Another Popping Out of Second Gear Thread

1941 - 1945, MB, GPW Technical questions and discussions, regarding anything related to the WWII jeep.
mooecow
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Re: Another Popping Out of Second Gear Thread

Post by mooecow » Fri Nov 17, 2017 5:04 pm

Thank you everyone for your help! I had missed putting the shield on the output side of the mainshaft. Combined with poor shimming second gear was not fully engaging. With these two issues corrected it goes into second and stays there.
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Re: Another Popping Out of Second Gear Thread

Post by dinof » Mon Jan 21, 2019 6:00 am

Oldtimers just held second with their hand waiting to shift to third.
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Re: Another Popping Out of Second Gear Thread

Post by Joe Gopan » Mon Jan 21, 2019 6:47 am

Not on my Jeeps. I repaired them. :wink:
Most commonly caused by worn second gear bushing on Jeeps driven with care. The rougher the use, the more causes. Double clutching and compression braking will contribute to early failure. This is a weak point on Jeeps with T-84 and T-90.
Last edited by Joe Gopan on Mon Jan 21, 2019 11:02 am, edited 1 time in total.
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Re: Another Popping Out of Second Gear Thread

Post by artificer » Mon Jan 21, 2019 10:50 am

Dino wrote: Oldtimers just held second with their hand waiting to shift to third.
Not a very good idea on any vehicle, whether jumping out of any gear or not.
This practice is responsible for wearing shift selector forks.
John GIBBINS Member Institute of Automotive Mechanical Engineers [Ret], ASE Master Medium/Heavy Truck & Auto Technician USA -2002 Licensed Motor Mech NSW MVIC 49593 Current 2015
TO DIAGNOSE, TROUBLESHOOT OR FAULT FIND ANY AUTO SYSTEM....
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Re: Another Popping Out of Second Gear Thread

Post by Chuck Lutz » Mon Jan 21, 2019 3:06 pm

As artificer has pointed out, holding the shift cane just wears down the shift fork, only a Bubba-fix that eventually requires replacing that fork. Since NOS ones are rarer than hen's teeth, and repop ones may be third rate, that "solution" is about as wise as using your hand brake to stop the jeep because you have trouble stopping when you step on the brake pedal.
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Re: Another Popping Out of Second Gear Thread

Post by Joe Gopan » Tue Jan 22, 2019 12:10 am

Do the inevitable, repair or overhaul the gear box while it is still rebuildable.
"A stitch in time, saves nine."
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Re: Another Popping Out of Second Gear Thread

Post by artificer » Tue Jan 22, 2019 12:45 am

I notice the recently edited previous post about an hour ago from something offered a day or so ago. More expert advice?

How about instructing the OP on establishing what may be wrong so that he & others can fault find then repair inexpensively or is the US Army method of shotgunning then as usual replacing everything with Ordnance rebuilt or new surplus units, in the advice pipeline?

My 'practical' experience is not the 2nd gear bush but worn 2nd gear dog teeth & synchro hub cone to sleeve fitment/wear/misalignment issues.

Then I didn't sell surplus parts but fixed "Jeep" things.
John GIBBINS Member Institute of Automotive Mechanical Engineers [Ret], ASE Master Medium/Heavy Truck & Auto Technician USA -2002 Licensed Motor Mech NSW MVIC 49593 Current 2015
TO DIAGNOSE, TROUBLESHOOT OR FAULT FIND ANY AUTO SYSTEM....
Understand how system parts interact with one another. GOOD parts can then be established & the NOT GOOD problem/s part/s isolated for repair or replacement.

