H55F and 3rd gear problem

[We Sing]

Hello experts,
I have an H55F gearbox, and it works fine! However, it keeps popping out of 3rd gear. If I hold the gear lever, it stays in gear. Even when the engine isn’t running, the lever just slips out of 3rd gear, as if a spring or something inside is loose.
Has anyone experienced this problem before? Thanks in advance!

 

[Eurasiaoverland]

Most likely the 3rd/4th gear shift sleeve and index teeth are worn.

Another possibility is that the detent mechanism on the shift fork shafts is faulty. How does it feel when you put the gearbox into 3rd? Is there any feeling of positive engagement?

Start by getting a FSM for the gearbox. Then remove the gearstick and check the retaining pins are not loose in the cover. Check also the rubber gearstick seat/base, as they commonly wear.

Next, remove the gearbox cover and inspect the index teeth on the input shaft/3rd gear.

You can strip down the shift fork/shaft assembly in the cover with nothing more than a hammer, some pin punches and a screwdriver.

To go deeper and change gears is a lot more involved.

 

[We Sing]

Most likely the 3rd/4th gear shift sleeve and index teeth are worn.

Another possibility is that the detent mechanism on the shift fork shafts is faulty. How does it feel when you put the gearbox into 3rd? Is there any feeling of positive engagement?

Start by getting a FSM for the gearbox. Then remove the gearstick and check the retaining pins are not loose in the cover. Check also the rubber gearstick seat/base, as they commonly wear.

Next, remove the gearbox cover and inspect the index teeth on the input shaft/3rd gear.

You can strip down the shift fork/shaft assembly in the cover with nothing more than a hammer, some pin punches and a screwdriver.

To go deeper and change gears is a lot more involved.

Thanks for your answer. When I shift into 3rd gear, it feels normal. You hear the shift noises, but the gear lever just falls out due to gravity. This happens even when the engine is off. I have the FSM and a complete gearbox rebuild kit. I want to rule things out first. I’m going back to investigate today! Thanks so far!

 

[We Sing]

Most likely the 3rd/4th gear shift sleeve and index teeth are worn.

Another possibility is that the detent mechanism on the shift fork shafts is faulty. How does it feel when you put the gearbox into 3rd? Is there any feeling of positive engagement?

Start by getting a FSM for the gearbox. Then remove the gearstick and check the retaining pins are not loose in the cover. Check also the rubber gearstick seat/base, as they commonly wear.

Next, remove the gearbox cover and inspect the index teeth on the input shaft/3rd gear.

You can strip down the shift fork/shaft assembly in the cover with nothing more than a hammer, some pin punches and a screwdriver.

To go deeper and change gears is a lot more involved.

I took a closer look. You don’t hear a click in 3rd and 4th gear. In 3rd, the gearstick just falls down when the engine is off, and when you shift to 4th, there’s no proper click either... no positive engagement I think.
Sounds like a detent mechanism issue... The gearbox probably needs to come out from under the car.

 

[Trevin]

Older thread, but...

Did you find a solution?

Mine jumps out of third on deceleration, after a complete rebuild, including the shifter. If actually feels like it's being pushed into neutral when this happens.

 

[Eurasiaoverland]

Older thread, but...

Did you find a solution?

Mine jumps out of third on deceleration, after a complete rebuild, including the shifter. If actually feels like it's being pushed into neutral when this happens.

Why was the gearbox rebuilt and what parts were replaced?

Sounds like the rebuild was either too focused on a specific issue, or just not done properly.

Is the rebuilder not taking responsibility to return a fully working transmission to you?

 

[Trevin]

Thanks for the reply...

I did the rebuild, the problem I wanted to solve was essentially worn syncro rings. When I got it apart, I found that it was in pretty rough shape, I replaced the following parts:
Bearings & bushings
Countershaft
1-2 shift assembly
3rd gear, syncro, shift hub, sleeve, detent shoes and springs
4th & 5th gear syncros

I also rebuilt the shifter, new detent balls & springs, shifter bushings, pins and circlips.

This thing has me stumped, everything seems to work as it should, the shifting feels normal, very crisp engagement, it just gets pushed out of 3rd when decelerating. I may well have missed something, but I've put a lot of time into going through it, and I can't find anything out of place.

 

[Lead Head]

Are you sure no part of the shifter is hitting the body? Does 4th gear stay in fine?

 

[Trevin]

I have the floor panel off above the transmission, so I can see the entire unit when driving... nothing comes close to the shifter.

Yes, 4th, and all other gears are fine.

3rd is fine under acceleration, but it will "shift" into neutral even driving on a flat road as soon as I ease off the throttle. It feels as if the gear lever is being pulled back into the neutral position. It's very strange, because when there is a load on the shift hub (either under acceleration or deceleration) it should be harder to get it to slide forwards or backwards.

I had replaced the output shaft on the rebuild, and I thought maybe the new one was bent, but it doesn't apperar to be.

The frustrating part is that it didn't jump out of 3rd before the rebuild... it just wouldn't shift smoothly due to the worn syncro rings.

 

[Lead Head]

If you hold the shifter in 3rd, how hard does it try to push it out of gear?

 

[Trevin]

Right after the rebuild, it was fairly violent... to the point that I didn't want to try and hold it in gear for fear of breaking the shift fork. However, since then, I have replaced 3rd gear and rebuilt the shifter, now I can easily hold it in gear with one finger on the shift lever.

 

[Lead Head]

Are you sure the the detent mechanism on the shifter linkage rods are working properly?

 

[Eurasiaoverland]

So you're saying you rebuilt it twice?

 

[Trevin]

The shifter appears to be working properly, new detent balls and springs. It does take a reasonable effort to move the shift forks by hand.

Not really 2 rebuilds... First was the rebuild, everything worked fine, except popping out of 3rd gear quite dramatically on deceleration.

Then transmission out and apart to try and identify the 3rd gear problem. I couldn't identify anything so just to cover the bases, I replaced 3rd gear. Transmission back in, problem improved, but still present, so I ordered parts to rebuild the shifter. After rebuilding the shifter, the problem was again better, but still present.

It's gone from violently jumping out of 3rd to just slipping into neutral. Always only on deceleration, even on flat road.

It's always felt as if the shift lever was being pushed back towards neutral in a continuous motion, rather than being knocked out of gear.

 

[Lead Head]

The shifter appears to be working properly, new detent balls and springs. It does take a reasonable effort to move the shift forks by hand.

Not really 2 rebuilds... First was the rebuild, everything worked fine, except popping out of 3rd gear quite dramatically on deceleration.

Then transmission out and apart to try and identify the 3rd gear problem. I couldn't identify anything so just to cover the bases, I replaced 3rd gear. Transmission back in, problem improved, but still present, so I ordered parts to rebuild the shifter. After rebuilding the shifter, the problem was again better, but still present.

It's gone from violently jumping out of 3rd to just slipping into neutral. Always only on deceleration, even on flat road.

It's always felt as if the shift lever was being pushed back towards neutral in a continuous motion, rather than being knocked out of gear.

I'd be taking a real careful look at the engagement dogs and their mating partner. They should be square cut, or slightly undercut (think upsidedown trapezoid). If they appear rounded, triangular, or trapezoidal (the normal way), then they're probably worn or damaged or not manufactured correctly.

Also make sure they're engaging fully.

 

[Trevin]

I think that's about the only thing left to look at... I can't come up with anyting else. Those parts are all new, and it looks like I'll be pulling the transmission again. Unfortuneatly, that can't be inspected in place.