Itinerant Air-Cooled

OK - I just got a good German MC.

Is this a simple R&R job, or is there more to it? I have read about some MCs needing "bench bleeding" but not sure what that is and when it is required.

My MC came with the big o-ring that mates to the booster. Do I need anything else?

Thanks

Mr Blotto wrote:OK - I just got a good German MC.

Is this a simple R&R job, or is there more to it? I have read about some MCs needing "bench bleeding" but not sure what that is and when it is required.

My MC came with the big o-ring that mates to the booster. Do I need anything else?

Thanks

Get a reservoir on the master cylinder, unless it already came with one.
Fill it with a little fluid. Get the 3/8" drive extension out and use it as a pushrod. Remove one of the caps from either the front or rear port. Push the extension and release and repeat until you get a squirt of brake fluid. Now cap it and remove a cap in the other circuit. Repeat. Recap.

You can remove the old master cylinder easily enough by bending brake lines out of the way, but please be careful not to bend under the fitting itself, or you will find that it jams up when you are trying to find the threads on the new master cylinder.

Clean out the booster if it has a pool of brake fluid down inside. Get the lines started before you have the new master cylinder fully tightened, and it will make it easier to get the threads started. Clean and smooth the flange where the master cylinder joins the booster, you need an air-tight seal.

I bleed at the master cylinder itself by loosening the lines one at a time while I pull down hard on the brake lever under the car, do not release the lever until you have the fitting re-tightened. It IS fun.
Colin

Hi from the voyeur watching from the shadows. I have a question.

Amskeptic wrote:I bleed at the master cylinder itself by loosening the lines one at a time while I pull down hard on the brake lever under the car, do not release the lever until you have the fitting re-tightened. It IS fun.
Colin

Is this procedure in order to continue bleeding the master cylinder? Once this is done, do you continue on to each wheel cylinder/caliper? I promise I'll write it down this time, but what order do YOU prefer to do your bleeding? Farthest to nearest? Nearest to farthest? Nearest to the current moon phase?

dtrumbo wrote:Hi from the voyeur watching from the shadows. I have a question.

Amskeptic wrote:I bleed at the master cylinder itself by loosening the lines one at a time while I pull down hard on the brake lever under the car, do not release the lever until you have the fitting re-tightened. It IS fun.
Colin

Is this procedure in order to continue bleeding the master cylinder? Once this is done, do you continue on to each wheel cylinder/caliper? I promise I'll write it down this time, but what order do YOU prefer to do your bleeding? Farthest to nearest? Nearest to farthest? Nearest to the current moon phase?

I was able to bleed at the master cylinder only and did not need to bleed the rest. It is a good idea to bleed the rest. R/R L/R R/F L/F.
Colin

Amskeptic wrote:It is a good idea to bleed the rest. R/R L/R R/F L/F.
Colin

Thanks... back to the shadows.

dtrumbo wrote:Hi from the voyeur watching from the shadows.

You sick bastard

Amskeptic wrote: Get a reservoir on the master cylinder, unless it already came with one.
Fill it with a little fluid. Get the 3/8" drive extension out and use it as a pushrod. Remove one of the caps from either the front or rear port. Push the extension and release and repeat until you get a squirt of brake fluid. Now cap it and remove a cap in the other circuit. Repeat. Recap.

You can remove the old master cylinder easily enough by bending brake lines out of the way, but please be careful not to bend under the fitting itself, or you will find that it jams up when you are trying to find the threads on the new master cylinder.

Clean out the booster if it has a pool of brake fluid down inside. Get the lines started before you have the new master cylinder fully tightened, and it will make it easier to get the threads started. Clean and smooth the flange where the master cylinder joins the booster, you need an air-tight seal.

I bleed at the master cylinder itself by loosening the lines one at a time while I pull down hard on the brake lever under the car, do not release the lever until you have the fitting re-tightened. It IS fun.
Colin

Thanks!

Amskeptic wrote:
Clean out the booster if it has a pool of brake fluid down inside.

Does this mean that it is okay to reuse a booster that has been tainted by brake fluid?
I have a suspicion that my MC is bad. I am low on fluid and don't see where it's going so I'm assuming it is in the booster. While researching this many say that the booster is toast once fluid gets inside. Can I reuse my booster or should I get it rebuilt?

^^^^^^
brake fluid levels go down considerably as disc brake pads wear out. the amount of fluid needed to keep the calipers full would surprise you. when you spur of the moment decide to check brake fluid level, and haven't checked in quite some time, it will appear low. especially if the rear drum brakes need adjustment. wheel cylinders have to be kept full as well. think of the combined movement of the caliper and rear wheel cylinder pistons outward in their bores as pads and shoes wear.

yondermtn wrote:

Amskeptic wrote:
Clean out the booster if it has a pool of brake fluid down inside.

Does this mean that it is okay to reuse a booster that has been tainted by brake fluid?

When I replaced my master cylinder last summer, I asked the boys at Kombi Haus about that. The feeling was that as long as I got all the brake fluid out of the booster, and that everything was 100% functional afterwards, it was probably OK. I guess I'll find out by and by. But so far, so good.

JLT wrote: I asked the boys at Kombi Haus about that. The feeling was that as long as I got all the brake fluid out of the booster, and that everything was 100% functional afterwards, it was probably OK.

Absolutely. You have nothing to lose by cleaning out the booster and trying it. I would only add that brake fluid does absorb water and can cause rust in the booster's control valve. A little spray of water-displacing oil helps, right into the opening where the master cylinder will bolt up. If master cylinder is already in, you can spray in the air-inlet on the pushrod, soak the foam filter and the normal operation of the booster will bring it to the control valve. I did a booster free up in Missoula Montana, it had rusted "on" (pedal would not release). Took it out, hit it with PB Blaster and pounded the control valve carefully. Rusty crap bled out. The booster finally let go of the control valve and it worked like a charm after we got in the bus. Pretty rugged stuff, but it does appreciate being dry and clean.
Colin