Real time help: H55f, engaging reverse also engages 2nd.

[hotgemini]

Have a new and exciting issue with my BJ74.

Went to back it out of the driveway the other day and when I went to engage reverse, the box dropped into second gear. So if I engaged reverse, the gearbox was locked up, if I disengaged reverse the car would drive forwards in second.

Pulled the floor plate up and removed the top plate selector mechanism. Sure enough, 1-2 selector rail was in the 2nd gear position, everything in the box looked normal. Shifted the 1-2 selector back to neutral reinstalled the selector mechanism and upon attempting to engage reverse, the same thing happened again.

Removed the cover plate again, manually pushing the reverse shift arm to engage reverse, as the reverse idler gear meets the gear on the outside of the 1-2 synchro hub, if they're not aligned, then it will push the 1-2 synchro hub forwards and engage 2nd gear.

What normally stops the 1-2 synchro hub from moving when trying to select reverse? Is it just the detent force or is there some form of mechanical lock-out?

I rebuilt the box in December last year and it has done 7,500 km (37,282 furlongs for US and Liberian readers) since.

Drove fine with no unusual behaviour prior to the sudden occurence of this issue.

Thoughts? Help? Suggestions?

 

[hotgemini]

Eyeballed everything, it all looked fine. Reassembled it a second time, haven't yet managed to recreate the problem.

My only theory is something weird going on with the reverse idler selector arm. I don't suppose anyone can tell me what the adjustment on it's pivot stud actually does? Eg. is it an eccentric cam or something?

 

[Delancy]

A few miles after a buddy, that owns and operates a renowned local differential shop, rebuilt an H55F in my HZJ73, similar event occurred, with R stuck regardless any other gear selected.

Could push the selector out of R, drive trying to replicate, and 1 out of 5 times I could, so tore back into and discovered the pin on the reverse rail completely missing.

At first, couldn't figure out how it may have happened, until tearing apart another H55F top plate for clues, turning it over at, what must've been the perfect angle, and that little bastard pin flew out onto the workbench.

Don't know that it's what's going on with yours, but the symptoms are similar, and only takes a few minutes to check the pins in your top plate.

 

[hotgemini]

My issue is slightly different, in that it will happily go in and out of reverse once it occurs, but you can't disengage 2nd.

Checked all the pins and circlips on the selector rails and everything was intact as best as I could tell.

Will have to wait and see if it reoccurs...

 

[hotgemini]

Aaaand 16 months later it happened again, I've still got no idea.

 

[peterb]

This issue has not happened to me on my h55 but did on the 4 speed in my 40. It turns out some PO had removed (or forgot to reinstall) the springs for the detent balls on the top of the tranny. I presume you have checked your balls <smile> but are the springs in place? Does the h55 have detent balls on the top of the tranny?
Good luck!
Peter