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MG MGB Technical - Synchronizer (Balk) Ring Assessment & New Quality

I’m in the process of getting an overdrive together for my 77 roadster. The used overdrive box I bought has a worn reverse gear and a worn counterpart to the reverse on the laygear. It is a Blue Label LH, side fill, supposedly from a 75.

I pulled two other non-overdrive boxes apart (both 4-syncro, one side fill, one dip stick) to scavenge for parts. I would like to assess the condition of the syncro (balk) rings, but the Haynes is not much help. The last gearbox I built (a long time ago) was for a Saab 99. To check them, as I recall, you dropped the syncro onto the cone, and slid a stack of feeler gauges into the gap. If the gap was large enough it was good.

So, is there a spec like that for the MG box?

I thought I read here that there have been quality problems with the new syncro rings. Is that true? Also, are all four of them the same? I have seen them listed under the same part number, and I have also heard that one or two of them were supposed to be steel, and the others were bronze. Any advice is welcome.

Are there any problems with quality of new layshafts and layshaft bearings?

If I decided to put a new bearing on main shaft (third motion shaft) are they available? I have seen them listed as NA on some sites. I am speaking of the large bearing just before the shaft enters the intermediate casing that connects the trans to the OD.

Thanks,
Charley
C R Huff

I have same questions & issues

- Moss UK online substitutes the 1-2 synchro number for the 3-4 synchro when you try to order - that suggests they know they are interchangeable?

- Moss US has had them on my backorder for over 6 months

- I did locate a NOS 3-4 synchro hub on eBay a few months ago

Larry Moeller

Well, I’ve done some archive searching and some Google searching for the spec of the distance between the baulk (synchro) ring and the hub face. Here is what I found:

1) From the mgexperience (aimed primarily at the 3-synchro box):

Check the synchro rings after removing the side cover but before disassembling anything else, press the brass ring as tightly as possible against the mating cone surface, then try a 0.020 inch thickness gauge between the flat surface of the brass ring and the adjacent steel surface. If the feeler gauge fits without binding, the synchro will probably work OK for at least the next 40,000 miles or so.

2) From the mgaguru (again probably aimed primarily at the 3-synchro box, and discussing the difference between steel and bronze synchros):

When you get them on the correct gears the both sit at about the same level around 0.030" to 0.040" apart face to face.

3) From a Feb 11, 2010 archive search here, a response from FR Millmore:

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 –

4) From a Feb 22, 2007 archive search here, a response from PRC, he is speaking of a pdf file from Chris at Octarine Services, which seems not to be available now. Chris was in this discussion and did not confirm or deny the info. The problem was binding gears, not the synchro wear:

Chris, I just read your article on the gearbox rebuild and it said that there should be 1/8" between the baulk ring and the face of the 2nd or 3rd speed gear.

5) From Chris at Octarine Services current website article titled MGB 4 synchro overdrive gearbox servicing guide:

Inspect the synchro ring to hub gap – if less than 1/16 inch the mainshaft will have to be disassembled and rings replaced


So, that’s what I have found on the synchro to hub gap so far. The range is from 0.020 to 0.125. It would be comforting to see some confirmation of some of these specs. If I get no confirmation, I will probably go with the 1/16 figure inch from Chris.

I suspect that some of the differences in these values may be that some are speaking of new spec, some of service limit, and some of wear limit.

As to the steel vs bronze (or brass) synchros, it seems that the steel are used with the black ceramic (or metal spray) coated cones, and the bronze go with the plain polished steel cones.

I still have not found anything definitive regarding all four being the same or not other than the steel bronze issue.

Charley
C R Huff

Hi Folks:

When it pertains to British car gearbox synchro technical issues; I would contact John Esposito at Quantumechanics for assistance. John has a web page and is located in Monroe CT. I know from personal experience that he rebuilds a gearbox/overdrive or more everyday. I think he can help resolve the subject concerns.

Cheers; Rich Boris 67 MGB
Rich Boris

Charlie:
I've done hundreds of 3 synch, but only one 4 synch, c.1972, which might tell you that they are tough. And we had a hell of a time getting parts even then, since there was essentially no need for them. But synchros of this design are all pretty similar, so, with the caveat that I have little experience with 4 synch boxes, and quoting you as req:

.....
Check the synchro rings after removing the side cover but before disassembling anything else, press the brass ring as tightly as possible against the mating cone surface, then try a 0.020 inch thickness gauge between the flat surface of the brass ring and the adjacent steel surface. If the feeler gauge fits without binding, the synchro will probably work OK for at least the next 40,000 miles or so.

>>>>>> likely correct, but see end notes

2) From the mgaguru (again probably aimed primarily at the 3-synchro box, and discussing the difference between steel and bronze synchros):

When you get them on the correct gears the both sit at about the same level around 0.030" to 0.040" apart face to face.

