Rear disc brakes and a soft peddle

Ron,

I installed RotoHubs on the rear of my car and like you the pedal had more travel than I wanted. I haven't yet adjusted the rod between the pedal and the back of the master cylinder yet, that may do it.

Reading an article in HotVw magazine re brake conversions: "The best master cylinder for the disc brake conversion is one designed specifically for this application, such as the '67 and later type 3 unit, also used on the 79-74 Karmann Ghia. This carries a 311-611-015J Vw parts number..." It goes on to say, "Even the 72 and later Type 1 master cylinder, which does not use the residual pressure valves, is not the optimum part for this application, due to its larger internal drillings."

I am planning on replacing the rubber brake lines so I will likely change master cylinders at the same time.

I know we've covered this somewhere, but I couldn't find the posts. I installed my rear discs and I'm finding that my brake pedal goes down too far (half way) when I apply the brakes. Someone had mentioned that it would be a good idea to install a different master cylinder (from a bus?). Anyone remember?
Ron
(Message Edited 7/29/2003 6:01:42 PM)

Thanks Eric.
Okay, that should read soft PEDAL. You can travel around and peddle your goods and you can have a soft brake pedal, but you can't peddle soft brakes....
Ron

Ron,

A while back John Steele posted something that I found interesting but haven't tried yet. He said with new rear disks if you can't firm up your pedal by normal means to try bleeding the front right first, front left and then the rear. He gave a logical explanation but I was having a conversation with Mr. Budweiser at the time and I don't recall his reasoning.

Try this before you go out and buy lots of parts. There's an adjuster on your brake pedal. Adjust it so that the pedal has only 1" of slack. Turn the screw OUT. You might find that this is all you need to do. It worked for me.

When I first installed the rear brakes the pedal was near the top and firm. Unfortunately, the passenger side rear brake was dragging and I had to take out a washer to center the caliper. That's when the pedal firmness changed. The brakes work fine....the pedal just goes down too far.
Trying something that won't cost me any money is ALWAYS the right thing to do (because, Lord knows, I've spent enough money on this car). Is the adjustment on the base of the brake pedal itself?
If that doesn't work I've found the Type 3 master cylinder at the California Imports site, and they're only a 45 minute drive from my house.
A new master would probably be a good idea, since the one I have is 20 years old and while I was bleeding the brakes the pedal went to the floor a number of times, which is not a good thing.
Ron

Ron, is it possible that the rear calipers are backing off after you release the pedal? If you apply the brakes, and then apply them again right away (pumping the brakes), is the pedal firm then? If so, then perhaps the rotor is not turning true. This would open the caliper up, requiring more pedal travel to get the pads into contact with the rotor.
Just a thought,
Ron

Ron B,

I can scan and send you the Hot Vw article about the T3 master cylinder if you like. Maybe you should talk with a pro before spending the money, that said, a 20 year old master cylinder is not a bad thing to replace.

Ron: Does the pedal just have more travel than it use to but still feels firm every time at the bottom or do you have to pump them to get a firm pedal. If it has too much travel you will probably need a residual pressure valve. This is a small check valve (about 2 psi for disc brakes 12 psi for drums) that you should install in the rear brake line just as it leaves the master cylinder. This will stop the fluid draining down and back to the master cylinder, which pulls the pistons and pads away from the discs. So once installed the pads only have a couple of thou to move before they touch the disc instead of 100 or so. Most of the residual pressure valves that come on the master cylinders are the higher pressure ones for the drum brakes (it takes more pressure to hold the shoes in close proximity to the drums than it does pads to disc). Using the drum pressure valve on a disc setup will cause the pads to drag on the discs all the time.

The newer stock bug master cylinder is a dual circuit style. If you were to develop a leak in the braking system chances are that you would only loose two wheels. The bus unit that can be retrofit is a single circuit style. Loose one wheel and you have no brakes. Just another thing to consider. Getting a residual pressure valve for the front and rear first is the safest thing then swap to a larger master cylinder if that is not enough.

