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Transmission Synchronizer Assembly
Fits 46-71 Jeep & Willys with T-90 Transmission

Part # 640391

New Transmission Synchronizer Assembly (1 required per vehicle)

Comes complete with brass blocking rings, shift plates and springs.

T-90 Transmission

46-49 CJ-2A
49-53 CJ-3A
53-64 CJ-3B
55-71 CJ-5
50-52 M38
52-66 M38A1
46-64 Truck
46-64 Station Wagon

Part # Price





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Questions & Answers

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Does this synchro assembly include the brass bushing as identified in the main shaft assembly diagram as part #5? If not, can it be purchased? Thanks...

Willys Jeep Parts Tech:
No, #5 does not go into the synchro it goes into the 2nd gear.

I have rebuilt this on my 46' CJ2A. I am curious though cause I have seen pictures both ways. Does the tab on the end of the spring go inside the groove of the shift plate or on the outside as shown on this synchronizer assembly?

Willys Jeep Parts Tech:
Not sure exactly what you mean. The spring will go to the inside and the shift plates slide around.

I have a 1968 CJ5 with dauntless. Not sure if T86 or T90 for transmission. Reverse, 2nd and 3rd shift perfect. 1st gear even when in complete stop to shift once gas is applied makes terrible noise and pops out of gear. No issue with reverse. I am thinking the gear might be broken/ damages. Do you sell the 1st gear? and it is common between T86 and T90. I know T86 parts are hard to find. If I have a T86 what gears and parts if any can be reused using your T90 rebuild kits

Willys Jeep Parts Tech:
Most likely a T86 in that set up. It will be stamped on the side of the case. Please email to help out.

Hi there. I have the T-90 in my 1964 Universal. What do you recommend for the proper lube. To follow up, do you sell it. There is so much out there about GL4 vs 5 and I even saw GL1 out there as well.

Spencer Crawford:
The consensus on the various forums per the Owners Manual appears to be Sta-Lube SAE 85/90 GL-4 as safe for yellow metals, meets requirements of manufacturer for transmission and transfer case
Willys Jeep Parts Tech:
Straight GL-4 non synthetic (80/90 weight gear oil) its good for yellow metals.

Does this assembly have both second and third gear synchronizes. The picture is not clear

Willys Jeep Parts Tech:
There is only one sychronizer in the T90 between 2nd and 3rd.

I have a 56 CJ5 with a T-90 transmission, first gear is not synchronized. Can I make first gear synchronized when I rebuild the transmission?

Willys Jeep Parts Tech:
Sorry, the T90 will not do this. Youll need to come to a complete stop when shifting from 2nd to 1st.

I have a 48 cj2a with a t90 when coasting there is a noise that sounds like a bad bearing. The noise is not present as long there is pressure on the trans such as acceleration of slowing down in gear. Any suggestions
There are a few directions to go on this. Please give us a call toll free and we can go over what to check. 888.648.4923. Thanks

I have a71 cj5 with a225 buick en. It keeps tearing out 3rd gear Y thanks

Willys Tech:
If you have the T90 transmission in there the synchronizer is a good place to start. I would also check out your poppet balls and springs.

What transmission should be in a 71 jeep cj5 with a225 biuck eng.

Willys Tech:
They typically used the T86AA, T14 or T90 transmissions.

I am looking at a 1948 CJ-2A with the T-90 Transmission to buy but it will not shift into third gear. Took the shifter off to inspect the gears and everything looks OK with the gears and synchronizer. Could the synchronizer be bad or is there something else to look at. It shifts fine in the other gears.

Willys Tech:
I would inspect your sycronizer closer. I would also look at any excessive wear and make sure any needle bearings havent dropped.

I have a T-90 transition in my 46 willy There was a clicking noise in the tranny I removed the top and found the shift plates had came out of the synchronizer assembly what causes this.

Willys Tech:
Sounds like your schronizer is very badley worn and your brass blocking ring is done.

Mine is now popping out of 3rd gear, same question, will this assembly solve 3rd too?

Willys Tech:
The sycronizer may be the problem but you may need to check your poppet balls and springs.

Was driving in 1st low and herd a noise from the transmission like a bearing spinning that was dry. Now I still have first but it won't shift into 3rd. Opened up the top and don't see any visible signs could this be it..

Willys Tech:
Sounds like its your syncronizer if it wont shift. I would take it apart and check for damage.

Hi there. I couldn't get my t-90 to shift into second gear, opened the top, and discovered the second gear brass gear is broke in two pieces. Since I will have to tear down the tranny to fix the problem, what parts would you recommend replacing? Thanks!

Willys Tech:
We have a T90BSG kit as well as they syncronizer assembly or just the brass rings if you need them. Call us toll free. We are more than happy to help out.

never changed third gear syncrolize before is it farely easy?

Willys Tech:
We do sell mechanics manual that will walk you thru the process.

I have a 1971 cj5 with a t90 3 speed. The problem is is that everytime I shift I have to let the motor idle down b4 I can shift. The other problem is is that i can't shift from 2nd gear to 1st with out being almost stopped. Do I needa redo my tranny?

Willys Tech:
Your 1st and 2nd speed gear are not syncronized. You have to come to a complete stop when shifting from 2nd to 1st or you will grind gears.

I have a 1956 CJ5 with a 225 odd fire Daunless. I'm pretty sure the transmission is a T-90 (3 speed). My question is... I have a syncronizer assy. (new complete) from a 1966 M-274 military Mule (3 speed) transmission. It looks exactly the same as the one you guys have for sale. Same number of slots (6) for the shaft and everything. will it fit my T-90 3 speed ?

Willys Tech:
Somebody put an unoriginal engine in there so you may want to check the transmission as well. It will be stamped on the drivers side case. As long as you have a T-90 they should be the same for either.

I have a 1966 CJ5 How do I tell which transmission is in it? Model # 8305A Serial #200778.. I thought it was a T90 But some others say no way?

Willys Tech:
In 1966 it was optional to have a T90 or T86AA. It will be stamped right on the side of the transmission in the housing.

I assume this requires the motor to be pulled? Thanks, Bill

Willys Tech:
Not the motor no. You can just drop the transmission down to get to it.

My transmission unless i hold the shifter wants to pop back a bit out of 2nd then it makes this terrable grinding noise and i cant get it to want to shift down from 3rd to 2nd unless im going really slow i understand its a syncro issue but is this the only part i need to make things better?

Willys Tech:
This should probably do the trick. I would check for any excessive wear on the gears themselves too.

What causes these to go bad, and make it jump out of second gear? Hard shifting or just wear out over time? Thanks, Harry

Willys Jeep Parts Tech:
There are thrust washers and some things to check. Please email to help out on.
Willys Tech:
The brass wears over time. Really any transmisison that is that old will have alot of wear. Also the springs, shift plates ect take wear.

jumps out high gear whats up

Willys Tech:
Its your syncronizer. This should take care of it for you.

I have to completely stop to downshift from second gear to first, is this what I need? Thank you.

Willys Tech:
The T90 is not sync'd between 2nd to 1st. You always have to come to a complete stop. This is the syncronizer between 2nd and 3rd.

I am having trouble with the transmission popping out of second gear. Will this fix it or should I look at the forks and poppet springs?

Willys Tech:
This should solve your problem.
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