>>>>>>>> this figure is low but acceptable

3) From a Feb 11, 2010 archive search here, a response from FR Millmore:

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 –

>>> as stated "by memory". I just looked at a very good original 67 box w c50,000 mi in it, dismantled in 75 and untouched since. The clearances are about .075-.080 for 3/4, and .065 on second. More wear on 2nd is the norm.
I believe that (the quote)I was referring to some known issues of wrongly machined rings supplied by "M" c.1995 - the bore was too big and the rings sat flat (and loose) on the gear face. A customer brought me a box that had been rebuilt and installed in Washington state, then brought here, and found not to work. And NO they did not pay the customer's labor, or acknowledge my letter of complaint/analysis, but did replace the part

4) From a Feb 22, 2007 archive search here, a response from PRC, he is speaking of a pdf file from Chris at Octarine Services, which seems not to be available now. Chris was in this discussion and did not confirm or deny the info. The problem was binding gears, not the synchro wear:

Chris, I just read your article on the gearbox rebuild and it said that there should be 1/8" between the baulk ring and the face of the 2nd or 3rd speed gear.

>>>sounds way too high

5) From Chris at Octarine Services current website article titled MGB 4 synchro overdrive gearbox servicing guide:

Inspect the synchro ring to hub gap – if less than 1/16 inch the mainshaft will have to be disassembled and rings replaced

>>> about right and what we would do when parts were cheap and good and easy to get and the customer was likely to drive the car a lot of additional miles. But they will certainly work at much less than this; and today's parts are suspect indeed, see below.


So, that’s what I have found on the synchro to hub gap so far. The range is from 0.020 to 0.125. It would be comforting to see some confirmation of some of these specs. If I get no confirmation, I will probably go with the 1/16 figure inch from Chris.

I suspect that some of the differences in these values may be that some are speaking of new spec, some of service limit, and some of wear limit.

>>>> Correct

As to the steel vs bronze (or brass) synchros, it seems that the steel are used with the black ceramic (or metal spray) coated cones, and the bronze go with the plain polished steel cones.

>>>> Correct, but I think all 4 synch are steel/sprayed

I still have not found anything definitive regarding all four being the same or not other than the steel bronze issue.

>>>> Moss show all four the same. TRF very old catalogue (reprint/copy of factory book) shows 1/2 as 88G397; 3/4 as 22H1028. Not quite so old SICP book shows all 4 as 22H1028
Suggest you call Quantum Mechanics or TRF Tech 814 446-4491 for definitive info here.

&&&&&&&&&&&
Basic info:
The synchro is a cone clutch, and as such, the tapers must make solid contact in order to lock the two rotating parts together at a constant speed. So anything which prevents that is a problem. The thing is designed to allow for tolerance, wear, and heat effects, so there is nothing very critical about it.
Wear or size errors that let the ring contact the gear face before the tapers lock will disable it. It is rare but not unknown (only very bad driver can do it!) to have this much wear before the rest of the box is DOA. It is possible sometimes to have enough wear that the ID of the ring contacts a radius at the root of the taper on the gear, subject to machining tolerances.

The inside face of the ring taper bore has grooves in two directions to act as oil wipers, so that the oil is forced out before the metal makes contact - if there is still oil in there, it is a bearing not a clutch. IF there is enough wear to make these grooves very shallow or absent, the syncro will work poorly if at all. Not common on any but the very old A series box that had the brass rings shrink fitted to the gear ("inside out" synchro); never seen it on a steel ring box.

There can be a lot of wear on the three ears of the ring, but again it is extremely rare for this to kill the synchro before the box dies. You can expect bore wear and ear wear to (usually) go together, but it is quite possible that the forcing that results in ear wear will actually prevent bore wear! Again, it takes a v bad driver. I think Barney has pics of wear on ears.

Synchros can be killed if the gearbox has excessive endfloat that allows engagement of multiple synchros at once, but this usually results in obvious and terminal malfunction. I have very rarely seen the sprayed metal come off, which will certainly kill the synchro - this only on an A series transverse box that looked like it had had water/AF in it.

All four synchros are essentially the same, even if the actual parts are different. Wear will normally be greatest on 2nd, and least on 4th, so use 3 & 4 as gauges to get an idea of what they should look like. On good boxes that have all four the same, I have been known to switch the 2nd & 4th rings to equalize wear. The face clearances should be in the ranges given above, say .080-.020.

FRM
Fletcher R Millmore

Thanks Rich. I have thought of calling John at Quantum, but was saving that as a last resort if I can't figure it out from searches or from regular posters. Since he is primarily a service shop instead of a parts vendor, I felt a bit awkward about bothering him.

Thanks FRM. I was hoping to hear from you. Yes, I think you remember the situation correctly as to where I found your 0.080 recollection. I think it might have related to using the wrong steel vs bronze synchros when it was in Washington.

I haven't done any measuring yet because I didn't have any standard to compare it to. But, at a glance I think I probably have around 1/16, but maybe not quite 0.080.

