Help with pinion angle on a lowered car?

Hopefully someone can help me out here. I'll try to be as clear as I can and as simple as possible. A little about the project. 1927 RPU jalopy. The frame in front is Z-'d with 25" tall tires. The rear frame has a high kick up with 30" tall pie crust slicks on it. Rear suspension is fixed with a set of split wishbones. The truck sits VERY low. 3 1/2 inches at it's lowest point.

I have always set up the rearend pinion angle on a leaf spring cars at 6 or 7 degrees. On a fixed rear such as a ladder bar set up I will give it 3 or 4 degrees of pinion angle.

The problem I'm looking at is the way the 27 is built. The rearend is sitting way higher than the trans tailshaft. It's the opposite of what I'm use to dealing with. With the pinion angles I normally use the pitch on the short driveshaft looks like it's going to snap a U joint quick.

Should I drop the rearend pinion down to make driveshaft more in line with the trans? I hope some of this make sence to someone. Maybe I'm just overthinking here but it just doesn't look right to my eyes.

 

With the split bones, you are not going to get a lot of pinion angle change. I would just try to match angles on the rear end and trans (parallel shafts). Don't worry about the offset heights...really.

 

X2.
Pretty simple just pretend the diff is the tranny out put and the tranny out put is the diff. Same measurements apply.

 

as you know, pics are worth 1,000 words - post some of your ride

 

Setting pinion angles is easy with a digital angle finder. Set it on the trans yoke and '0' it, now set on differential yoke and measure. The angle should be nose down for the rear housing. Does not matter if the axle is above or below the trans. Like others have posted you should not need more than 2 degrees nose down unless your running leaf springs on a drag car. Once the rear is set; Its a good idea to check the working angles of both u-joints. The front should never be less than .5 the rear should never be more than 4.

Drag racing and raised trucks will be different but this set up has worked very well for me.

 

I do hundreds of these, rule of thumb is to keep the angles parallel. i.e if the transmission points down at 3 deg (typical of factory cars) then the pinion should point up 3 degrees. You want to keep imaginary parallel lines through the centerline of the trans and the centerline of the rear. There will be times when it varys like leaf springs where you would subtract a few degrees due to "leaf spring wrap" under accelration, but for a low riding car with a bones style setup stay with keeping them parallel to start. Check out Rossler transmissions website if in doubt. In a car like yours where ride height may not be set in stone till the end put the motor and trans in level at (as close to) finished ride height and the pinion at 0 degrees. Pm me with any questions.

 

Above in red is the problem area that I am talking about. The trans is pitched down and the rearend angle is pitched up. Unlike a normal car the whole rearend is sitting a lot higher than the trans. The driveshaft looks like it's sitting in a lifted 4X4 with it's angle. Making it worse is the pinion angle on the rearend going up and the drive shaft shoots down. Someone said just reverse the pitches. While that would work for the driveshaft it would make the engine look funny in the bay. I can maybe lift the trans tailshaft up getting it to (0) and then do the same with the rearend that may help with U joint life. Even at (0) I'm worried about what the engine will look like at the firewall. I don't want to look like it's leaning forward. With the intake I have made higher in the back to level out for the degree the motor sits. So if I can get the tailshaft up to (o) and not look funny in the engine bay then this should work right? (0) and (o) on both?

 

Measured from the floor/ground, how many inches separate the heights of the pinon and the tailshaft? How long is the driveshaft?

If it is that far off, you can use a double-cardain driveshaft, not unlike what you'd find in the front of most 4x4 trucks. It is the same thing, turned upside-down.

My A is setup like this. Like the picture here, just with the driveshaft angle flipped over (up to axle, not down). This is also the man who made my shaft: http://www.4xshaft.com/ Vibration free at 120. Got the idea from working on 4x4 rigs for years and years.

 

That is the $64,000 question, isn't it????

Help us help you, Rebstew. Wow, poetry.....

 

the pinion angle should never be up,leaf spring 3 down,ladder bar or 4 link pretty much 0,if the trans tail shaft is down,more pinion angle down...,thats the problem with lowering the car or truck to low

 

Never say never... On something like a truck arm setup, you can point the pinion up to match the engine angle without any problems, because it isn't going to change much, even with anti-squat under acceleration.

 

All of the multi-link setups I have done have a 3-degree up-angle on the pinion, to match the 3-degree down-angle on the tailshaft.

 

that don't make it right

 

Well, I am a pro suspension builder by trade, and an engineer, so what would make it right?

