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Brake System Questions


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11 replies to this topic

#1 general0ne

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Posted June 7, 2004 at 05:28 pm

I was (hoping to be) finishing up the brake work on my '68 Polara today. I upgraded it to power brakes, with a new makter cylinder as well. I was bleeding the brakes without much luck, so I went to Pep Boys and got two sets of SpeedBleeders (in the HELP! section). Front brakes went fine (the fluid coming out looked more like grease than brake fluid, and I started on the rear wheels. Passenger side went okay, and when I went to the driver's side, it had a smaller bleeder fitting :blink: Okay... so I didn't do that one right now. Tried the brakes out, and they worked well enough to get the car moved to where it's supposed to be in the driveway. I noticed though, that I still have to pump the brakes to get them to work, and the pedal easily goes to the floor, even with the engine off. With the engine running, I can push the pedal to the floor with one finger...

I noticed that with the master cylinder cover off, when I push on the pedal, brake fluid will bubble up into the resivoir. If I push quick enough, it will actually squirt out the top... I'm thinking that I got a messed up master cylider... Isn't there supposed to be a check valve or something in the master cylinder to keep the fluid in the pistons?

I know that the front brakes have been bled properly, since there were no more air bubbles going through the hose, and clean fluid was coming out. The rear brakes probably need redone, since I didn't bleed the one side, but even with only the front brakes working properly, it should still stop the car fairly well at less than 5 MPH. What I did was let the car coast forward in the driveway, then stomped on the brakes, and it pretty much just coasted to a stop in about 2 feet. If I pump the brakes about 5 times and do the same thing, it'll nearly send me through the windshield. In both cases, the brakes will hold as long as I keep the pedal down.

Any suggestions :huh:

#2 KOG

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Posted June 7, 2004 at 06:18 pm

Everything sounds normal for a partly bled system. Continue with the rear bleeding.

#3 Bob Lincoln

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Posted June 7, 2004 at 08:56 pm

I noticed that with the master cylinder cover off, when I push on the pedal.

Don't do that. You'll aerate the fluid and possibly splash it on the paint, eating through it instantly.

You want to top off the fluid, REPLACE the cover, then pump the pedal and open the bleeder valve with the pedal down. Close valve before releasing pedal so as not to suck air back in.

Then you have to remove the cover and refill what you pumped out at the bleeder. Tedious, but you can't pump the pedal with the MC cover off and expect to keep air out.

#4 general0ne

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Posted June 8, 2004 at 12:58 am

Don't do that. You'll aerate the fluid and possibly splash it on the paint, eating through it instantly.

Heh... it already splashed on the paint on the inner wheel well... Didn't eat through it, but it did get the grease and crud off :unsure: There's a nice 'ring' on the rad support where the bottle was sitting, though. The grille support was repainted (it's got brush marks on it), while the wheel well still has the original paint...

You want to top off the fluid, REPLACE the cover, then pump the pedal and open the bleeder valve with the pedal down. Close valve before releasing pedal so as not to suck air back in.

Then you have to remove the cover and refill what you pumped out at the bleeder. Tedious, but you can't pump the pedal with the MC cover off and expect to keep air out.


Now THAT's gonna be fun... I've got one of those MC's that has the bolt-on cover... Think I'm gonna put a 1/2" socket on my electric screwdriver for this one :P

Oh, well... At least I got the lines flushed out, so I won't have to be doing it as much. Now... how do you know that you've gotten all the air out of the system? I didn't notice any air bubbles coming through the hose, and once the fluid coming out looked like the stuff going in, I figured it was enough... This is the first time I've bled brakes... The SpeedBleeders really help, just wish I knew why I have one odd-sized bleeder screw, :angry: so I have to either get another speedbleeder to fit that one, or try to figure out how to fit a wrench in there and do it the 'old way'

#5 Bob Lincoln

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Posted June 8, 2004 at 12:02 pm

Yes. When all bubble streams stop, and pedal and stopping distances are normal, they're bled.

