Rear drums won't bleed!! - Team Camaro Tech
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post #1 of 6 (permalink) Old May 18th, 08, 02:54 PM Thread Starter
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Tim
 
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Rear drums won't bleed!!

I just added front disc brakes to my 68 from SSBC (via Summit). The stock drums are on the reat for now. The installation has progressed well. I have begun to bleed the brakes and tried to start with the rear but could not get them to bleed. I then started with the fronts. They bled well and appear to be air free and working well.

As I started again on the rears I couldn't get them to bleed like the fronts. After pumping the breaks to pressurize the line and holding my foot on the pedal the pedal no longer hits the floor and holds half way. With the pressure still on the brakes and loosening the bleeder valve, the fluid only barely dribbles a few drops then stops. The break pedal never fully released to the floor like the fronts did when those were bled.

The bleeder valve was removed from the back of the rear drums and they did gravity flow. I didn't pump the brakes with the valve removed from the drums to try and avoid a mess!

The rear proportioning valve is positioned properly as per the instructions and the brakes were attempted to be bled in the positon recommeded by SSBC as well as fully turned both ways.

The master cylinder was bench bled and appeared to function properly, but obviously not under pressure.

I cannot figure out if this is a blockage in the rear line somewhere since it gravity drained or is it a problem with the proportioning valve or master cylinder itself.........or is it me????

What the heck am I doing wrong?

Tim
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post #2 of 6 (permalink) Old May 18th, 08, 05:07 PM
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Jim
 
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Re: Rear drums won't bleed!!

It just takes a while... thats a long skinny brake line, and the front third of it is all air.

The pressure in the front's is why the pedal won't go to the floor. You might loosen one of the front bleeders and put a hose from it into a can of brake fluid, that will give you a full stroke again.

I would use a mitivac in one of the rears to suck all the old fluid and air out. They make em that are made for bleeding brakes, or I just used a regular on, a plastic quart brake fluid bottle, a couple pieces of hose and some silicone.

You could also just open the rear bleeders and let gravity do it, it might take a couple of days.

Regardless, be sure not to let the master run dry.





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post #3 of 6 (permalink) Old May 18th, 08, 05:08 PM Thread Starter
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Tim
 
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Re: Rear drums won't bleed!!

I just removed the rear fitting to the master cylinder and left it in place and attempted to "bench bleed" it in the car. It wouldn't bleed and clear the line like it did on the bench. I just kept getting bubbles in the line despite keeping a "closed system" of fluid while attempting to bleed it.

I removed the master cylinder again and inspected the O-rings and housing for the pump. It looks clean......any suggestions other than get a new one!!! lol!!

Thanks

Tim
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post #4 of 6 (permalink) Old May 19th, 08, 03:22 AM
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Re: Rear drums won't bleed!!

There is air in the master cyl. During the bench process, push in for fluid, place finger over hole, release for return stroke. Plus, all the tiny pores in the cyl bore.

You won't get all the air out, it will come out in time. You're looking at a large cylinder volume, but a small hole from the reservior. Every time you slowly stroke it forward, you'll see air bubbles come out the hole.

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post #5 of 6 (permalink) Old May 19th, 08, 05:27 AM
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Re: Rear drums won't bleed!!

Two thing to look at, the repop brake conversions including master booster..... have been a problem. They made the shaft from the master to the booster just a touch too long.
I will cause the master to not fully retract. When you push the pedal it is not picking up fluid and pushing it in the line. If your pedal moves easy while pumping it thats the problem.
to test this try using a couple of whashers on each stud of the booster then mount the master. Try to bleed again.
If you bench bleed the master and have a real hard pedal you could have a problem with the rear hose above the axle. If its original change it no mater what.
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post #6 of 6 (permalink) Old May 19th, 08, 02:15 PM
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Re: Rear drums won't bleed!!

Could be as simple as blocked bleeders....take them right out, and clean or replace.

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