Another MC brake question

[bas123]

Hi all; I'm new to post, I just did discover this site and think it is great. I'll get some pictures of my car and post shortly. My question -I have a EM 64 Monza that I have been working at replacing all of the wheel cylinders and upgrading the MC with a new duel system kit from Clarks. I read as many of the blogs here before regarding bench top bleeding and wheel bleed orientation etc. I replaced all of the rubber hoses and have tried bleeding the brakes twice already, yet I still have mushy brakes. I noticed at the last go around (when I left the cover off of the MC) that when pressing the brake pedal, that the MC has a fountain of brake fluid shooting up from the center orifices. I did not notice this before as I'm usually working at the wheel and I cover the MC with the cap. Is this normal? (and of course my son never mentioned this as he is pressing the brake) I have bleed brakes before but I do not recall ever seeing this occur. I asked Clark if this was normal and they responded that I need to bleed the brakes again. Any thoughts? is the MC defective? is there a way to check and see if the MC is allowing blow back when I depress the pedal.
thanks for your help

[tiger13]

Yes, a small spurt of fluid coming up is normal. When I bench bleed a new master cylinder, I try to find plugs that fit the outlet holes, and put them in, then fill the master, then slowly, SLOWLY pump the cylinder while it is in a vise using a large Philips screw driver being careful not to gouge the bore and watch for the tiny bubbles to come up from the the inlet hole. You can tell when your master cylinder is fully bled out because there will first be no more little air bubbles coming up, and secondly, you will not be able to push in the Philips screw driver, it should be rock hard. At this time your master cylinder is now bench bled.
Remember the adjustment of your brakes themselves will also have a lot to do with how the peddle "feels" as the shoes expand out against the drums. If they are adjusted correctly, and bled correctly, your peddle will be within a 1/2 to 3/4 of inch of travel, if they are not adjusted right, it will take a couple of pumps to get the shoes to make contact.

[66vairguy]

If you used the BLEEDER PLUGS that come with then new MC's now it may not have bleed correctly. I learned this the hard way. I used to just run some fluid out the side ports, messy. So I tried the new style plugs that came with the new MC and all seemed to go well - piston became firm.

I installed the MC and got a mushy pedal. Took it out and went back to the my little auto parts store and the owner listened to me and said "I get a lot of MC's back because the plug bleed system doesn't seem to work well. I have a kit that recycles the fluid out the ports and back into the reservoir like the old days - works every time. He lent it to me and I bleed the MC and installed it and it worked perfect.

So if you used the plugs then ditch them and buy a re-cycle bleeder or do it the old fashioned way.

[terribleted]

Bench bleeding is really not necessary, altho it may expedite the time it takes to bleed the system. Installing a dual conversion requires setting the brake pedal push rod length properly and complete pumping of fluid thru the entire system starting LR, RR, RF, LF a couple times through or more.

First make certain that the brake pedal rod length allows the proper clearance before starting to move the master cylinder piston. There should be around 1/8"-1/4" of clearance with the pedal held up to the stop. I have had to shorten this rod before to allow this clearance and allow the master cylinder to draw fluid properly (if the clearance is too small ...rod too long...the master will never fully disengage and may not fill properly).
Next fill the MC and proceed to bleed LR, RR, RF, LF. Use a hose (clear preferred) and glass or clear plastic catch container. Have helper push down, open the bleeder while the pedal is down, let fluid go into catch container while observing for bubbles, close valve, helper off pedal and then back on pedal...repeat until no bubbles are seen. Be sure to re-fill the master cylinder when it gets down to about 1/2 way...letting it get empty may allow new air in and make you start again. I go around the whole car and once I have seen no bubbles at all 4 wheels I usually have some brake pressure. I can see or hear the brake shoes moving. (If not repeat the bleeding steps). I then adjust the adjuster wheel of all 4 brakes to supply a firm drag. (when you do this adjust the adjuster until a firm drag is felt then press the brake pedal... let off.... and adjust it some more.......it is normal for it too feel pretty tight and after pressing the pedal it is loose again...you will likely do this a few times per wheel before a firm drag is felt after releasing the brake pedal, the pedal presses center the shoes allowing more precise adjustment).

At this point if the pedal is nice and solid with no sinking or pumping up you should be good. I often find, however, that when installing a whole new or mostly new system that I may have a slightly spongy pedal still. Re-peating the bleeding steps once more around the car finishes the job.

[tbird55]

well im having the same problem and have bled every wheel seriously about 10 times. its getting better but still have to pump the pedal several times before it feels like it should. i extended the rod and now i wonder if i should have left it where it was or maybe even shortened it. any suggestions? thx again for all your help. tom

[66vairguy]

Well I guess it's time to mention "power bleeding". I have replaced all the lines on a few cars and found the "pumping the pedal" just does not do the job with a lot of air in a system - period. You need a power bleeding system. Either a few pounds of pressure and at the master cylinder (too much pressure will force brake fluid past the rear seal and into the passenger compartment and that will be a mess) with a reserve sump to flow fluid for a few seconds. The alternative is vacuum suction at the wheel cylinders which is difficult to get a seal around the bleeder fitting, but doable with the right equipment.

WHY POWER BLEEDING? Because with a lot of air in the lines the air tends to go to the high spots and you have to have fluid flow long enough to drive the air pockets to the wheel cylinders and OUT.

When you pump the pedal you get a little fluid movement and the air starts to travel, the you stop to close the wheel cylinder valve and let the pedal come back up and guess what --- the air moves back up to the high spot of the line. No matter how often you "pump the pedal" you won't get all the air out. BTDT.

