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MG MGA - Input shaft

I have a 1960 MGA 1600 with an MGB competition clutch/pressure plate installed. Its a great unit but the clutch pedal action is very stiff and with a recent injury this makes the car very difficult for me to drive. I would like to go back to the standard MGA clutch but I do not know which input shaft was used and hence what the spline number is.
Does the early MGB gearbox and clutch use the same input shaft as the MGA Mark II? And, hence , the same spline number (23)?
If the shafts are the same, then (hopefully) I will just need to replace the clutch/pressure plate with late Mark II components.
What are the spline #'s for the late MGB shaft?
As always thank you for everybody's help.
John

JH Hays

John,
I have trannys from a 77 and a 67 MGB's and they are both 23 splines. I can't be sure they are the origional trannys. Hope this helps and have a good day!

John
John Progess

The B input shaft uses 23 splines, MGA uses 10. The flywheel is also different for a B clutch (positioning dowels are spaced differently). The B clutch uses a different gearbox front cover and operating fork. So to return to a standard MGA setup, you need an input shaft, a release fork and front cover and a flywheelm plus the new clutch. If you can't find an input shaft, just use a standard A clutch cover and release fork and bearing and a standard MGB friction plate with 23 splines. That will work just fiine.

The easieer option may be to install a standard B clutch, which although a little heavier than a standard MGA one, is much lighter to operate than a B competition clutch and can be installed using all the other bits that you alrrady have installed.

The MGB clutch has the advantage of being lighter in weight and more robust than the MGA setup, and the lighter MGB flywheel makes the engine much more responsive.
dominic clancy

My 1962 MGA MK-II came with a 23 spline input shaft. I believe it is the same as the early MGBs.
Ed Bell

Late MGA uses the 23 spline shaft - same as MGB, but it is easy and not uncommon to change the shaft, driven plate, etc. As an early 1600, you could have any combination. I think that 60 still had 10 splines; it's near the change point.

As Dominic notes, the MGB diaphragm clutch uses a different fork and front cover, which changes the leverage ratio from pedal to clutch. IF you have MGA parts here, with the B clutch, the pedal will be way hard, and will overtravel the clutch, damaging it.

You need to figure out what all the parts actually are, and use the correct "set".

FRM
FR Millmore

The leverage ratio did not change, but the B pressure plate is thinner than the A unit, so the release bearing has to be positioned farther forward. The B front cover and release arm have the pivot point farther forward (and larger release bearing).

All of these parts can be changed as a set. To install the B clutch in the A use the B parts for front cover, release arm, release bearing and pressure plate (everything between the gearbox face and flywheel). Ditto to change back from B to A pressure plate.

The A pressure plate uses two alignment pins where the B uses three pins on the same basic circle. Put an extra hole or two in the flywheel and you could change alignment pins to accommodate either A or B pressure plate.

The standard B pressure plate is a bit stronger (in grip, not more robust), but not much difference in pedal force requirement. The competition pressure plate has stronger springs and requires considerably more pedal force. Since you already have the B parts installed for the competition pressure plate, I suggest you simply install a standard B pressure plate (which I happen to like very much in my MGA).

When MGA pressure plate wears it can be rebuilt (almost indefinitely). When MGB pressure plate wears it has to be replaced. Common first point of failure of the MGB diaphragm type pressure plate is the thin metal eyelet securing the release thrust ring. If it rattles toss it in the trash. Similarly the MGA pressure plate might break a spring securing the release thrust ring, but those can be replaced.

Any A or B clutch can interchange friction discs. Use whatever disc will match the splines in the gearbox input shaft. For years now I have been using early MGB flywheel and B clutch parts combined with 10-spline disc to match original early MGA gearboxes.
Barney Gaylord

I am totally willing to concede that Barney may be correct re the leverage ratio. I know the Spridgets changed ratios with the diaphragm clutch, and the principles would be the same - less travel required but stronger spring pressure, and thought that the B series were similar. Moss show a different release fork, but that may be a matter of a different bend to accommodate the longitudinal reposition of the pivot point only. I don't have the parts to hand for comparison.

FRM
FR Millmore

The B release fork is a different shape, but it also holds a larger release bearing.
Barney Gaylord

Thanks Barney.

FRM
FR Millmore

Thank you all for your help. I live in SE Wisconsin so I better get on it soon. As a matter or fact I have a friend coming over to help me this week. We've decided that Barney's solution is the best. Since my car is already set up for the "B", we're installing standard "B" pressure plate, disc and throw out bearing. Following the KISS principal.
The competition parts I'm removing (pressure plate. friction disc and release bearing) only have @12,000 miles on them and it seems a shame just to throw them away. Does anyone want them? I can send them for the cost of UPS.
Thanks again
John
JH Hays

This thread was discussed between 28/08/2009 and 02/09/2009

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