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K5 rear driveshaft vibration

JT88K5

JT88K5

1/2 ton status
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Hi evryone, first post here.

I have been a non premium member for about 6 months and have read a lot of posts while working on my project. All good stuff.

To give some background, I have an 88 K5 that been in the barn (thus the handle). I spent the winter months reading posts on this site and others and finally was determined to restore the k5. Upon inspection the body was way more gone after 12 years than I thought it would be. New plan. Found a stock California k5 with 140k miles and no rust. Had it shipped back to the rust belt.

I wanted to build something stout, so I procured a set of 1 tons, rebuilt the d60 front and installed one of the new gen4 elockers. The 14b with Detroit locker already had a disc conversion done and just needed the spring pads welded on. I had someone help me with that, and welded the spring pads on so we had 4-5 degrees of angle on the pinion.

The rear end was lifted with ORD 4" Rsf and stock springs. In the front I thought with the d60 and some of what I read that 3" would make it sit like I wanted, but the front was too low so I added a 1" zero rate from ORD.. Perfect ( should have listened to Chris as he recommended the 4" front leaf from the get go). I went with the bilsteins an installed new front shock mounts. Also did their crossover steering setup.

Received tires an wheels this week. Tooled around the yard, put it in a bind and checked for tire clearance, everything looked good. I'm running the stock rear driveshaft, with a conversion joint at the axle end. Replaced both u-joints on driveshaft.

Took it out on the road yesterday an it was all good until I got up to about 40 and left off the gas. Had a loud ratcheting god awful noise until I picked up on the throttle again and it went away. I could repeat this at will.

i put it up on jack stands and put it in gear this morning. Once I get it up to 35 or so, it looks like all of the vibration is at the front of the rear ds and it sounds like its tearing up the transfer case. With the truck on the ground, the tail shaft on the t-case looks to be hanging down 4 degrees. The driveshaft is at 21 degrees, and the pinion on the rear axle is at 10 degrees. I believe the rear shackle flip adds to the pinion angle and that is why the rear pinion is now 10 degrees.

You thought I'd never ask... So what do I do to remedy this situation?

Here are the before and after pics if you want to look.

image.jpeg

image.jpeg
 
I've heard some of the conversion joints can also contribute. Long term I would plan on moving to a standard joint
 
Not necessarily wanting to rip the rear our and reweld the perches, and maybe tabs... I'm thinking new shaft with cv.

From what I've read, with a cv on the front, the pinion and ds should be pretty much in line. With a ~10 degree difference between the pinion and ds, would that be a problem? (Ds=21, Pin=10, tcase=4) Doing the math, if the tcase is at 4 degrees and the shaft is at 21, gives me a 17 degree angle between tcase and shaft. Going to a cv would cut that in half to 8.5 for each u in the cv... Which should be the optimum angle between the pinion and ds if I understood the article correctly. So the 10 degree angle in the current pinion is probably close enough?

Any thoughts either way?
 
i just posted this same issue and have talked to tom woods drive shaft
the cv shaft is the way to go there is to much angle for the 2 ujoint shaft to handle and after you put a cv shaft you will have to shim your axle to get the correct angle
 
Funny
F-ingrob said:
i just posted this same issue and have talked to tom woods drive shaft
the cv shaft is the way to go there is to much angle for the 2 ujoint shaft to handle and after you put a cv shaft you will have to shim your axle to get the correct angle
Click to expand...

That's funny, just talked to them today. I think I'm going to go with their 208 sye and flanged driveshaft together. Trying to build this to stay functional for a while. Wtf, got a lot of $$ wrapped up in this already what's another $800. Just another month of buying less than premium bourbon. Gotta get this on the road b4 hunting season.
 
Should have said " I want to get this on the trails before Hunting season".
 