#6 gearhead

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Posted June 8, 2004 at 12:20 pm

"you can't pump the pedal with the MC cover off and expect to keep air out."- I'll disagree. If that were the case, the MC would have to be 100% full all of the time, and I've never seen a MC that was 100% full. Whether the MC cover is on or not will make absolutely no difference as far as aeration is concerned. The ports are at the bottom of the resevoir. As long as they're covered by fluid, the brake system isn't going to get any air in it from the MC. As long as you stroke the pedal s-l-o-w-l-y, there wont be any aeration, and there won't be any mess.

#7 KOG

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Posted June 8, 2004 at 01:00 pm

I'll sort of go with Bob on this one. I keep the M/C closed during bleeeding except when actually adding fluid. Brake fluid will suck up moisture RAPIDLY when exposed to air and the less exposure the better.

#8 68RT

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Posted June 8, 2004 at 01:01 pm

The check valve is in the nose of the master cylinder and is used to guarantee that the cups stay expanded and that the system stays full even when the front or rear of the car is on a steep hill. The spout you see is extra fluid being expelled until the small relief port is covered by the front cup of the master cylinder as it is pushed in. (It is a small port and when you push fast it will create quite a spray.) That port must be open when the master cylinder is released or you will trap the extra fluid from either pumping up the brakes or from heat expansion of the fluid. If not released, the brakes would drag and from there it all goes downhill. I believe that you will not find that check valve on disc circuits as they use a different style of seal instead of cups.

#9 dana44

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Posted June 8, 2004 at 01:20 pm

Start bleeding the brakes a second time. Start with the shortest distance hose/tube length to the master cylinder first, then work farther , meaning driver front first, then passenger front, then driver rear, then passenger rear, that way air is bled out of the shortest distance to the MC so it won't interfere with pressurized wheels. Do keep the cap on for the squirts, and the speed bleeders you are talking about, was it for the MC itself to bench bleed the MC, then hook up the brake lines? It always speeds up the process when the MC can be bled first, then the wheels. All it takes to do it quickly after the MC has been bled is one or two pumps at normal speed, hold, release bleeder, pedal to floor, tighten bleeder, do until clear fluid comes out without air, check MC level after each five or six bleeder cycles. Two people helps, and be aware, if the car wasn't set up with power brakes to begin with, the pedal will definitely feel differently.

#10 gearhead

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Posted June 8, 2004 at 01:29 pm

If you're talking about the residual pressure valve, the only difference between disc and drum is the pressue that it holds in the system (drums having a higher pressure RPV). Except for the RPV, a MC for drums is functionally no different than a MC for discs. Disc MC's generally have a larger bore than drum MC's though. As far as moisture getting into the system from leaving the MC cover off while bleeding, the amount will be negligible, no more than would enter from removing the cover every time you need to top it off while bleeding (you're introducing fresh, moisture laden air every time you remove the cover, aren't you?).

#11 general0ne

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Posted June 8, 2004 at 08:12 pm

The speedbleeders that I got actually replace the bleeder screw. They're a standard bleeder screw, with a check valve in them so you don't have to tighten the bleeder after each pump. I'm not sure how you would tighten them anyway... There is absolutely no room to get to the front bleeders with a regular wrench - I had to use a socket , because the spindle is in the way. I don't know if there's supposed to be a special tool to get to them or what.

I didn't "bleed" the master cylinder, so to speak... I filled it up, pumped a few times till some fluid came out, then let it sit until fluid was actually dripping from it, then put the brake lines on.

#12 Cudapete

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Posted June 8, 2004 at 10:07 pm

Standard brake bleeding procedure is farthest point to closest. Right rear, left rear, right front, then left front. Cover must be on reservoir and master cylinder must be bled first. Bolt on master cylinder lid only needs to be finger tight during the bleeding prcess.


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