Onto My Next Issue Brakes.

[Shep69 149]

I have my mustang up on stands while working on it and so i decided to run the motor and put it into gear. While the rear wheels were turning i applied the brake and the wheels stopped and then after about 2 seconds they started turning even though my foot was still applied to the pedal. I then checked the fluid level in the master and that was fine but while the lid was off i pushed on the pedal and noticed that it shot a shirt of fluid up out of the front reservoir.  It does this every time the pedal is pressed. Is this normal? Is my proportioning valve gone bad? Anyone got any ideas.

[unilec 57]

Has the brake light come on? Could be the piston inside the brake distribution valve has moved.

[Shep69 149]

54 minutes ago, unilec said:

Has the brake light come on? Could be the piston inside the brake distribution valve has moved.

No . The brake light hasn't come on. 

[JayEstes 172]

I don't think that fluid shooting up is necessarily an indication that anything is wrong.  It could have to do with how hard you hit the brake.  If you apply brake gradually I would expect it not to do that, but if you slam the pedal I would expect it.

The light coming on and piston valve movement would be related to having one chamber not working. Sounds like yours are both working.

there is another valve in the proportioning system that controls pressure to the rear brakes.  It is possible this valve is sticky (or stuck) and need to be serviced.  Muscle car research.com has an excellent rebuild kit with instructions I would recommend.

i do find it strange that your application of brakes initially stops the rear wheels and then can't hold it- that does imply something not quite right in the rear brake line pressure.

i suppose it could also be rear drum cylinders that are a little leaky or have air in the lines.  That might have same effect. In fact air in the lines could very well explain the stop initially and then release...

I'd recommend inspecting the rear hydraulics cylinders, and if they are good, then bleed the back brakes (RR first then LR). Ensure clean new fluid when you do it.  Also you can  use a shuttle valve centering tool in place of the light sensor when bleeding- it will ensure the shuttle valve stays centered.

if that doesn't work, i'd rebuild the prop valve and see if that fixes it. It's kind of a big job and getting the prop valve out is a pita- so dont go there unless the other doesn't work.

Best of luck- let us know what you find

Jay

[Shep69 149]

16 minutes ago, JayEstes said:

I don't think that fluid shooting up is necessarily an indication that anything is wrong.  It could have to do with how hard you hit the brake.  If you apply brake gradually I would expect it not to do that, but if you slam the pedal I would expect it.

The light coming on and piston valve movement would be related to having one chamber not working. Sounds like yours are both working.

there is another valve in the proportioning system that controls pressure to the rear brakes.  It is possible this valve is sticky (or stuck) and need to be serviced.  Muscle car research.com has an excellent rebuild kit with instructions I would recommend.

i do find it strange that your application of brakes initially stops the rear wheels and then can't hold it- that does imply something not quite right in the rear brake line pressure.

i suppose it could also be rear drum cylinders that are a little leaky or have air in the lines.  That might have same effect. In fact air in the lines could very well explain the stop initially and then release...

I'd recommend inspecting the rear hydraulics cylinders, and if they are good, then bleed the back brakes (RR first then LR). Ensure clean new fluid when you do it.  Also you can  use a shuttle valve centering tool in place of the light sensor when bleeding- it will ensure the shuttle valve stays centered.

if that doesn't work, i'd rebuild the prop valve and see if that fixes it. It's kind of a big job and getting the prop valve out is a pita- so dont go there unless the other doesn't work.

Best of luck- let us know what you find

Jay

Thanks Jay. I will have a look and see what I can find.

[danno 128]

Could the problem also be the master cylinder?  What if the pressure on the rear brake side is leaking around the rear brake piston in the master?  You would get the initial stopping force, but as fluid leaks past the compressing cylinder, the pressure goes down.  Maybe that pressure leaking fluid from the rear brakes  reservoir into the front brakes reservoir  is what caused the squirt of fluid out of the front brakes?  

[lanky 44]

Its air in the line (s) somewhere. Rebleed them is my recommendation.

[Shep69 149]

3 hours ago, danno said:

Could the problem also be the master cylinder?  What if the pressure on the rear brake side is leaking around the rear brake piston in the master?  You would get the initial stopping force, but as fluid leaks past the compressing cylinder, the pressure goes down.  Maybe that pressure leaking fluid from the rear brakes  reservoir into the front brakes reservoir  is what caused the squirt of fluid out of the front brakes?  

Danno the front reservoir feeds the rear brake and the rear feeds the front brakes. If it was bypassing I would have thought that I would see fluid go from one to the other but I'm not . The pedal feels firm , not spongy like air in the system but I won't rule that out just yet. Could be leaky rear cylinders . There only a couple of years old and no sign of fluid from the outside . That's today's job to have a look. 

[DocWok 30]

The squirt of brake fluid shooting up in your master cylinder is normal, it is the front brake piston displacing fluid until fully travels past the brake fluid inlet port from the reservoir, it is only then when the piston has passed the inlet port that the trapped fluid begins the apply the brakes.

[unilec 57]

You can check if the valve inside the block has moved by check with a meter on ohms, one lead to the block(ground) and the other to the contact, should be open circuit if central.