Sounds exactly like the situation I went through a couple of months ago. Working angles were too tight causing vibrations. Was getting mine just off of a stop and smoothed out above 15. Vibrations at low speed were vicious - like a paint shaker. Also caused some banging sound in the t-case. Had gotten 'conventional' driveshaft from tom woods. Nice shaft but wasn't right. Talked to them some more and they recommended a cv shaft. Sent it back and they upgraded it for the diff in price and sent it back. New perch angles and it was smooth again.
 
put a string between your tailcone and your axle yoke. Whatever that degree is minus 1-2 is what your axle yoke should be at. Either perches or shims. When I did the shackle flip, it lined up perfect, no shimming needed.

Also, I have the TW 208 kit. Works great. Well, that is till I went 241, but it works great as a spare too! :D
 
K85 Octane said:
Also, I have the TW 208 kit. Works great. Well, that is till I went 241, but it works great as a spare too! :D
Click to expand...

Octane, what caused you to convert to the 241? I am thinking of sourcing a 241 and doing the JB kit. I read another post somewhere where someone thought the JB kit was a better solution.

Thanks
 
slightly better design and lower 4L gear
the 241 JB kit is better than any 208 kit but that is because the two piece tail cone allows for better adapters and even shorter SYE kits
both work fine
I would only switch if you can find a good deal on one and are after the lowest 4L you can get without going doubler or aftermarket box. Also, the 241 can be cable or VSS. So down the road, when time and money allow, it will get an LS motor and switched over to VSS to send a signal to the computer.
 
4" of lift is into the area where a single cardan may never be perfectly smooth. It can be made to work OK, but you will probably have some speeds where there is minor vibration. The SYE eliminator reduces the angles by adding something like 4 - 6" of driveshaft length. An anti-wrap bar also helps, which is something to consider if you're already thinking about one of those. At that point the standard shaft might be good enough. But if you want to do it once with best results and long U-joint life, just go right to the C/V.

Before grinding your perches off, you can try angle shims. Bolted into the spring pack with the right angle compensation on the center bolt, they can even be your long-term solution.
 
I have a line on a NP241 from an 89 K1500 ($100). I've read this won't work due to speedo on the 89 k1500 to be electronic? If it is, can it be reverted to mechanical speedo? I know I need to verify the spline count on the tranny and tc.

I was figuring on going with shims if I need to. My rear perches were welded on at 4-5 degrees and with the rear shackle flip, my pinion is already pointing skyward at 11degrees, (I posted earlier that it was 10, but double checked last night and it's actually 11).
 
Also, any input on how far you can point the pinion up until it impacts the pinion bearing getting lubed? I filled the rear 14bff with the recommend amount of gear oil (3.6 quarts). If I add more, how much? Is this done via hairy eyeball or what :zombie7:? Based on verifying the level of the oil and projecting that to the pinion, I would assume? Assuming has got me into trouble at least a few times.
 
JT88K5 said:
I have a line on a NP241 from an 89 K1500 ($100). I've read this won't work due to speedo on the 89 k1500 to be electronic? If it is, can it be reverted to mechanical speedo? I know I need to verify the spline count on the tranny and tc.

I was figuring on going with shims if I need to. My rear perches were welded on at 4-5 degrees and with the rear shackle flip, my pinion is already pointing skyward at 11degrees, (I posted earlier that it was 10, but double checked last night and it's actually 11).
Click to expand...

No, on the blazer/suburban 89 is still cable driven. Only 90 and 91 are electric. However if it's from the new body 88+ trucks, isn't the output on opposite side?
 
Output on the wrong side would be a bit of an issue. You're probably right about that, I remember reading that those wouldn't work but can't recall exactly why. I had one yard call me back and the guy said he had a 241c but it was from a chevy truck older than 88? Gonna have to go check it out, I have a 241 to check out tomorrow morning at two different yards.
 
I tilted my rear up and put enough to just run out of the plug, to ensure the front pinion gets lubed. Don't remember how much that came to but it was quite a bit more. If it turns out to be too much I'll find out...
 
To state it again, start saving for a new cv shaft. I didn't do a sye on mine, 241/14b ord flip for lift. Ended up using 8 degree shims to line up the pinion with the shaft. Also dropped the tcase 1/4" too.
 
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