Brake Bleeding Problem 1965

[Frank D.]

Rebuilt calipers,master cylinder (PB with 2 milk caps), and all new lines. We are bleeding with a Mity Vac and three of the wheels bleed fine but on the front left wheel, the pistons will only close on the outboard side of the caliper. The rear half of the pistons won't close. Has this happened to anyone else? I checked the archieves, lots of information but not an answer.

As usual, thank you in advance for your help. Aren't we a great organization?

Frank O'Donnell
Troy, VA
Heading for the Nationals, hope to see you there!

[Michael G.]

Re: Brake Bleeding Problem 1965

Frank,

I've work with these systems for many years. and unclear what your stating"rear half of the pistons won't close". With caliper mounted how are you determining which side is doing what? I've used the Mity Vac with very slow results. Unfortunately doesn't move much fluid. The tried and true process of one person working the pedal and the other working the bleeder valve is more efficient.....and moves more fluid. Possibly your pistons are sticking. With the Mity Vac your not getting enough fluid movement to remove trapped air which would eventually help move those pistions.

[Paul J.]

Re: Brake Bleeding Problem 1965

I agree. Frank, pedal bleed the left front. It gives you more pressure to force the air out.

Paul

[Jim T.]

Re: Brake Bleeding Problem 1965

Rebuilt calipers,master cylinder (PB with 2 milk caps), and all new lines. We are bleeding with a Mity Vac and three of the wheels bleed fine but on the front left wheel, the pistons will only close on the outboard side of the caliper. The rear half of the pistons won't close. Has this happened to anyone else? I checked the archieves, lots of information but not an answer.

As usual, thank you in advance for your help. Aren't we a great organization?

Frank O'Donnell
Troy, VA
Heading for the Nationals, hope to see you there!

Did you try the old tried and true method of gravity bleeding?

[Paul J.]

Re: Brake Bleeding Problem 1965

Did you try the old tried and true method of gravity bleeding?

Gravity bleeding works, but I've found that it usually leaves just a little bit of air. Pedal bleeding is best.

[Frank D.]

Re: Brake Bleeding Problem 1965--Update

Yes. Thanks guys. There are two of us and we did use the pumping the pedal method. When I say the back half of the pistons are not closing, I mean you can look down on the disk pads in the calipers from the top and see the outboard pistons move to the disc pad but not the inboard pistons closing on the disk pads.

We will bench bleed the master cylinder one more time first, before we go to the gravity method.

Will update you as we progress during the day. Thanks again for your help.

Frank

[Michael G.]

Re: Brake Bleeding Problem 1965

Stay vigilant Frank. During the restoration don't know which process frustrates me more....electrical or brake. Patience will win in the end.

Keep us posted maybe we'll learn something here.

[Terry M.]

Re: Brake Bleeding Problem 1965--Update

Yes. Thanks guys. There are two of us and we did use the pumping the pedal method. When I say the back half of the pistons are not closing, I mean you can look down on the disk pads in the calipers from the top and see the outboard pistons move to the disc pad but not the inboard pistons closing on the disk pads.

Dumb question here, and I mean on offense -- the bleeder screw is on the top of the caliper, right?

Something is wrong with that caliper if only the outboard pistons are moving. If it were my car I would take that caliper off the car and disassemble it to see what is wrong. I don't think brake fluid in the lines is your issue. It could be brake fluid, or the lack of it in parts of the caliper -- but dis-assembly will tell the tail. One of the internal passages could be blocked.

[Michael G.]

Re: Brake Bleeding Problem 1965

Don't think it can't be done Terry. Restoring a '69 Z-28......bleed the system silly.......only to figure out the calipers on the front were mounted upside down, both sides. Of course that placed the bleeder screws on bottom

Frank, I agree with Terry the caliper needs to come off to ensure pistons have free movement....or possibly find out if there's another issue.

[Joe C.]

Re: Brake Bleeding Problem 1965

I was gonna' ask these questions this morning: "Who rebuilt your calipers? You? Are they still original type with phenolic pistons?"

