few items---rules of thumb??????


The suspension doesn't raise and lower the tire,rear axle, pinion-they stay basicly same distance from the planet EARTH!!!!!!!!!


Most people didn't have these problems until they got a magnetic angle finder


The idea that you mount the engine so the carb is level is a false assumpsion


The angle of the trans output shaft to the GROUND (planet) is irrelavent


The angle of the pinion shaft to the GROUND (planet) is irrelavent


However, the angles of those two shafts to the driveshaht tube is RELAVANT


The pinion may twist upwards a minor amount, but is not a factor if the suspension mounting points are close tolerant


The travel of the body up and down from the PLANET will change the angles of the shafts to the drive shaft------this angle change ideally should be less than 3 degrees----------


The angle that the u joint people discuss ( 1-3 ) is so that the needles in the u joint caps rotate to spread grease and wear to eliminate the needle pounding noutches and failing


This angle in lots of oem designs is addressed AND maintained by slight offset of crankshaft to pinion shaft centerlines


IN STREET RODS----we have progressed blindly down a lane getting installs of multispeed overdrive lengthy transmissions which then ends up with a very short drive shaft which then multiplies \the incidence of these extreme angles profounded by the prepounderance of some dude selling driveshafts over the internet---------the original vehicles that these transmissions come out of have because of length, in order to reduve the drive shaft unit length,have severely lengthened the trans tail shaft housings, which in turn , as a concequence of bottom line engineering then passed on to the aftermarket hobbists who want a short wb hot rod but want to get rid of the old scholl torque tube not must because of ordering parts online totally screw up a few basics of vehicular drive line engineering with the commonly mistaken idea that if they read it on the net, it must be true.

I was taught that if your transmission output shaft is 3 degrees down, the differential should be set at 3 degrees up. I used that theory on both of the street rods I built, and I never had an issue with either u-joints wearing out or vibration.

I would guess that the driveshaft u-joints are 90 degrees
out of phase causing vibration with trans down pinion up
condition but running smooth with trans down pinion down.

https://www.google.com/search?q=driv...w=1084&bih=668

Tell ya what!!! There is no hard and fast rule. Do what works for you and I'll continue doing what works for me. Don't feel it necessary to sit and nit pick someone else's assumptions and observations to death!!!

Dave I hope you don't think I'm nit pickin you---I am actually just trying to poke a little fun into the thread, suggest a few thoughts to maybe open somme eyes and also playing with posting a link-




Io agree with 100% on the facts that most of these are out to lunch, but it seems that no one wants to bother reading what we try to point out as being some simple basic issues-------I found all those pics and it took me 5 times before I got it in the post.


In fact I wish you would PM me a phone number, I'd like to talk to you about a thing or two---

In my experience, the equal but opposite angles theory is a basic starting point - Eg: trans at 3* down, Pinion at 3* up, or vice-versa. But in practice, sometimes that doesn't work, and the final solution may be something so out of whack from that theroem that it will cause an engineer palpitations. I have set up a lot shaft operated equipment, with just about every, and any type of flexible joint, and seldom has the equal and opposite idea been the true final solution, only the starting point. So, in reality, the answer is "whatever works, and works well" - within reason, of course; at some point, the angles will become un-workable.