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Hello all

Recent rebuild (not by me.. a freind I asked to put another set of eyes on)
of a very clean T90/D18 in a 51 M38

Actually, all bearings, gears and even syncros in the transmission looked fantastic upon inspection so left the T90 alone. It just looked and felt darn near new

Dana 18 transfer, however, after disassembly, noticed intermediate shaft “scoring” a bit so was replaced w/ a
Complete kit from Novak w/ specially hardened intermediate shaft, O-rings, thrust washers, bearings and snap ring.
All gears looked like new here too

Upon initial drive I did NOT notice anything crazy with noises or anything at all.
However, as I put a few miles on it around neighborhood, I’m noticing
What I’ll describe as low “chattering” while in 1st or 2nd gear under driving load. I just drove it again/ I “think” I can hear the same noise, albeit a bit less pronounced, while coasting too

In 3rd gear, no noise at all. Perfect. under load or coasting or whatever: nothing in third.

What did I (we) miss in the tranny/transfer?

(The following might not be even related issue, but will note)

In the last few days I noticed a heavy dripping of gear oil at the rear output/e-brake
This hasn’t had a leak here all these few months; just started the other day after parking. Might not be applicable like I wrote, just mentioning.

Anyway...anyone want to fathom a guess as to the “chattering” I’m experiencing?

My initial thoughts was something was missed in the transmission inspection and I should have torn it apart. But everything looked and shifted so good I left it alone.

I do notice that the noise is less pronounced when very cold. Louder as it warms up (thinning of the GO maybe?)
I’m using 90 wt mineral oil.. maybe some heavier GO?

The other culprit I’m wondering could be is this:

Could end play of the T90 output to Dana18 shaft but be loose or incorrectly tightened?
I DID have one or two very sporadic issues of jumping out of 2nd the first few drives..Happened once or twice and I’ve tried making it happen again but I just can’t now!!
What’s with that? How can it go away?

I guess I could drain the GO and remove the rear D18 cover and see if the end nut securing T90 main to the transfer case is tight?
What should I look for on this nut?
Torque setting?[/i]

Daveyboy wrote: In the last few days I noticed a heavy dripping of gear oil at the rear output/e-brake
This hasn’t had a leak here all these few months; just started the other day after parking. Might not be applicable like I wrote, just mentioning.

I always suggest to check your fluid levels first. Nice and easy check to make sure you have enough fluid before we start chasing geese.

Daveyboy wrote: I do notice that the noise is less pronounced when very cold. Louder as it warms up (thinning of the GO maybe?)
I’m using 90 wt mineral oil.. maybe some heavier GO?

Page 54 of your TM 9-8012 will tell you what weight Gear Oil is recommended for your given expected temperature range. I personally would not deviate from these.

Daveyboy wrote: Could end play of the T90 output to Dana18 shaft but be loose or incorrectly tightened?

Possible, but probably less likely.

Daveyboy wrote: I DID have one or two very sporadic issues of jumping out of 2nd the first few drives..Happened once or twice and I’ve tried making it happen again but I just can’t now!!
What’s with that? How can it go away?

These transmissions are known for jumping out of 2nd when the syncro is bad.

Daveyboy wrote: I guess I could drain the GO and remove the rear D18 cover and see if the end nut securing T90 main to the transfer case is tight?
What should I look for on this nut?
Torque setting?

I believe either one or both of Rick Stiver's rebuild guides will answer most if not all of your questions.

http://www.willystech.com/wt/T90Rebuild ... ebuild.htm

http://www.willystech.com/wt/Model18TCa ... rCase.html

Thanks, Jake for taking the time to answer all this.

Any idea about the “chattering” noises as described?

Chattering noise is very little to go off which is why I suggested checking your fluid first, but if you want I could take a few wild guesses:

• Bad bearing- even though they all looked fine, it's recommended changing the main drive bearing regardless
• Bad needle bearings in the cluster gear- when you're in 3rd gear, the transmission is 1:1, which means the countershaft is freespinning, hence no noise. When you're in 1st, 2nd, or reverse, there will be a load the countershaft. The needle bearings on your countershaft could be loose and need to be replaced, or the countershaft itself is damaged, also requiring replacement. Which leads to my final guess:
• Countershaft loose in transmission housing- the countershaft slides through the transmission housing at the rear, and if the hole in the housing is too loose for the shaft, it could cause misalignment of the cluster gear, as well as a fluid leak.

Here is a picture from Rick's guide which shows the countershaft partially removed from the transmission, without the cluster gear:

I have found If you mix different manufactures parts they sometimes do not mesh correctly and can cause noise/ wear even though they look okay. I have seen the use of engineers blue painted on gears to see if they mesh correctly or not before you refit.
As one of the videos said "not all parts are equal" Sorry no quick fix.

Horse

You did not mention the clutch but I have to ask - did you change anything of the clutch?
Is the chatter all the time or only when letting your foot off the clutch?
For clarity is your “chattering” a noise? Or is your chattering a bucking feeling when you are getting underway before your foot is completely lifted from the clutch pedal?