Replaced Master Cylinder Today

[Eyelawdoc]

I replaced the original master cylinder on my 84 SVO today. Darn, they just don't build things to last anymore! It was almost 21 years old and only had 219,000 miles on it. I guess I should have taken better care of it! It had not yet failed completly, but was going almost all the way to the floor before the brakes were engaging. I replaced the MC, flushed and bled the system and the brakes work great once again.

On a more serious note, I was quite surprised at how light the original aluminum master cylinder is. Only weighs a couple of pounds. I'm not as happy about the cast iron replacement's weight. Maybe I'll look for a rebuild kit for my original and send it out to be sleeved with stainless. Anyone done this with their's?

[kiwi]

...somethin' still wrong....

.....Having problems right before gettin' on this trip to KY!! Replaced front cals with good 'used' steel ones due to sticky original front plastic piston & still no pedal after bleeding a quart thru' it (on a lift/crossbleading).......Is there any way that the pressure built by the pumping the pedal can blead past the front 'good used' pistons without an external leak? The rear tires won't even lock up now on the lift rotating them by hand~pumping the pedal/goin' to the floor.....
Hard to swallow if the MC went out at this same time/ Air bubble still trapped in the system???

[Eyelawdoc]

It is very common for the master cylinder to go out while bleeding the brakes. When bleeding, the pedal is depressed fully which moves the piston into an area of the cylinder bore it does not normally travel. That area of the bore is rough from accumulated corrosion. The roughness takes out the seals and no more master cylinder. Put on a new one and you'll be good to go.

One can prevent this by measuring how far down the pedal goes BEFORE opening the system and then not going beyond this point while bleeding. (Tough to do!) Alternatively, you can get one of those Mittyvac tools and vacuum bleed the brakes with it. That's what I use.

[kiwi]

Re: EyeLaw

..You are right......I probably damaged it/ Have to hustle it out fixin' it now........

[Jman]

the rebuilt MC I got was aluminum and just as light as the original?

bought it from a local oreilly auto parts store

https://www.oreillyauto.com

made by cardone industries, and was 19 bucks after the core charge.

a good way to keep the pedal from going down to far, is to just put a 4x4 block of wood under the brake pedal, allows a decent amount of travel, but not too much.