91 Bronco 351W Auto trans 4wd Pinion/Driveshaft angle problems

[DSOUTHERNER]

I just installed a 6" Rough Country suspension lift kit with ad-a-leafs and blocks to my 91 351W Auto Trans 4wd and the driveshaft angle on the rear is now way off. It's a stock Double cardan shaft, everything I've read says I need to get the Pinion angle to match the driveshaft angle to eliminate the VERY BAD vibrations it's causing.

I measured my angles with two magnetic angle gauges, and from front to rear they are:

Transfer case 4° Down. U Joint #1 to #2 "H" ****** 12° Down. Main Driveshaft 25° Down. Pinion at ****** 10° Down. Shaft length Ctr to Ctr 28 3/8". Difference between Driveshaft and Pinion angle 15°

If I understand all of the guides I have read on aligning the Pinion and shaft correctly, that means I need additional axle shims at 13-15° (-2° was recommended to account for flex at "cruising speed")

The highest pre-made shims I can find anywhere top out at 8° max. Which is making me question what I'm missing since I need nearly double that.

The best cause for the angle being so extreme seems to be the Automatic transmission being longer than a standard, thus using a shorter shaft at a more extreme angle.

I know people throw 6" lifts on full size Broncos all the time, so I'm sure I'm not the first one to encounter this; thanks for any help.

 

[miesk5]

Yo DSOUTHERNER,

Welcome!

I gave up on keeping notes on lifts after we sold our 78 with a 4".

But here is info that I can remember;

Did you leave out the factory shims?...shorter end faces the front.

 stock shim is 10 degrees I believe ( getting old, ya know?).

The cast shims weaken over time and can crumble.

if stock shims are trashed, 10° shim is available  at,  

 http://jkwoffroad.com/offroadproducts.php

So, you need only the stock shim if I read your info correctly.

When you put them in, unbolt both both u-bolts on both sides at the same time. Dont try to do one side at a time.

The block has a taper to it so be sure you have it in correctly. The shorter side needs to be to the front so it pivots the pinion up to a better angle.

The rear driveshaft for the BKO is so short, that angle changes often result in a vibration.
You will have to pitch that pinion up and this will solve two problems.
The first is that nasty vibration, and the second is the amount of driveshaft slip exposed.

"If you stack that block on top of your factory wedge, or the other way around, be sure that you tighten the snot out of the u-bolts. When you think they are tight, lean on them again. lean on them and then tighten them some more.
If you are not a big ol boy, or using a giant tool up for that task, find either one or both.
Keep in mind that you will have to do this again after some miles are on the rig.
Now if you stack the blocks, then consider that you will raise the vehicle. If you lose the block and install just the wedge, consider that the ride height in the rear will be lowered.
Also keep in mind that the ALL will settle after a few cycles, and you might be chasing the overall ride height for a little while." by chromo79

How are the u-joints?

..

This is the 3rd tine that I have tried to reply.   I lost the first due to an error message and the 2nd because i was tined out, screen refresher and ended up missing all my typing.

Is it slow here for you too?

 

[DSOUTHERNER]

Thanks for the info, I have the factory shims on there now and the angle is 15° off with them included. (I know really heavy angle) I do have a couple Big ole boys and a piece of pipe to crank down the U bolts. The U Joints were just replaced right before the lift, and I'm already planning to buy an aftermarket driveshaft once I get the angle worked out.

Does anyone know of a place that would sell 15° shims? Highest I can find online has been 8°.

Thanks.

 

[miesk5]

Yo,

YW,

Leave the factory shim beneath the new block.

"The RC block goes directly under the spring, then the factory shim, then the axle."

by Scoop

Some known BRONCO LIFT  EXPERTS AGREE with the above.

But, Ryan at Rough Country for some unkown reason claims that "You will put the factory block on top of our block and then tighten everything up." 

this is incorrect.

So this is how it would look;

hey 

Very shaky, right?

 

[DSOUTHERNER]

Yeah the factory shims are on the bottom at the axle. If I could get pics to upload from my phone I took a few of everything.

 

[miesk5]

Yo D,

OK, Bottom of the axle?

Did you mean to write, top of axle?

Hopefully, others will be able to offer suggestions.

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[miesk5]

Yo D,

Did you mean to write,  "factory shims are on the TOP of the axle?

Hopefully other membersmembers will off help.

 To post a pic from your PC, TABLET, etc., just below the reply box in lower right corner, click More Reply Options

Screen will change
See Attach files
pick out the pic
Click Attach This File

or click, Try our advanced uploader (requires Flash 9) 

 

[DSOUTHERNER]

Thank; I had to disable the mobile version of the site to get the "more reply options" to show (I'm stationed in Alaska and both my PCs are back in Florida) I meant to say top of the axle. Here are the pics from the T-case back.

 

[miesk5]

Yo,

Ok.  My tablet has poor resolution.

So,

"The RC block goes directly under the spring, then the factory shim, then the axle."

by Scoop

Correct?

If that is how it is, I really have no idea why the angle is that much.

Try calling RC. http://www.roughcountry.com/customer-service/

Ok,tooka6break, banged my head against a wall a few times and finally foundthis by RC; "REAR   BLOCK INSTALLATION 1. 2. 3. 4. 5. 6. 1. 2. Raise the rear  of the vehicle with a floor  jack.  Support  the frame with  jack-stands. Disconnect the axle vent tube (if so equipped). Remove  the lower shock hardware and  retain  for  later  use.  Remove the u-bolt hardware  and u-bolts.  Raise or lower the axle as necessary to clear it from the rear  springs.  Do not allow the drive shaft to slip out.

Install the new lift blocks between the axle and the stock blocks.  Thick end  of  the block should be placed  to the center  of the vehicle.

 Jack the axle up  to meet  the blocks. Be sure to properly  realign the center-pin when  reassembling the  rear  axle assembly. Reconnect the vent hose and install   the Rough  Country u-bolts, nuts and washers. Torque the u-bolts  to 75 to 90 ft./lbs..  NOTE:  It may be necessary to enlarge the holes in the spring  plate for u-bolt installation. Lower vehicle  to the ground and install  shocks.  The rear shock number is  #650328 (8113).   Install bushings  and sleeves  REAR SPRING INSTALL"

But as the guys mentioned, this looks like a disaster. Have a local 4x4 shop nearby to ask?  You'll  need a good shop to align anyway.

 

[DSOUTHERNER]

Thanks for looking that up, I have the "Thick end of the lift blocks" facing center (towards front of the Bronco) like the instructions say. However that might be the whole problem because adding angle to the front of the axle would angle the Pinion down increasing the problem. I will give rough country a call and see if the the instructions are wrong and the blocks should be reversed.

At the very least turning the blocks around would lessen the size shims I would need (if the blocks can be installed 180° opposite).

This helps a lot!

 

[miesk5]

Yo D,

Good!

From what I mentioned earlier the RC info is disputed.

Here it is;

"The block has a taper to it so be sure you have it in correctly. The shorter side needs to be to the front so it pivots the pinion up to a better angle."

Hope it works!

 

[DSOUTHERNER]

I was able to get the Rough Country lift blocks turned around this weekend and that solved the problem. Thank you for all the help; now I can focus on finding some good wheeling spot up here.

 

[miesk5]

Yo D,

Great!

Snap some pics out there and enjoy yourself!