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No brakes
Posted by: kaminski45 ()
Date: September 01, 2021 06:23PM

Completely rebuilt my brakes system. New dual master cylinder, hard lines, front disc conversion, new rear shoes, rear wheel cylinders, new rear spring and adjuster hardware, new steel braided soft lines. The only thing reused was the rear drums. Vacuum bleed each corner until fluid was present. Then flowed until there was a steady stream of fluid with small bubbles. Pressure bleed each corner but never got all the bubbles out. Had many leaks the were stopped and readjusted the rear drums and rebleed but still never got a good pedal. I never bench bleed the master cylinder because the instructions from Clark's said not to. Any ideas on how to get a good pedal? The car does stop on it's own but not well enough to drive safely.

64 Spyder

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Re: No brakes
Posted by: MattNall ()
Date: September 01, 2021 06:51PM

You've still got air in lines. Park the front as high as possible and walk away for a few days...

do NOT let the MC reservoir run dry or low! keep it full...no pedal pumping!

MODERATOR
Sea Mountain, between Charleston Harbor and Coos Bay! SW Oregon Coast
Click HERE for My Website...Click HERE for My TechPages!
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Re: No brakes
Posted by: Frank DuVal ()
Date: September 01, 2021 07:32PM

This is one reason for bench bleeding. It proves the master cylinder is working properly.

Little bubbles bother me. It should be a steady stream of fluid once the lines have expelled their air. Do a hard HARDER test and check for leaks everywhere possible. Joints on the plumbing, wheel cylinders, master down the firewall on the inside of the car.

You can adjust all four wheels to lock for this test and bleeding.

I have done it like Matt says, open all four bleeders and keep the mater full for several hours.

Did you wrap the bleeder screws with PTFE tape or something else to keep the threads from leaking air into the system while using the Mighty-Vac or such? I find this helps alot!winking smiley

Frank DuVal

Fredericksburg, VA

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Re: No brakes
Posted by: TerribleTed ()
Date: September 01, 2021 08:01PM

Did you ensure the brake pedal push rod is adjusted properly to allow the master cylinder to fully return to rest with a little play . If not the master will not fully push or refill with fluid resulting in poor or maybe no braking.

---------------------------------------------------------------------------------------------------------

Avid Corvair hobbiest since 1984.
I have personally performed ground up restoration on over 20 Corvairs.
I currently work full time at restoring and repairing Corvairs.
Located in the Atlanta Georgia area.
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Re: No brakes
Posted by: kaminski45 ()
Date: September 01, 2021 09:38PM

I've done a few pressure checks of stomping on the pedal looking for leaks. Don't know if it worked.thay well since there is barely any pedal pressure. I did not adjust the pedal rod but it seemed to be set correctly.

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Re: No brakes
Posted by: 66vairman ()
Date: September 01, 2021 11:31PM

kaminski45 Wrote:
-------------------------------------------------------
> I never bench bleed the master cylinder because the instructions from Clark's said not to. Any ideas on how to get a good pedal? The car does stop on it's own but not well enough to drive safely.

Clark's is just repeating the MC manufacturers directions. The problem with bench bleeding is some folks ram the piston hard to the stop and that can damage the pistons seals ---- soooo now the MC folks advise against bench bleeding the MC rather than warning NOT to push the MC piston in to the full stop while bleeding.

There are kits that runs hoses from the MC outlets back into the reservoir so you can see if there is air. I usually do a bench bleed in a vise with the back end up a little, then the front end up a little.

BTW the MC should have adequate volume for a disc brake setup.

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Re: No brakes
Posted by: Lane66m ()
Date: September 02, 2021 03:35AM

I hope you got a dual master cylinder for a front disc/rear drum brake system. I got one for a 68 Camaro to put in my 66 Coupe.

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Re: No brakes
Posted by: kaminski45 ()
Date: September 07, 2021 04:46PM

So I've let the car sit for a few days. Adjusted the brake push rod and rebleed the brakes. Still have no pedal pressure. When looking at the pedal stop its pretty soft. With lite pressure I can move the pedal back slighty but with a decent amount of pressure I can collapse most of the pedal stop. Should I adjust the brake push rod so all the travel is taken up with the pedal stop collapsed or just leave it like it is with little travel and light pressure? At this point I'm out of ideas.

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Re: No brakes
Posted by: RexJohnson ()
Date: September 07, 2021 05:33PM

Get some metal plugs for the 2 ports on the M/C. With the plugs installed do you have a good pedal? If not pump the pedal a few times and it should work out any air in the M/C. When the pedal feels good and firm remove 1 plug and connect the line to the port. Now do you still have a good pedal? If not bleed the wheels on that circuit. When the pedal is good again connect the remaining line and repeat as needed. By plugging the ports you will know if the problem is in the M/C or the wheels. If the M/C has air in it you are wasting your time bleeding the wheels. With the M/C good and connecting 1 line at a time you are narrowing down where the problem is so that you aren't doing things over that are good to go.

RJ tools
Salem,Oregon

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Re: No brakes
Posted by: Wagon Master ()
Date: September 07, 2021 07:00PM

thumbs up 100% what this guy said thumbs up

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Re: No brakes
Posted by: kaminski45 ()
Date: September 14, 2021 07:58AM

So I plugged the ports and got a good firm pedal. Connected the rears and bleed until I had a decent pedal through flowing fluid and not pressure bleeding. Connected the front and did the same process and had the barely any pedal pressure. This makes me think that there is something wrong with the front. I have Michael LeVeque front disc brakes set up and a dual master cylinder from Clark's. Is the master cylinder from Clark's to small for the disc brakes or am I just not getting all the air out?

