MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

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 - 3 Syn Gear Box condition

Hi All,

I have taken some photos of my 3 syn Gearbox through the inspection cover. I think that things are in pretty decent nick in there, but I am not familiar with how a good box should look. If you are then I'd appreciate any feedback on the pics. They are at http://www.mymgb.co.uk/Projects/3SynGBox.htm
Be warned, there are 5 pics at 400kb each, so broadband users only!

Also, the 1st and third photos show the balk ring at the left hand side of the third motion shaft. These have quite a bit of play when visible. Is this normal?

Cheers
Iain

67 BGT - 3 Sync OD Gearbox.
I D Cameron

First and reverse look a tad worn but not so bad. The balk rings have very slight wear, esp the most forward one. There should be quite a bit of play, yes. What strikes me is the amount of general corrosion and discoloration. I don't know whether that's good or bad as I only opened a handfull of gearboxes and none had that amount of discoloration. fwiw.

Were you having specific issues with the box? Are you going to dismantle it anyway? If so, then I replace the bulk rings as the are not that expensive. More imortant are the needle bearings and layshaft wear. hth

Paul
Paul Hanley

Wonder what kind of oil has been used in this gearbox? May be that can explain the stains and corrosion? Or may be it has been lying around without oil for some time?

Mechanically it looks quite good to me. Very much better than my own 3-synch that I rebuilt last year. The baulk ring wear is not so bad. If the 2nd speed synchro is working all right, it should not be any reason to change them. Unless of course you are dismantling the gearbox anyway.

Paul is right - the important weak point in these gearboxes are the needle bearings on the layshaft. The needles eat into the layshaft, you get metal debris in the oil, and at some point the gears are getting slightly out of mesh. Then they wear pretty fast.

Tore
Tore

Thanks for the comments. I assume that you need to dismantle the box to get the layshaft out to check it over? The box has been bought to replace the non-OD box that is in my 67 BGT. It also came from a 67 car and that chap I bought it from assured me that it worked very well with no crunching in 2nd gear (which my current box does) and a good positive change. Also that the OD worked well. I'd prefer not to take it apart as I'd like to get it into the car! The car is daily use so I can't take the current box out to compare or steal parts from.

I don't know any actually history of the box, but I do wonder if it has had a rebuild in the past. The bearings on the main shaft (best visible on top left of 1st picture) look to be newer than everything else with no discolouration etc.

Cheers
Iain
I D Cameron

Iain,

The gearbox does not have to be disassembled to pull the layshaft. Stand the box on end (bell housing up) and remove the front cover. The layshaft can be withdrawn and replaced, provided you are very careful not to jostle the gearbox and knock the laygear or the bushings out of alignment. As a precaution, once you remove the layshaft, insert a dowel, long screwdriver, anything to hold the lay gear in place. If the layshaft is slightly worn, simple replacement will do. If the wear is severe, I would recommend a tear down and replace the roler bearings in the laygear. Of course, once you have it apart it makes sense to replace synchro rings also. It can be helpful to turn or grind a taper to an old layshaft and use it as a pilot before installing the replacement.

Good luck.

Steve Mc
Steve Mc

Iain,

Good advise all around here but if you trust the chap you bought it from, button that thing up and stick it in the car! Now that I've been shown the great mysteries of the gearbox, they are quite simple and I can tear one down and have it back together in one evening--as I suspect many here can also. However, if you don't know what you're doing, it can be quite intimidating. As far as what Steve mentions as to standing it on end, he's right but what will you do if you inadvertainly "jostle" something? Bench test it with a drill and make the determination. I'd make sure the o/d ball and plunger, lock-out switch and electrics are working before putting it in the car. Now would be a good time to clean the o/d filter screens also.

T'aint broke concept here!

Cheers,

Paul
Paul Hanley

I think I'll take the layshaft out and see how it looks. I have some plastic conduit to cover electrical wiring in the house. I suspect it will be closer to the correct diameter than any screwdriver and I can cut a decent legth of it so it is ready to go. If it goes wrong and I knock the lay gear then I guess I'll be learning to strip a box! I have rebuilt an engine, so I'm not afraid of mechanical stuff, just not sure I want to learn right now!! When I get it out (might not be this evening in which case it could well be the weekend) I'll take some pics and let you all know for feedback.

Paul, going to clean filter etc on the OD. How do you go about testing the electrics? Do I just put 12 volts across the solinoid and see what happens?

One other question to all. I am planning on fitting reverse lights if possible. The box doesn't have a reverse light switch, having a blanking plate instead. Do I simply removing the blanking plate and screw the switch in? Seems almost too easy, but I can't see any other parts that are specific to car with reversing lights. Suggestions on removing the plug would be appreciated as well!

Many thanks
Iain
I D Cameron

Hi Folks:

I know a few of my MG Car Club friends that have played overdrive roulette with LH types, and usually win, however; we are talking about a 3 synchro "D" type which is not as roboust as the 4 synchro box. Unless you know the actual history of the overdrive unitsuch as age and mileage of the cone clutch; the cost affective approach is to rebuild with new clutch, o rings and fucntional test. I have seen enough worn and shattered clutch's in my time. Almost all these units are 30+ years old; the clutch lining may look great; but will shatter under load and heat. Remember the LH clutch diameter is close to double the D type.

Good Luck: Rich Boris 67B roadster
Rich Boris

Iain,

Paul, How do you go about testing the electrics? Do I just put 12 volts across the solinoid and see what happens?