[danno 128]

On 10/31/2017 at 6:39 PM, DocWok said:

The squirt of brake fluid shooting up in your master cylinder is normal, it is the front brake piston displacing fluid until fully travels past the brake fluid inlet port from the reservoir, it is only then when the piston has passed the inlet port that the trapped fluid begins the apply the brakes.

Ok, that makes sense. I had not thought about that. 

[JayEstes 172]

How did this one come out?  Is there a resolution?

[Shep69 149]

10 hours ago, JayEstes said:

How did this one come out?  Is there a resolution?

JayEstes I ordered the distributor block tool so I can bleed my brakes properly without the piston moving. I’m going to do it this weekend so I will keep you posted.

cheers Mark. 

[Shep69 149]

On 22/11/2017 at 12:00 PM, JayEstes said:

How did this one come out?  Is there a resolution?

JayEstes I ordered the distributor block tool so I can bleed my brakes properly without the piston moving. I’m going to do it this weekend so I will keep you posted.

cheers Mark. 

[Shep69 149]

So I tried bleeding the brakes again now that I have the distributor block tool. It seamed to bleed fine with no issues but I still have poor brakes. 

Next thing will be to change out the master cylinder even though it’s not that old. Gggggrrr. Bloody frustrating.

[jmlay 80]

A residual pressure valve should exist in the path of the rear breaks, either in the master or inline. This keeps some pressure so the pistons in the rear cylinders do not retract all of the way. Worth checking. Also the shoes need to bee properly adjusted, slight drag. I like adjusting them close the backing up and stopping with steady but agrssive pressure for the final self adjustment. This is assuming the mechanicals inside the drum are in good working condition, make sure the adjuster have plenty of antisense as well as where the shoes and backing plates meet are lubed well.

[Shep69 149]

3 hours ago, jmlay said:

A residual pressure valve should exist in the path of the rear breaks, either in the master or inline. This keeps some pressure so the pistons in the rear cylinders do not retract all of the way. Worth checking. Also the shoes need to bee properly adjusted, slight drag. I like adjusting them close the backing up and stopping with steady but agrssive pressure for the final self adjustment. This is assuming the mechanicals inside the drum are in good working condition, make sure the adjuster have plenty of antisense as well as where the shoes and backing plates meet are lubed well.

Jmlay

Yes the rear proportional valve has been serviced with new seals and spring. The rear drums are in good condition with new parts including cylinders. I’m leaning towards the master cylinder at this stage. 

It may have been a dud from new. It’s a raybestos . Even though I bench bled it maybe it’s still got some air in it that I can’t get out. I’m going to get a new one and have another crack at it. 

 

[unilec 57]

Are you using a booster, if so you may be using the wrong brake pedal.

[Shep69 149]

2 hours ago, unilec said:

Are you using a booster, if so you may be using the wrong brake pedal.

It’s a factory disc brake car so yes it has a booster but nothings off the table at this stage.

[unilec 57]

OK, just make sure you have the correct pedal, should be 4-1 ratio, similar to this one.Master should be 1" as well.

https://www.cjponyparts.com/brake-pedal-assembly-manual-transmission-power-brakes-1967-1969/p/PDS/

[bryonbush 85]

On 11/26/2017 at 5:29 AM, Shep69 said:

It’s a factory disc brake car so yes it has a booster but nothings off the table at this stage.

Hey partner,  any update? For as long as I have had my 69, even with all new every thing related to the brakes and they still suck. At this point I'm thinking it's maybe just the pads because I've bled this system a gazillion times and nothing seems to change 

[unilec 57]

6 hours ago, bryonbush said:

Hey partner,  any update? For as long as I have had my 69, even with all new every thing related to the brakes and they still suck. At this point I'm thinking it's maybe just the pads because I've bled this system a gazillion times and nothing seems to change 

Does it still feel like you have air in the system?

[bryonbush 85]

I can honestly say I don't know. I switched out boosters last summer and since then I have way more pedal travel than I did before. I have bled these things still my legs fell off and never get any more air bubbles out. So I'm thinking that either 1: i need to just bring it to a place and have them vacuum out the system on a machine, 2: try new and better pads, or 3: find someone who is very familiar with these systems, have them take a ride and see what they say. Unfortunately I don't have a good idea of how these stock brakes feel as I feel as they have never been what they should be 

 

[unilec 57]

Yeah, was just wondering if you still had a bit of air in the master cylinder, always a good idea to bench bleed masters. The push rod between the booster and master is also adjustable.

[Shep69 149]

On 6/24/2018 at 8:37 AM, bryonbush said:

Hey partner,  any update? For as long as I have had my 69, even with all new every thing related to the brakes and they still suck. At this point I'm thinking it's maybe just the pads because I've bled this system a gazillion times and nothing seems to change 

Sorry for the late reply. I’ve been off the grid for a while.

So I replaced the master cylinder after bench bleeding it. Still crap brakes. So I decided to do a vacuum test on the recently installed new booster using a hand vacuum pump and gauge. BOOM . The new booster had an issue. It wouldn’t hold vacuum. I was lucky enough that I had another new spare one . I tested it and it held vacuum overnight. 

After installing the booster I finally have brakes. So I guess even though the parts were new they still were defective. I’m kicking myself as I didn’t think of it earlier.

hope this helps

Mark