Setting Pinion Angle

[rustbucket49]

I did a search on pinion angle and didn't find an answer to my question, hence a new thread....

I have the car up on jack stands such that the body appears to be level on the stands (when measured on the top of the rocker panel... just to give me a zero reference). When I check the tailshaft on the tranny, it is -8 degrees. Everything I read says you want zero to -3 deg of pinion angle so I would need to set the rear pinion at an upward angle of 5 to 8 degrees. That don't sound right to me.... Will the car hook-up right on acceleration with that kind of upward set-up on the rear (it's not a race car - just a cruiser - but I don't want to break a driveline....). I have also read that leaf spring suspensions can be set up w/ -5 to -7 deg pinion angle, which would only require about 1 to 3 deg of upward angle, right??

I have no room to change the tailshaft angle by moving the tranny up due to the design of the Walton xmember. I could cut the motor mounts and reconfigure to lower the front of the motor, but I would only gain about 1/2". I haven't crunched the numbers to see how that would impact the tailshaft angle, but I suspect it ain't much..

Can somebody give me some guidance here?? I will be calling a driveshaft shop as well..

 

[Gearhead10]

When I jig up 9" rears I go no more than 6 degrees pinion angle. Thats for racin and street apps. Remember that when you get on the gas it will pull up a couple degrees. Too much angle and you'll bind up.

 

[rustbucket49]

When I jig up 9" rears I go no more than 6 degrees pinion angle. Thats for racin and street apps. Remember that when you get on the gas it will pull up a couple degrees. Too much angle and you'll bind up.

Gearhead, so correct me if I'm wrong - pinion angle is calculated by subtracting the angle of the tailshaft at the tranny from the angle of the pinion flange on the differential, right?? So if I'm at a -8 degrees at tailshaft and i set the differential at +5 deg, then my pinion angle is a -3 degrees???? Or am I just stupid.?

Your comment about the differential pulling up on acceleration is the reason I don't want to tilt the pumpkin up too far. What is a normal set-up for one of these cruisers?

 

[Gearhead10]

Your formula sounds right to me. I usually start at 0 and work off that. Most the rears I did were for metric GM so the geometry was already in place. I'd say you might want to set the trans end down if ya can but you don't wanna go too far either or the level of the engine and carb might be messed up.

 

[rustbucket49]

I found another post that shows a diagram.... check this out - I think I'm screwed and need to re-set the motor and tranny.... #$@!!%^#$@!!

 

[rustbucket49]

Your formula sounds right to me. I usually start at 0 and work off that. Most the rears I did were for metric GM so the geometry was already in place. I'd say you might want to set the trans end down if ya can but you don't wanna go too far either or the level of the engine and carb might be messed up.

I checked the intake and I'm off a little anyway. I think the formula is right, but the fact that I am STARTING at a -8 deg on tailshaft is not good - the angle needed to get to the correct pinion angle would not be good.... I need to pick up the rear of the tranny a bit and drop the front of the motor a bit. Hey, just more freaking work, right ????!!!!

 

[Gearhead10]

You might be right man. When buildin race cars we used to set the engine in, get it level, front to back and side to side. Remember to check level at intake where carb bolts on cuz the intakes are designed with engine tilted back in the rear a bit. Then we'd check pinion angle at 0, and set it at the 5 or 6 degrees we wanted and see what angle the driveshaft was. Sometimes we were nuts on and sometimes we had to set the engine mounts up or down to make it come out right. Hope any info helps.

 

[rainman]

My opinion is that you also have to take into consideration what type of rear set-up you are using, 4 link, leaf, coils, etc. because you have to have some idea of wrap-up under acceleration. On most all of our oval tack cars we would end up with the rear end at about 3 to 5 degree's in a downward position.

 

[rustbucket49]

My opinion is that you also have to take into consideration what type of rear set-up you are using, 4 link, leaf, coils, etc. because you have to have some idea of wrap-up under acceleration. On most all of our oval tack cars we would end up with the rear end at about 3 to 5 degree's in a downward position.

That's what I want too, but the way the stock front crossmember is set and the way the Walton tranny cross member is configured, it looks to me that it is impossible to get a flat or up angle on the tranny tailshaft.

 

[fuzz]

Rustbucket...don't panic, you don't need to remount your motor and trans for 8 degrees downward angle of the trans. The 3 degree negative pinion angle recommended for racing purposes isn't that important for your street cruiser. The important part is that your u joint angles aren't exagerated. If your trans is angled doward 8 degrees and your drive shaft is at 0 degrees, level with the body line, your u joint angle is only 4 degrees and won't wearout or break sooner than normal. Even if your front u joint was as much as 8 degrees you will not have to worry about wear or breakage, it's not that much of an angle. The pinion angle should be set at about 1 to 3 degrees negative, thats downward, do not adjust your pinion to an upward position. Don't try to compensate for the trans angle by adjusting pinion angle. If you look at some of the big trucks on the road you will see some with two piece driveshafts that have some serious drive shaft angles. Thats what u joints were made for.

