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MG MGB Technical - Gearbox Question

Some research help please. Review of Clausager's "Original MGB" states a gearbox second gear synchro was changed at engine number 18GB-U-H/31472 but does not specify the change. Was this a change to the steel synchro? My gearbox has the brass synchro with engine number 18GB-UH-38323. Can find no gearbox serial number, but a casting date stamp of
14/2/66 (February 14,1966) On overhaul a brass ring was used and replaced a brass ring present, but don't know if the grarbox had been worked on prior as I bought the car used. Guess what, 2nd gear is starting to have problems. Any ideas?

Jim
Hanks5

The bronze synchro ring uses a smooth, shiny, steel gear mating surface; the steel ring uses a gear with a sprayed metal mating surface - dull, grey, porous.

FRM
FR Millmore

Hi Folks:

The issue associated with the factory effectivity break in for the 22h230 and 22h249 steel synchro and the new 2nd gear is very fuzzy. I bought a new 1966 mgb roadster in May 1966 with engine #18gb-uh-29xxx and the gearbox casting is late 1965. A decade ago I converted this original gearbox to a "D" type overdrive. The 2nd gear synchro was steel, as verified with a magnet. The interesting aspect was that the synchro had a bronze color/tint. I am the only person to have opened and rebuilt this gearbox. I would venture that BMC used any parts they could find to build gearbox's at that time, regardless of effectivity points.

If you do a new gear/synchro upgrade; use only NOS parts. unless you can check hardness; since most of todays aftermarket parts are either too soft or hard.

View John Twist's video regarding the 2nd gear differences.

Best of luck
Rich Boris 67 B roadster
Rich Boris

Boris,
The info on what was present in your 66 is quite interesting. I would think that my system would also then have a similar gear and synchro system as yours since it is considerably later in manufacture.
Jim
Hanks5

Jim -
"don't know if the gearbox had been worked on".
Since the parts are interchangeable, correctly as pairs, incorrectly if mixed, what are you after? No reason to think it is as it left the works, unless it is very low miles and/or known to not have been apart previously. There were, at the time and for years, a million brass rings in stocks, since the MGA/early B/sedans used the same parts, and a lot of "mechanics" who did not have a clue, and would install anything to hand, especially if they weren't dealer based. And so it is up to today, when there is a lot of repro stuff that isn't good for boat anchors, and worse "mechanics" working off rumour. Anything over 30,000 miles is likely to have been apart, especially if the driver was incompetent at gearchanges to 2nd; I did a zillion of them - some people destroyed the synchros in under 20,000.
The brass/smooth is OK if the driver is up to the job, steel/coated type are much better, mixed is NG.

FRM
FR Millmore

FRM,
What I seek is a correct functioning gearbox. While I am currently in a unit that has a brass synchro, and can function well transfering from first to second at very low speeds, there is no ability to downshift without grinding gears. This is so at speeds around 20MPH. When the car is first started and has gone just a few miles the system works better than when driven 30 minutes or so when the gearbox is warmed up a bit. I am using 20/50 oil in the box.

Just thought someone may have a good idea when the changes were made and then I would have a handle on what direction to go. I agree that likely the gearbox has been overhauled as I am sure the car has had over 100M miles. I have pulled the gearbox out and did the standard overhaul using Moss parts and replaced the brass synchro that was present with a catalog series brass one from Moss, but the problem persists.

Thanks for the comments.

Jim
Hanks5

Jim -
The direction to go is with the steel baulk ring and the metal sprayed gear, however:
The brass ring/steel gear worked adequately for years, but it will not work as long as the later type, especially with heavy handed/footed driver.
So, there is some other fault.
Examine the clearance between the ring face and the gear face when the ring is hard against the gear cone. This should be around .080 min by memory - compare to the 3/4 synchro rings & gears. (I think Barney has info on his mgaguru site)If it is much less, worst case ring nearly touching gear, it won't work. This could be a result of wear on the gear, or incorrectly machined ring.
I once had a customer MGA box (same as yours) that was rebuilt with Moss parts before the customer moved here, and the ring actually contacted the gear - but not on the cone surface!
Moss replaced the part, but did nor pay the customer for labor, nor acknowledge my letter of explanation. I found that there were other incidences of this at the time - was pre internet for me so I do not know how widespread the bad parts were.
Weak or missing detent springs/balls in the 1st gear hub will not actuate the 2nd synchro correctly. It is not rare for people to lose one or more of these on dissassembly, and thus to have them missing. See the current threads on MGA board "laygear shaft", "c vassallo, Malta" in particular, though you should also attend to the shaft discussion.
Otherwise, the synchro has to accelerate the entire gear train from crankshaft to the gear on the third motion shaft in order to function. So, any drag in the system will cause trouble - clutch drag, gearbox/engine misalignment, bad pilot bush in crank, bad bearings, etc.
The alternative is to learn to shift without synchros at all, but you have to be always sharp to do it all the time. I taught my daughter to drive clutchless - up or down - in a day's journey. My wife used to have no trouble at all in my AC w. 289/4speed,(not at 20 mph either!) which had no 2nd synchro at all, since it was busted and I never got around to fixing it in several years daily driving - didn't seem worth the trouble, since it was our only working car. Getting at least close to this skill will let even the old style parts last forever, or will let you drive all sorts of clapped out junk when necessary, including lost clutch hydraulics.

FRM
FR Millmore

I haven't been able to find new 2nd gears for the steel synchro. Too bad as I'd love to upgrade my gearbox. My 65 is brass. I can almost make every upshift without a grind unless I try to shift too fast.

Downshifts around 15 or so I can do with double declutch and not grind 80% of the time. Above that I don't try. I've never fully gotten the knack of clutchless of double declutch.

When I replaced my syncro quite some time ago (likely 40,000 miles) the ears on the synchro ring had deep grooves made by the hub knife edges. Obviously the syncro had little room for engagement before the synchro hub clashed. I suspect the same for this. Plus in the first oil change after the new synchro there was a lot of fine brass dust in the oil. I guess that is from bedding in.

FRM - thanks for your hint on the hub springs and balls. I didn't change those on the last overhaul.

I guess another solution is go with the 4 synchro or 5 speed. But, I like to stay somewhat original.

Bob McCoy
Robert McCoy

Hi Bob:

When having difficulty finding 3 synchro spares, call John Esposito at Quantumechanics, located in Monroe CT. If John doesn't have the upgraded 2nd gear, he has his sources in the UK. John rebuilds most LBC gearboxes, overdrives & differentials; and has supplied many hard to find parts to me in the past. Give him a call!

Rich Boris. 67B roadster
Rich Boris

This is a key point " try to shift too fast." It is much easier to do clutchless/synchroless shifts at higher engine speeds. It takes a certain amount of time for the bits to slow down when shifting, and this time is more than what it usually takes to make the shift, so you have to wait a bit. That means your internal clock has to be agreed with the physics of the engine, which slows down much faster as the speed increases. At the "right" speed, on upshifts, the engine/geartrain slows down just the right amount as you are moving the stick from one gear to the other, and it slides right in. On downshifts, you control engine speed with the throttle, and again the engine is more responsive at higher speeds, plus if you overspeed (in the neutral/blip phase) slightly you get a second chance as the engine slows again. I find gear changes easiest at around 4000 rpm in most cars. MGA is a little tricky since the 2-3 split is bigger (=slower) than the gap between the other gears, but you learn. I shift with two fingers on the stick usually - if you need more force than that you are probably rushing things, and wearing out synchros.

FRM
FR Millmore

This thread was discussed between 10/02/2010 and 13/02/2010

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