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MG MGB Technical - 2nd Gear type

Hello. How can I tell if my second gear is the early type that uses the brass sync or the later type. I ask this because my '67 Roadster had a steel 2nd gear sync but I thought the older style gear was fitted to that model.

When was the second gear changed to the later type and is the part number of the later type. If I use the brass ring on the later type what effect will it have?


Tony Oliver

I don't have the exact date when the steel sychro was fitted but it was in 1967. You may also have the later 4 bearing laygear with the larger shaft...good if you do.

The synchro and 2nd gear have to be matched. ie you can not use brass on a 2nd gear designed for steel and vice-versa. I think the 2nd gear for steel synchros had a moly sulfide or similar coating to get the right friction characteristics. The brass 2nd is just hardened steel. Hopefully the parts weren't mixed by a PO.

Hopefully someone else will have the gearbox or motor numbers when things were changed.
Robert McCoy

Thanks Robert. I do have the 4 bearing layshaft but it is a 3 sync box.

For my information only, why can't you use the brass ring on later gears? Does it cause damage or difficult gear changes?

Tony Oliver

Check the archives regarding steel synchros for experiences of others. Some swear by the steel rings others aren't so sure.

You can use brass rings IF you use the gear for brass rings. If not they don't fit right, will wear badly, and the friction characteristics will be all wrong resulting in all sorts of shift problems. The same hold for using steel rings with the brass gear. You have to use them in sets. You can just replace the synchro with the proper one if the gear looks okay.

The brass synchros in the 3 synchro gearboxes wear badly that's why the factory went to steel. There is a lot of inertia to overcome in bringing the heavy first gear sliding hub up to or down to speed. I think this is why this synchro wears so quickly.

Are you having shifting problems? I replaced the brass 2nd synchro on my 1965 gearbox with a new one reusing the old second gear. The old synchro was badly worn with the grooves worn down and divots dug into the dogs at the back of the ring. Unfortunately after about 20,000 miles I'm having trouble again. Think I'll go the steel route next. Wish I had the 4 bearing version.

In 1968 the 4 sync was fitted. So, you have the latest version of the 3 sync box. It wears much better than my older version.

You might want to use a synthetic gearbox lube (not hypoid). I found it quieted the gearbox down especially in higher operating temperatures and helped the shifting. Here I use Redline brand.
Robert McCoy

I think the brass to steel change came at the same time as the smll input diameter to large input shaft diameter change. By the by the latter trans should work once the shaft is turned down to the correct size.

Thanks Gents. I have fitted a brass ring to the box as I didn't realise that the steel and brass rings were not compatible. I bought and fitted a set of brass sync rings to suit the car. I now live in hope that the gear is not damaged but the box has only done about 500Km since the work was done to it.

I assume that it is only second that has the steel sync ring.

I need to take the box of anyway as the release bearing chatters terribly as the clutch is slowly released so I'll get a new steel ring when I do it. Another engine removal/install looms.



Tony Oliver

FWIW according to a combination of the Parts Catalogue and Clausager the 2nd speed baulk ring changed in December 65, at engine 18GBUH31472, L29123, or 18GBRUH31003, L25995.
Paul Hunt

Hi Folks:

I don't agree with the engine break point; my 1966 MGB; purchased new in May 1966, (gearbox manuf date 12/1965) had a steel synchro & moly-coated 2nd gear cone; and the engine number was 18gbuh29xxx series. I am the only person to have ever opened this gearbox. Also check out John Twists videos; where he explains the difference between the gears.

Good luck: Rich Boris, 1967 mgb roadster
R. Boris

Thanks once again gents. The video shows a very easy way to identify the type of second gear. The gear that uses the steel sync ring has scallops between the engagement teeth. Should be easy to get it right this time.

Off I go to start pulling the motor!


Tony Oliver

Tony, some things I learned the hard way, after I rebuilt the box ! There are reproduction brass rings that are not as origonal, they go on to far on the gear cone. I checked this on mine and it was passable, but now I believe I should have also checked the contact points of the three lugs, if they are not pushing the brass ring on true and square, the syncro action can't slow the gear properly.
I should have seated the ring with fine grinding paste. Mine works just ok but it is very notchy. I tried redline synthetic gear oil which didn't help. It is approx. 20 weight when hot and gets out where ever it can !! I am back to 2060 engine oil [ non synthetic ] Are you in the Sydney basin ? if so I would welcome the opportunity to have a close look at 2nd syncro. Thanks Sean
S Sherry

Sean that may be the problem I have but I did buy my brass synchro in the mid-90's. I don't know when the bad parts started. I reused the old 2nd gear which may have been a mistake. I did notice that the steel hub engagement mechanism has dug down quite a ways into the brass lugs meaning you didn't get much pressure on the synchro. Others have complained about that.

I use Redline 75W90NS lube and get better shifting and I think less thinning out than 20W50. (2nd gear still crunches on some quick upshifts. For downshifts I have to double declutch.) Certainly quieter when the gearbox was hot from a long run than 20W50. I've had no leak problems. I think the standard Redline MTL is too thin for our old gearboxes.

But, there are lots of opinions on what lubricant to use in our gearboxes. I could be in the minority with my experience using Redline.
Robert McCoy

Robert, I'm wise after the event. My understanding now is ,that the syncro cone as such, doesn't wear that much, the problem is ,as you say, the brass lugs are dug into, so that the cone can't do its job. With a new ring on an old gear hub they take a long time to bed in, hence the advice to lap them in. As with the after market syncros being hit or miss maybe new gears are tarred with the same brush.For the record I always double clutch into second ,up or down. Eventually the shift will come good, if I live long enough. Sean
S Sherry

Thanks gents.

Sean, I am in Gloucester so I won't be able to show you the sync, but I have got the side cover off the box and it is clearly the later type of gear. I will have the brass sync out today and will take a picture of it, if that is what you are interested in. If you want I'll post it to you.

Do you use a fine valve grinding paste to lap the rings in? I'll try that as I have a strong feeling 3rd sync is jamming on the gear.

Tony Oliver

Tony ,I found out about lapping in new rings after the event but I think fine paste would be the way to go. I would have liked to see how the drive pins mated to the syncro lugs , all three simultaneous for a square push. also to check [with bearing blue ]the contact of the ring to the gear cone. Just for fun ! Sean
S Sherry

This thread was discussed between 28/12/2008 and 31/12/2008

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