If you can pump your brakes up then you just need to bleed them again. Don

Pedal goes half way down and then gets firm. Car stops like before. Going to put some more miles on it before I decide.
I don't know about the rest of you, but sometimes I think I will never get this car totally right. Washed it last night and then took it for a drive. Felt like it was running on 3 cylinders. Ran like crap. Then, going down the mountain road (I live on a mountain side overlooking the Fraser Valley) my tail pipe became loose and dragged on the ground....and I've got two small oil leaks. Grrrrrrr!
Ron

Bill is right about the master cylinder actuating pushrod but you can have less than 1.0 mm (about .039") clearance when the pedal is fully released; about .5 mm or .020" should be OK.

Re Wildwood "residual pressure valve," I read in a different Hot VW article that they are the ticket for a low pedal after installing RotoHubs in the rear. I purchased two, not sure if they should be mounted by the mastercylinder or back at the brake hub. Anyone?

Ron: I finished up my rear rotohub conversion a few weeks ago. I put in the 4 lb. residual valve in-line to the rears. John at Jps told me to bleed the fronts first because of the valve keeping the rear circuit
pressurized somewhat. I also adjusted the bolt at the base of the brake pedal. This sets the length of the plunger that contacts the piston in the master-cyl. The manual warns to not turn it in to tight. The plunger
has to be 1 mm. clear of the piston with no pressure on the brake pedal. If you turn it in to far you'll push the piston in, which will cause the brakes to drag. I did get a good bit of slop out of mine as it was set
way too loose.
BD
(Message Edited 8/2/2003 3:24:51 PM)

Erik: You should only need one valve. Mine threaded into the port for the rear circuit at the master cyl. then threaded the line into the valve.
Pretty simple if you can work the line into position. I had just enough of the line to make it into the valve. Although I don't know if it would hurt,I have no valve for the front brake circuit.(CB Perf. didn't prescribe it.) The valve, in addition to properly adjusted e-brakes, keeps the pads in close proximity to the rotors. This helps with the pedal travel thing.
BD
(Message Edited 8/2/2003 3:27:57 PM)

Thanks Bill. Maybe I will be lucky with the line being long enough too.

I have the type 1 master w/rear disc brakes and realy didn't have a pedal problem. Bleeding them were quite a task. Had to go around them three times to get all th air out. The problem I am having is the rears seem to be locked up. I do have the rear disc w/ the emergency brake mechanism. The cables are set loose. I have to use a pry bar to spin the rear wheels. The right rear pads are half gone with only 1000 miles on them. Any suggestion to fix this problem?
Joe S

I had a conversation with a brake specialist whom has been in the racing industry for twenty years.. He recommends installing a 2# Residual Valve in series with your back brakes. The valve acts a sort of check valve which will not let all the pressure revert to the MC. This keeps the pads in close proximaty of the rotors. This item cost around $20. He also said to check and see if you are getting the full stroke of the pedal to MC piston.

Joe: Check to make sure the calipers are centered exactly over the rotors. The best way to see is to pull the pads and measure the distance from the rotor to each side edge of the caliper. I had to try different washer shims between the caliper and the mounting bracket until I got it just right. I would also make sure the plunger at the bottom of the brake pedal is not set to long into the master cylinder. This can cause brakes to drag.

BD
(Message Edited 8/5/2003 4:35:54 PM)

I also had to move my caliper so that the rotor was centered. Took out a thick washer and put in a thinner one. Everything looked fine (to begin with) and then I torqued the axle nut and that moved the rotor in slightly, causing it to drag.
Ron

That was a good catch Ron! I'll have to double check mine to see if it moved out of center.
Thanx!
BD

I took the car for a spin around the block. I heard and felt a vibration from the right rear. When I returned home I took the caliper off the car. The inboard pad was warped and cracked in half from the dragging brake. The rear rotor is centered. Is there some sort of procedure to set the rear emergency brake ? Is there a certain amount of tension to be set? The brake tech guy I talk to had not clue about the aftermarket empi brakes.

Joe: My e-brake locks the wheels with 4 or five clicks of the handle.
Pull up your e-brake boot and check the cables to see if they are set evenly. The metal piece that they go thru should be sitting straight on it's nipple, not cocked towards the right or left.
BD