Rear Pinion Angle/Leaf Spring '67 Camaro

[67rally]

I've read non-stop for a couple days now and can't seem to find a concensus...

What are you're thoughts on the ideal rear pinion angle in relation to driveline angle on a 1967 Camaro. With the subframe level, my driveline angle is at about 3.5* down, and I may be able to get to 3* down with shimming the rear of the trans up, but I'm getting very close to the tunnel.

-Hotchkis 1.5" rear lowering leafs/Hotchkis 2" lowering front springs
-Bilstein shocks all around
-Solid aluminum body mounts
-LS/T56 458hp/410tq
-Strange S60 rear w/4.10's


-One school of thought says the engine/trans should be pointed down (3* ideally) and the rear pinion angle should be equal but opposite (3* up).
-A variation on that says they should be equal but opposite, but then angle the rear pinion down 2* (roughly) to allow for pinion wrap = (3* down/1* up)
-The other school of thought says the engine/trans should be down 3* and the pinion should be down 3* as well to allow for pinion wrap (5-7* in a leaf spring car)

[67rally]

Not trying to add too much info, but...

I did the LS/T56 swap last year and had some vibrations at around 65mph with my 12 bolt. I shimmed the diff up 2* and it got better. Up 4* was even better. Up 6* seemed to get worse. I just swapped in the S60 this winter and would like to get this car vibration free for the spring. I don't have my new driveshaft yet, so I can't road test it now. I'm not completely convinced that my old driveshaft was balanced perfectly, so that why I'm going with a new high quality/high speed balanced shaft this time.

My main concern is street driving. I'd like to be able to cruise at any speed with no vibes. I'll probably auto-x it once or twice and drag it once or twice, but it's not my main concern.

I'm also thinking about adding a 1" lowering block at the same time, if that adds into the equation.

[mmosley]

What does Hotchkis say?

[67rally]

What does Hotchkis say?

From their FAQ's:


Q) Is there an optimum pinion angle?

Answer: Due to the nature of an automobile chassis, the various angles are constantly changing, which adds to the complexity of obtaining optimum pinion angle. Engines may not sit squarely in their motor mounts, motor mounts may not sit properly between the frame rails, cross members may not sit straight, and where the rear end is positioned. Despite all these factors affecting the positioning of our drive trains, they seem to work well enough in most cases, at least on the street in basically stock applications. We owe this functionality to the universal joint, which, by design, corrects for slight misalignments between the driving components (crankshaft and transmission) and the driven components (driveshaft and differential) of the drive train. (Please see the tech section to learn how to set your pinion angle.)

In other words...They don't know either.

[mmosley]

In other words...They don't know either.

Wow... I am disappointed.

OK... consider the source. I am reading the "gasp" Mopar Performance Chassis manual. 9th edition. Chapter 6 "Driveshafts and Rear Axles" Page 252.

Recommend that the front joint angle is 2.5 degrees or less relative to the driveshaft. (but not zero!)

Rear:
Standard Leaf Spring: 5-10 degrees nose down relative to the driveshaft (5-7 degrees preferred).
Leaf Link: 3-5 degrees nose down relative to the driveshaft
4-Bar: 2 degrees nose down
Ladder Bar: 1 degree nose down
Oval Track Leaf: 4-5 degrees nose down

Based on discussions I have read here and elsewhere these numbers all seem realistic. Hope this is helpful.

[67rally]

Recommend that the front joint angle is 2.5 degrees or less relative to the driveshaft. (but not zero!)

Rear:
Standard Leaf Spring: 5-10 degrees nose down relative to the driveshaft (5-7 degrees preferred).

Based on discussions I have read here and elsewhere these numbers all seem realistic. Hope this is helpful.

5-10* down just sounds like it would eat U-Joints. I could be wrong.

Maybe one of the suspension guru's will chime in.

[mmosley]

5-10* down just sounds like it would eat U-Joints. I could be wrong.

Maybe one of the suspension guru's will chime in.

How much do you think the pinion climbs under power? I think the idea is to get 1-2 degrees at max torque. Also consider, Mopars are unequal length springs. The race springs have a 20" front section and a 35" rear. Your's are equal length... you probably get more spring wrap than I would expect with a Mopar.

[rickpaw]

I have the same Hotchkis springs front/rear, and IIRC my pinion angle is 1* down. No vibrations so far (up to 98 mph).

Have you looked into driveshafts with CV joints, especially since you have to get new ds anyway? Andrew70 has one in his GTO from Drive Shaft Shop. With CV joint, operating angles become irrelevant.

[67rally]

I have the same Hotchkis springs front/rear, and IIRC my pinion angle is 1* down. No vibrations so far (up to 98 mph).

Have you looked into driveshafts with CV joints, especially since you have to get new ds anyway? Andrew70 has one in his GTO from Drive Shaft Shop. With CV joint, operating angles become irrelevant.

Do you remember what your transmission angle was relative to the ground (or subframe)? And was the pinion angle 1* down relative to the ground or the DS?

I looked into andrewb70's GTO. It sounds like he had good success with the CV joint, although it looks like it would add an extra $450 to the cost. That's always an option, but maybe one I'd look into if I can't get it vibration free. I can always send the driveshaft back to have the front U-Joint replaced with a CV.

