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Rear 4” shackle flip with 3” shackle, pinion correction.. CV shaft or shims?

Cntymnty77

Cntymnty77

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Just finished up the rear ORD shackle flip with 3” shackles. I noticed it’s obviously thrown the pinion angle off.. I know a lot of guys on here have done the same thing with their trucks, what’s the best approach to correct it? I tried searching on here but for some reason I was coming up with nothing.

The shims would be the cheaper fix but I feel like I might be looking for a new drive shaft instead.
 
just did a np205 with a flange on the rear inplace of the fixed yoke .

then a ford super duty mid 2000 range front drive shaft for the spicer 1350 shaft and c/v head . had it shortened to the length we needed for his combo in the blazer .

set pinion at 1.5* down from direct inline point to flange on t-case and welded on the new perches .

she is smooth and nice at highway speed and or in town . . . . even at 90mph with 37" mud tires it was smooth .

all in done was the beefyest option in my opinion .

few pics .weld on new beefy perches and option to move axle forward or rear 1" . 1350 joint direct to stock 14ff yoke . could swap to a trick joint if other size yoke is needed . c/v flange inplace of yoke on 205 . shaft installed and in .

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The approach will vary based on what you have for t-case and rear end. What t-case you running? 208 I think? If so you got a slip yoke output to the rear. Based on those guesses, you will need to do some correction. The smartest way to fix it is to change out the slip yoke output for a slip yoke eliminator (SYE) and that will require a change to a drive shaft with a slip shaft built into it. The SYE will gain you some driveshaft length and soften the angles some. Even then you'll probably have to run a CV on the shaft too. IF you end up running a CV style shaft, you'll need to set your pinion angle to match your driveshaft angle.

If you don't change the t-case output with the SYE, you could still have a CV shaft built with a slip yoke to fit. The same thing will need to happen to match your pinion angle to the shaft angle. This is the way mine is done with a slip yoke output 241 and once pinion angle was set it has been flawless. Been that way for 3 years and no issues. By the time I got done with the custom rear shaft I was pretty close to what it would have cost for an SYE and changing to the slip shaft from the stock one.
 
ZooMad75 said:
The approach will vary based on what you have for t-case and rear end. What t-case you running? 208 I think? If so you got a slip yoke output to the rear. Based on those guesses, you will need to do some correction. The smartest way to fix it is to change out the slip yoke output for a slip yoke eliminator (SYE) and that will require a change to a drive shaft with a slip shaft built into it. The SYE will gain you some driveshaft length and soften the angles some. Even then you'll probably have to run a CV on the shaft too. IF you end up running a CV style shaft, you'll need to set your pinion angle to match your driveshaft angle.

If you don't change the t-case output with the SYE, you could still have a CV shaft built with a slip yoke to fit. The same thing will need to happen to match your pinion angle to the shaft angle. This is the way mine is done with a slip yoke output 241 and once pinion angle was set it has been flawless. Been that way for 3 years and no issues. By the time I got done with the custom rear shaft I was pretty close to what it would have cost for an SYE and changing to the slip shaft from the stock one.
Click to expand...
Yeah, it’s a 208 with the slip.

I found this earlier, not sure if this company is any good..

C7F8B3D1-F22D-4902-8B3C-8AD375D636EA.png
 
denny's is a solid company in the biss for years . there 2hr north of me .

that shaft and correcting pinion angle will be the key to no vibes at speed .
 
My 89 K5 that originally got a 4" lift with ORD flip and stock axles had the same issue. I ordered a new rear driveshaft with a double CV. Used that for awhile. That truck got extreme but I saved the rear driveshaft.

Few years later I put a 4" lift on my 86 M1009. That got a DIY4X flip. Same exact issue. I swapped in the same rear driveshaft and the problem went away. I put over 50,000 miles on that setup before I sold it
 
I havent run that shaft, but based on how torn up the splined shafts get comparatively (in my experience) I'd prefer a slip yoke CV setup to an SYE. I'm running a splined shaft with SYE and CV now FWIW, and trying to see if I can keep as much grease in, and dirt out of, the splines as I can. Grease just doesnt stay put on exposed splines, in my application.

Yeah, can't run with a broken rear driveshaft. That's happened to me once, on the street, a couple hundred feet from the house. For the hassle and expense of the SYE, I dont see the benefit if you can go CV on a slip yoke. At least for myself.
 
@sweetk30 box those spring perches in, the open ends are a problem. Or can be.

blazers need CVs over about 2-3" of lift, one way or another. often longer stuff too.
 
@Stephen i have never heard of them folding in unlike stock units . there the 3/8" plate units .

we will keep a eye on them tho . thanks for the heads up .
 
dyeager535 said:
I havent run that shaft, but based on how torn up the splined shafts get comparatively (in my experience) I'd prefer a slip yoke CV setup to an SYE. I'm running a splined shaft with SYE and CV now FWIW, and trying to see if I can keep as much grease in, and dirt out of, the splines as I can. Grease just doesnt stay put on exposed splines, in my application.

Yeah, can't run with a broken rear driveshaft. That's happened to me once, on the street, a couple hundred feet from the house. For the hassle and expense of the SYE, I dont see the benefit if you can go CV on a slip yoke. At least for myself.
Click to expand...

I've worn out the splines on multiple front drive shafts, but have been on the same rear one for 10 or 12 years and it's still like new. Since the splines don't have to travel much on a leaf spring rear shaft, it's a good application for a boot.
 
Exactly what I'm doing. However that is because I have to, not because I want to. Perhaps I would feel different if the splined driveshafts were all designed for, and provided with, a boot.

A slip yoke will apparently go unlimited miles without issue, and no special attention.
 
Yes, when angles are low. They are always lubed. Lifted trucks will wear out the bushing and seal more often and eventually the slip. That's why SYE helps so much on lifted/short wheelbase. The driveshaft gets longer, the angles get better and you don't have a 10lb C/V joint hanging a foot behind the main case. Of course at stock height you don't really need a C/V.
 
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