So, if you were seeing them work okay with 0.065, I'm probably okay. I believe my 1-2 cluster is the spray metalized version. I haven't pulled my mainshaft stacks apart yet to see if that is true for the 3-4 cluster yet.

I did see the picture on Barney's site of the wear on the ears (I think someone called them dog houses), and I haven't seen any of that on mine. But, at the moment I have only done a rough teardown of the three boxes, I haven't done the clean up and inspection. I decided to clean up the shop and make a fresh start for that.

Since I have three boxes to pick through, I am hopeful that I can come up with acceptable synchros. And, if I can figure out that my 1-2 synchros are interchangeable with my 3-4 synchros, I should be able to put a set of 3-4 into my 1-2 position. I'm kind of thinking that the interchangeability depends on being spray metalized steel vs polished steel cones.

I want to end up with a pretty solid box because I'm putting it a solid rust free 50k mile 77 roadster.

Are you making any progress with the rough B that you drove home in the dead of winter?

Want to see a pic of a very badly worn layshaft? See the attached image of this one that I almost couldn't get out. You can see the tracks where it dragged the needles down the shaft on the way out. It was in a 77 non-OD.

Charley

C R Huff

Charley -
Could be wrong but I think all the 4 synch boxes are spray metal/steel; the 4 synch transverse boxes were all that way at the same time. I came across a well used one of those while looking for B stuff and all 4 synch are down to about .035 and it worked fine; theoretically .001 would be OK if it stayed there when hot.

Your layshaft is a real disaster, and I suspect it was not hardened correctly - probably a repop. Try a file on it. No way should you have been able to plow a groove like that in a real one.

Very unusual to have bad wear on the steel ears.

My B is resting - no money and less energy.

If you want to contact me, my email is on every post

FRM
Fletcher R Millmore

Fletcher,

I hope you are right about all of them being the spray metalized type. I agree that the layshaft must have been defective. It really had me puzzled that I couldn't get it out easily until is saw it. I was surprised to see that the laygear looked okay (still subject to clean up and closer inspection).

Maybe when the fall weather gets here you will get invigerated to work on your new B. It's been tough to get anything done in this heat wave. I thought it mostly just needed sheet metal and welding wire, but I guess there is always something to spend money on with an old B.

Thanks again,
Charley
C R Huff

Charley, John Esposito does sell parts, and quite reasonably, and is very helpful. Call, don't email.
Art
Art Pearse

Thanks Art. I knew he sold assemblies and relined OD hubs, but I didn't know he sold the individual parts for a rebuild.

Charley
C R Huff

I assembled my main shaft stack today. I got the low-side gear float to 0.006 inch and the high-side gear float to 0.008, so I'm in spec there.

For the synchronizers, I picked out my best hubs and rings and got 0.059, 0.063, 0.055, & 0.053 inches for first through fourth respectively. So, I think I will be good with that.

With the exception of the reverse gear on the mainshaft, I used the gears that came with the overdrive because the gears looked good and the hubs where the synchronizers ride were better than those in my parts boxes.

I saw no part numbers on the mainshaft reverse gear, but there were three radially oriented hash marks on them arranged at 120 degrees to each other. The one I removed had three single marks. The one I put on the stack had one single mark and two double marks. Is this some kind of tolerance indication? Am I likely to run into trouble swapping these gears around between these gearboxes?

The laygear that I intend to use will be from the same gearbox that the mainshaft reverse gear came from, but it will be riding on the mainshaft set from the overdrive box. The fist motion shaft I intend to use is also from the same box as the reverse gear.

In general, can you get away with putting used gears from different boxes together as long as they look to be in good condition?

Thanks,
Charley
C R Huff

Charley, re your last question - it looks like you will be the one who can provide the answer! Hope it works.
Why did you switch laygears anyway?
Art Pearse

Art,

The reverse teeth on the laygear were pretty hammered, as were the reverse idler and the reverse gear on the mainshaft. If it weren't for that I would have just taken a chance and put the OD box in without taking it apart. I've swapped gears around in Spridget boxes before and it worked okay, but it was an autocross car so it would not have mattered that much if it was a little loud.

Charley
C R Huff

There has only ever been the same guide to servicing the 4 synchro OD gearbox on my website - created on and unmodified since January 2006!

Clearly he misquoted the measurement and I would stick to the 1/16" or 60 thou as a guide to "acceptable" condition.

Yes, the ring will work at less than this but I wouldn't waste my time with the box apart - just change them!

If you are checking though the side cover with the box in situ, than that is a different matter and I wouldn't pull a box unless failure was imminent!

Late 3 synchro 2nd gears and all 4 synchro boxes have steel rings and coated cones.

Yes you can get away with a mix & match if the gears are in good condition.
Chris at Octarine Services

Thanks Chris. I'll get the new synchros.

Charley
C R Huff

This thread was discussed between 19/07/2010 and 08/08/2010

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