[rickpaw]

Do you remember what your transmission angle was relative to the ground (or subframe)? And was the pinion angle 1* down relative to the ground or the DS?


Transmission angle is between 3 and 3.5* (depending where in the garage). Pinion angle is relative to the ground, so transmission and pinion form a V.

[regal454]

I also had the same set up as you. My transmission angle was 3.5* and my rear end was set to 2.5*. I have driven the car like that for 5 years and never had a vibration at any speed.

[67rally]

Transmission angle is between 3 and 3.5* (depending where in the garage). Pinion angle is relative to the ground, so transmission and pinion form a V.


I also had the same set up as you. My transmission angle was 3.5* and my rear end was set to 2.5*. I have driven the car like that for 5 years and never had a vibration at any speed.

Alright. I'm going to re-measure my driveline and pinion angles this weekend. Last time I had the axle supported with jack stands and that may have prevented a true reading. This time I built some blocks so the rear wheels will be on with full weight, and I'll jack and support the front so it's level with the rear. If I fall somwhere in the 1-3* down on the pinion range, I'll run it as is and see if I have vibrations.

I guess it's pretty stupid to be troubleshooting when I don't even know if there's an issue. I just remember chasing my tail last year and I'd like to start out in the right ballpark this year. The new DS still won't be here for another week and a half or so.

[67rally]

I measured again today, this time with the full weight on the rear wheels. I was also able to shim the trans up another 1/4".

With the subframe level, I'm at 3.2* down on the trans, and 2.2* down on the pinion. I think I'm going to run it as is first and see if I get any vibrations.

[mmosley]

I measured again today, this time with the full weight on the rear wheels. I was also able to shim the trans up another 1/4".

With the subframe level, I'm at 3.2* down on the trans, and 2.2* down on the pinion. I think I'm going to run it as is first and see if I get any vibrations.

I am assuming these are relative to level. What then, is the angle of the driveshaft? I can only assume it is higher at the transmission side. If so, sounds like you are in a good place. That angle will tell us the relative angle of each to the driveshaft. For example. If the driveshaft is 2 degrees down, then the transmission U-joint angle becomes 1.2* and the pinion U-joint angle becomes 4.2* and you are in definitely in the ballpark. I am curious for completeness sake and your feedback on how it runs.

Thanks.

[CarlC]

For the Camaro with the T56 the least transmission angle that could be obtained is 3.5* down. Pinion is 2.5-3* up. There are no leaf spring pads and the spring ends are either spherical or delrin, so pretty rigid.

At some higher cruising speeds there is a very mild cyclic harmonic that I have not been able to eliminate. Most everyone that rides in the car cannot sense it. Due to the solid nature of suspension connections and the nature of overdrive harmonics, it may require a CVJ to fully cure, but it's basically a non-issue for me.

[dutch55]

Here is a Car Craft article from 2002 which covers the basics in easy to read language: http://www.carcraft.com/howto/91758/

I would strongly advise against lowering blocks.

Moving the axle further away from the spring will increase spring wrap and wheel hop.

Lowering the back of the car also reduces anti-squat, which will hurt how soon you can get on the power off the line or at corner exit.

[67rally]

I am assuming these are relative to level. What then, is the angle of the driveshaft? I can only assume it is higher at the transmission side. If so, sounds like you are in a good place. That angle will tell us the relative angle of each to the driveshaft. For example. If the driveshaft is 2 degrees down, then the transmission U-joint angle becomes 1.2* and the pinion U-joint angle becomes 4.2* and you are in definitely in the ballpark. I am curious for completeness sake and your feedback on how it runs.

Thanks.

Yes, as I mentioned in the last post, the measurements were with the full weight on the wheels and the subframe level to the ground.

I'm waiting on the new DS to be made, so I can't take angle measurements until it arrives.

[67rally]

For the Camaro with the T56 the least transmission angle that could be obtained is 3.5* down. Pinion is 2.5-3* up. There are no leaf spring pads and the spring ends are either spherical or delrin, so pretty rigid.

At some higher cruising speeds there is a very mild cyclic harmonic that I have not been able to eliminate. Most everyone that rides in the car cannot sense it. Due to the solid nature of suspension connections and the nature of overdrive harmonics, it may require a CVJ to fully cure, but it's basically a non-issue for me.

Thanks Carl. I'm not running leaf spring pads either. And I have felt those harmonics with the old setup.

It sounds like you're in the equal but opposite angles camp, and then dropped the rear angle only about 1* from there.

[67rally]

Here is a Car Craft article from 2002 which covers the basics in easy to read language: http://www.carcraft.com/howto/91758/

I would strongly advise against lowering blocks.

Moving the axle further away from the spring will increase spring wrap and wheel hop.

Lowering the back of the car also reduces anti-squat, which will hurt how soon you can get on the power off the line or at corner exit.

Thanks, I've read that article a couple of times. Which part did you think would help? It seems that there are more than one opinions in that article.

[dutch55]

You are right, it doesn't have specifics. My recollection (although it has been a while) is that a stock Camaro was 3 degrees down, so with a lowered car, and maybe a little less spring wind up than a stock spring, you should be pretty close with what you have (2.2 degrees down).