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Discussion Starter · #1 ·
92 Ramcharger - 5.9 / 46RH / NP241 / Chrysler 9.25 rear

I know a ton of people have had issues with driveline vibration after a suspension lift. I had hoped that my 'mild' lift of only 4 inches would cause fewer problems than I've heard with other lifts. No such luck.

So, the angle from the tcase output shaft centerline to the driveshaft is about 15 degrees (high), and the angle between the driveshaft and pinion centerline is also 15 degrees. In other words, the tcase output shaft and pinion input shaft are nearly parallel. See attached pic. I had always read that this was the ideal case, so I was pretty excited after I got the springs in and started measuring.

However, the stock tcase ujoint just coudn't handle that extreme angle and bound up really badly.

I had a driveshaft shop in town have a look, and he suggested a double-cardan joint at the tcase side, and a standard single ujoint at the pinion side. That confused me since a double-cardan is supposed to nearly cancel any vibration, and then the pinion to driveshaft angle should be as close to zero as possible.

Well, I'm starting with 15 degrees of angle, so in order to cancel out any vibration at the pinion side, I'd have to raise the pinion input joint 15 degrees! That's a bunch. The driveshaft guy suggested a 4 degree shim to see if that would help. I did that shim, installed the new driveshaft, and the driveline vibrates really badly.

The vibration is really bad at low speed, getting somewhat better after about 20-30 mph.

I asked the driveshaft guy again about just doing two 'high angle' ujoints on the driveshaft (no double-cardan) and he suggested that this was too much angle at the tcase side for that. This again confused me a bit because the pinion rotated cleanly with the new driveshaft, before any spring shim was added, so at about 15 degrees driveshaft to pinion angle.

As of right now, the driveshaft guy thinks we still need to raise the pinion more. I'm afraid I'm going to lift the carrier bearings out of the gear oil bath if I tip it up much more.

Anyone else have some helpful ideas here?

Thanks,

Mitch
 

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Discussion Starter · #2 ·
Thinking about it some more, I'm wondering if maybe the answer is using *two* double cardans, one at each end of the rear driveshaft. Sheesh, that seems like overkill. This was *supposed* to be simple. :)

Mitch
 

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the factory rear blocks are "angled" almost a half inch , short side towards the front / your pinion angle is way off , it should be almost straight with the driveshaft
 

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bearings / oil , I'm thinkin the bearings are lubed by oil that is "picked up " by the ring gear as it passes thru the sump , gets splashed into the tunnel , drains down to the " front " pinion  bearing ...
 

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Discussion Starter · #6 ·
I didn't think to measure my old blocks before I threw them out (and trash came yesterday). Ugh.

According to DODGEBOYS estimate, 1/2 in of 'drop' on the block lifts the pinion 1/2 in over about a 4 inch length. Some quick math shows that as about 7 degrees of incline.

I'm thinking my 4 inch drop (from the pinion's perspective), over about 40 inches of length from tcase to middle of the pinion just about accounts for the other 7-8 degrees of incline I see in the driveshaft.

So, the question is, should I try to put 12 degrees of shim in (about 5 degrees more than the 7 degrees that were there before the lift)? Is having a driveshaft to pinion angle of 3 degrees small enough?

To get 12 degrees of shim, I'd probably need to weld an 8 and 4 together. I don't see any ready-made 12 degree shims around. I wonder if this is the point where a wise man would suggest I have the spring perches rotated and welded?

Mitch
 

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15* is a lot - if it were me I'd do a DC joint at the t-case output, then cut the perches loose on the rear axle, rotate the pinion up until the shaft is about 2* shy of 'zero' to the shaft coming into the yoke, and re-weld the perches.

- Sam
 

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Discussion Starter · #9 ·
Mad Max, I was afraid someone would suggest moving the perches. :)

I'm thinkin to drop a Posi unit in the rear anyway. I could just have my driveline guy do the perches and the Posi center section at the same time (now).

DODGEBOYS, not sure what I'd do with a set of old blocks. I already have more lift in the rear than I can handle, and that would assumedly give me more (unless you are suggesting cutting them down somehow).

