Messing with the master brake cylinder
 

Hi,

as a favour to the wife, I am upgrading to the bigger servo. Less effort on the pedal for the same effect. OK, So I need to take off the master cylinder. Would this be a good time to put in an overhaul set, as the car is 22 years old and has 265k km on the clock? On various Brittish cars I worked on people begged me not to touch the cylinders if they were not broken, overhauling them would usually make things worse, But this is a Japanese quality vehicle. So what to I do? And secondly , on most cars I worked on, there is a gasket between the cilinder and the servo. On the pics of the overhaul kits for the cylinders (like this one: https://www.ebay.co.uk/itm/MX5-Clutc...5/362804362197) I don;t see such a gasket. And I cannot seem to find it separately. Am I missing someting?

Any advice is appreciated,
Cheers,

Hugo

That kit is for the clutch, not the brakes.

I've never heard of someone rebuilding the brake master before, probably a waste of time. I'd leave it.

How did I overlook that. Thanks, and sorry. I googled for brake cylinder overhauls and all these popped up.

Cheers,

Hugo

A rebuild kit will be cheap and easy if you can find one. I can't see a reason not to, if you are so inclined.

Aluminum master cylinders commonly wear the bore enough after 10 years to cause a step you can feel with your fingers.
It is why I never push an old master past normal "stroke" when bleeding.
I never push full stroke.
Even Japanese masters wear in this manner.
Rebuilding is not a good idea unless the bore is perfect.

Do not berry hone a master bore. They almost always seep after "honing".
The hones do not produce a fine enough finish.

Chinese hydraulics suck big time.
Always find something made in Japan, Germany, or USA

Another option, which is what I did, is to find a used servo from a scrapped, low mileage car which already has a bigger master cylinder on it. Going from the base 7/8" cylinder from most 94-'02ish cars to a 15/16" reduces the pedal stroke nicely. If I'm not mistaken, the '03 and up cars all had the biggest servo along with the bigger master cylinder. Short stroke and low effort. Personally, I went with the parts from a Mazdaspeed, which have a smaller servo than the '03's, but bigger than the '94-'00. With that setup I ended up with a shorter stroke and just about the same pedal effort compared to stock.

I'm not sure that the 7/8" master from the older cars fits without modification to the bigger servo from later cars. One more reason to just buy the parts together.