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T5 transmission any good?

MomoJeep

Basic User
Member
City
Seattle
State
WA
I've clocked close to 300,000 miles on two T5s running 33x10.50 tires. Overall they have been good boxes but the first one did have issues, but I've learned a few things and think they make a decent 5 speed behind an inline 6 cylinder. If you are an aggressive driver with a heavy foot I would look elsewhere though
Issues:
In my experience they are very sensitive to what oil you run and ensuring it is topped up. I know some people run ATF in them and I ended up running Pennzoil Synchromesh fluid which the transmission seems to love, it shifts really smooth. If you go with a T5 be sure you check the fluid level and keep it topped up. My first T5 had one of those small drip leaks, that never looked major. I took it on a long trip up to Tahoe doing 75 most of the way and I actually overheated it pretty good climbing Donner pass which goes up about 7500 ft elevation. I initially smelled something a little off then noticed the jeep started to slow down a lot. When I pulled over I could tell the box was blowing fumes out the vent and felt really warm. After cooling down it was able to drive again but had a serious gear whine. But I think this was all largely due to me running it with low oil. My second box is leak free and going on 100,000 miles with no issues.

Second problem I had was the T5 has a bolt on the drivers side of the transmission (mine was a tamper proof Torx head) and it is the reverse/5th gear pivot bolt. My first gear box that bolt started to back out causing me to temporarily lose 5th/reverse until I figured out the problem. I ended up using loctite on it and it held firm with no more issues. The current box the bolt has never backed out.

Third issue I had was the input shaft bearing retainer, which is what the throwout bearing slides on, is a relatively soft metal on the Jeep T5 at least. Over time it can get scored and gauged which caused me clutch issues, but if you use a little disc brake lube or copper anti-seize (just a very little amount) it will help prevent that from happening. Or you can buy an iron bearing retainer to address the issue.

Yeah in retrospect that sounds like a lot of issues, but that's over almost 20 years and hundreds of thousands of miles of driving so I think it is a decent gearbox. And One thing that doesn't get mentioned much is it has a pretty good low first gear ration at 4.03:1
I've always wanted to add this internal brace to beef up the gearbox too, but will likely swap to something different if my current T5 ever goes down.
https://www.5speeds.com/t5.htm

Bill
Good to hear...

I had one seize up on my going 65mph and it scared the shit out of me. Could've caused a dangerous wreck. However, it was new to me at the time, and it's likely a slow leak caused it to be low on lube, which as you point out will lead to failure. Good to keep an eye on that!
 

spankrjs

Scrambler Junkie
Lifetime Member
SOA Member
City
Biloxi
State
MS
I've clocked close to 300,000 miles on two T5s running 33x10.50 tires. Overall they have been good boxes but the first one did have issues, but I've learned a few things and think they make a decent 5 speed behind an inline 6 cylinder. If you are an aggressive driver with a heavy foot I would look elsewhere though
Issues:
In my experience they are very sensitive to what oil you run and ensuring it is topped up. I know some people run ATF in them and I ended up running Pennzoil Synchromesh fluid which the transmission seems to love, it shifts really smooth. If you go with a T5 be sure you check the fluid level and keep it topped up. My first T5 had one of those small drip leaks, that never looked major. I took it on a long trip up to Tahoe doing 75 most of the way and I actually overheated it pretty good climbing Donner pass which goes up about 7500 ft elevation. I initially smelled something a little off then noticed the jeep started to slow down a lot. When I pulled over I could tell the box was blowing fumes out the vent and felt really warm. After cooling down it was able to drive again but had a serious gear whine. But I think this was all largely due to me running it with low oil. My second box is leak free and going on 100,000 miles with no issues.

Second problem I had was the T5 has a bolt on the drivers side of the transmission (mine was a tamper proof Torx head) and it is the reverse/5th gear pivot bolt. My first gear box that bolt started to back out causing me to temporarily lose 5th/reverse until I figured out the problem. I ended up using loctite on it and it held firm with no more issues. The current box the bolt has never backed out.

Third issue I had was the input shaft bearing retainer, which is what the throwout bearing slides on, is a relatively soft metal on the Jeep T5 at least. Over time it can get scored and gauged which caused me clutch issues, but if you use a little disc brake lube or copper anti-seize (just a very little amount) it will help prevent that from happening. Or you can buy an iron bearing retainer to address the issue.

Yeah in retrospect that sounds like a lot of issues, but that's over almost 20 years and hundreds of thousands of miles of driving so I think it is a decent gearbox. And One thing that doesn't get mentioned much is it has a pretty good low first gear ration at 4.03:1
I've always wanted to add this internal brace to beef up the gearbox too, but will likely swap to something different if my current T5 ever goes down.
https://www.5speeds.com/t5.htm

Bill
Your experience is definitely the opposite of mine :thumbsup:

I never hammered on my T5's, but I did not "baby" them. Mine always failed on the highway. BUT, I think wore out countershaft bearing bores in the cases themselves caused me most of the catastrophic grief. The non-catastrophic grief, unfortunately, was caused by poor surface hardening of the counter shafts where the bearings ride directly on the shaft, no fix for this :shrug:

The brace you mentioned/linked to is for "World Class" T5's, not our Jeep "NWC" versions :(

IF someone made a stronger case, AND you could install different style bearings on the counter shaft, I think that would beef up a T5 pretty good. Not as strong as an AX15, but much better :twocents:

All that being said, 2 out my 3 CJ's have T5's, so I hope to keep them alive :fingerscrossed::fingerscrossed:
 
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