If you, or somebody else spread the pistons too wide before fixing them in place to clamp the rotors, the pistons may have jammed in the bores. The only way to free them is to disassemble and clean them, or by applying massive hydraulic pressure to the isolated caliper half.

[Terry M.]

Re: Brake Bleeding Problem 1965

Don't think it can't be done Terry. Restoring a '69 Z-28......bleed the system silly.......only to figure out the calipers on the front were mounted upside down, both sides. Of course that placed the bleeder screws on bottom

Oh -- I KNOW it can be done. And that is all I will say.

[Frank D.]

Re: Brake Bleeding Problem 1965

UPDATE: Have spent the whole day on these @%&! things.

The calipers are correct-side-up on all four spindles. We bench-bled the master cylinder and it seems our real problem is that we can't get flow to EITHER of the front wheels. The rear wheels seem fine. We know the problem is confined to the front half of the system (front half of the two milk-cap master cylinders). We also bought one-man bleeder valves today and employed the two-man pumping method to no avail.

Terry--my cousin did the rebuilding of all four calipers himself, many years of Corvette experience and ownership. But we will still dis-assemble the left front tonight to see if there is a problem with the internal passages on that caliper.

Any ideas on why we don't have flow to the front wheels?

Thanks again,
Frank

[Terry M.]

Re: Brake Bleeding Problem 1965

UPDATE: Have spent the whole day on these @%&! things.

The calipers are correct-side-up on all four spindles. We bench-bled the master cylinder and it seems our real problem is that we can't get flow to EITHER of the front wheels. The rear wheels seem fine. We know the problem is confined to the front half of the system (front half of the two milk-cap master cylinders). We also bought one-man bleeder valves today and employed the two-man pumping method to no avail.

Terry--my cousin did the rebuilding of all four calipers himself, many years of Corvette experience and ownership. But we will still dis-assemble the left front tonight to see if there is a problem with the internal passages on that caliper.

Any ideas on why we don't have flow to the front wheels?

Thanks again,
Frank

Frank,

If you have no flow to either of the front wheels I am now confused though because you said the outer pistons move but not the inboard on the front left wheel. If the pistons move there must be some fluid flow, perhaps not enough, but that is another matter.

I am not so familiar with 1965 brakes, so please explain "master cylinder (PB with 2 milk caps)" -- What does that mean? I thought 1965 brakes were a single circuit design, and that dual circuit systems did not come into production until 1967.

[Michael G.]

Re: Brake Bleeding Problem 1965

Frank,
I am not so familiar with 1965 brakes, so please explain "master cylinder (PB with 2 milk caps)" -- What does that mean? I thought 1965 brakes were a single circuit design, and that dual circuit systems did not come into production until 1967.

Terry, believe his system to be a PB master cylinder with dual reservoirs that use opauqe (milk colored) colored caps. It is confusing as Frank stated he is getting movement on the front left capliper however possibly not enough. There may be blockage leading from the front reservoir to the front calipers. I dealt with a similar problem on a '66 with a PB master cylinder. There was blockage coming from the bore....wasn't allowing front system to be fully pressurized.

[Frank D.]

Re: Brake Bleeding Problem 1965

Terry, what Michael said about my 1965 brake system having two separate reservoirs is exactly right. One sits behind the other in the same unit, the front reservoir controls the front calipers and the rear reservoir controls the rear calipers

Yesterday, we had some fluid and movement in the right front and both rear calipers, but the left front only pulled the outboard pistons and not the inboard pistons.

Today, after we bench bled both reservoirs of the master cyclinder we had no fluid flow at the front calipers at all. Rears are still fine. Everything in my system is new or rebuilt. The only original piece is the 3-way brake line junction attached to the front left side of the frame. We will remove that and check for blockage first thing this morning.

Thanks for both of you staying with my post. So many times after a post is started, answers dry up when new questions force it down the list and off the first page.

Thanks once again for your help.

Frank