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Re: No brakes
Posted by: MattNall ()
Date: September 14, 2021 08:33AM

As stated before...ask Clarks if it is a Disc/ Drum MC.

MODERATOR
Sea Mountain, between Charleston Harbor and Coos Bay! SW Oregon Coast
Click HERE for My Website...Click HERE for My TechPages!
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Edited 1 time(s). Last edit at 09/14/2021 08:33AM by MattNall.

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Re: No brakes
Posted by: Timothy Shortle ()
Date: September 14, 2021 08:49AM

Sounds like you are on the right track using RJ's diagnosing tips. Very good tips by the way Rex.
Not to change the subject but what kind of brake fluid are you using? I know some folks (here) swear
by Dot 5 but I DO NOT care for the feel of it. Give me Dot 3 or 4 anytime and I will change it every
2-3 years. YMMV. (Flame suit on).

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Re: No brakes
Posted by: 66vairman ()
Date: September 14, 2021 08:54AM

kaminski45 Wrote:
-------------------------------------------------------
> So I plugged the ports and got a good firm pedal. Connected the rears and bleed until I had a decent pedal through flowing fluid and not pressure bleeding. Connected the front and did the same process and had the barely any pedal pressure. This makes me think that there is something wrong with the front. I have Michael LeVeque front disc brakes set up and a dual master cylinder from Clark's. Is the master cylinder from Clark's to small for the disc brakes or am I just not getting all the air out?

I've been down this road helping others with a "disc" brake installation. You may be able to power bleed the front disc system to get a firm pedal, BUT what I often find is the MC volume vs. the rear wheel cylinders and front disc caliper volumes prevents the dual MC from working if one circuit goes open (or has a lot of air in the circuit).

The purpose of a dual MC is when either the front or rear circuit looses brake fluid is to have ENOUGH MC PISTON TRAVEL remaining to operate the other good circuit - albeit at reduced stopping power and the pedal will go nearly to the floor. This is accomplished by a spring in the MC between the two pistons. It requires good engineering to get right, yet often folks install a disc setup on the front and don't calculate if the MC is up to the job.

It's easy to test --- If you open a rear wheel cylinder the brake pedal should go nearly to the floor, BUT STOP SHORT AND HAVE PRESSURE to the front disc. calipers. Same when you open the bleed the front disc caliper, the rear wheel cylinders should stop the wheel from turning. If the pedal goes to the floor, then you don't have enough MC volume when one circuit is open. Which voids the whole purpose of a dual MC.

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Re: No brakes
Posted by: RexJohnson ()
Date: September 14, 2021 10:12AM

Disc brakes DO NOT take more volume than drum brakes. They have a larger capacity for brake fluid to back fill the piston as pads wear down. It takes more fluid to fill 2 wheel cylinder pistons and then move the shoes out to the drums than it does to clamp 2 pads that are already dragging on the rotors with the piston tight behind them.

RJ tools
Salem,Oregon

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Re: No brakes
Posted by: joelsplace ()
Date: September 14, 2021 10:15AM

Matt - disc/drum? What difference does that make? The reservoir size is all.

Joel
Northlake, TX
5 Ultravans, 119 Corvairs and counting...

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Re: No brakes
Posted by: kaminski45 ()
Date: September 14, 2021 10:49AM

So if the master cylinder from Clark's is the wrong size what size do I need? Clark's only offers one size dual master cylinder.

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Re: No brakes
Posted by: Frank DuVal ()
Date: September 14, 2021 10:54AM

Are the calipers mounted so the bleeders are on top?

Tim, you are with Steve on that, you high elevation dwellers smiling bouncing smiley), but down here at sea level we get the same pedal feel with DOT 5 as DOT whatever else.thumbs up

Frank DuVal

Fredericksburg, VA

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Re: No brakes
Posted by: 66vairman ()
Date: September 15, 2021 07:59AM

RexJohnson Wrote:
-------------------------------------------------------
> Disc brakes DO NOT take more volume than drum brakes. They have a larger capacity for brake fluid to back fill the piston as pads wear down. It takes more fluid to fill 2 wheel cylinder pistons and then move the shoes out to the drums than it does to clamp 2 pads that are already dragging on the rotors with the piston tight behind them.

Yes and NO -- It depends on the volume of the disc brake caliper vs. the rear wheel cylinders. That's my point -- few do the math. Also why many disc/drum cars had "proportioning valves" that would let higher volume to the rear wheel cylinders, yet reduce pressure vs. the pressure to the front disc calipers once the brake shoes made contact with the drums. In a few rare cases there were MC's with different piston sizes for the disc vs. drum circuits. Of course there are limits to pedal/MC geometry and why many disc systems require a vacuum booster to keep pedal pressure from being excessive. All this is knowable if you do the homework.

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Re: No brakes
Posted by: RexJohnson ()
Date: September 15, 2021 10:25AM

If you look at a new F550 and check out the brake lines they are tiny and those are some big calipers.

RJ tools
Salem,Oregon

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