Jud Chapin

I just rebuilt the front calipers and master cylinder and installed new front rotors, hoses and pads. After bleeding the system, both by gravity and with a Mity-Vac pump, the pedal feels fine and the brakes operate normally except they will not lock up when trying a hard stop. Any ideas?

Durango_Boy

First try on smoother surfaces or loose surfaces. Maybe you have too good of traction and tire foot print.

If you have trouble even when it should be easy then I would think you still have air, maybe trapped in the master where the vac gun would be almost ineffective. Did you tap on the master with a dead blow rubber mallet when bleeding?

Jud Chapin

I'm pretty sure they'd lock up on gravel as they're not that bad. When bench bleeding the master, while not tapping on it, the tubes were bubble free. There was some air still coming out of the valves on the bottom of the reservoir but I believe that is normal and I couldn't get to stop anyway. The only thing I noticed was that after driving there was a very slight amount of fluid on the tubing thread going into the master which I then tightened. I wonder if it's possible if that that little bit ofleaking could suck air back into the m/c?

bashcraft

If the pedal feels good, you should be able to lock them. Did you have the rotors cut? Maybe the new pads glazed.

Jud Chapin

The rotors are new so I didn't have them turned. I pulled the rf pads and they are not glazed.

Durango_Boy

Were you bleeding with standard bleed screws or check valve bleeders?

I had the same problem almost when I was bleeding...I was getting TONS of air out. I came to find out the air was leaking past the threads of the bleeders, and then back out. I was not even really bleeding. I replaced them with check valve bleeders that had a much better thread seal, and it worked like a charm and I got all the air out.

Jud Chapin

I don't think the bleeders should be a factor when gravity bleeding, should they? Anyway, I posed this question above regarding bench bleeding the m/c. When doing the bench bleed, the tubing showed no bubbles after 15/20 pumps. However, there is a valve (or something) in the bottom of each section of the reservoir that I continued to get bubbles from, even after many, many pumping strokes. Should there be no bubbles coming from them for a proper bench bleed?

Artsvette73

Threads on the bleeders wont be a problem unless you are vacuum bleeding. I wrap the bleeder screw with teflon pipe tape. Works great with the vac method.

Durango_Boy

It is my understanding that ANY air bubbles visible in the fluid, even while bench bleeding, means air is being pulled in from outside either at the bleeders or past one of the piston seals.

ANY air visible in the fluid means air in the system.

Jud Chapin

Well, maybe that's my problem. Guess I'll pull the m/c off and try to get the bubbles out from the valves.

Durango_Boy

I think you can do it while it's in the car. The fluid won't drop down into the lines too far because all the bleeders are closed. Just be ready to install the nipples and tubes as you pull the brake lines. Then, making sure you have a good seal with the nipples, pump and pump, and tap on the master with a wooden handle or a rubber mallet and keep pumping.

big_G

Don't pull the m/c off. The small bubbles will work their way out. Might take a while, but re-bleed the calipers to help it move along.

bashcraft

Maybe you're using you "girlie foot" to press the brake pedal. Try the other one.

Jud Chapin

Thanks for the tip. I went for a half hour drive or so and the brakes are now fine. I guess the bubbles coming from the bottom of the reservoir worked their way out by themselves. Thanks again...You da man!

Durango_Boy

Where do you think the bubbles went? It's a closed system...not vented so that air is purged automatically. Air just moves around if it's in the system.

turtlevette

NOT true.

Bubbles just below the master could work their way out as the pedal is pumped.

Remember air is lighter than brake fluid.

Durango_Boy

But out where? Brake fluid can get out anywhere that air does.

turtlevette

the bubble could slowly work its way up to the master. When you pump the brakes the master purges the air bubble.

I've run my master dry before and had the spongy brakes. If you let it sit a while and pump the brakes the air will work its way out.

Durango_Boy

I'm sorry but I have to disagree. Is there a source you have that tells you this?

If all you had to do was let the air rise, and pump the pedal then no one would have to bleed their brakes, and runout rotors wouldn't cause so many issues with spongy brakes.

Big2Bird

Just tear it all out, and install BIMBO brakes. All the great cars of our time have them.