Nv4500 ‘rattle’ between acceleration and deceleration…

I swapped in an NV4500/np208 into my 1975 Jimmy - 3rd vehicle I’ve swapped in the NV4500.

I had both rebuilt before the swap by Standard Transmission in Fort Worth TX.

Here is the problem: in 3rd or 4th or 5th gear, when there is no ‘pressure’ on the tranny (so not accelerating or decelerating) it ‘rattles’.. not a ‘grind’ per se… but very noisy…

Thoughts on what could cause this? I’m at a loss…

Any help much appreciated!

Has your truck got 3.07 gears? These trannies were in front of 3.42 plus gears in OBS trucks. That may be an issue but I'm not certain. Just fishing. The internet police will find me out soon...

HS

Strick said:

Has your truck got 3.07 gears? These trannies were in front of 3.42 plus gears in OBS trucks. That may be an issue but I'm not certain. Just fishing. The internet police will find me out soon...

HS

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It worked perfectly before the swap so it has to be something that changed (clutch, transmission, transfer case). The other thing that was modified was the rear drive shaft. Originally it had a CV joint at the transfer case end of the drive shaft, the rebuilt drive doesn’t not (it is a slip yoke, single ujoint).

I'd rather have the slip yoke as opposed to the CV. I don't think that clutch adjustment (minimal) would be a culprit either. IDK what the issue could be if it were not present upon conversion. Keep us posted should you find the issue.

HS

The problem you describe is it's a NV4500. I got two of them. One I just rebuilt with premium parts and mic'd every dimension. It sounds like a bucket of bolts, no different than the worn out 4500 it replaced. It will be most noticable in 4th gear when the countershaft is spinning freely making racket. Drive it and don't worry about it.

Thread 'Seriously bummed with this drivetrain setup right now ' https://www.gmsquarebody.com/threads/seriously-bummed-with-this-drivetrain-setup-right-now.40197/

I have a '79 that I'll probably do thus swap on soon. Thanks for the info.

HS

IDK why in the world my phone (smart) always corrects "this" to "thus" either...

Struggling

The 4500/208 is almost certainly longer than the original combo so I’d bet you have a rear driveshaft vibration. Get an angle finder and check the ujoint angles.

7900_Blazer said:

I swapped in an NV4500/np208 into my 1975 Jimmy - 3rd vehicle I’ve swapped in the NV4500.

I had both rebuilt before the swap by Standard Transmission in Fort Worth TX.

Here is the problem: in 3rd or 4th or 5th gear, when there is no ‘pressure’ on the tranny (so not accelerating or decelerating) it ‘rattles’.. not a ‘grind’ per se… but very noisy…

Thoughts on what could cause this? I’m at a loss…

Any help much appreciated!

Click to expand...

Normal.

nvrenuf said:

The 4500/208 is almost certainly longer than the original combo so I’d bet you have a rear driveshaft vibration. Get an angle finder and check the ujoint angles.

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The transfer case is at 4.5 degrees, the drive shaft is at 17 degrees - so a 12.5 degree difference ...

I'm thinking that is the issue with no CV joint to mitigate. The driveshaft I had built for the 203 (2 years or so ago) had a cv joint built into the transfer case end of the drive shaft. I've driven that '75 to the mountains of Colorado, to New Mexico, to the Gulf coast... and my youngest son drove it daily to high school - no issues at all.

When Inland built the driveshaft for the 208 - they had no access to a 32 spline slip yoke CV joint - so they put a single u-joint on it.

In speaking with Tom Woods driveshafts - two single u-joints (one at the diff and one at the transfer case) try to overspin the input shaft of the transfer case which is what can cause that rattling when coasting (neither accelerator or decelerating) through the transmission - the 2nd u-joint in the CV joint keeps that from happening.

I'm having Tom Woods build a new driveshaft as they can source a 32 spline slip yoke with a CV joint... it should be here on Friday. I'll keep you all posted.

You're measuring driveshaft slope. You need to measure of the u joint caps at the front and rear of the shaft. The difference is the u joint angle. Should be 3-4 degrees.

SquareRoot said:

You're measuring driveshaft slope. You need to measure of the u joint caps at the front and rear of the shaft. The difference is the u joint angle. Should be 3-4 degrees.

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The rear diff is angled up to point almost directly 'at' the transfer case input shaft... so the rear diff and thus the u-joint and drive shaft are 'in line'.

Again, this has all been working perfectly for a number of years... until I swapped the transmission, transfer case and Inland remove the CV joint off the transfer case end of the drive shaft...

You're measuring driveshaft slope. You need to measure off the u joint caps at the front and rear of the shaft. The difference is the u joint angle. Should be 3-4 degrees. A 4500 with a 208 slip case means a short driveshaft in a blazer. Even worse if it's lifted. If that's the case, I almost guarantee you need a CV in the shaft. My driveshaft is 60 inches and I demanded a CV for the smoothness and long life.

SquareRoot said:

You're measuring driveshaft slope. You need to measure off the u joint caps at the front and rear of the shaft. The difference is the u joint angle. Should be 3-4 degrees. A 4500 with a 208 slip case means a short driveshaft in a blazer. Even worse if it's lifted. If that's the case, I almost guarantee you need a CV in the shaft. My driveshaft is 60 inches and I demanded a CV for the smoothness and long life.

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Thanks for the feedback... it is a blazer, and it is lifted and it had a CV at the transfer case. I'm hoping getting that added back to the new drive shaft will allow it to run smooth with the NV 4500 as it did with the SM 465.
Here are a few pics...