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MG TD TF 1500 - Brakes Wheel Cylinder Size

Hello, Firstly thank you to all the community who have made my life with Rita 1952 MG TD 9069 so much easier over the years of reading and researching problems I have experienced. However now it is my turn to post a question as I have been unable to find any mention of this issue anywhere on the internet. What size is the bore on the wheel cylinders 7/8" or 3/4"? I received a set from a supplier in Melbourne Australia which are 3/4" bore. The ones on my TD are 7/8". I was unable to get brake pedal height more than 1" from the floor and assumed the wheel cylinders where the wrong part. I have returned these parts and ordered a set from Moss Motors in CA. While waiting on delivery I am researching these wheel cylinders and cannot find any information about the correct size. Any ideas Gentlemen?



R.G. Thornton

7/8" is the correct diameter for the rear cylinders. I don't understand why the smaller diameter units prevent the brake pedal from returning. It seems that you have another problem.

John
J Scragg

Thanks John, The brake pedal is returning OK but I push the pedal to within 1" of the floor before the Brakes operate. I have bleed the brakes several times X10. I now suspect this is a common change from 7/8" to 3/4" simply because of parts availability. But I don't see anywhere on the internet what can be expected with this change. I think the force onto the brake linings would be increased but am unsure how this would affect the brake pedal. I think it would have a harder feel. There is an enormous amount of discussion about brake fluid Dot 3 or Dot 4 Or Silicone But no where is there any discussion about what affect this major change from 7/8" to 3/4" would have on the system as a whole. I find it very puzzling. Regards Ray
R.G. Thornton

I now better understand your problem. Changing from a larger diameter cylinder to a smaller diameter would have the reverse effect on the system. As the volume in the rear cylinders is smaller, the displacement would be greater. This would make the brakes lock sooner. It doesn't seem to be a hydraulic problem. Have you correctly adjusted the shoes?


John
J Scragg

Force = pressure x area. The smaller diameter cylinders would put less force on the rear shoes, resulting in major forward brake bias. John is right about something else causing the pedal travel issue. Could also be master cylinder problem. Lots of failures of fairly new ones. If you bleed brakes on an old crusty one, the longer pedal travel can hit some rust or debris in the bore and cause it to fail. George
George Butz III

Try a brake hose clamp on each hose in turn. This will tell you where the problem is.
It looks as though you have been sold Morris Minor rear cylinders .
If the front ones are also 3/4" they will not be MM as they are single leading shoe (double piston)
Ray TF 2884
Ray Lee

This thread was discussed on 15/08/2019

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