Topic: t-case experts... Marlin?

[Saber]

Here's my sad story...

I recently purchased a new CV joint drive shaft from High Angle (thanks Jesse).  This was to replace a one piece that had standard u-joints on it.  The old shaft was giving me all sorts of heartache due to the u-joint angle, as I have 5" springs in the rear.  I drove with old shaft for several months and it only annoyed me at around 45+, so it wasn't a huge deal.

Now, I'm afraid it may have done some damage to my tcase (possibly the output bearings), as the new shaft from High Angle is worse.  The old shaft gave off a really loud hum in the cab, the new shaft vibrates the hell out of the cab.  Nasty noises.

If I grab the CV joint, I can move it a bit up and down, which I can't imagine is a good thing.  Do any of you know how much (if any) play there might be in the rear tcase flange?  The new CV shaft angle looks awesome and I'm sure the shaft is well balanced.  Any thoughts would greatly appreciated...  Thanks in advance!

Oh yeah, here's my rig:  1994 Ext Cab V6 Auto (don't laugh!)  It's SAS'ed, so that's all that matters.   

[Shamb]

by hand there should be NO play, you shouldn't be able to budge it up and down.

If there's slop in there then the bearing is probably shot, is it leaking gear oil out of the rear of the t-case??

[Marlin]

First comment:

  If you replaced a two part rear drive shaft with a one piece shaft, it may too long and going out of line in the center.
This happened to us when we installed a single Marlin 470:1 t-case behind a 3.0 V6 5 speed in a 89 x-cab truck. After having a new one peice rear shaft made and going on a test drive, it sounded like the Marlin gears were going away.
 After installing another 470:1 single case, we decided it had to be the driveshaft. Amazingly, when we took the driveshaft back to our local shop, [I wish Jessie was closer, he does first class work], they proceded to tell me that whoever built this shaft was an idiot. They had used 3" tube [factory size] and explained that because the shaft was so long, the tube was going out of line in the center like a spinning piece of spaghetti. They informed me that the tube would need to be 5" in diameter to make it stronger.
 When I showed them their receipt from two days before, they still did not believe me. They simply stated that "they" would never build anything as dangerous as what I brought back to them. In the end, I paid for the original two piece shaft to be redone and balanced, and the truck was as good as new.

Second comment:

The output shaft of your chain driven t-case must have up and down movement, because the output shaft is turning on roller bearings. Unless you are low on oil, I have never seen the rear 63/32 bearing go away.

Are you using a c/v joint at the t/case? If you are, there can be NO angle at the rear end. The pinion must be pointed straight at the rear flange of the t-case or you will get driveline vibration.

In closing, I have tremendous respect for Jessie and his quality work.

Marlin

[Saber [OP]]

Thanks Marlin.  I did exactly that; I replaced the factory two part shaft with a one piece.  I was experiencing some issues with the double cardan joint and got the hair to replace it after reading this article:

http://www.4x4wire.com/toyota/tech/driveshaft/

In retrospect, re-balancing and possibly installing a longer slip would have been a better choice.  I bought the same monster tubed shaft from Steve at South Bay Driveline, just like the article above.  That was the one that gave me the obnoxious humming in the cab around 45+ mph.

I checked the pinion angle and it looks pretty damn good.  It could go up 1-2 deg, but it's real close at pointing right at the tcase.

Just as you said, I am getting a little play in an up-and-down motion, but none side-to-side, so it sounds like things are just fine with my tcase.  My initial thoughts led me in the direction that adding the new CV (much heavier), was exponentially increasing vibration, mainly due to the spinning weight of the CV itself.

I'm with you... Jesse makes great quality stuff, as I bought a front shaft from him a while back, hence the reason I went back for the rear.  He and I talked for a while, discussing all sorts of things (tcases, gearing, e-brakes, etc.) and somehow you came up in the conversation.  He has the same kind words for you.  Actually he said, "That man really knows his ."     Can't disagree with that...

One last question, do you think the addition of a high-pinion 3rd in the rear might help?  The drive shaft wouldn't have much of a angle on it, but the pinion angle wouldn't be as straight either.  I've been thinking about putting in a soft locker in the rear anyway, so it might not be a bad place to start.

Thanks again for all the expertise on this board, as it's a daily ritual to visit.

[Marlin]

So at this point, we are in agreement that the one piece rear drive shaft is your problem. 

Putting a high pinion front diff from a FJ80 in the rear of your truck would be a great idea if it wasn't weaker when run backwards.

With a standard rotation ring and pinion, when you rotate the pinion to go forward, by design, the pinion is being pulled into the ring gear. However, when you shift into reverse, it is much weaker because the pinion, by design, is being pushed away from the ring gear.

The high pinion when mounted in a front end of a truck is stronger when going forward but weaker when backing up. This would be reversed when installed in the rear of a truck. By design, going forward would push the pinion away from the ring gear making it weaker than your current rear diff, but driving in reverse would pull the pinion into the ring gear making it stronger than your rear diff.

You have a great idea, but the 8" ring gear is too small for the task. Even Dana 44 high pinions fail. The only reason why Dana 60's high pinions live is because of there brute size and strength.

[Saber [OP]]

Are you using a c/v joint at the t/case? If you are, there can be NO angle at the rear end. The pinion must be pointed straight at the rear flange of the t-case or you will get driveline vibration.

Marlin - Just for shits, I pulled the rear shaft and put a 90 deg laser level on the diff flange.  I was shocked that the pinion was pointing 5.5" below the center of the tcase flange.  Eye balling this one obviously didn't work.  I can only assume this might be adding/causing my vibration issues.  I suppose I have two options:  shim the rear and try and get it close, or weld on some new spring perches.  I'm thinking new spring perches would be best, as I can get it exact.  I don't plan on changing/swapping my rear springs, as they're brand new 5" Alcans.

Thanks again for all the help you provide...