I just swapped the trans, cross-member, and driveshaft out of one of my cars into another. I picked up a slight vibration. After doing a search here, I am thinking my driveline angle is too much: -trans is pointed down 7.5 degrees from horizontal (more than before, due to the cross-member allowing the trans to sit lower in the back) -pinion is pointed up 3.5 degrees from horizontal (shouldn't the pinion be pointed be down????) Doesn't that make it 4 degrees at rest and around 2 degrees under power? That's not perfect, but it should be OK, shouldn't it? Do I need to look elsewhere or is my problem hidden here?
From everything I've heard about driveline angles, it sounds like you may have alittle too much angle for the Ujoint at the trans. Yes, 4 deg. is correct, I would call a drive shaft shop and ask them about the angle mentioned at the trans. If they think it's OK, I'd look into balancing the shaft. Is this shaft a "stock" shaft, just from another car?? Gary G.
Thanks Gary. Its a custom shaft straight out of my race car that I had a shop build countless passes/years ago. Who knows, the vibration may have been in the race car the whole time, but with open headers, no interior, and solid motor mounts and body bushings, I never would have sensed it. The new car is more like a Caddy, so it's easy to sense something's off.
Pinion angle If I understand your math it would appear that you have 11 degrees pinion angle at rest and more like 13 going down the track! If your rear pinion was pointed down 3.5 degrees then your math would be correct but if it's pointed up and your trans down then you will have a big vibration. Double check it before you break something like a trans, driveshaft and rear. Tom Rix
Hi Tom. I had to dig through a few years of GSXtra's to find an article by Ron and L.J. Ryglski (Mar/April '02) to see if what I was doing was wrong. So I think I found my answer: driveline angle (trans pointed down) is -7.5 degrees rear end angle (pointed up) is +3.5 degrees The math makes my pinion angle -4 degrees. I do need to check it to make sure I measured correctly though. I think I will need to elevate the trans crossmember and the mount a ton, but it may not make much of an angle change, if any. Maybe a good excuse for adjustable uppers.
Re: Pinion angle Tom's absolutely right:TU: My car was as he described, i was breaking tailshafts. Randy
I have to respectfully disagree with the above.... If your tranny is pointing down, you need the rear to point up. Allthough your tranny is pointing way too far down in my opinion. Here's a pretty good article about pinion angle: Click here Here's another article One more article I would tilt your tranny UP about 2 or 3 from where it's at and see how it goes from there. How's your control arm bushings? (How much is your rear going to twist under full throttle?)
Angle My post is incorrect. My brain translated what I read to the wrong answer. I don't run positive rear end angle on mine if I can help it and prefer to only have the trans down a little. The stiffer rear suspension bushings you run the less pinion angle you want. Stock style bushings will need a little more to compensate for flex. Tom
I'm no pro at this, But what I think your saying is that your tranny is pointing down too much and need sto come up a taste. If this is the case I had the same problem with one of my other cars a while back and heres what I did, mayby this could help. I had a 5-speed with an Energy suspention trans mount and the tranny had to come up so what I did was musred the plat on top of the mount, cut some steel 1/16--1/8 shims drilled out the holes and put them on top of the mount and bolted it in.. I shimed it untill the vibration went away.. Its been like this for a little over a year now and havent had one problem... Hope this helpes
OK, so here's the final story.:Smarty: My measurements were as stated above when the car was on stands right before I dropped it back down after a trans and cross-member swap. I remeasured last week and boy were things way different. :spank: Trans was -11 (down) and rear end was +1 (up) for a whopping 10 degrees of angle!! :jd: I put my the other cross-member back and got the trans at -3 and rear at +1 for -2 total which is where it should be. So the vibration wasn't my imagination (I have a way of doubting myself). I hope I didn't crack the tail-shaft on the trans or trash the bearing in there. :error: Thanks to all you guys that chimed in to help. I learned a lot. :beer
so you have your rear end pointed up? I have the same thing as you, witch is not common, my tranny is pointing down 4 deg. so I put my rear up 2 deg. still had a vibration. while I was at the GSNats. I talked to a few people about it and they said the rear should never be up. so I put the rear @4 deg down and tranny 2 deg. down, still have a little vibration between 55-65, real slight, pulsates. so what setup you finally end up with?
Mike, that was almost 3 years ago, and my notes are buried under 2 years worth of rebuilds and other mods since then. I should still be at -3 trans and rear +1 for -2 total. Re-reading the above posts, I had 2 problems: measuring while on stands (should have been on the ground) and a cross-member that allowed the trans to sit too low in back (it was perfect in the race car, but no good in my other).
Doesn't matter which is up or down, as long as they are opposite! In an ideal condition, under power, the two angles should effectively cancel each other out when you do the math. The same goes for a side-to-side install in case output shaft and pinion don't follow the same centerline from the top view (offset pinion). Us big-car guys can get away with breaking this rule because of the use of one or more constant velocity joints: Devon
Wildcat is right, but I would add the following: a) From a vibration standpoint, ideally you would want zero degrees working angle at both ends. However, from a durability standpoint you don't want zero because then the roller bearings inside the cups don't rotate and you would brinnel a small indent into the cup. So - the compromise is you want a very small angle (like 1 degree) to rotate the rollers inside the cup, and you want the same angle at both ends, so that it cancels out. b) Additionally, it probably doesn't matter if the pinion nose is up or down, based on the above. However, I would suggest you want it down, because the rear axle nose is always going to wind up during acceleration. On a leaf spring car, it's huge (like 4 - 7 degrees); on a coil spring/4 link car it is relatively small but still there (like a degree or maybe two). If you start with the axle nose up, then it is directionally worse during acceleration; with the nose down you are moving directionally correct. And, of course, all these measurements are taken with the vehicle weight on the wheels (ie, at the correct ride height, not with the rear axle hanging). FWIW - K
ok, I've got the rear down 1', and tranny is down 1'. better but its still there. I would think you wouldn't want rear up cause when you take off the rear will tilt up more, correct?
Sorry, what is 1' ? one degree? (obviously it's not one foot) Without knowing how much the pinion rises under load we're still guessing, unfortunately. Devon
IF YOU DON'T LIKE THE PINION TO POINT UP, PARK YOUR CAR ON A DOWNHILL SLOPE. PARALLEL.....PARALLEL....PARALLEL.... NOTHING ELSE MATTERS. TRANS AND PINION ONLY . NOTHING ELSE MATTERS ON OUR FACTORY A-BODY FRAMES. FORGET THE DRIVE SHAFT ANGLES UNLESS YOUR BUILDING A BIGFOOT or have other than 2 u-joints on one drive shaft. Parallel at wide open throttle on race cars ( will be nose down -2 to -4 or so on strip cars when no torque is applied). Parallel at cruse and rest for street cars. Parallel to -1 for mild performance, is OK if you have stiff aftermarket bars/arms with polyurethane and not a roll bar class car. PARALLEL MEANS: TRANNY POINTS DOWN -2, REAR POINTS UP +2, ETC,ETC PARALLEL MEANS: TRANNY POINTS LEVEL 0 DEGREES, REAR POINTS LEVEL ALSO, but will be above the tranny line. Both above examples are the same car but SECOND example has a board under the rear tires.
well my tranny cant go up anymore its hitting the shifter, tranny is down 2 deg. now im measuring this on the pan. rear is down 2 deg. Im running Metco rear control arms with poly bushings. still has a little pulsating vibration around 65. So your saying I need to go straight or up with rear?
