MG-Cars.info

Welcome to our Site for MG, Triumph and Austin-Healey Car Information.

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - Where can I get quality gearbox synchro's ???

For the second time I have had my C gearbox professionally rebuild here in Germany, the first time the synchro's were failing after 6000 miles, after a second time I have only got up and down the street a few times to know the replacement sychro's are worse, can't select 1st, 2nd or R from a standing start, just 3rd & 4th with a bit of force, and I have detemined its not the clutch or its adjustment, so can anyone recommend where to source original quality and size synchro's ? I will contact a few good MGC workshops for a chat but welcome any experiences and advice as one gets a bit tired of taking a C engine & gearbox in and out, thanks regards Bill.
Photo of the first set of replaced worn out synchro's
PS also in the rebuild I think that end spacing/end float could be an issue, they have been fitted in too tight and thus have worn out, or they are too thick

Bill Lambert

Bill -
You are describing the classic case of clutch or other drag between crank & gearbox. The synchros are doing their job under extreme duress, and will block you from getting it into gear until they are destroyed. There is no synchro on reverse.
Either the clutch is dragging for one of the usual reasons, or the pilot bush is tight, or the engine and gearbox are seriously out of alignment.
The professional rebuilders ought to know this, and how to figure out where the trouble is.

FRM
Fletcher R Millmore

As Fletcher said, if the clutch is working correctly there is nothing turning in the gear box when stationary and it should change in and out easily. If the gears change with the engine switched off it can only be a clutch or misalignment problem. Spigot bush, clutch plate splines dragging or warped center,warped or cracked pressure plate diaphragm to name a few possibilities. If you have replaced the clutch my first guess would be a warped clutch center. Denis
Denis4

See "cant shift to reverse in od car" for hydraulic problems.
Paul Hunt 2010

Thanks Fletcher and Denis, useful advice, still may mean another engine and gearbox out job, despite the new re-surfaced clutch plate, and clutch itself which was also new 6000 miles ago, it was always fiddly, but not with force, that I had when mating the gearbox and engine even with a correct clutch plate alignment. I will also have a look at Paul's link, thanks regards Bill
Bill Lambert

Bill -
I'd be looking at hydraulic trouble before pulling the power unit again. What's been done with master and slave cylinders through all this?

How much free play do you have in the pedal? Should be 1/8" free motion if you push on the pedal with a finger; more is wear on the pedal/clevis pin and MC pushrod, or a bad MC.

After that, you should have zero free play, otherwise there is air in the system. Somebody hasn't fitted a return spring on the clutch slave have they?

Carpet stopping the pedal from full travel is not uncommon either!

If the car is jacked up (rear wheels off ground), you should be able to easily turn the gearbox output while in gear with somebody holding the clutch down. Easier with the DS disconnected from the GBX.

FRM
Fletcher R Millmore

I had this problem after an engine rebuild. The gears were almost impossible to engage. I was at my wits end before an idea hit me. I loosened the engine to trans bolts by 1 turn and placed a jack under the bell housing. I raised the trans a small amount and tried to shift the gears. Better but not fixed. I repeated this step, raising the trans again. This time there was no problem engaging the gears, even reverse. I quickly tightened all the engine to trans bolts and have not had a problem since. That was 15 years ago. The MG doesn't use self centering dowel pins on the rear backing plate and misalignment is not uncommon. RAY
rjm RAY

Ray is right, but:
Two bolts holes are close fit in the bell housing and mounting plate - top right and bottom left. With the original bolts in place, the alignment is sufficient. Misguided people have been known to drill the holes out because they can't get the bolts in since they already bolted it tight with the other bolts, or because the clutch is out of line on assembly, or replacement bolts with smaller shanks may have been fitted.

FRM
Fletcher R Millmore

Warped clutch plate?. How far does the pedal come up before engaging the clutch? - should be about a inch.
Dry 1st motion spline? TYhe 4 syncro box can often be difficult to get into reverse - not grating gears - but just not sliding in because the gears are out of line. Brutal changing by pulling the lever hard back or pushing hard forward can break the syncro rings.
Garth
Garth Bagnall

Hi Bill:

In response to your question regarding where to buy acceptable quality synchros I would recommend the following:

1. Find an EBAY supplier who deals with OEM NOS components to be sure of correct material composition and hardness.

2. Contact John Esposito at Quantumechanics (Monroe CT) for decent aftermarket components (if any), most likely John can find useable synchros to satisfy you needs. John has rebuilt hundreds of LBC gearboxes, overdrives and differentials has a decent supplier base.

Best of Luck:

Rich Boris 67B roadster
Rich Boris

Thanks Gents,
Well as a non technical person I think I may have found and solved my gear selection / clutch problem, and I thank a number of MGC & B contacts from the UK/Germany/and Australia for various advice that has let me to the diagnosis,

In effect I was still missing about the last 4-5mm in clutch fork movement, had 12-13mm, but the last few were missing to finally disengage the clutch which I could tell by levering the clutch fork in with a big screw driver. So that as it was in gear with the clutch depressed the final movement with a screw driver as lever disengaged the clutch and you could turn the rear wheel/tail shaft.

So the hydraulics were fully bled, no air, but the volumes in the master and more so slave needed to be increased, to move out the travel I was already getting by taking up the play at the clutch fork.

A bit by chance I got this by taking the slave cylinder off the gearbox and bleeding it out by pushing its cylinder in with the clutch depressed, bit tricky to get the cylinders in that position. I also need to critically look at my master, which is the second correct 5/8'' new one I have put in, to ensure its cylinder is moving enough (and the return to its own resovior) to fill up the volume in the slave to take up all the play in the clutch fork movement so in effect I have the 0 point of the clutch fork movement out as far as possible.

So now I think I know why it has been so tricky to find this last 2-3mm in clutch fork travel and thought that it was synchro's or clutch itself.

At least its a sense of relief I don't have to take the engine and gearbox out again but more closely look at the clutch hydraulics and its travel/volumes.
my regards and thanks, Bill
Bill Lambert

This thread was discussed between 04/04/2010 and 09/04/2010

MG MGB Technical index

This thread is from the archives. Join the live MG MGB Technical BBS now