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Re: Another Popping Out of Second Gear Thread

Post by Joe Gopan » Tue Jan 22, 2019 1:14 am

Jeeps will "talk"to experienced "hands on" mechanics who have actually worked on more than a few and recognize familiar symptoms.
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HONOR GRAD-WHEELED VEHICLE MECHANIC SCHOOL 1960 - US ARMY ORDNANCE SCHOOL(MACHINIST) ABERDEEN PG 1962 - O-1 BIRD DOG CREWCHIEF - 300,000+TROUBLE FREE M-38A1 MILES
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Re: Another Popping Out of Second Gear Thread

Post by artificer » Tue Jan 22, 2019 1:31 am

This so called experience does not apply to many G503 folk asking questions. They are not wanting/expecting answers from blow hards on re building/conditioning things that don't necessarily require any such thing.
John GIBBINS Member Institute of Automotive Mechanical Engineers [Ret], ASE Master Medium/Heavy Truck & Auto Technician USA -2002 Licensed Motor Mech NSW MVIC 49593 Current 2015
TO DIAGNOSE, TROUBLESHOOT OR FAULT FIND ANY AUTO SYSTEM....
Understand how system parts interact with one another. GOOD parts can then be established & the NOT GOOD problem/s part/s isolated for repair or replacement.

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Re: Another Popping Out of Second Gear Thread

Post by roberturen » Fri Jan 05, 2024 1:18 pm

I have repaired a few t84 transmisions and find watching the u tube rebuild videos so so helpfull, I also notice the Hotchkiss gearboxes have shims on the shafts to reduce the end float on the main shaft and take it away completely on the 2nd gear, can anyone tell where to buy extra shims so any extra float can be reduced back easily , I have in the past had to send repro main shafts back due to in correct internal machining for the needle bearings , allowing them to slide in to far and then not contact very much of the output shaft , even the groove for the sirclip that holds the needle bearings in the input shaft was so shallow it wouldnt hold the circlip in place, the second gear cog needs to be super snug and zero side slopp, I think end float on second gear cog can be removed with shims but so often we cant buy the shims so it gets put on with a little end float remaining , I always tighten up the front main bearings in place and the rerar one with a clamp before securing the transfer box up to double check each bronze synchro ring has a little end float as the u tube videos show , but only a little like 40 or 50 thou, you are right about the t84 being a weak gearbox, Its just so small and everything is so tiny inside compared to a t90 gearbox is so much stronger, 100hp stronger and the stiff gear selection can be lightened up by shortening the selector poppet springs very slightly and then the gear change is as light and slick as a t84

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Re: Another Popping Out of Second Gear Thread

Post by JAB » Fri Jan 05, 2024 3:30 pm

-Jeff

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Re: Another Popping Out of Second Gear Thread

Post by Wolfman » Sat Jan 06, 2024 7:26 am

The source of second gear jumping out on an old, worn transmission is sometimes a worn second gear bushing.
If you slide second gear on the mainshaft by itself and rock the gear around, it should be a tight but free turning fit.
If the gear "wobbles" around, there is a problem. Since second gear has angled teeth, when "under load" and with a worn bushing, the gear wants to tilt sideways, which will "walk" the 2nd/3rd synchronizer sliding collar off 2nd gear to neutral.
Shims would take up any side clearance second gear has on the mainshaft and the synchronizer hub when assembled. It will not correct a "wobble".
The synchronizer inner hub should fit up tight to the section of the mainshaft second gear is on and second gear at this time should have very little "side play", but still turn free.
One more issue I have found, when installing a new sealed rear mainshaft bearing on a rebuild and clamp the mainshaft and clutch shaft in place, with the gear & nut in place and tightened up on the rear of the mainshaft like you do to check clearances in the transmission, is too much clearance with the 3rd gear brass blocking ring. The brass ring flops around. This is bad.
This situation also has the complete mainshaft assembly too far to the rear of the transmission case.
To correct this, shims have to be placed on the mainshaft in front of the rear mainshaft bearing to move the entire, assembled mainshaft assembly forward in the case.
Not sure what causes the difference with a new bearing. I suspect the width of the new sealed rear mainbearing inner race but have not confirmed this.
On the U.S. T-84s I have rebuilt, there was not originally any shims where I just described.
I am not sure the A-738 shim pack covers both the mainshaft and second gear ??
Second gear shim is a smaller O.D & I.D.
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Re: Another Popping Out of Second Gear Thread

Post by ja020 » Tue Feb 20, 2024 9:27 am

What about the detent springs. They may be a bit weak, and allow the jumping out of gear as described?
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