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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 MGA - Twincam trans questions

What is different about the twincam transmission other than the slightly different look of the case? There are two holes on top of the bellhousing, but I don't know what would mount there. The front cover/clutch fork looks different too. It would be interesting to know why they changed the casting for just this model. Did the tranny change between the 1500 and 1600 models? My tranny came out of a '59 with the 1600 body. Did they base the 1600 tranny off of the twincam design, i.e. high starter position and flanged tailshaft?

The 1600 shift tower seems to bolt right in, the dunlop slave cylinder bolt centers are the same as the lockheed, and it sits in the car just as pretty as she pleases.

How does one tell if he has a close ratio gearset in his box?

Mark
Mark J Michalak

We don't know why but they specced a Magnette main case for the Twincam. The Magnette slave mounts on the top, but the same case when used for a Twincam is either blank on top or occasionally has some mounting holes drilled and tapped but not the large hole where the pushrod would go through.

The gearbox internals are identical (although more Twincams were ordered with close ratio gear sets than was the case with pushrod cars)

As for the high starter mount location, it actually changed in the late 1500 - any engine with a 15GD prefix will have high mount and flanged, not sliding spline driveshaft (going on memory here - check me with a parts book)
Bill Spohn

I thought that mounting location looked a lot like my Magnette's. Without, as you said, the hole for the pushrod. I checked the archives and will try to determine the gearset by counting the rear wheel revs. Something tells me that if I have one, I'm not going to like it with my 4.3 rear end.

In a fit of "I can do this!" I was hurriedly attempting to get my car roadworthy for the Grand Lake Tour. My gearbox is shot, but I had a twin cam transmission in very nice shape out of a parts car so I chucked it in there. I didn't make the rally, but at least I can enjoy the end of summer and the warm part of fall.

That is, when I get around to putting it all back together.

Mark

All of the ZA-ZB Magnette and MGA and early MGB three syncro gearboxes (including Twin Cam and Deluxe) use the same internal parts between the front and center main ball bearings. The primary differences are in the mainshaft and tail housing which can be interchanged as a set. The front cases have different external ribs and starter position. The input shafts can have different splines, 10 splines for 1500/1600, 23 splines for 1600-Mk-II from October 1961 and all MGB, and are also interchangeable. This is all quite handy, as I sometimes use early MGB parts as spares for my MGA gearboxes.

All of the three syncro gearboxes use the same gearsets, either standard or close ratio. See here: http://mgaguru.com/mgtech/gearbox/gt102.htm

There is one change of internal parts. Last half of 1967 production MGB has a larger diameter layshaft and four bearings on the layshaft. Nice improvement, but only for half a year before they went to the larger four syncro gearbox. You can assemble the 1600 style tail housing to the early MGB gearbox to convert it to MGA style rear mount. This can allow you to have a four bearing layshaft in your MGA with no machining, if you use the late 1967 gearbox.

I do not know if there is a close ratio laygear available for the late 1967 gearbox. I suppose an earlier style close ratio laygear could be bored out and honed to accept the later shaft and bearings.
Barney Gaylord

Barney,

I took the larger layshaft and early casing to John Twist's gearbox rebuilding seminar. There, the box was hand reamed with a large tap to accept the larger layshaft. About 30K hard-run miles on it and still ticking! Same thing could be done on any MGA box, I believe.
Paul Hanley

Yeah, it can be done with the right tooling. In the late 70's when I started the restoration on my MGA, the MGA and early MGB layshaft was not available. Moss was selling the special reamer tool to modify the case to accept the larger shaft which was available. At the time special reamer was very expensive, like half the price I had just paid for the car, or several times the cost of a used gearbox. I didn't buy it. I put the gearbox back together with the used and somewhat worn layshaft. Nine years later the car was back on the road, and a few years after that the gearbox finally got a new layshaft (original size).

If you do change to the late 1967 four bearing lay gear with larger shaft, I hope you never break a tooth. The replacement layshaft is cheap, but that half year laygear is expensive, very rare, and may be available only as a used part. Moss currently has it listed for $299.95 as a used gear with the bearing kit. I have never paid more than $50 for a used MGA or early MGB gearbox with a good laygear included. I can afford to change a three bearing layshaft a few times for the difference in price.

Barney Gaylord

This thread was discussed between 24/08/2006 and 25/08/2006

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