(This is for the '57, but I figure disk/drums are disk/drums.)

I'm converting the '57 to front disks, and purchased a manual master cylinder for the job. When I did the bench bleed, the front port (rear brakes) primed and bled almost immediately, but the rear port took forever to start flowing, didn't flow very much, and took a long time to get the bubbles to disappear.

After installation on the car, the rear bled readily with good flow each stroke. The front (rear port, remember), however, would hardly flow anything with each stroke. When all air disappeared and I locked the system down, the pedal will go almost to the floor with the first stroke, and then will "pump up" and feel mostly normal with subsequent strokes. After it sits for half a minute, the first stroke is down to the floor again. I've driven it around to see if things needed to "settle in", but it hasn't changed. If I hit the line lock before the 1st stroke, it doesn't go down quite as far, but it still doesn't feel right, and pumps up with subsequent strokes.

I called the outfit that sold me the master cylinder (Danchuk, in case you were wondering or that matters), and they said I still have air in the master cylinder and need to re-do the bench bleed (it didn't come with a bench bleed kit, by the way - I just used two pieces of line I had). I spent over an hour pumping that thing on the bench the first time, dwelling between strokes, etc.

I think I've got a defective part (new, not rebuilt). What do you all think?

I'm using an adjustable proportioning valve on the rear brakes, to clarify that. I have it full open for the bleeding.

 

A correct bench bleed entails forcing fluid backward through the master cylinder. You use a large syringe with a cone shaped rubber tip on it and press it against the ports and then force fluid through them. This will get all the air out. I agree with the company that sold it to you, you still have air in the line. Also make sure if you have disc/drum combo that they are correct, more fluid to the discs, so the larger chamber on the master cylinder goes to the discs. But I'm assuming drums all the way around in which case you should check your adjustment.

 

For drum brakes (front port in this case), you can't force fluid through backwards because there's a check valve in there. One thing they told me yesterday is a vacuum pump can help bench bleed by drawing the fluid through the cylinder, rather than using the piston to force fluid through.

I took it off last night to redo the bench bleed and observed very carefully what was going on. For the 1st part of the stroke, fluid would flow out of the front port (which is for the rear brakes, the drums). A little more than half-way down, the rear port would flow, then soon after the front port would quit flowing. I would get more flow out of the front port than the rear for a full stroke.

I agree the disks should get more flow because there's more volume. This operation seems weird, though, but this is the first time I've ever had to bench bleed a master cylinder.

I got a few bubbles out in the early going (could have been from the line change for all I know). I kept this up for a good hour, varying how I did it (waiting between strokes, rapid pumps - but not too rapid to form foam or bubbles - w/o letting it back all the way, tapping the side with a mallet, etc.). All of the bubbles were in the first 15 minutes or so. By the time I quit, there hadn't been any bubbles for a long time. But, when I put it back on, it acts the same - 1st stroke is almost to the floor but then it will pump up to what I would expect as long as I keep some pressure on. If I let it all the way off for even a few seconds (not even the 1/2 minute like I said earlier), it'll go back to needing almost a full stroke the 1st time, then pump up, etc.

 

Okay, so you have drums all around. Then you should get the same flow out of both ports at the same time. I would suggest calling the company back that you bought if from it sounds like the may have put the wrong plunger in the master cylinder, yes I've seen it before, with dramatic results.

Also, when you let off the brake the pedal and plunger return to the normal position and this opens the ports allowing the brake fluid to return to the master cylinder that was forced into the wheel cylinders. So you CAN force fluid backward through the ports when the plunger is in the unengaged position and this is how to get a proper bench bleed.

 

It was 4-wheel drum. The conversion to front disk is what this was all about.

I did talk to them again today. They want me to check for the volume of fluid it is producing to the front brakes and get back with them. They're suspecting a bad master cylinder as well after all I've described to them.

They did say, though, that the rear requires more volume because the shoes have to move farther than pads do. The caliper piston is certainly larger, so I'm not sure which is correct on that point. The guy I talked to said he had a '57 Nomad and a '57 driver, both with the disk brake conversion - and he didn't come up against anything like this.

Maybe I'll pull that spare Camaro master out of the garage attic and do a sanity check on it.

 

"This is for the '57"

Then what are you doing here lol hope you get the prob fixed.

 

this is a site dedicated to tech questions about thirdgen f bodys. take your questions to www.whywontmybrakeswork.com
you migth want to look into a pheniox injector. cost is a little hard to accept but after you use one you'll be sold on them.

 

My original plan was to use the left-over booster & master cylinder from my donor car. That turned out to be more fabrication than I wanted to tackle, so I went to the aftermarket for a "direct fit". Then, it started gaving me fits. I am using the Camaro calipers, for what that's worth.

As I said at the beginning, disk/drum should be disk/drum, so I was hoping someone had come across this working on their 3rd gen.

I did see the Phoenix mentioned when searching for similar problems.

I'll go away now...

 

Well, I'm back.

Just for the record, it was a bad master cylinder.

And just to make it 3rd-gen related, someone somewhere on the Board (came up on a search) posted a link to a 3rd-gen NHRA stock class racer's website that included the blow-by-blow build-up of the car. They listed the master cylinder they used (manual brakes) from Master Power Brakes and the MPB link. I called MPB, told them what was going on, asked them which of their "Made in USA" master cylinders they would recommend for my application - they recommended the same one these 3rd gen racers used. I ordered, it arrived, I installed, problem solved. The made-someplace-where-English-isn't-the-native-language* Danchuk MC is on its way back to them.

There, I'm using 3rd gen calipers and a master cylinder that can be used for 3rd gen manual applications (such as drag racing), so now it's 3rd gen related.

Well, I guess there's more. The MPB MC came with threaded hard plastic plugs on the outlet ports. The enclosed instructions said to use these to bench bleed the MC prior to installing. Worked like a charm. This past weekend, I was doing the front brakes on the Camaro and decided to go ahead and install the MC that I bought, intending to use on '57, that was purchased based on the '82 Camaro application; since I had it and the brakes on the Camaro weren't "quite" right. I used the plastic plugs to bench bleed it, and again, worked like a charm.

(I still think this experience was general enough to be worthy of this site, but, whatever...)

*No, I don't mean California

 

heh, i got all the way to the next to last thread, and was going to post, "hey, you got a bad master cyl, return da biotch" but ya beat me to it.

 

Oh, yeah, the front brake hoses are for 3rd gen application, too...