Rear Axle Housing/Driveline Angle

[PJ Walters]

Post #2 on the day... I recently took my 89 to a dyno shop to get my sniper dialed in and the guys basically ridiculed me for my rear driveline angles. My blazer has a 4" lift and the Tcase has spacers to lower it about an inch (like every lift I have ever seen). I have built numerous chevys and nobody ever told me that my angles were dangerous. This dude wanted to sell me angled shims for the axle housing to rotate the axel for a better angle. How many of you fellas are doing this? What shims are you using? Are you turning your rear shocks upside down to provide the space needed? Is this guy nuts? I have wheeled blazers a long time with the exact setup I am running now and never had an issue. Should I worry about this?

 

[swettysblazer]

Are you running the stock driveshaft with the slip yoke still? What's your angle look like?

 

[PJ Walters]

Are you running the stock driveshaft with the slip yoke still? What's your angle look like?

Yes it is the stock setup. I mean, the angle doesn't look any different than the other 3 Blazers I built. It does not appear to be binding or anything like that. Dude was adamant that it will not last the way it is.

 

[swettysblazer]

I run mine like you are saying as well. My truck has an 8 inch (ish) lift with the case dropped. It works and it goes down the road fine. I did do an SYE and new shaft on the wheeling rig though.

 

[cheavyk10]

The angle at the output of the tcase and the angle of the pinion should be within 1 degree, if you are not running a cv.
When I did my shackle flip, I needed 4 degree shims to nose the pinion down, although my truck is a long bed.

 

[Truckman4life]

If it doesn't vibrate or do weird noises going down the road it's fine. Mine is off and I get a weird noise/vibration when I just barely touch the gas pedal while driving or when I coast while driving. Been running it like that for years. I've already messed with shimming mine and didn't feel like doing it again. Dude probably doesn't know what he's talking about.

 

[TJ1978]

Plug in your numbers

Spicer Driveline Operating Angle Calculator

Measure the angles of each component in your drivetrain, then use the Spicer Driveline Operating Angle Calculator to find the operating angle of each u-joint in your drivetrain.

spicerparts.com

 

[Wes Harden]

I have shimmed mine. As @Cheavyk10 says the t- case output angle should be within 1° or less of pinion angle. If you have a cv style t case output the pinion should point at the output.
I have CV driveshaft, a 4° degree shim pointing the pinion up. With 4" shackle flip and 4" shackles my driveshaft was 10.3° and pinion was 8.1° had a strong vibration in overdrive between 2k and 2300 rpm.
Changing to 6" shackle affected my angels and got me within .5° felt vibration is much better now.
All the pieces matter. I had at 1 time spacers on my t case, I removed them when I redid the motor mounts, my engine and trans alignment are as manufactured. Nothing else is original. trans and t case are not original equip drive shaft was 2 piece now 1 piece.
Yours may be fine, might need a degree or 2.
Personalty I don't care for the shimming the t case, it changes the drive line angle effects fan and shroud, distributor gets close to firewall, exhaust pipe can be put on a bind. By correcting the pinion angle to match your t case angle you can bolt it up original.

 

[PJ Walters]

Thanks fellas this is all good info. I will be looking into this stuff over the winter months AFTER I get a few other bugs worked out. I'm battling a TCC lockup issue at the moment that takes precedent. You all are the best!

 

[jimmyleetn]

Check out my build on here where I rectified the same problem. I installed a 3in lift from ORD. I had horrible driveline problems, lots of vibration. Much of this was due to junk u-joints but some was due to terrible angles. I put the NP208 tcase back in the factory position (same length as your NP241). This helps your front driveshaft angle when you put it back where it's supposed to be. I then used the shim calculator on the Tom Woods website. Determined I need a 10degree shim in the rear. I would not worry about shimming the front since you'll never see speeds over 40mph on that driveshaft and it'll really overcomplicate your steering. Installed those shims under the rear leaves and topped off the diff oil since I changed the angle of differential. From there, I measured my driveshaft lengths and ordered new double cardan style driveshafts from Denny's Driveshafts. It took a month or so for the front and rear shafts to come in since they're custom made, but holy smokes they're smooth at all highway speeds. Tom Woods is also a good place for driveshafts and High Angle Driveline but I've purchased from Denny a time or two and he had earned my business. Sean Woods was super helpful too over the phone so you really can't strike out in my opinion. Good luck.

 

[TJ1978]

I wish could I tuck my Tcase back where is should be. The distributor being so to the close the fire wall is unsettling , but fixing that would require me doing the exhaust for 3rd time among other possible expenditures . I just don't have the money to do that. My tcase is lowered 1 inch and no odd vibrations. I rarely use 4wd so the front drive angle is not so much a concern at this point. This expense also assumes I won't have to them spend more $$ or yokes, shims and new front and rear drive lines, which are brand new themselves.

Down the road, when I get some extra cash I may rectify this but until then, I'm sending it as is.

 

[jimmyleetn]

I wish could I tuck my Tcase back where is should be. The distributor being so to the close the fire wall is unsettling , but fixing that would require me doing the exhaust for 3rd time among other possible expenditures . I just don't have the money to do that. My tcase is lowered 1 inch and no odd vibrations. I rarely use 4wd so the front drive angle is not so much a concern at this point. This expense also assumes I won't have to them spend more $$ or yokes, shims and new front and rear drive lines, which are brand new themselves.

Down the road, when I get some extra cash I may rectify this but until then, I'm sending it as is.

Probably could keep your yokes and get special u-joints if you changed drivelines but none of it is ever cheap. If you start going u-joints more regularly you'll need to revisit that part of your ride, but I don't blame for not wanting to go through an area you've already fixed. That's the worst.