Another Popping Out of Second Gear Thread

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

Post by mooecow » Fri Oct 13, 2017 5:07 pm

Yes, it's another second gear popping out thread. I've been searching and reading every thread I can find but am at my wits end. Most threads I found either never had a solution or devolved into discussion about not using new parts. Seeing as my case sat for years with water in it before I got it that wasn't an option.

Due to all the damage I had to completely rebuild the transmission. I went hog wild and ordered basically one of everything for it from Ron and followed all the guides here on how to do it. As far as I can tell everything is in spec but when I finally installed it in the GPW I found that it popped out of second while coasting. :(

So from what I found the usual culprits are:
Worn main shaft: Brand new
Worn second gear bushing: Brand new
Second gear to main shaft endplay: .005"

Comparing it to pictures I've found of good T84's I only see one big difference, the shift fork on my transmission doesn't move the synchronizer back onto second gear as far as I think it should. There is still a fairly large gap (.069") between the edge of the synchronizer and the gear. Unscrewing the shift fork from the rail allows it to slide back all the way. Is gap right or should it be closer to the gear itself?

Or does anyone have any other ideas of what I should check?

Here is what it looks like in second gear:
Image

Image

General overview shot, in third gear:
Image

The patient:
Image
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ghiltgen
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Re: Another Popping Out of Second Gear Thread

Post by ghiltgen » Fri Oct 13, 2017 6:04 pm

When I look at the picture, it looks like you have a flat head screw holding the shift fork in place. The original tapered screw had a bristle head and the after market one have a hex head. If you replace that it might bring the shift fork over more. Also, I remember hearing about problems with the 3 "dogs" in the synchro that were put out as aftermarket replacements. They were made to the wrong size and no one knew it until the T 84 they were put into had trouble. Im not sure, but poping out of second gear may have been one of the problems reported. Go to "you tube" and watch the videos put on by Portrayal Press on the T84 rebuild, the guy who did the video discusses those shoddy pieces.
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Re: Another Popping Out of Second Gear Thread

Post by Michael Browne » Fri Oct 13, 2017 11:48 pm

Hi mooecow,

First lesson, just because parts are new doesn't mean they are right within specifications, regardless of who supplied them.
Some observations...
As ghiltgen noted the fork screw doesn't look right.
Too much float in the countershaft gear, second gear, main shaft, and main drive gear will all contribute to popping out on coast.
Looking at overall photo the main shaft is too far back in the box with more third gear blocking ring exposed than normal. You did fit the spacer and slinger next to the circlip before putting the rear bearing on, right.
The syncro hub has been thrown too far forward and too much of the three keys are exposed which will only end in jamming in third gear. Or did you push it forward by hand for the photo?
Is the front bearing correctly retained in the case?
Not knowing your experience and the condition of the case you have used makes it a little difficult to help more that noting things that don't look right.
Good luck
Michael Browne
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REAL jeeps have BAR GRILLES and FLAT FENDERS. The rest are imitations.

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Re: Another Popping Out of Second Gear Thread

Post by artificer » Sat Oct 14, 2017 12:29 am

Best to list what parts were replaced, then we won't have 10 pages of conjecture but be able to pin point & prioritize what issue/s need addressing.

The 3 shifter plates don't cause jumping 2nd.

The 2 assumed culprits mentioned are not the primary contributors & the shifter fork is not usually involved either, provided the selector shaft is correctly manufactured & the Bristol screws are correctly engaged.

Jumping 2nd is primarily caused through wear misalignment/improper engagement between 2nd gear dog teeth & the synchro sliding sleeve.
I have posted a picture showing this dog gear teeth wear on 2nd gear numerous times. Wear on the sliding sleeve will cause this jumping problem even when & if 2nd gear is new.

As well the transmission output shaft position inside the transmission case must be correctly shimmed/adjusted.

When this is done 2nd & 3rd gear synchro sliding sleeve engagement will be similar. Plus the brass baulking rings will exhibit similar play against 2/3 gear cones when neutral is selected.

Gustl's videos shows this mainshaft adjustment aspect.

That's the starting point.
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Re: Another Popping Out of Second Gear Thread

Post by Michael Browne » Sat Oct 14, 2017 1:33 am

John G, you may have missed reading the OP statement "new parts right through" :roll:

Wear on the syncro sliding sleeve is caused by a wobbly or rocking second gear which leads to misalignment. Wobbling or rocking because the main shaft or second gear bushing or both are out of spec.

Keys don't contribute to popping out of gear unless badly worn or broken but mentioned to highlight a future failure point.

Judging by the position of the mainshaft there is an assembly/procedure problem possibly combined with out of spec new parts.

Cheers
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Re: Another Popping Out of Second Gear Thread

Post by artificer » Sat Oct 14, 2017 4:20 am

John wrote:Best to list what parts were replaced, then we won't have 10 pages of conjecture but be able to pin point & prioritize what issue/s need addressing.
Having a new 2nd gear bush doesn't necessarily mean that particular gear was replaced. The photos are not clear enough to show 2nd as new, but facial wear marks seem apparent.

