Brake master cylinder wear

[davidj]

Hi,

I don't suppose anyone knows the allowable tolerance on the Girling brake master cylinder bore? (single circuit design) I have pulled mine apart to replace the seals and had the bore checked. At the area of maximum wear it measures 0.0007" oversize, (0.7 thou) which I would have thought would be OK. The end face where the reservoir seal sits is OK.

What does the team think? Before anyone mentions it, yes, I know I should spend ?70 on a new one, and this may be the sensible approach. However, I come from Yorkshire, so if the existing unit is fit for purpose, I will refit it with new seals.

Cheers,

David

[gjz30075]

That's less than .001 wear. Pretty insignificant, I think. A rebuild should be fine.

Greg Z.

[rgh0]

As long as the bore is still round and smooth then this amount of wear should not affect the sealing ability. They were probably not made to better that accuracy originally anyway.

cheers
Rohan

[neilsjuke]

No problem go for a repair brakes are for wimps and it's so easy to get at the master cylinder and easy to see if leaks .
As you are not sure and will be thinking about it when you are out driving and that tree is closer than you thought.
Fit a new one
Neil

[gerrym]

David, I take it you didn't measure the bore yourself. Did you query the measurer as to the instrument used, accuracy. As Rohan has said, its also about roundness and surface finish. Were these checked as well.
Regards

[davidj]

It was checked with a bowers gauge, accurate to 3 microns. The bore surface finish is fine and surprisingly, the unworn portion was bang on size! There is a slight step in the bore close to the oil exit, which is also visible on another unit I have. I guess this must have been made by the original reaming process.

Thanks for your help.

David

[gerrym]

David, this is indeed high precision metrology. With that small amount of wear, I'm guessing you could order a brand new component and it would not be any better. Does the seal stroke over the lip/step

If you really want to be compulsive-obsessive, you could get this honed out.

Regards

[john.p.clegg]

I'll have to get an electron microscope to set my tappets...

John

[davidj]

Hi,
In answer to GerryM's question,the step is between the inlet and outlet, so the seal does not stroke over it. Being an engineer, I am always interested in how things were made. I guess in this case, the bore was machined undersize, and honed/reamed to size, hence the step.

Cheers,