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Another Driveline vibration.....

jeff in co

jeff in co

1/2 ton status
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My 16 year old is going to be driving the Blazer now to school and the 2.5" lift and 35's were a little too much for her. So I sold the 35's and put on 33's. I also decided to remove the lift kit because I did have a very slight vibration around 65....definitely livable. However, I did have a t-case drop and it was bugging me just having it.

So, off I go to remove the old, and install the "stock" height. I used the 3 leaf pack up front and then the stock springs with an extra 1" overload spring in rear. I'm thinking everything is now back to stock location so any vibration I had would now be gone. :waytogo: Unfortunately, that's not the case.:confused:

I head to work yesterday and it's actually worse than I had with the lift. Drive shaft is new and I did have it checked for balancing 2 weeks ago...still good.

So I got home last night and measured the angles. Pinion was at 8 degrees, T-case was at 6 degrees. I just happen to have a 2 degree shim so I slapped that in last night. For some reason, I got the shim the wrong way and now the Pinion is pointing more towards the t-case, but now at 10 degrees.

I took it to work this morning and, well, it feels better than the day before. Still, not gone in any means, but BETTER. :dunno: I would of expected it to be much worse! I'm just getting tired of taking it apart each time.....

If I reverse the shim tonight, it "should be" closer to 6 degrees each, it should theoretically be spot on. Am I really that far out of wack?!?

The only other difference is the 14SF that was taken out of a 3/4 suburban. I guess the perches could be slightly different angle than the stock blazer 10 bolt.

First is 33's with 2.5" lift
Secon is 33's with stock (or maybe 1" lift)

2_5 inch lift 33 on 15-8 rims 2.jpg

1 inch lift 33 on 15-8.jpg
 
Last edited:
jeff in co said:
The only other difference is the 14SF that was taken out of a 3/4 suburban. I guess the perches could be slightly different angle than the stock blazer 10 bolt.
Click to expand...

That's the difference. Pinion pointed differently from the factory for the longer wheelbase.
 
Well, I got a 2.5 degree shim and pointed the pinion down. Both pinion and tcase are at 6 degrees and the driveline is at 15.degrees from horizontal. The truck can barely get to 25 mph with the amount of vibration now! It's just terrible.....

I don't know what to do other than remove everything and go the double cc route.....but it's just insane to do that at stock height!!
 
Just a thought, hows the trans/transfer rubber mount? That's where most my vibration was coming from. Also found the 4 bolts holding the rear drive shaft clamps in the yoke were tightening but not pulling the clamps down on the U-joint caps enough. Took the bolts out and ran a tap down each hole. The holes were full of rust and preventing the bolts from pulling down the straps. Once I did that the vibration was gone.
 
The transmission mount looked pretty good and I do have newer motor mounts as well. New driveshaft with all new 1350 (I believe) u-joints. New slip yoke too.

Transmission was overhauled a year ago.

For this go around (parallel pinion and t-case), the vibration was pretty bad. I only made it up and down the driveway and it was vibrating on load and coasting. I could hear the thing pretty good too.

So, my conclusion....it was better at "lifted height of 2.5" than stock" so I began last night putting the lift back on. I need it drivable. At least I know 90% of the vibration is gone with the lift and tcase drop. To get it completely vibration free, I'm going to have to pop for a CV joint in the driveline and point the pinion towards the tcase.

The ONLY improvement I felt through all this is having the tcase back in stock location. I no longer had a jolt feeling when I put the truck in reverse while holding the brake.
 
Here are the shots I took last night with the 2.5 degree shim as well as the driveline angle.

Pinion and Tcase at 6 degrees
Driveline at 15 degrees

IMAG0703.jpg

IMAG0704.jpg

IMAG0705.jpg
 
Just to be clear...

T-case is 6* down
Pinion is 6* up

Right?

That's only a 9* working angle on the u-joints.
 
After looking at the pics, it looks like the rear joint cap is deep inside the pinion and not out towards the retaining tab. Is it possible the u-joint is smaller than it's supposed to be and not centered in there?

Also looks like you have a pinion leak, maybe an issue there? Is the pinion tight and not flopping around?

attachment.php
 
I believe the oil on the side is from the filler plug when they checked for the axle level at the lube shop. I don't think the pinion is leaking.

The yoke has two locating tabs on each side and the u-joint is between those two tabs. It went in pretty smoothly last time I installed it and didn't appear to get hung up. I also put the straps on and a few light taps with a hammer to be sure they were seated all the way into the yoke.

Prior to all this work (at 2.5" lift). The only vibration was a very slight one at 65 mph. I have not removed the driveshaft since then. The only work was removing t-case drop (placing back to stock location), removed rear block and installed front factory springs. Nothing else. The vibration is varying based on lift/drivetrain angles.

Start:
2.5" lift, t-case drop - Very slight vibration at 65-70 mph

0 lift, t-case in factory position (Pinion at 8 degrees, T-case at 6 degrees) - Pretty decent vibration around 45 mph and continues all through highway speeds.

0 lift, t-case in factory position (Pinion at 10 degrees, T-case at 6 degrees) - Definitely better than the 8 degrees but still not as good as starting, 2.5" lift.

0 lift, t-case in factory position (Pinion at 6 degrees, T-case at 6 degrees) - Probably the worst and didn't want to drive over 25 mph due to vibration.

So, I'm in the process of putting lift back on and will find out how much it would be to add driveshaft CV joint similar to yours Brian. Still slip yoke but CV joint by T-case. This should be my permanent solution.
 
Got the lift back on and it's much better now. Did a drive up to Denver over the weekend at 75mph and it was great! A little, slight vibration around 65 but otherwise good. I did check the angles and here is what I found:

2.5" lift, t-case at stock height:
Pinion - 10 degrees
T-case - 6 degrees
Driveline - 15 degrees

I did not drive it at these angles but can only assume it would not have been good (based on previous experience). But I did want to at least document so I know where they are for future reference (and CV driveshaft).

Final Position -
2.5" lift, t-case drop:
Pinion - 10 degrees
T-case - 8 degrees
Driveline - 12 degrees

And to boot, both my wife and daughter like the lift better than the stock height (and so do I). :)

I went to the driveshaft shop and to add a 1350 CV joint and a new 1350 slip yoke is $450. :eek1:

And the new (used gears) in the 14SF are whining now too. Went to shop that did the work and he said, yep, gears are whining and all he can do is replace with a new GM set to fix it. $550. I need to sell some stuff!!
 
Did you use a conversion u joint or just the one that was on the drive shaft? Does the drive shaft front yoke have any travel, how close is it to bottoming out? Is the front slip yoke tight or does it have a lot of wiggle?
 
cyclic said:
Did you use a conversion u joint or just the one that was on the drive shaft? Does the drive shaft front yoke have any travel, how close is it to bottoming out? Is the front slip yoke tight or does it have a lot of wiggle?
Click to expand...

No, everything on the driveshaft was new. New 1350 u-joints, new slip yoke, and it was measured to fit at this same height. So driveshaft fitment was pretty good. My only other guess was some slop in the Tcase (although the slip connection felt tight). So I went to the junkyard last month and grabbed a used one. Dropped it in and same vibration at 65mph.

With the vibration changing each time the angles are messed with indicated to me it really is a driveline/pinion/tcase angle relationship. The ultimate/final fix is a CV driveshaft but that's expensive. :mad1:
 
This might seem pretty weird, but get a long straight edge and make 100% sure the front and rear yokes are welded in phase. Place the straight edge along the drive shaft to verify the yokes are perfectly aligned.
 
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