im putting discs all around my bug what master should i use?

[kuleinc]

I take it its a safe bet to go with four wheel disk brakes and a stock super beetle M/C then? Right now my super is all drum and despite bleeding and adjusting and all that jazz, after driving down the freeway for a while the brake pedal goes to the floor once and then works fine, it is very firm and high around town, just goes to floor after being on freeway not using it for a while, not sure why. So I'm going to put new hoses, disk brake conversion, and stock SB M/C in, and pray for the best...

[FJCamper]

Gentlemen,

Four-wheel disk brake upgrades have a couple of hidden gotchas, and we've had experience with them. We installed four wheel disks on our 1965 Ghia (from Chirco), which ran and finished top three in Historic A class in the 2007 Carrera Panamericana.

The symptom is loss of pedal, which is usually fixed by pumping the brakes.

The problem can be either or or both of two things. Bleed down (in which case you do need the 2-lb residual valve for the rear brakes), or "knock back" which is rough-road suspension movement causing the caliper mounts to flex, and the pads get knocked away from the rotors.

We caught the double whammy on this. We had the standard caliper brackets, which are apparently prone to flex, and no residual pressure valve -- believing the special "4-wheel disk master cylinder" we bought for the install was right for the job.

After the race, Joe Chirco (a good guy and one of our sponsors) pointed me to info on how the FV guys counter the knock-back problem on swing axles, which are worse case for knock-back.

The axle is of course "floating" where it is inserted into the transmission, but the axle tube, to which the brake caliper bracket is bolted, is mounted rigidly. The problem is the rotor is mounted to the axle -- which has some in and out movement -- and as the swing axle swings, the rotor itself can pound the pads into the caliper!

The FV guys do a little machine work to make it all fit tighter.

For those of you with IRS rear ends, get the heavy duty or racing caliper brackets, and a residual pressure valve.

FJC

[kuleinc]

I've got IRS do I need a heavy duty bracket for the fronts too? I love FJCamper, he has the know how! FTW!

[turbobaja]

So........the risidual pressure valve is only used on the rear circuit, correct? And should there only be one installed in the single line running back to the 'T' or should there be a RPV on each of the rear lines after the 'T' ?

I've got (3) 2 psi. valves. 4 wheel discs on a baja with stock '73 replacement MC (dual ckt). I was going to install one valve on each front caliper line and one to the rear to do both back calipers (none installed yet)

I was thinking of trying without any valves initially and see if I need to add any for better pedal feel. Just want to make sure I don't add valves in the wrong order .

[kuleinc]

or more valves than you need, as I think, this creates undue break wear...

[FJCamper]

Gentlemen,

HD brackets for the rear only, and one 2lb valve in the single brake line to the rear.

The single valve just keeps up a little pressure to stop the pads from retreating. It doesn't take much.

If you run a brake proportioning valve as well, it should be between the master cylinder and the residual valve.

FJC

[turbobaja]

Gentlemen,

HD brackets for the rear only, and one 2lb valve in the single brake line to the rear.

The single valve just keeps up a little pressure to stop the pads from retreating. It doesn't take much.

If you run a brake proportioning valve as well, it should be between the master cylinder and the residual valve.

FJC

Perfect. Thanks alot FJC. I've got a prop vavle too. Another one of those 'got it if I need it' kinda things. I'm starting to think it would be easier to just install both when everything is going together rather than try and add them later.


Thanks again for shedding some light on this subject. Your experience is very much appreciated.

[bender]

[bender]

FJC is correct....one 2lb valve is all we use...The MC is older MB 23mm..It will put you through the windshield ...It bolt's up with no mods.

[kuleinc]

I hate to sound stupid BUT:

I've replaced everything from the stock master cylinder (with a stock replacement SB master cylinder as that's what I drive) to the wheel cylinders. Hoses, shoes, switches, blue lines, EVERYTHING.

I also got the front disk conversion kit for my super, which came with DUAL piston calipers. Awesome, right?

WRONG, I have a SUPER soft pedal, and it does stop the car very nicely, but the pedal is so near the floor my leg is hardly long enough to push it that far.

I've bled it more times than I can count and no more air comes out, AFAIK, and I did the MC prime thing with my thumbs over the holes.

Do these double calipers up front need a different MC or am I missing something here?

I've adjusted the rear stock shoes very tight twice now and doesn't seem to help.

I do notice that when the hand brake is ON I the pedal only goes half way to the floor (still too low) and is A LOT more firm, so is something going on with the back breaks causing this poor pedal feel and excessive travel, or is the MC wrong for the job?

I did have a piston pop out of a wheel cylinder by accident, but I'm pretty sure I put it back together right, I put the little cup (bowl side first) back in and then the seal and plunger thingy... But maybe thats where I'm losing pressure not sure, and kind of stuck at my house till I get this sorted...

Thanks for any help!

FYI I have front disk rear drum, in case I wasn't clear.

[turbobaja]

I'd be looking at the rear drums if applying the park brake makes such an improvement with pedal feel. I just installed front disks on our '74 Super with drums in the rear and the pedal is absolutely rock solid. I put a new Stock SB MC in and all 4 rubber lines got changed out for braided stainless. How well do the rear shoes fit inside the drum? If the adjusters are set with the shoes starting to drag on the drums, how much travel do you have with the park brake lever? Should be only 1-2" to get good park brake apply pressure. If you've got more park brake handle travel than that with correctly adjusted rears, somethin's funny with the rear shoes. Are they new? Could just need to get the brakes seated well before getting them adjusted and 'feeling' good.

[kuleinc]

After driving to work today (scary), I think that I didn't get all of the air out of the M/C as sometimes the pedal feel is good, but then drops and other times it just goes to the floor.

[turbobaja]

Air in the system would always give you soft pedal feel. Sounds like you've got a bad Master Cylinder. I put 3 new MCs in our SB that all leaked internally within a year. I got a German unit now and...........so far so good.

By the way, every time I suspected the MC was bad it was because the pedal feel was very unconsistant. Usually a slow/normal apply would give long pedal travel, especially if it had been a few minutes since applying the brakes. If I jammed on the pedal it would have a firmer feel and travel less. Everytime, if I pumped the pedal, I would get a firm pedal on the second pump. Its an internal MC bore/seal problem. Every time there was considerable amounts of brake fluid inside the rear dust/water boot where the push-rod goes into the MC. Check there for fluid and you'll know if you've got a questionable MC.

[kuleinc]

Its a raybestos brand one, but its all german inside the box, I'll check the boot for fluid tonight when I try bleeding it again...

[Derrick from NC]

Bender59 what year & model MB mc are you using?

FJC is correct....one 2lb valve is all we use...The MC is older MB 23mm..It will put you through the windshield ...It bolt's up with no mods.