 

i don't want to a pissing match with you, i've been messing with rearends myself for a long time,learned from the best fabman around here...just saying

 

i have spent alot of time researching this myself, i set up mine with the "standard" 3 up on diff. 3 down on tranny, and had a bad vibration in 5th gear took 1 1/2 degree out of rear and i have less vibration now. still a little so i think im headed in the right direction,i have the same slope up to rear,problem you have, im gonna take more out of rear, to prob. 0 and see if it goes away completely....i think you have to consider the angle of the driveshaft into it, because that increases the angle of the u joint itself, im no expert but i know what is starting to get rid of the vibration, and it is not the 3 down 3 up for my car.

 

HAhahA. Pinion up or down? I always set my pinion up too. This is the first low, low car I have built. I don't think the pinion up will work here because the rearend is higher than the trans as stated above. When I get back to the garage I'll do some measuring. I really think I was just over thinking it. Too many hours in the garage that night. I'm thinking (o) and (o) will work.

I don't know if I have ever seen a double cardain driveshaft. Pretty cool set up. I don't think mine is off that far to use one. It's a good one to remember though.

This raises another question for me. I always run the pinion angle up. It's been posted here a couple times that it goes down. So does it normally sit at (o) or down or does it sit with the pitch up? If it sits at (o) or down I have been doing it wrong for many years.

 

I think this is interesting. 60 Chevy factory manual. Notice pinion down.
Notice how having the front shaft with the yokes at 90 degrees ,the angles are additive.

 

It may be a good idea to make some adjustable mounts sounds like.

 

hello, dont forget that these angles are for the relationship between trans and drive shaft and drive shaft and rear diff. they are not just to be set up or down from 0 degrees. height and length between trans and diff have to be concidered as well.

 

Once again I will stand my ground and I agree with Gimpy. I have (no shit) well over 300 chassis on the road with the 3 up 3 down setup and ya know how many calls I get about driveshaft vibration? NONE. Many of the driveline vibrations we have encountered over the years are due to bad driveshafts. I use A good quality USA driveshaft balanced and we have zero issues. For a lowered car you can run 3 up on the tailshaft and three down on the pinion or if you are more comfortable zero and zero. There will always be some misalignment and that is good, U-joints need to move through an ellipse to properly grease all the bearings. In a street rod with limited use that is not so important, you may need to replace a U-joint at 25k instead of 75k but thats still many years of driving in a rod. There are a multitude of ways to do anything and even though not correct they will work. Sometimes you just have to fit ten pounds of shit in a 2 pound bag. But if you keep in mind that a line through the axis of the transmission and a line through the axis of the pinion should never meet (parallel) you will always be ok. Many of the "professional" opinons online are based on race car geometry with a level crank/trans...then you certainly would want 0 or a degree or two down on the pinion to account for pinion coming up on acceleration.

 

Or for all the guys with too much money in their pockets (not me lol) you can run a reverse rotation ring gear and high pinion carrier like the 4x4 guys. Just sayin...

 

Not to be a pedant, but it is "reverse spiral bevel", not "reverse rotation". If it were reverse rotation, you'd be going backwards in forward gers. On offense, just a pet peeve of mine.

 

so, rebstew187 no pics of your ride?? we just have guess as to exactly what set up you have? hope you have searched for other posts on pinion angle threads: my pinion angle..again, pinion angle...is this right?, etc one thing I have found is that most aftermarket angle wedges are 2 or 4 degrees-3 degrees is not so common.

 

My most humble apologies, I should have said "reverse cut" gear......one more reason not to hit the Tequila before 5pm...............

 

2pc driveshaft, Andy. Different story...

The trans output shaft and pinion shaft should be parallel under max load...and that is the key. That's exactly why you see so much down angle on the rear of a leaf spring car...the axle wrap is factored in to the pinion angle. We run a couple degrees down on 3 and 4 link suspensions to allow for anti-squat.

As I stated above, on truck arm, torque arm, and traditional wishbone rear suspensions, the pinion angle can run uphill to match the trans, as there is far less pinion climb with the solid mounted links.

ANYBODY who thinks this is wrong can argue with these guys...
http://www.spicerparts.com/measuring.asp

 

Naw, I'm already on the mimosas here, and it's not even 2.

 

Thats a good Sunday beverage and you can tell yourself it's good for you too! I try to get more vitamin c by eating two limes before the shot of Patron.

 

The output shaft of the transmission should be set up parallel to the pinion shaft of the rear differential. Their relationship to each other such as up, over, sideways or down really don't matter unless you exceed the maximum operationing parameters of the joint... Two piece driveshafts are really nothing more than an early version of a constant velocity joint...

 

If the transmission and pinion are at different heights, couldn't they both be set to 0 degrees? The angle of the driveline would be the same on both U-joints and the driveline angle would be the needed angle to have the U-joints functioning properly. Don't mind me, I have 0 chassis under my belt ; ) I'm building my first Rod and have been reading a lot on this subject. Please correct me on what I'm missing here.