 

[rustbucket49]

Fuzz, this makes sense to me, but if you don't mind check post #5 in this thread where I attached the diagram. On the last example it talks about a 6 degree tailshaft angle and offsetting the angle the other way @ the differential. It says it won't work w/ that kind of angle - will have vibration and ultimately failure. However, this is a little different than what you suggest - that is have the angle at the tranny, but DON'T offset the angle at the rear end.

So you're saying, leave it the way it is at the tailshaft (-8 deg) and point the differential down maybe -1 to -3 deg ??? This goes against everything I've read that says you should have a parallel lines w/ opposing angles..... but what you say makes sense - just want to make sure I'm clear on this.

Also, with the Ford rear end, the shaft is off center to the tranny, so there is an inherent angle in the u-joints introduced by this anyway. How would you compensate or set up the rear end with this in mind?? I presume you'd still leave the engine and tranny alone ????

Have you done a lot of these set-ups Fuzz ??

 

[fuzz]

The 9 inch rear is offset in passenger cars about 2 1/2 inches and in some vans the pinion offset is 6 inches. This offset is probably 8 degrees or more. See my point? When you build your new driveshaft be sure the u joints are in "time" that is the u joints need to be inline. Out of time u joints in home made drivshafts will cause vibration. If a professional builds your drivshaft he will know this and can explain it better than me.
When folks publish articles in magazines they must 100% correct in what they tell the customers or they will be critisized by detail freaks that nit pick. And most articles about pinion angle are written for the racers that are putting high horsepower to the ground all the time so driveline angles are more important.

 

[rustbucket49]

Fuzz, "in time" I presume means that the u-joint caps are 90 deg apart, right?

So with the -8 deg on my tailshaft and fact that I'm using the Ford rear end, how do you recommend that I set up the rear?

 

[fuzz]

When you look at a stock driveshaft you'll see that the u-joint mounting flanges are inline from front to back.When you cut the drivshaft to shorten it you need to keep those flanges in alignment.
By set up I assume you mean the pinion angle? I mount my rears this way! Set the chassis leavel, I think you already did that, Set the rear housing on jack stands close to level, front back, side to side, I use a carpenters "angle finder", get one at Lowes or Home depot, and rotate the housing til I get 1 degree negative angle and weld it in place. Install your driveshaft and don't worry about how it looks. Imagine how the driveshaft angles change in an air bagged car as it is raised and lowered.
If I were building a 700 horsepower race car I would mount that motor and trans level with the chassis and mount the rear at ride height with 1 degree negative pinion for ladder bars or 4 link and 3 degees for leaf springs and I would want it exactly the way that diagram shows it should be done. When the slicks grab the track the rear will rotate 1 degree so the driveshaft is perfectly straight so I have minimum stress on the u-joints.
I read aricles about pinion angles and bump steer that scare the heck out people to the point that some new rod builders give up on thier project cuz they're scared they'll mess it up and the project is a total loss. Don't worry about it, get it done and have some fun!!

 

[rustbucket49]

Fuzz, thanks - sounds great to me. One other question, how much travel should you allow for on the tranny yoke?? Or how much is too much....

 

[fuzz]

Fuzz, thanks - sounds great to me. One other question, how much travel should you allow for on the tranny yoke?? Or how much is too much....

At least 1 inch is good, 2 inches is too much, depends alittle on the length of the yoke and type of rear suspension. Control arms don't allow much travel but leaf springs would allow driveshaft to travel further.
Post some pictures if you can.

 

[rainman]

I agree with Fuzz the only thing is if you're running leaf set-up you might run a little more angle, 4bar or fixed set-up a little less. OOPS I didn't notice a second page.

 

[rustbucket49]

Thanks guys - I just got it set up for -2 deg. Plan to weld in the spring perchs manyana in between my son's baseball games.

 

[shakey56]

Hey Rustbucket. This discussion has ruined a lot of friendships but here's my 2 cents. I have friend who has a rod shop. I asked him because I just installed a 9 inch and I have a vibration in my F100. A bad one at 45 mph up! He sets his at the same as the trans angle but opposite. Trans -8, diff +8. He's been doing it that way for 30 years. High dollar cars! Whatever trans angle, diff is the same but opposite. I'm going to have to make a couple of panhard bars....mine is wrapping up. Good luck...hope we're still friends!

 

[ratrodderlc]

I'd like to jump in for a moment and relate what I've been through in the last couple of years with regards to pinion angle problems. The shop I trusted to install a set of ladder bars on an 85 silverado for strrip and show ended up with an angle of plus 8 degrees! I knew very little at the time but through a painful learning curve I solved it. My truck experienced severe vibration between 3200 and 4000 rpm. Changing the angle to minus 1 degree solved the vibration problem. As long as the angle is negative, at rest , you will be good to go!