scottjamison

Hi All,

I am having something strange happening to my 68 brakes.
I have Wilwood brakes all around with a Wilwood master cylinder. MANUAL brakes. No booster.
I bled them months ago and have had a firm pedal. When I push hard on the pedal, it does not slowly sink at all. However, starting a month ago, every once in a while when I go to push the brakes, the pedal goes down about half way before it starts braking. If I let the pedal up and push again it is back to normal. It seems weird that it is very inconsistent as to when it happens, so it doesn't seem like there is air in there. Wouldn't that do it every time?

Figured I would check with you all before taking to the time to bleed the brakes again.
Any thoughts?

pauldana

Please post a picture of the brake fluid in the bowl


If the fluid is black or dark/greenish, this comes from water entering the system and then super boiling, when this is done it creates air in the system, giving the symptoms you are describing.

MelWff

would rotor runout cause this issue on Wilwood calipers? It does happen with factory calipers.

scottjamison

Looks ok

cagotzmann

Try this to see if you have any air in the MC

https://www.corvetteforum.com/forums...-cylinder.html

What brand of brake fluid are you using ?

Gunfighter13

Start by cleaning all the dirt out of the master cylinder, then flush out the entire brake system. Use DOT 5 fluid (Wilwood recommended). You may just be pulling dirt through the master cylinder causing a bypass of fluid.

Fredtoo

It sounds like the brake fluid is bypassing the pressure seals in the master.

I would rebuild the master.

scottjamison

It is only 6 months old. Brand new from Wilwood.
I have DOT3 in it right now so I just ordered a boatload of DOT5 and I will flush it.
between now and then I will back up my driveway which is steep enough to get the back of the MC higher than the front to bleed it more.

Fredtoo

I'm not a big fan of DOT 5 Silicone fluid.

With light pressure on the brake pedal, can you get the pedal to sink to the floor?

Does wilwood have a warranty on the master?
What do they think about the issues you are having?

scottjamison

Pedaldoesn’t sink to the floor with light or hard pressure.

Wilwood seems Ed’s to be closed today so I haven’t had a chance to talk to them.

scottjamison

I take it back. When it is acting up it does slowly go to the floor.
i backed it up and pumped it more. About five bubbles so small I almost couldn’t see them came out. That’s good. But then I took it for a test drive and it still does it once in a while.

I will I’ll call Wilwood and see what they say Monday.

Fredtoo

That is a big clue.
Make sure you tell them that.

I have run into a similar issue with M/C clutch masters that we fixed with Ate brake fluid.
Ate fluid tends to swell the seals a little.

however

brake are too important to use that as a cure.

scottjamison

I just talked to Wilwood. They think I have a stubborn bubble somewhere in the system. They suggested I reverse bleed them to try to get the bubble out.
It will be several weeks before I get around to that (Vegas this weekend and Savannah, GA next weekend) but I will try that. I will figure out how to build a fitting for that between now and then so I can use my power bleeder.

BTW he said that DOT3 fluid is fine. They only recommend DOT5 for show cars. So I am going to send back the $123 of DOT5 I bought!

Jstan2014

Lurking to learn. Good luck OP.

Fredtoo

A few issues with Silicon are that:

It is hard to bleed, air forms micro bubbles in it, that are difficult to get rid of.

If any water gets in the system it pools at the lowest parts. Since it is not miscible in water, it tens to stay there and cause rust.
Any residual water in the caliper will boil at a lower temp than brake fluid does.

It does not lubricate EPDM seals as well as brake fluid does.

Gunfighter13

This is the brake fluid I use in my cars and customer cars. Most parts stores sell it.
https://www.oreillyauto.com/detail/b...6231635?pos=16

scottjamison

What advantage does the synthetic fluid have over like DOT 3?

Gunfighter13

Boiling point and water contamination. At $16 a bottle it's worth the expense. Also this is compatible with DOT 3 and DOT 4 fluid.