Master Brake Cylinder ?

[WB9MCW]

WVZR-1 You caught me in edit mode and my old photos posted before my edits did in your quote capture. LOL

[WB9MCW]

Originally Posted by scottfab

It maybe a common failure but I've never experienced it in 15yrs of ownership and 92k miles. Maybe it's in how I flush and bleed them.
Don't know. I learned on my 72 vett not to just push a lot of fluid through the system. And to flush every few years even if the pads are ok. I'll be doing that service again this fall. We'll see if my luck holds.

I think you are lucky SF

I bet olde Murphy will visit your MC soon.

Then again perhaps the constant attention is making a difference for you.

My Z is a only @ 64K now and the MC has been bad since 62K.

[VetteMed]

I hope I didn't jinx myself. Driving home from work yesterday, my brake pedal was quite soft, with a long travel. Got home, and the forward reservoir was nearly dry (scary!). Today, I inspected the entire system, I can find no evidence of a leak (other than some bubbling caliper powdercoating near the RH front caliper bleeder screw.

Here's where it gets weird.

I bled all 4 calipers -- all the while checking for leaks (none). However, the LH front caliper really didn't give me a good solid fluid stream like the other calipers did, so I'm kind of scratching my head about that one. I did use a vacuum bleeding system, BTW.

So, I tightened the bleeder screws, topped off the fluid, and the brake pedal is now firm as it used to be. I don't get it at all. No signs of leaks anywhere. Perhaps master cylinder leaking into brake booster, only from the front portion of the cylinder? I don't know if that is even possible...

[scottfab]

Originally Posted by VetteMed

I bled all 4 calipers -- all the while checking for leaks (none). However, the LH front caliper really didn't give me a good solid fluid stream like the other calipers did, so I'm kind of scratching my head about that one. I did use a vacuum bleeding system, BTW.

Had a similar experience using vacuum on an Explorer.
Used the peddle to bleed them and the softness went away.

[gbrtng]

Originally Posted by VetteMed

I hope I didn't jinx myself. Driving home from work yesterday, my brake pedal was quite soft, with a long travel. Got home, and the forward reservoir was nearly dry (scary!). Today, I inspected the entire system, I can find no evidence of a leak (other than some bubbling caliper powdercoating near the RH front caliper bleeder screw.

Here's where it gets weird.

I bled all 4 calipers -- all the while checking for leaks (none). However, the LH front caliper really didn't give me a good solid fluid stream like the other calipers did, so I'm kind of scratching my head about that one. I did use a vacuum bleeding system, BTW.

So, I tightened the bleeder screws, topped off the fluid, and the brake pedal is now firm as it used to be. I don't get it at all. No signs of leaks anywhere. Perhaps master cylinder leaking into brake booster, only from the front portion of the cylinder? I don't know if that is even possible...

Wifey's 91 base car is leaking fluid from the front to the rear reservoir, so
that might be your problem. I just transfer fluid back where it belongs every so often.

[POWERBRAKEBOB]

IF the master is sucking air in, then there is no venting between the booster and the master. Perhaps someone put sealer in between? They must vent.
I do HYDROBOOST conversions, and can build for the C-4's. With a HYDROBOOST booster, I run a c0ommon 1" master, even one from a C-5 can be used. Gives outstanding braking performance, AND a firmer pedal

[FU]

Originally Posted by POWERBRAKEBOB

I do HYDROBOOST conversions, and can build for the C-4's. With a HYDROBOOST booster, I run a c0ommon 1" master, even one from a C-5 can be used. Gives outstanding braking performance, AND a firmer pedal

Got my attention.
Mind starting another post about this hydroboosting etc. and tell us a bit more ?

TIA

[POWERBRAKEBOB]

I have rebuilt many of the C-4 masters, and thousands of the C-2,C3 masters.
In looking at the vacuum boosters on the ZR-1's, I notice how ugly that computer wiring harness is, and how ugly the computer looks sitting where it is.
With a HYDROBOOST brake booster, which runs off of the p/s pump, the wiring harness can be run under the booster. The battery can be relocated to the rear compartment, and the computer put in it's place.
The stopping power of a Hydroboost is unbelievable! It can deliver up to 2000psi to the calipers at idle pump speed.
We can use a more conventional master cyl, say of of the C-5, which is 1 inch. This gives you a much firmer pedal, and the stopping power will stop the car faster than you can accelerate.
Many pluses start to stack up with this system.

[POWERBRAKEBOB]

These are the before photos of the wiring harness and computer wrapped over the vacuum booster. With the Hydroboost, and the battery moved back to the compartment, the harness can be rerouted to under the Hydroboost and the computer relocated to where the battery was. . We use a 1 inch master for a better pedal feel.
There are just so many advantages here.

[POWERBRAKEBOB]

My dual dia booster was getting tired finally at 260,000 miles, and so was the Master. I rebuilt it once 15 years ago. In looking at it, I decided that the placement of the computer and wiring was unsightly. I elected to move the battery to the rear compartment, and install the Hydroboost. This eliminates the Australian Booster, and 7/8" marginal master cyl. This also works well, if you want to install C5 calipers, which came from the factory with a 1" master. The Australian booster has an odd bolt pattern where the master bolts on. Hydroboost uses std GM 3.375" spread. Stopping power is phenomenal. Stretches the seat belts.