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Brake cleaner and master cylinders

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Scorch

Scorch

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I used some brake cleaner spray to clean the inside of my brake master cylinder, now I cannot get the brake to bleed the air out & build up pressure. I even used my bleeder vac pump and bench bled the mc. Does the brake cleaner have a bad effect on the piston and cup parts?

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Did you read the instructions?
 
I doubt it. It evaporates fairly quickly. It's harsh as far as chemicals go, but shouldn't break down the rubber in the master cylinder as quick as it does plastic.

You most likely have air trapped at the banjo bolt. Unclamp the master cylinder and point the lever straight up so that any air trapped in the banjo bolt goes up to the MC. Then squeeze the lever a few times. You'll prolly feel it firm up.

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That stuff is for external use only. The rubber parts inside should be washed in clean brake fluid only. The cleaner will damage the rubber cup in the master cylinder beyond safe usage.

Time for an overhaul with new rubber bits.
 
ed29 said:
That stuff is for external use only. The rubber parts inside should be washed in clean brake fluid only. The cleaner will damage the rubber cup in the master cylinder beyond safe usage.

Time for an overhaul with new rubber bits.
Click to expand...

+1
 
Hmmm, I sort od disgree. Brake clean is specifically made to clean brake components, even the soft parts. I use it almost everyday to clean some of the nastiest master cylinders and calipers you've ever seen.

Now with that said, solvent, like in a parts washer or "carb cleaner", will damage the soft parts.

My professional experience is to........fill the master cyl, and lightly work the lever only a small amount, like 10% of the lever travel. Look inside the reservior and watch as the bubbles bleed themselves out. When the bubbles stop coming out, wait a few seconds and then do it again. Keep doing this unitl there are no more bubbles. Then try to bleed the brakes normally.
 
The Big Spank Daddy said:
Hmmm, I sort od disgree. Brake clean is specifically made to clean brake components, even the soft parts. I use it almost everyday to clean some of the nastiest master cylinders and calipers you've ever seen.

Now with that said, solvent, like in a parts washer or "carb cleaner", will damage the soft parts.

My professional experience is to........fill the master cyl, and lightly work the lever only a small amount, like 10% of the lever travel. Look inside the reservior and watch as the bubbles bleed themselves out. When the bubbles stop coming out, wait a few seconds and then do it again. Keep doing this unitl there are no more bubbles. Then try to bleed the brakes normally.
Click to expand...

I agree. If you have rubber lines you can grab the line and GENTLY pull on it in a straight line with the fitting on the brake caliper and the stretch will also remove bubbles from the line.

Any time you are using the bleed fitting on the caliper to bleed the line, the bubbles tend to go up the line as fast as you try to push them down with the brake lever. In that case, you have to bleed from the top banjo bolt or use quick flicking motions on the lever of less than 10% of the lever throw.
 
I only use brake cleaner on the pads. It is a lot like electrical cleaner and I would expect it to eat up the rubber parts.
Line 2 of the instructions on my can: Protect all rubber parts and painted surfaces.
Brake cleaner is used to clean oily residue off brake linings and honed cylinders.
Vee Stroms Rock!!! RH
 
Yeah, I didn't think "Protect all rubber parts" meant in the brake system I was trying to clean. I could have used gasoline to clean if I wanted to protect my rubber parts :)

I've got a rebuild kit on the way.
 
Brake cleaner won't hurt it. I use it all the time on things like this without ever an adverse affect. I would dissasemble the master cylinder and make sure it didn't get assembled wrong the first go around. Also make sure both hole leading into the reservoir are open and not clogged.
 
Why do you think I asked if they directions were read? Not all brake cleaners are the same--some will eat plastic and rubber, some won't, and some will eat some kinds of plastic and rubber but not others. Kind of explains the varied results reported. I don't think anyone's report is 100% wrong, but neither is anyone's report 100% right. Read and follow label directions on any product.
 
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