[672brlbaby]

Hi, hoping to hear from someone else who has been thru this. came out one morning, no brakes pedal on the floor. found no leaks. since it was all original, started to rebuild. master had very dirty rusty fluid in it. cleaned, honed rebuild kit, seems to work normally. metering valve that hangs on the stud, cleaned, seems to work normally. didn't find a rebuild kit for that. dist block on the frame soaked, cleaned, seems to work normally. blew air thru all of them. new steel front brake lines. cleaned out system with denatured alcohol and used Dot5 fluid. fluid leaks from all 4 screws if opened. when I took off the calipers there was a piston stuck on each side. tapped on it and they all seem to move well. did not rebuild them at this time.

at this point, if the car is off, the pedal almost can not be pushed down. if the car is on, pedal goes to the floor. am assuming the switch in the dist block is working as the idiot light comes on when pedal hits the floor. realized the only thing that hadn't been touched was the booster. when the car is on, and pedal pressed, it does sound like air is escaping somewhere. I thought I always had that noise so I never thought of it. the vacuum line from the back of the carb seems normal.

at the moment I assume I need a new booster. would request ideas and suggestions as to what I might have missed before buying one. can a booster be tested? thanks for your time.

Jim

[squidtone]

I'm no expert, but I've messed with this brake system a bit.

The "hard as a rock" "pedal doesn't move" when the car is off is normal. It's downright scary how hard the pedal pressure has to be when the car is off.

It's possible you happen to need a brake booster rebuild, but it sounds to me that it's just a side issue. (by the way, if you need a brake booster rebuild, consider steve gregori rebuild/replating service...you get to keep your original booster so it will retain the original look...repop boosters have obvious differences....he'll rebuild it, replate it as long as it's in decent shape with no major rust.)

It sounds like your system still has air in it. It might be in the master, or in the calipers.

How are you bleeding your system? Did you bench bleed the master cylinder? Definitely have to do that, or you can use the bleeders on the side of the master.....using tubing looped into the reservoirs.

You have to press the "button" on the metering valve under the master when bleeding too....Otherwise I don't think you get proper fluid flow to the fronts.

The 4 piston calipers are infamous for needing seals every few years. They work fine when new, but an odd symptom of aging is they allow air to enter past the seals, while still keeping the fluid from leaking out. It gets almost impossible to bleed this way...you just can't get the air out of the calipers; air seeps in when you let up on the pedal during bleeding. To fix this, you might get lucky for some months with just gravity bleeding, but soon you must rebuild calipers.
This is assuming you have no pitting in the cast iron of the caliper bores. If there are pits, you may never get them to bleed correctly (air leakage). Do not despair, they can be sleeved with stainless...Inlinetube sells sleeved calipers. (actually, I think you can get new ones now too)

Dorman sells seal kits for the calipers, but they do not have the correct boots. Inlinetube sells rebuild kits, I'm not sure if they have the proper boots.

Good luck..

[Goatracer1]

Did you get fluid from the back of the master cylinder in the booster? If you hear air from the booster ,especially under the dash, the booster needs to be fixed/replaced what ever your other problem is.

[672brlbaby]

hi Dave,

will probably get the caliper kit and take them apart in april. will be taking the front end apart at that time, replacing the motor mounts and probably a hundred other things. they are not the original calipers. we put new ones on when I got the car in 2007. will try the 2 other boosters I have here and keep bleeding, may be get lucky for a few months. wanted to run around a bit til about new years, but i'll live til april if we don't get it going now.

thanks goat racer, there is definitely the air sound under the dash. please check these pics and see if you think these boosters are original style. I would like to keep the original style. we are pretty sure the MC is not original, no casting marks on it. there was crud between the MC and the booster so its very possible fluid got in there. is there a gasket for that spot? thanks guys.

Jim

[gtospieg]

I'm pretty sure you can vacuum test the booster. Hook up a vacuum pump to the port on the booster and see if it holds a vacuum. If it doesn't then the diaphragm is leaking and you need a rebuild. Good luck

[lust4speed]

The downfall of the '67 calipers was a design flaw in the caliper itself. Probably all calipers after these had the seal in the caliper and the piston slides against the permanent seal. This has two positive points, the piston can be anodized and is pretty corrosion proof, and the piston can be easily replaced giving a new sealing surface. The '67's (67-68) had the seal attached to the piston and the seal slides on the cast iron of the caliper, and it doesn't take much corrosion to have a leak. Other problem is the cast iron is pretty rough and that in itself contributes to seal wear.

A one-time whoosh heard when applying brakes is normal, and will be more noticeable if the foam is missing around the brake rod, but if you can continue to hear air escaping there is a problem.

[squidtone]

The same design 4 piston delco moraine calipers were used on all the vettes from something like 1965 to 1981. So those guys have used this brake system for years.
I think however the vettes might use a slightly bigger bore piston (but still fundamentally the same design)
One strategy some vette guys go with are kits to convert the corvette calipers seals to "O" rings. I think one company is appropriately named "corvette stainless steel brakes" I've been meaning to contact one of these companies and see if they would make a kit for the 67-68 A and B body cars caliper bore size.
But, still, all in all, I've been happy with my brakes. They work really well. If fact I really can't discern a difference in braking performance compared to my modern (albeit pedestrian plane jane) cars.

672brlbaby,
There is a small tab on one half of the booster on the outer edge that has a date code stamped onto it. I think it's a 4 digit code. You can check it out to see if it's original to your car's build date (of course plus or minus a month or so) I don't remember how to decode the date...maybe google to find out how...

[lust4speed]

I believe our brake bores are a little larger that the Vette's. I snagged a set of 4-piston calipers off a 67 Eldorado, but never disassembled them to see if they were the same. They're just sitting on a shelf for now. In hindsight, I should have grabbed the rotors, spindles and everything else.

My blue GTO came from the factory with the 4-piston brakes, and I commandeered the complete 1-piston disc brake system from a '69 Grand Prix for the Cruiser. The Cruiser stops really good, but the 4-piston equipped car definitely stops much better. My 2-cent seat-of-my-pants opinion is that the blue goat pulls down better and has better pedal modulation.