Yes. It should snap smartly. If not, there is a procedure with a drill bit to adjust the nut. Its in the book. I'd also replace the lockout switch and replace/reshim the lockout switch gaskets. The gaskets are shims. Sorry, can't answer the reverse light question. Don't know. Suggest email to Chris at Octarine Services.

If you are mechanicaly inclined, the gearbox rebuild is no big deal. However, Haynes takes one thru some unnecceary steps and would suggest advice from here and other sources. Let me know via email if you'd like, and I can talk you thru it.
ie I believe Haynes has you cutting the safety wire--not! No point.

Paul
Paul Hanley

One thing that I would do for sure and this is a warning from experience. Replace the cluster gear shaft. It can snap and drop the cluster gear and all sorts of terrible noises will ensue! I know, I have the D type in my 67B and it did this to me several years ago.

Hi Paul!

Mark
M Whitt

Hi,

Just for information, I have been in touch with Chris and it seems that the reverse switch is not as straightforward as I had hoped (ie there are internal differences) and so it is not just a case of threading the hole and fitting the switch. I'll probably just leave it. I have managed this far without them! I might fit a manula light, but I'll need to check MOT regs in the UK for this. I think I need a visible warning light on the dash.

Didn't get round to trying to remove the layshaft, so it will be at least the weekend before I tackle that.

Mark, "cluster gear shaft" Is this in the OD unit? I can't see anything by that description in the workshop manual, but I may just be missing it! Or are you refering to the reverse cluster shaft in the box?

Cheers
Iain
I D Cameron

Iain,

Cluster gear = laygear

Paul
Paul Hanley

Thanks Paul.
I D Cameron

Hi:

Just looked at the gearbox photos, does anyone know the nature of laygear P/N 22H55? variant? the usual MGA/MGB part number is 22H54. Could this be a close-ratio box? if so it becomes valuable!

Thanks: Rich Boris, 67B roadster
Rich Boris

Well,

I have had the layshaft out. Looks pretty good to me, but I'm not sure what is acceptable! You can see where the needle bearings have been running, but only as a more polished surface. You can't feel it at all. There is also a few very minor pits in places on the shaft.

Pics at web address above. Comments welcome!

Iain

PS Any further info on Rich's point would be interesting.
I D Cameron

Regarding the D-type OD solenoid, even if it *does* snap smartly back and fore you should still use the procedure in the manuals (with the drill bit) to confirm the travel is correct. This sets up the travel to disconnect the pull-in winding leaving only the hold-in winding connected. If travel is incorrect and the pull-in isn't disconnected you can overheat the solenoid.
Paul Hunt 2

Hi Iain:

I am still searching for the part numbers associated with the 3 synchro close ratio-gear set (there are 2 types; straight cut and helix cut). You may want to start another thread regarding this issue. Close-ratio gear sets may not be for your normal driving routine. If you look at Brown & Gammonds web page, a new/aftermarket close-ratio gear sets are very expensive.


Good Luck: Rich Boris 67B roadster
Rich Boris

Regarding the reverse light switch, I've got an illuminated dash switch on my '67. I spent ages getting the lights working one time, but when I pointed out the location of switch to the tester he said they never check them anyway; reckoned it wasn't included, maybe because of the age?
Steve Postins

From my BBS:

Part number 22H54 WILL have 22H55 stamped on it - BMC casting or stamped numbers are ALWAYS one greater than the actual book part number!!!
Chris at Octarine Services

Of course - how logical!!! Thanks for the clarification Chris. Happy that it is standard!

Iain
I D Cameron

Hi Iain:

Still searching for close ratio part numbers, and found the following from the competition section of the Bentley manual: not sure if helical or straight cut gears.

1st motion:Std 22H56(18G/GA) 22H472 (18G/GA)
1st motion CR 22H843 (18GB) 22H846 (18GB)
2nd gear Std(improved)22H230
2nd gear CR 22H1094 (use bronze synchro)
3rd gear Std 1G3594
3rd gear CR 1H3300
Laygear (4 hole) Std 22H931 or 22H1301
Laygear (4 hole) CR 22H932 or 22H130x
Laygear (3 hole)Std 22H54 Laygear (3 hole) CR 22H5x

I still feel you have a close-ratio gear set; you should check with Auto Gear in UK. Investigate now, not after gearbox is back into the car.

Good Luck: Rich Boris



Rich Boris

Hi Iain: corrected below:

Still searching for close ratio part numbers, and found the following from the competition section of the Bentley manual: not sure if helical or straight cut gears.

1st motion:Std 22H56(18G/GA) 22H472 (18GB)
1st motion CR 22H843 (18G/GA) 22H846 (18GB)
2nd gear Std(improved)22H230
2nd gear CR 22H1094 (must use bronze synchro)
3rd gear Std 1G3594
3rd gear CR 1H3300
Laygear (4 hole) Std 22H931 or 22H1301
Laygear (4 hole) CR 22H932 or 22H130x
Laygear (3 hole)Std 22H54 CR 22H5x

I still feel you have a close-ratio gear set; you should check with Auto Gear in UK. Investigate now, not after gearbox is back into the car.

Good Luck: Rich Boris
Rich Boris

Iain

Looks like you have a good one. Most of the layshafts I have seen (including the one in the OD unit I just installed) have a spot where the bearings have flaked off metal on the shaft.

One of the reasons for this is the small single set of bearings in the one end of the lay gear. The other end has two sets of bearings.
BEC Cunha

This thread was discussed between 14/11/2006 and 30/11/2006

MG MGB Technical index

This thread is from the archive. The Live MG MGB Technical BBS is active now.