Mitch
 

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MitchUpton said:
Mad Max, I was afraid someone would suggest moving the perches. :)
well, while yer at it ;) you might also consider replacing the 52" rear springs with a ProComp 13511 4" lift Chevy spring and 1) potentially eliminate the rear blocks completely and 2) gain the benefits of a better ride because of the longer leafs - double bonus
 

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Discussion Starter · #12 ·
Mad Max said:
well, while yer at it ;) you might also consider replacing the 52" rear springs with a ProComp 13511 4" lift Chevy spring and 1) potentially eliminate the rear blocks completely and 2) gain the benefits of a better ride because of the longer leafs - double bonus
Note, the Tuff Country lift kit includes springs that do replace the original blocks on the rear springs. No blocks in there anymore. Those springs are the stock length though, so I don't expect any real ride improvement beyond that fact the old springs were so flat they were riding on the override leaf. :)

I'm probably about done puttin' stuff in this truck for a while. This lift has cost a pretty penny so far (new driveshafts, adjustable drag link, new exhaust, perch work, etc.) :eek:

Mitch
 

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yes missing in your photos IS a constant velosity joint AT the transfer case .. I'd start there ,with some shims to aline it,  ( steering wheel return ) worry about it again if that don't help .
 

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Have a look under just about any 78-96 Bronco. They used a fat shim - easily 10* - to tilt the pinion up for use with a factory double-cardan shaft. IMO, that's the right way to do it.

You can create a similar pinion tilt by doing a rear shackle flip.
 

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Discussion Starter · #16 ·
Figured I'd update this thread and give a resolution...

I just wasn't comfortable with putting 15 degrees of shim in there (and read about the shackle-flip option a bit too late to do anything with it). Not sure if the shackle-flip could have given me 15 degrees of pinion angle change. Others that have done it feel free to comment.

I had my driveline shop rotate the spring perches so I now have a very low pinion angle. That required about 15 degrees of rotation on the pumpkin. It now sits at a very noticeable incline. 

I was a bit worried that bearings and such wouldn't get sufficient lubrication, so I got a new diff cover that has a higher fill hole opening than normal. Note, the cover's manual says this is for a diff temp sensor, but it works for filling as well.

They also cut and rotated the drum brake backing shields so they were in the same relative orientation as they were before the rotation.

The shop charged me about $700 to do that work. With the new double-cardan shaft (about $500), I'm about $1200 and change into the driveline work alone.

End result is that the diff looks great, and drives with no vibration whatsoever. Nice.
 

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MitchUpton said:
The shop charged me about $700 to do that work. With the new double-cardan shaft (about $500), I'm about $1200 and change into the driveline work alone.
and the rookies always give you a dirty look when you tell them there is no such thing as a cheap lift lol. We should refer them to your post.
 

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Discussion Starter · #19 ·
ToxiDoc, truer words have never been spoken.  ;D

"Just do a 'mild' lift, like 4 inches" they said... "It'll be easy." they said... LOL

In case anyone is actually interested in a fully tally:

- Lift kit with new/full springs and shocks, + steering block (~$1200)
- New exhaust (~$700)
- Lengthen front shaft, clearance double-cardan 'ears' (~$300)
- New double-cardan rear shaft (~$500)
- Rotate pinion (move perches and brake back shields) (~$700)
- New diff cover (~$150)
- Lengthen new rear shaft after pinion angle correction (~$100)
- Adjustable drag link (~$160)
---------------------
~$3810

And then you have new wheels/tires (35s on 17s, which was the whole point of this exercise anyway right?): $2600
And then a swing-out tire carrier bumper since no way you are getting these monster tires inside the truck anymore: $200 if you build it yourself using one of the handy hinge/latch kits out there.

The things we do for our toys.  ;D

Mitch
 

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MitchUpton said:
ToxiDoc, truer words have never been spoken. ;D
Very true, but consider it's also all relative. As an example, if you were lifting a truck equipped with IFS you would spend a whole lot more for the same amount of lift, and you might had spent less on a longer wheelbase truck (w/ a solid axle)

In any mod, theres always a lot of hidden costs. Most people add a lift to clear bigger tires. You gone thru the expense of lifting but the bigger tires are going to need the axles to be re-geared. It's the domino effect. Mess with one thing and the next thing in line has to be addressed. After you re-gear, you'll note that the truck won't stop as well as it did with the smaller tires, then you'll need to address brakes…thats the next domino, and so on, and so on.

I could tell you that I've got a bunch of money wrapped up in my Dakota and I'm still looking to do more to it…..I've been thinking about doing a pair of selectable lockers, next, but my wallet is currently on life support and the credit card companies are already sending me new cards in the mail, that are already cut in half.

Ed
 
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