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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 TD TF 1500 - Master Cylinder Holes

Hi guys, quick question - just taken my brake master cylinder out, upon examination inside it has one hole to connect the resivoir to the piston chamber but it also has another smaller hole that has not been drilled all the way through so it doesn't connect the resivoir to the chamber. Should this be like this? Does anybody have an explination for what this is for? Pretty sure it is origional - been in the car for decades.

Thanks

Ian.
Ian

Ian -- That little hole you see that you say doesn't go all the way through does continue through but the part you don't see is very small. It allows the pressure in the lines to bleed off. Try poking with a very small diameter piece of music wire. One of these days I will have to see if I can measure that little holes diameter and get the information in the archives. Let us know how you make out.
Cheers,
Bob
R. K. (Bob) Jeffers

Look very very closely...you will find a tiny (very tiny) hole in the middle of that hole. Use a light in the piston chamber.
That is the relief valve...if it wasn't there the brakes would stay on.
If it is clogged, you can use a 'welding tip' file (they come smaller then pins) to clear it out.
gordon lawson - TD 27667

Cheers guys, I will poke an e string from my guitar down there. Second time I have changed the seals in this thing!!
Ian

Hi, Ian - Never measured one in a TD, but the front hole in a midget and MGB is 0.029", or just under one thirty second of an inch. The reason it has to be so small is that the front cup actually passes over the hole every stroke. If it were larger, pieces of the cup would protrude into the hole and get nipped off, eventually ruining the cup.

As Gordon and Bob have noted, this is a "stepped" hole, which is about 1/8" inside the reservoir. Just be careful not to enlarge the hole, or give it sharp edges, or you'll have to hone the cylinder bore to clean it up.

Cheers - - Alec
Alec Darnall

I guess I'll restrain myself on the "G" string comment..
Tom

This thread was discussed between 25/05/2006 and 26/05/2006

MG TD TF 1500 index

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