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MG MGB Technical - G/box problems post o'haul

G'day. I have just finished an o'haul of the g/box. Prior to this the box was working well but was very noisy. No shifting problems were present.

After replacing all the bearings, the lay shaft and the sync (baulk) rings I now have the following problems.

Difficult to shift from 3rd to second, gears crunch from second to third and from 3rd to fourth no matter how slowly I change. Gears crunch from fourth to third but only on fast changes. Randomly pops out of third on overrun, but this seems to be getting better as I drive it. The shift into third and fourth feels "mushy" for want of a better description, not the nice "snick" that it used to feel like.

Is it possible that this will all settle down as the new components settle in, or am I up for another gearbox strip down.

Thanks

Tony
Tony Oliver

I had similar problems with a midget gearbox once, particularly the trouble changing into third and fourth. When I opened it I found that the three small springs in the synchro hubs were broken, obviously during a previous rebuild. They are very easily damaged when you put them back again if you dismantle the hub.

When I replaced the baulk rings in my 3 synch MGB gearbox a few years ago the shift into second was heavy for some time after the rebuild.

Tore
Tore

Tore, I did a simular repair to my 1500 A gearbox and find that the 1-2 shift is notchy. I'm now running Redline gear oil. I haven't had a good hot run yet.
Can you expand on "was heavy for some time"
Thanks Sean
S Sherry

Hello Sean

Which bit of NSW are you in?

It was Tore who mentioned "heavy". Mine is just hard to shift from 2nd to 3rd, 3rd to 2nd and 3rd to 4th. Going from 4th to third is normal. I think it has something to do with the 3rd gear sync ring.

Tony
Tony Oliver

Hi Tony, I live in Sydney, Hunters Hill.After I personally over hauled my gearbox it was very, very stiff between all shifts. The syncros worked ok.
I could not understand it, as everything was free including shift action on the bench. I loosened all the bolts on the shift mechcanism housing plate and worked the gear lever to allow it to self alaign. It helped a bit and after a couple of thousand miles all is well except for the notchy 1 2 shift. Double clutching helps a lot. I suspect that a lot of brass ring types from early UK gear boxes were iffy at the best of times. I'll let you know how I go with the Redline oil, I'll be giving it a good run with the VSCC this Sunday going to Maittland Air Port. If we can get together I would like to swap cars for a short drive to compare notes
Sean 98162107
S Sherry

Thanks Sean. It's not the stiffness that worries me, it is the crunch from 2nd to 3rd to 4th. It is OK if I change very slowly, but I can change as fast as I like from 4th to 3rd when the sync ring really needs to work. I still think the 3rd sync ring is sticking. It was a bit tight on assembly but I thought that all the engine and 3rd motion shaft power would free it up.

I am going to give it a couple of weeks driving before I rip the box apart again. Heres Hoping.

Tony
Tony Oliver

Sean,

What I mean is there was a lot of resistance going from 1st to 2nd, but this gradually freed up in a couple of hundred miles or so. I replaced the old brass synchro ring with a steel one during the overhaul. It still has a peculiar feel when the oil is cold, but that is more going out of 1st than going into 2nd. Feels like it wants to remain in 1st, and I have to use a little force to get it out. This disappears when the oil is warm.

When I rebuilt the gearbox I used a new 1st/2nd gear hub, and of course wonder about the quality of the new parts. The gearbox has worked well for the 11.000 miles driven after the overhaul.

Tore
Tore

Tore , I think you are on the right track as to the quality of replacement parts. I'm mind full of the fact ,that, with replacement tires for example, they are never as good as the origonal equippment. Probably because suppliers can't get away with, " not to standard " goods, supplied to the factory for the production line. With what we are now stuck with , they "fit where they touch". Sean
S Sherry

Tony A quick way to bed the new synchros in is to hold pressure on the lever as if trying to push it into gear without pushing the clutch in. Hard enough to feel the synchro loading but not enough to grate, (engine running of coarse) Do it for ten seconds then a short rest then again for up to a few min. Sounds rough but it works "if the problem is the synchros not bedding in". You are trying to mate a worn gear taper with a new flat surface and that takes time. As I said it sounds rough but it does not do any harm unless over done and certainly not as bad as the damage crunching does.
DENIS4

Thanks Denis. I'll give it a go. I have just completed a 300Km trip with no apparent improvement. It's very frustrating and the thought of another engine gearbox removal is not a pleasant one.

I had no syncro problems before the overhaul but replaced the sync rings anyway. Perhaps it was a case of "if it works don't fix it".

Tony
Tony Oliver

My gearbox was stiff 1 to 2 after it's rebuild 4 years ago. I had completly forgotten it until reading this thread so it can wear off.
Stan Best

Denis, I gave the second gear your treatment. The shift is much improved ! I had also changed the oil to Redline gear oil which improved the ease of shifting for the other gears but made no difference to second notchy change. I still double clutch on the 1-2 as I want to apply as little force as I can on the
apply pegs of the brass syncro ring. Apparantly they wear out long before the cone of the syncro.
Thanks for all the input Sean
S Sherry

Thanks Sean nice to know when you can help. When you do this task the steel outer ring has already ridden over the brass pegs so the bedding in is only on the tapered surface.
DENIS4

Tore,

You say "I replaced the old brass synchro ring with a steel one during the overhaul"

Did you replace the second gear too? The steel ring ONLY works with the sintered cone 2nd gear and the brass ring ONLY works with the plain cone 2nd gear
Chris at Octarine Services

This thread was discussed between 04/11/2008 and 12/11/2008

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