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Rear brakes won’t bleed - no fluid

Still nothing. Overnight the level in the MC for the rear reservoir went down so I know fluid is going into the system. Decided to start at square one again and bleed the MC. Nothing but air bubbles using the vacuum pump, but when I pump the brakes it does nothing. Gotta be either the MC is bad or it’s just not being activated right .

Either way I’m this close to throwing a cover over it and coming back in the spring
 
Andy69 said:
Still nothing. Overnight the level in the MC for the rear reservoir went down so I know fluid is going into the system. Decided to start at square one again and bleed the MC. Nothing but air bubbles using the vacuum pump, but when I pump the brakes it does nothing. Gotta be either the MC is bad or it’s just not being activated right .

Either way I’m this close to throwing a cover over it and coming back in the spring
Click to expand...

Take a break for a day or two, then step back into it. Clear your head.

Don't give up now, it'll only piss you off later to step back into it. I'd start over with a new master and go from there. It ain't rocket science, it either works or it doesn't. Bleeding brakes is usually a 1,2,3 deal and you're done.
 
Took the MC off and took it apart. Everything looks good. But the piston has a recess like a manual one, so the insert I took out needs to be there or there is no action for the first inch of rod movement. Trouble is, there is only about an inch of total travel of the MC piston. Seems like it should be more than that. That explains why I’m hitting a mechanical limit with the insert in, because I’m reaching the end of the travel.

Here is the MC I’ve got.

www.ebay.com

GM Chevy Raw Cast Iron Brake Master Cylinder 1" Bore 2Port Disc-Disc/Drum Camaro | eBay

Raw cast Dual bowl Cap Top 1" bore cast Iron body Master Cylinder GM Disc Drum Brake. High quality 1" bore Master Cylinder. Universal master cylinder that will work with most boosters.
www.ebay.com
 
Okay, look under the dash and observe the full travel of the brake pedal. Look to see where the rod is attached and measure the full travel. That will tell you definitively if there is an issue with travel in the master.

You should have full travel all the way to the floor in the absence of brake fluid. If you do not then it's either the wrong master, or the booster/rod is wrong.

Start simple and work forward.
 
This thread is about LS1 4 wheel discs on Chevelles.
I forgot my MC is disc/drum and all Right Stuff told me to do was change the proportioning valve to a "PV4" for 4 wheel discs.

www.chevelles.com

98-02 Camaro disc brake conv.

Anybody do a drum to disc brake conversion in a 1970 chevelle using 1998-2002 camaro/trans am brakes? If so how did it bolt up and was there alot to it? I am interested in this route, just curious who has done this. Thanks
www.chevelles.com www.chevelles.com

PV4 valve
 
Nashville Cat said:
Raybestos MC39018 is a 68 vette power-assist 4 wheel disc MC for $40 ! Amazon has it :)
I'm ordering one

Click to expand...


Is that the same as Delco 18M72? That's the 1968-1976 Corvette disc/disc. Would I still need the PV4 valve or is that just for a disc/drum MC? Right now I have the same distributuion block that was on the car when I got it, with manual drums. Used it with the disc/drum conversion no problem.
 
it's been a long time since I had power brakes... think I used the '68 Corvette manual MC with the stock type vacuum booster, but don't remember off-hand what size bore that was. I recall it did work well.
 
Andy69 said:
Is that the same as Delco 18M72? That's the 1968-1976 Corvette disc/disc. Would I still need the PV4 valve or is that just for a disc/drum MC? Right now I have the same distributuion block that was on the car when I got it, with manual drums. Used it with the disc/drum conversion no problem.
Click to expand...
Yes it is according to RockAuto. I think the PV4 valve provides a way to plug in your brake warning light.
Using this MC with the PV4 makes sure there is unrestricted flow back to the rear brakes.
These MC are supposed to be used with a booster.
See RockAuto

1968 CHEVROLET CORVETTE 7.0L 427cid V8 Master Cylinder | RockAuto

RockAuto ships auto parts and body parts from over 300 manufacturers to customers' doors worldwide, all at warehouse prices. Easy to use parts catalog.
www.rockauto.com
 
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Gotcha. I picked one up. Feels like I have some pedal now just by swapping. Trying to vacuum bleed the rears. Stand by.
 
I did find this about the non-adjustable proportioning valve. The PV2 is for disc-drum and PV4 is disc-disc.
This says to never use a disc-drum valve with 4 wheel discs

Proportioning Valve​

The first question that most people have is about the Proportioning Valve and what to do with that part. In most instances, people are using a Combination Valve
of some sort if the car already has disc brakes on the front whether from a previously done conversion or factory. If a factory valve is present, it is probably best to
replace the valve with a disc/disc Combination Valve because of the unknown.
If the car already has a Universal Combination Valve, it may be able to be converted to a disc/disc. In both instances, what we are trying to do is remove the Metering Valve from the system.
The Metering Valve is what holds off line pressure going to the front brakes when applying the brake pedal which prevents the car from nose-diving as the drum brakes take slightly longer to apply.
In a four-wheel-disc vehicle, we want all four brakes to apply evenly.
 
Well that didn't fix shit. Still tons of air coming out and no pedal. I don't have any leaks at the metering block or the distribution block at the rear axle. Maybe my old metering block is bad? I have a PV4 that came with the original booster/MC combo I bought but it has to be one that is a direct replacement for the one that's on the car now because of the stainless brake lines. I hope they make one.

Beyond that maybe the booster? I already checked the calipers to make sure I didn't have them reversed. I'm at a loss here.
 
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