MDL

I just rebuilt all 4 calipers on my 88 and replaced the pads. I have a new power bleeder. I put everything together and began to bleed the brakes. The rears are bled and there is a slight drag on the disc as there should be. No problem there. The problem is this... I bled the fronts and all the air seems to be out of the system, however the pistons have not moved. If I remove the pads and push on the pistons they they move freely, not bound up at all. I bled the brakes in the correct order. right rear left rear right front left front. I used about 10 lbs of air pressure on the power bleeder. I went around the car 4 or 5 times. Why would I have no air bubbles and no pressure being applied to the pistons in the front?

Dan.

UPDATE: Problem solved. My neighbor just came home and I had him help me bleed the brakes the "old fashion way". Worked like a charm. I guess the power bleeder does not have enough pressure to push the fluid through the first time, or maybe I just chickened out at 10 lbs. Anyone else ever experienced this?

Steve Weiner-Rennsport Systems

MDL:

Pressure bleed at 15-17 lbs. That works better,.... Plus, tap the calipers with a hammer to dislodge the tiny bubbles that attach themselves to the piston's chambers whiule bleeding each one.

The old fashioned way can work very well, but it really puts your MC at high risk of failure due to its piston overtraveling into an area of its bore thats usually somewhat corroded.

MDL

Steve.

After letting the car sit for about 1/2 hour I bled all 4 again with my wife helping, and still got a good bit of air at each caliper. The pedal is better but not like it was with the old pads and before caliper rebuild. Do to my schedule, I won't have a chance to bleed them again until Sat.

What is the typical nature of the failure of the master cylinder when bleeding the old way? Would it make it leak or just suck air? I guess what I'm asking is how would I know if the M/C has gone bad?

Steve Weiner-Rennsport Systems

Hi Dan:


Brake bleeding can take a bit of extra patience to rid the system of trapped air in the calipers and MC, especially if one doesn't keep the reserviour full (some folks are reluctant to fill their pressure bleeders as required to work correctly). It can take a 2-3 litres of fluid to finish this job.

The MC fails when the piston seals get extended to the bottom of the housing well beyond the normal travel and this results in a a pedal that slowly sinks when the pedal is applied hard. One needs to pump it up to get a hard high, pedal. You'll not suck air unless it leaks at the seals or at a fitting.

MDL

Hey Steve,

The good new is the pedel does not sink as you discribed, it stays where it stops. I did not use fluid in the power bleeder either, shame on me. I guess I'll have to get off a buck and buy some extra fluid before next Saturday. (Glad I didn't use Castrol LOL) I used ATE Blue. I've been through 2 cans so far and I feel like I have gotten most of the air out, but I'm sure there is more. I think letting the car sit for a week before it's bled again will help.

Dan.

Marc Shaw

I have found thumping the calipers with my hand as well as tapping the brake lines a good way to dislogdge air as it does not damage the finish on the calipers like a hammer might.

Marc

Steve Weiner-Rennsport Systems

Hi Dan:

Those power bleeders were designed & intended to be filled with fluid and will not work properly if they are used, dry. In every case that I've seen someone who had difficulty ridding the system of air, that individual failed to fill lthe bleeder tank so NO air can enter the system.

These things work very well if correctly used and honestly, brake fluid is a pretty cheap product to buy, especially when one is not doing this all that often.

Put 2 litres into the bleeder and repeat the process; I think you'll be very pleased with the result.

With regard to tapping the calipers while bleeding, I use either a plastic hammer or a small brass one and if carefully done, will not damage any paint.

MDL

Ok Steve, I'll order 2 liters in the morning. What is the shelf life of the fluid unused in the power bleeder? Could the unused portion be put back in the original can and sealed for future use?

Dan.

randomhick35

my favorite tool is a glob of lead that i melted onto a steel rod. very dense, very soft, very effective, yet slightly toxic...

Steve Weiner-Rennsport Systems

Throw it away. After 30 days, its boiling point has decreased to a point where you don't want to use it and once a can is opened, it begins absorbing moisture.

I think its important to maintain some perspective here; brake fluid is far cheaper than gasoline, brake pads, tires (and a good dinner).

Its just a consumable like the above that one deals with when maintaining any kind of car and the LAST place to skimp on $$. I saw a local customer do $34K damage to his perfect '92 C2 Turbo at the track because he reused old brake fluid and they boiled on the 4th lap. Spending $24 on two litres of fluid would have been a better bargain, IMHO.

MDL

Steve, That is kind of what I thought as well. The last thing I would want do is skimp on anything to do with safety. I just want to make sure I use ALL my $$ wisely You are right on with your perspective. In the big scheem of things it really is a not a big expense.

I REALLY appericate all your help with this.

Dan.

Steve Weiner-Rennsport Systems

No worries, matey. Thats what I'm here for,....

MDL

I finally got a chance to bleed the brakes with fluid in the bleeder. I pumped it up to 17 lbs and bled all 4 calipers again. What a difference!!! I knew the second I began to pump the pressure bleeder and saw the blue fluid going through the tube into the master cylinder that it was gong to work. The brakes work great and the pedal feels nice and firm.

Thanks again Steve.