A good shop will have brake power bleeding equipment.

[terribleted]

well im having the same problem and have bled every wheel seriously about 10 times. its getting better but still have to pump the pedal several times before it feels like it should. i extended the rod and now i wonder if i should have left it where it was or maybe even shortened it. any suggestions? thx again for all your help. tom

There must be so slack before the brake pedal rod hits the MC piston. If you can not tell remove the master cylinder and re-install it without the rubber boot. Make sure there is proper piston to rod clearance and then re-remove the MC and install with the boot in place again (it is much easier to verify proper clearance with out the boot in place). If you have bled each wheel so there is no more air in the flow AND adjusted the adjuster wheels up to a firm drag like I said above and the MC is clearance properly, and you still have to pump up to get a firm pedal you have a defective part somewhere or have not properly done the adjusting and bleeding procedures.

[tiger13]

I looked at the "kit" for the dual master cylinder that Clark's sells and I do not see a proportioning valve in the kit. Does it come with one? If you are converting your single master cylinder to a dual system and they did not give you one I would love to know how they expect you to be able to make it work?
If they did give you one, and /or,it is the conventional old style GM valve with the little rubber looking plug in the front or top of it, have you held that in when you have been trying to bleed the brakes on the car? I cant imagine you putting a dual master in a car without a proportioning valve, but I don't see one in that kit.

[tiger13]

Another way to test your master is to install on the car, be sure it is bench bled, remove all lines from it. Install some plugs into to line holes, or get a short piece of brake line that you know will fit into both of the master cylinder line holes that you have brazed shut, install them into the master cylinder. fill the master with some brake fluid. put the top on the master, and step on the brake pedal, it should be ROCK hard, and not sink down at all. If it does this you can eliminate your master cylinder as part of your problem.
You may be able to disconnect your front and /or rear brake system by plugging it this same way, and testing it to narrow down your issues if you are not using a proportioning valve.

[91blaze]

I don't have a proportioning valve and it works fine. I've seen many others without them either.

[tiger13]

91blaze, How do they do it, do they just Tee off the front and rear brakes to the front and rear master cylinder? Is that how they split the system?

[bbodie52]

Here is some additional food for thought...
Corvair Brakes
http://autoxer.skiblack.com/brakes.html


http://corvaircenter.com/phorum/read.ph ... 280,486994
http://corvaircenter.com/phorum/read.ph ... 552,342666
http://corvaircenter.com/phorum/read.ph ... 783,161783
http://corvaircenter.com/phorum/read.ph ... 370,444456

Installing Dual Master Cylinders (CORSA Article).pdf

Installing Dual Master Cylinders (CORSA Article)

(243.35 KiB) Downloaded 99 times

[tiger13]

Does all those parts come in the kit from Clark's Brad? It didn't look like it did in the catalog, because that setup looks like it has a proportioning valve in it. It's just, to me, without on , I would think you would get a real hard brake pressure on the fronts, you know? an unequal brake pressure with a valve in there.

[91blaze]

Mine are nothing special, just ran a line from the rear brakes to the front of the cylinder and the front line to the rear of the cylinder.

Here's a picture, I know it's not pretty but it works pretty well. Im not sure if switching the front and rear lines would be better but maybe others will have some input on the matter.

[64powerglide]

91blaze's master cylinder photo.

[bbodie52]

A Corvair has an advantage over a front engine car under braking. Since the weight bias is to the rear, the car is much less nose heavy under braking, so it makes use of all four tires when stopping. Early model Corvairs had adequate, though not spectacular, brakes and the rear weight bias helped the car use all four when braking. Late models used GM intermediate platform (Chevelle, Tempest, etc.) brakes which performed very well on the 1000 pound lighter Corvair. FCs use full size Chevy brakes and they too work quite well on the lighter Corvair trucks....

...Drum brake improvements.

In many classes, you can swap Yenko parts onto your car, but you must keep the basic original system. This is not entirely a bad thing for an autocross/street car. Drum brakes are often lighter, and reducing unsprung weight in the suspension is a great help to handling. Finally, simply modifiying the stock system is less expensive than a complete swap. Modifications to consider:

• Dual master cylinder. Stock on '67 and later Corvairs, a dual system is safer since if there is a loss of fluid from the lines, it will only effect one half of the brakes. You can easily swap a dual master cylinder onto any '62 or later Corvair, kits are available from most of the Corvair vendors.
• Proportioning valve. Stickier tires not only put more stress on the brakes, they also create more potential weight transfer to the front tires. This leads to early rear brake lockup, which leads to spins.
• Bored front cylinders. A proportioning valve will help, but several racers have found that the real fix is getting more braking up front via larger pistons. According to calculations by Charlie Morgan, on a late model front cylinders with a 1" bore should yield a car that will evenly lock its tires at .89G, just about what we are looking for. Note that 1" front cylinders were part of the optional metallic brake lining package in 1962 and 63.
• Aluminum drums. The late Corvair shared its drum brakes with some other cars of the time, Steve Hammatt wrote this article on the subject:
  
  http://autoxer.skiblack.com/tech/Alumin ... ersion.pdf

http://autoxer.skiblack.com/brakes.html

http://www.corvair.com/user-cgi/catalog ... N&page=145


There is no indication of a proportioning valve in the Clark's kit. In fact, I could find no indication that Clark's even lists a proportioning valve in their catalog.