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MG MGB Technical - Can’t get the Layshaft out, 1977 side fill gearbox

I’m trying to get the guts out of a 1977 side fill non-overdrive gearbox so that I can put them into the side fill overdrive gearbox that I bought (reported to be 1975). The reverse gear and its counterpart on the laygear are hammered in the overdrive. My intent is to transplant the 1977 non-overdrive laygear, reverse gear, and probably the mainshaft gear stack from the non-OD into the overdrive box.

I got the overdrive box apart with no problems. With the non-overdrive gearbox, the layshaft does not want to drift out. I could only move it about one inch, and it was not all that happy to move that much. I am trying to drift it out from the rear to the front, but by looking at the one I already took apart, it seems the direction of drift shouldn’t matter. When I drift the layshaft back in, the laygear is stiff on the layshaft, and it was free before I started the disassembly.

When I look in the exploded view in my Haynes, the later gearboxes show circlips and space tubes on the layshaft. The overdrive box had none of these (that I saw), and if the other one does, I don’t see how they would come out before the shaft is removed.

Both boxes are side fill, and both have laygear thrust washes with the anti-rotating tabs.

Any suggestions?

Charley
C R Huff

In the MGA gearbox at least (maybe this also applies to the MGB) the layshaft can be removed from either end. It has to be drifted out, no other way. If tight, try heating the case - Al will expand more than the shaft.
When the shaft is out, you must remove the front and rear shafts in order to get out the laygear. as for the tightening up of the gear, you probably have a worn area on the layshaft, or the needles are very worn and may not be in straight any more.
Art Pearse

Thanks Art,

I hadn't thought of trying heat, which should help if it's just tight. My concern is that I need remove something that I haven't yet removed.

If anyone has an MGB Haynes manual, take a look at the all-syncro gearbox exploded view on page 118. It is parts 25 and 26 on the layshaft that have me puzzeled. These parts were not on my overdrive box, and they are not in the exploded view for the 3-syncro box, but I'm wondering if they are the problem in the box that I can't get apart.

Charley

C R Huff

I'm looking at the Moss catalogue for both 3 synchro and later gearboxes. the only parts are the bearings, a distance tube, the circlips and two thrust washers. The circlips and the tube fit into the gear, and should not obstruct the shaft from sliding. If you got the shaft to move 1", then one of the thrust washers might have dropped off. My new layshaft was a fairly tight fit (tighter than the old one). Warm it up and go for it!
Art Pearse

Thanks again, Art. I'll give it another go with some heat.

Charley
C R Huff

Looks like I found the problem (see attached pic).

Wear on the layshaft let one or some of the needle bearings jam between the case and the shaft. You can see the track from the bearing in the side of the shaft that it left when I drove it out.

I wonder what this transmission sounded like. Oddly enough, it all looked pretty good when looking in the side panel

Charley

C R Huff

Ouch! How many miles on the 'box and how many rollers in each bearing? The older boxes had 20 each.
Art Pearse

You will of course need a new layshaft and bearings, but did you damage the bore inside the laygear, in the bearing area?
Art Pearse

Art,

I took that gearbox out of a 77 that I bought for parts. The odometer said 69k miles. I don't remember the exact year of the license plate, but I recall it was old enough that I thought the miles might be correct.

I was watching one of John Twist's videos in the transmission section today, and saw him doing some kind of test on a layshaft with a file. Unfortunately, the sound quit on my computer so I couldn't hear what he was saying. If you are curious enough to take a look at it, I would be curious to know what he said. I assume it has something to do with hardness.

I haven't fully cleaned and inspected the laygear yet, but at a glance I think the bearing area is okay. I don't know how, but it seems that way. I will have to get one of the circlips for it since one was destroyed. I've got a couple good looking used layshafts, but I'll probably go for new unless I hear that new ones are of poor quality.

I'm going to start a new thread on syncro rings because I think I have heard of problems with some new stock. Also, the Haynes instructions for assessing the wear were to compare it to a new one, which is not a lot of help at the moment.

Charley
C R Huff

Charley, the MG circlips are a pain to remove. I replaced them with standard 7/8 internal clips, but ground the eyes down to clear the shaft. Then you can use circlip pliers.
Art Pearse

Art,

Do you grind them down a bit before you install them, or do you install them and then grind them down with a die grinder?

They do look like they would be a pain to remove.

Charley
C R Huff

I ground them down using a dremel tool with a cutting wheel, but whatever you have, need to grind leaving about 10 thou around the eyes.
I fabricated a special tool to get the inside clips out - a piece of hacksaw blade with a ground point to get under the clip in the groove, while bearing down on the other end to stop it sliding. I don't have it any more but it is easy to make if you have a welder.

Art Pearse

Art,

Again, thanks. Yes, I have welding equipment, so I could make one of those, and it's good to have the 10 thou spec so that I don't have to do it twice.

Charley
C R Huff

This thread was discussed between 18/07/2010 and 19/07/2010

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