I assume nothing, habitually ask questions & will wait for the OP's list or elaboration.

There is no doubt the answer to the OP's problem is somewhere in my 1st post.

His answering the question/s posed will nail down what really needs addressing.
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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 dinof » Sat Oct 14, 2017 5:32 am

The input shaft looks like it's where it should be-
Slop on brass rings looks a little too much, especially in second gear-
Second gear shift plates position way off-
Screw on shift rail needs to be changed-

I know I'm going to learn something (and hopefully more here) on what this situation is, and how it will get remedied.
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Re: Another Popping Out of Second Gear Thread

Post by yorkshireman » Sat Oct 14, 2017 5:54 am

Had same problem,
check the front end of the main shaft where it goes into the spigot shaft and all those needle rollers are.My brand new repo one was not chamfered like the original one,therefore not letting it go all the way home causing the gap you have in on the brass synchro ...Chris

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Re: Another Popping Out of Second Gear Thread

Post by dinof » Sat Oct 14, 2017 5:57 am

Gusti's videos show you but too many options not explained what to go with. This person sums it all up on what to do and how it should be:


https://www.youtube.com/watch?v=Wd-b4oFCAfA
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Re: Another Popping Out of Second Gear Thread

Post by dinof » Sat Oct 14, 2017 6:05 am

yorkshireman wrote:
Sat Oct 14, 2017 5:54 am
Had same problem,
check the front end of the main shaft where it goes into the spigot shaft and all those needle rollers are.My brand new repo one was not chamfered like the original one,therefore not letting it go all the way home causing the gap you have in on the brass synchro ...Chris
The OP did state he replaced the main shaft.....if it happened to you, why not someone else?


Anything repo in a T-84 worries me...Again! :(
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Re: Another Popping Out of Second Gear Thread

Post by Chuck Lutz » Sat Oct 14, 2017 6:10 am

Offhand I'd say that the main shaft is set too far to the rear....since the shift fork only has so much travel fore and aft, if 2nd gear is too far to the rear then the fork can't move the synchro slider far enough BACK tp engage the dog teeth on 2nd gear. I say that because in 2nd, you can see that the three shift plates on the synchro hub are almost to the point they will escape and jam the trans in gear.

Read Michael's post above.
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Re: Another Popping Out of Second Gear Thread

Post by GSS » Sat Oct 14, 2017 9:34 am

Good words of wisdom by the group.

It sure looks like the main output shaft might be a tiny bit too far back as pointed out by Michael and Chuck....adding shims next to the slinger, or using the correct thickness spacer (“H” vs standard case spacer) might be all you need. It wouldn’t hurt to replace the screw in the 2-3 shifter fork (less likely this is the primary issue), and to check whether the shiny new fork has correct offset etc. I am guessing your flywheel pilot bushing is good. Thanks.
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Re: Another Popping Out of Second Gear Thread

Post by yorkshireman » Sat Oct 14, 2017 12:18 pm

Believe me its the main shaft....it wont be chamfered,its got nothing to do with the rest of the stuff your on about...

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Re: Another Popping Out of Second Gear Thread

Post by tamnalan » Thu Oct 19, 2017 5:19 am

Having had the honor to rebuild a T84 numerous times now and doing a few long MVPA trips... Route 66 was outstanding, by the way! ...

It does not tolerate reverse thrust very well. It will wear and start popping out of 2nd when slowing down, especially after extended heavy use like driving through cities or pulling trailers. It's not a question of "if" it starts popping out... it's a matter of "when" ...

There's a good reason why Willys abandoned it after the war. The T84 is a crappy transmission for jeeps.

Keep your brakes up to snuff and rely on them. Avoid engine braking and the T84 will thank you by staying in spec a little longer. My $0.02.
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Re: Another Popping Out of Second Gear Thread

Post by dinof » Thu Oct 19, 2017 6:12 am

tamnalan wrote:
Thu Oct 19, 2017 5:19 am
Having had the honor to rebuild a T84 numerous times now and doing a few long MVPA trips... Route 66 was outstanding, by the way! ...

It does not tolerate reverse thrust very well. It will wear and start popping out of 2nd when slowing down, especially after extended heavy use like driving through cities or pulling trailers. It's not a question of "if" it starts popping out... it's a matter of "when" ...

There's a good reason why Willys abandoned it after the war. The T84 is a crappy transmission for jeeps.

Keep your brakes up to snuff and rely on them. Avoid engine braking and the T84 will thank you by staying in spec a little longer. My $0.02.
Alan-I can tell you one things for sure....When I was 16 years old, my first car was my brothers GPW that was turned into a street rod when he was finished. Said that, the T-90 trans in that jeep took so much racing abuse behind that Chevy 327. She would go for 20,000 miles or so before breaking.
Truly remarkable it survived all those speed shifts........ I think my T-84 would last about 100 miles in that environment. Guaranteed.
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