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MG Midget and Sprite Technical - 1275 release bearing movement ?

Hi guys
I'm about to adapt the T9 / conversion kit to my 1275 engine and I'm very cautious to have it all right before final assembly, measuring it all over and over again several times and preassembling the parts several times - just to have it all 101% correct......
Can someone tell me the release bearing distance when forth and back when actuating the pedal when fitted in the car with the hydraulic?
Second, does the diaphram on the picture look as if it is in the correct angle with the clutch housing fitted, I don't remember how it looked when I disassembled it,I have attached a photo. It's a normal 1275 housing, only with the pressure foot missing. The new friction plate has the same thickness as the old one.

Jan Kruber

Deduct 1% point for lack of perfection

The clutch pressure plate housing is way to silvery should be more gray in color

Please try again and get back to us for our approval

1 Paper

Don't mind Prop - he's only teasing you. Looks great Jan.

Re:your second question, it looks okay to me, but others here know more about A series than I do.
First question; it's dependent on the relative volumes of the master cylinder and the slave cylinder, or more specifically the ratio of their bores. It's easy to calculate. If the slave has twice the cross-sectional area of the master for example, its linear stroke will half that of the master.
Care should be taken in this area to avoid over-throwing the clutch.
There are people in this parish who have experience of setting up clutches for T9s on 1275s who will be able to give more specific advice. Hopefully they will be along shortly.

But Prop has a point. Way too clean and shiny lol!

My thoughts on that photo is that the gearbox release bearing guide tube is going to foul the pressure plate fingers when the driven plate wears if the gearbox is at the correct distance from the engine. As the driven plate wears it gets thinner and the pressure plate diaphragm fingers move backwards towards the gearbox. I've encountered that when fitting the earlier 4 speed gearbox to an A series but the problem was less severe as the release bearing guide was smaller and only just caught the fingers but still f**ked the operation. Either it needs to be cut back a suitable distance or as some have done, fitted a concentric release bearing which doesn't require the guide tube.
David Billington

I have been in contact with Jan directly, but in case it is of any interest to others:

When I was fitting a concentric slave to mine I needed to know that it would move the release bearing by the same amount as the original 1275 set up. I made up an extended hydraulic pipe so that I could operate the clutch with the car clutch pedal whilst the gearbox was out of the car. The result was I got a measured movement of 11mm for a single clutch pedal stroke. My suspicion was that the designed movement would have been a 1/2" throw (12.6mm) but it was close enough to give me a target for setting up the concentric slave.

Regarding that guide tube; from measurements it appears that the guide tube in contact with the diaphragm fingers would hold the bellhousing from making contact with the backplate by at least 2mm. The measurements may need double checking but either the guide tube needs sortening, or the diaphragm fingers need grinding out slightly so that the guide tube will fit clear through between them. I would favour shortening the guide tube in case the temper of the fingers is altered by grinding. But care is needed not to overdo it and end up with the release bearing inadequately supported and possibly jamming on the tube.

As David points out, the fingers will move even further out as the new clutch plate beds in, and then wears.

It has also just occured to me that Jan needs to be sure he got the pressure plate in the right way around as that could well alter the angle of those fingers!

As Guy mention I actually devided my conserns / questions into two, to spare the BBS for a VERY long post - because - as I understand, Guy was one of the pioneers in converting T9's into the Spridgets ( please correct me if I'm wrong here Guy)
I asked for Guy's experience in determing whether it would be an option to grind the center of the diaphram fingers from approx 26,5mm to 35-36mm, so that the guide tube would slide in with some clearance between itselves and the fingers. Looks as if they have done that here, or?? :
David, as you mention....but by doing that, I wouldn't have to play attention, when the friction plates are worn and the fingers will move further back towards the gearbox - and I could have the guide tube on the comfortable side of the fingers.
In the case this is a bad idea, (Guy wasn't that happy about that option) if I instead of this first opton, had to cut a little more of the guiding tube, it would be nice to know the working area of the release bearing, I would then be able to cut only as much as nescessary - but not too much - from the guide tube.
Right now I do not remember the thickness of my new friction plate and the minimum thickness, but I imagine that I could pretend a wear by loosening the 6 housing bolts, lets say one turn, and look / measure how far out the fingers will reach against the guide tube, right....?
The hydraulics are the same as when driving with the ribcase: Moss aftermarket master(plastic reservoir) and slave.
The new Gorg & Beck T9 version friction plate is not stamped "this way towards the flywheel" - but I fitted it with the longest part of the center spline bush towards the gearbox, with the slanted edge. Must be so, right?
My questions originally arrised when checking and rechecking the parts before assembling for good. I slided the input shaft into the clutch splines and spigot and when "bottoming out" there was a gap of 182mm between the engine plate and the gearbox. The guide tube touching the diaphram fingers, as you saw on the phote. The bellhousing is 180mm, so obviously I have to sort this issue out, with some play, so that it does not bottom out in the crankshaft:
grinding the diaphram fingers gently without heating them, which will destroy the hardening, or shortening the guide tube?
Eventually a looong post anyway - sorryyyyy :-)

Jan Kruber

This thread was discussed between 10/03/2018 and 11/03/2018

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