MGB More MGB gearbox questions

What I found: The end float on the third gear turned out to be .016/ should be .004-.006/ .012 too much.

A) would this cause the third gear syncro issue?

B) do I find a .1615 end thrust washer or do I find a shim?

C) wouldn't that just cause the third gear to be moved further away from the syncro and syncro ring? Would it be better to shim between the third and second gears?

Thank you, Shawn

64' MGB

Shawn , Do 2nd and 3rd line up perfectly with their mates on the laygear? 12 thou. does not seem like a lot but it could cause your problem. I'll go look at the shop manual and think about this. Sometimes you have an obvious problem , sometimes its harder to find. Is the change to 2nd gear without noise? This is the early non synchro first isn't it? Kevin

They do seem to line up fine. The 2nd gear syncro works great. I am very unsure why the 3rd syncro doesn't work, when everything else seems good. One suggestion was to roughen up the cone on the 3rd gear, but I hate to reinstall everything to find out that didn't work.

I’ll remind you that the cones of each gear are a ground finish. Engineers wanted to protect the gear so brass was a perfect alloy to work in this environment. Brass is a malleable alloy; the gears are a harden ground steel alloy. What has taken place is the brass has burnish it self into the cone. Doesn’t the cone look like a polish mirror? If you were installing a brand new gear it would have a surface ground finish not a polish finish. Your gear can not slow down enough to let the outer hub line up to make the shift, that is why you’re getting that crunch. You’re forcing the slide over the gear while it’s still spinning to fast. Your gear still has the sharp edges on it, doesn’t? If it does, which it should, then your road leads back to the synchronizer. If you were a very articulate driver and had the skills of matching RPM with transmission speed you wouldn’t need synchronizers, but the majority of us do not have this wonderful talent so that’s why the engineers installed synchronizers so that everyone can drive a manual transmission. From what I’ve read you are not that much out of spec with your clearances and the gears are properly align. I can only advise you on what is taking place; you have to decide what you want to do.

Yep, they look like mirrors. I do plan to roughen them up. One thing that is confusing though, is that the second gear surface (cone) is also mirror like and the second gear syncro works great. Any ideas why that would be?

Thanks for the help, Shawn

Not knowing what your issues with the transmission prier to you disassembly and whether your issues were with the 2nd and 3rd gears. However I assume you have replaced all of your bearings including the spigot bearing. Most people over look this bearing and consider this bearing none essential but it too is very important for proper alignment and thrust clearance. Are you running the right shims at your input shaft cover? Your 2nd and 3rd gear cone could have a little more wear on it. When you have the gear flat on your work bench lay the new synchronizer on the gear and measure how much clearance between the synchronizer and the gear to see how much your gear cone has warn. Compare to you specification for your transmission and replace if its out of tolerance. Also switch your synchronizers around to make sure that you do not have a defective synchronizer this can happen sometimes. Make sure that the slide assembly is on the main shaft the way it came off the main shaft. It can go either way I believe, but sometimes they get a ware pattern and need to go back the way the were remove. Scuff all the cones very well, blowing any grit off that gets left behind. I wish I could be their to see and feel what your dealing sorry!

Funny you say about the pilot bushing. The other reason I pulled the engine and gearbox was because of the pilot bushing. When the car was cold, I would push in the clutch and would get a whiney/ rubbing noise that made it very difficult to get it in 1st gear. I know there was an issue with the pilot bushing, but when the car warmed up it was fine. When I took it apart I noticed that it appeared the the end taper of the first motion shaft was making slight contact with the end of the pilot bushing.
I would think it could be possible that when going to 3rd gear that the pilot bushing could be making contact making it hard to syncro the gear speed. But only 3rd? Why not 1st and 2nd and 4th when warmed up?

I plan to also replace the pilot bushing. Another interesting thing is that the pilot bushing was only about 3/4" long, when it should be 1 1/16". Maybe a wrong one installed prior? Maybe worn down?