Transmission... Replace synchro, or whole new tranny

[JordanB]

The synchro in 2nd gear had been gone as long as I've had the car. My wife want's to get it fixed, because she doesn't like driving it that way, double clutching and all. Which is fine with me

So, would it be easier to replace the synchro, or just put in a whole new tranny? Maybe overdrive?

'67 MGB with 4 spd.

 

[JordanB]

I guess I should be asking how hard is it to replace the synchros?

 

[Guest]

good used trannys are cheaper than rebuilding a bad one. Talk to Tony Barnhill or Chris Roop depending on where you live

 

[Guest]

you'd be better off with Chris,, he's in Oregon

 

[Ed Wynne]

My question is
How do you tell if its a good used tranny, I have two non-OD units in addition to the one thats on my car. The installed tranny has a bit of a grind going into 3rd when speeding up. I have to pause to let the rpm drop when shifting from 2nd. I sort of "feel" it into 3rd.
The two spares I got from a friend (Phil Nazelrod) and I don't know their condition.

I would hate to swap tranmissions and find that the "new" one is worse than the old.

Ed

 

[steve mc]

Hope I can answer a couple of questions here. First, it's not difficult to replace the synchro rings, especially in the early non-synchro gear boxes. The early gearboxes are prone to worn layshafts and worn 2nd gear synchros. Any early box with significant miles (+50K) will likely show some layshaft wear and probably have worn synchros. The later non synchro MGB's have a special hardened second gear and matching steel synchro ring. These have to be used as a mathced set. If you decide to rebuild, I'd replace the synchro rings, layshaft and bearings, an input and output shaft bearings. Make sure the kit has the layshaft bearing circlips. These are a bit fiddly to get out of the laygear without damage, so a replacement set is handy.

Take a look at Barney Gaylord's "MGA with an Attitude" website. The MGA tranny is very similar to the early B gearbox. The Chicagoland tech sessions website is also a good resource. For general info, one of my all time favorties is www.howstuffworks.com. Go to the manual transmission pages.

Secondly, you can get a pretty good idea of the condidtion of an unknown gearbox by inspection. Take the side cover off the gearbox and look at the engagement dogs on each synchro ring. If the "nose" is worn away, its' replacement time. Also, look for a minimum of 1/16 inch between the synchro ring and the hub. Less than that means the clutch surface of the synchro ring is worn, replacement is necessary. Layshafts can be inspected without disassembly, but it must be done carefully. With the transmission standing on end, remove the clutch fork and the front cover. The layshaft can be withdrawn straight up and inspected. Be very careful not to tip of disturb the transmission because the laygear and thrust washers will fall out of place and it will be diffucult to get the layshaft back in. If the layshaft is worn, the bearings are shot, too, so it's rebuild time, which means disassembly. ALso take a look at the selector shafts to see if there is any wear from the detent balls. If they are worn, this could lead to the tranmission popping out of gear.

Finally, it's probably not worth rebuilding a late, full synchro box. These are plentiful, cheap and less prone to wear the early boxes.

If anyone is interested, I did take a few pictures of a gearbox rebuuild recently. I have some examples of worn layshafts, synchros etc.

Sorry for the long post. Email me offline if you have any questions.

 

[chris roop]

Assuming you have a 3-synchro in your 67, I'd probably opt to build it, unless your spares are also 3-synchros, and have been sitting since the dawn of time. Better, put new synchro rings, seals, bearings, and layshaft in one of your spares, then swap out. If you're in there, always replace the layshaft.