mysterious brake issue. Pedal goes to the floor and is binding.

[White75]

I have a 75 L48 Automatic.
The car had a leaky caliper that was discovered when it failed inspection because the pedal had no resistance (it still stopped but only when the pedal was all the way to the floor). I replaced the calipers and lines and bled the system with a pump bleeder attached to the caliper.
No Dice.
Replaced the Master cylinder because of obvious leaks near the booster. Rebled the system.
Still nothing.
I just replaced the Brake Booster and there is a bit more resistance in the pedal and when I depress the pedal with the M/C cover off I can see it squirt so I am getting something there.
However the pedal still goes to the floor. I also noticed that the pedal is binding on something but there is nothing that looks like it is in the way. I took some measurements. When the pedal is all the way forward it is 7 inches from the back of the floorboard. When you push on the pedal, it goes down 2 inches with no resistance and then you get the resistance where I assume the pedal is actually moving fluid. Release the pedal and it only goes up 4-5 inches from the floor (5 being the point where the resistance kicks in when it is depressed). To get it to come up to the 7 inch mark, I have to pull it up manually, when I do that it feels like it is binding or catching on something but I don't know what. I see a red spring at the top of the pedal and I sprayed some white lithium grease all up in there to see if that was the culprit but nothing.
So here I am with an entire new brake system (Pads, Calipers, flex lines, Master Cylinder, Brake Booster, and about a gallon of fluid) yet the problem is still there. There are no obvious leaks anywhere and all the hardline looks fine.
Is there anything else that it could be? I do not want to drive it in fear of nothing working at all (just my luck). If there is anything that anyone can think of to fix this so I can get some brake pressure and confidence in the car I would greatly appreciate it.

Thanks,
Greg Davis
1975 L-48 Auto.
"The white money pit"

 

[bill81vette]

Greg,I would start with where the pedal connects under the dash.that could be where your binding could be coming from.Is this a high mileage vette???
could be the pedal at the point it swivels under the dash is worn out and needs to be replaced.
it is about the only logical explanation I could think of based on your description of events
perhaps somebody else can think of something else
good luck

 

[White75]

Greg,I would start with where the pedal connects under the dash.that could be where your binding could be coming from.Is this a high mileage vette???
could be the pedal at the point it swivels under the dash is worn out and needs to be replaced.
it is about the only logical explanation I could think of based on your description of events
perhaps somebody else can think of something else
good luck

It's very high miles. It's hard for me to get up there and look (I'm 6'3 and flexibility is not my strongpoint). I'm gonna try and see if that may be the issue.
Thanks for the reply.

 

[tcolyer]

Has this problem been on the car the entire time you have had it or has it just started? If it has been there, since before you had the car check the master cylinder to booster rod it maybe the short rod vs the long rod which could account for the 2" of free travel.

 

[White75]

Has this problem been on the car the entire time you have had it or has it just started? If it has been there, since before you had the car check the master cylinder to booster rod it maybe the short rod vs the long rod which could account for the 2" of free travel.

Not 100% sure how long it has been happening. It wasn't driven much for the last 2 years From the time I've driven it, it hasn't changed.
When I installed the new booster I checked the length of the rod to make sure it was the right length. This was done prior to the discovery of the bind so that may very well account for the 2 inch discrepancy. Didn't really think of that so I'll give that a try too. Thanks!

 

[vigman]

A similar thing on my 73

The car SAT for so long in made a BIG CRUST of RUST in the master.

There were NO LEAKS.. however.... when I installed my NEW calipers..
I had to bleed the entire system.. on the first couple of strokes the master seized internally ( the O rings & seals beached on the rust reef ) and would NOT return back until I FORCED AIR ( bad idea ) back feeding the master.. and I could hear the shaft go POP.. back into position.

Needless to say.. I stopped.. and replaced that straight away~

You can take the master out.. loosen it just enough from the booster
have someone be the return " spring " ( via the outside while your pushig the brake) do you still have the binding?


This MIGHT be your problem....
Signs would be ...PRIOR TO YOUR BLEEDING
Could you see the bottom of the bowl in the master?
What color was the fluid?

Vig~

 

[White75]

The car SAT for so long in made a BIG CRUST of RUST in the master.

There were NO LEAKS.. however.... when I installed my NEW calipers..
I had to bleed the entire system.. on the first couple of strokes the master seized internally ( the O rings & seals beached on the rust reef ) and would NOT return back until I FORCED AIR ( bad idea ) back feeding the master.. and I could hear the shaft go POP.. back into position.

Needless to say.. I stopped.. and replaced that straight away~

You can take the master out.. loosen it just enough from the booster
have someone be the return " spring " ( via the outside while your pushig the brake) do you still have the binding?


This MIGHT be your problem....
Signs would be ...PRIOR TO YOUR BLEEDING
Could you see the bottom of the bowl in the master?
What color was the fluid?

Vig~

Thanks. The master cylinder is maybe a month old. The old one was leaking out the back (by the booster). The fluid in there is clear and when I bled them last it was coming out clear too so I think the lines are clean.
The binding was there when I had the MC off for adjustment of the booster rod.

 

[petes74ttop]

I find it a little easier to get under the dash with the seat removed.
Did you bench bleed the new M/C?
There a 4 bleed screws on the rear.
Hope this helps, PG.

 

[Hib Halverson]

One problem is that you cannot use vacuum bleeding on the 65-83 disc brake system.

1) Remove the master cylinder and bench bleed it. Some aftermarket suppliers of new or reman. cylinders actually supply the short hoses you run from the cylinder outlets into the reserviour. If you didn't get them with the cylinder, you have to make them before you bench bleed.

2) Reinstall the master

3) Pressure bleed the system per the service manual. When you do this, jack up the back of the car and remove the tires so you can easily access all four rear bleeders.

4) If you have a combination valve after the master, you may need to center it and the instructions to do that will be in the FSM

 

[White75]

One problem is that you cannot use vacuum bleeding on the 65-83 disc brake system.

1) Remove the master cylinder and bench bleed it. Some aftermarket suppliers of new or reman. cylinders actually supply the short hoses you run from the cylinder outlets into the reserviour. If you didn't get them with the cylinder, you have to make them before you bench bleed.

2) Reinstall the master

3) Pressure bleed the system per the service manual. When you do this, jack up the back of the car and remove the tires so you can easily access all four rear bleeders.

4) If you have a combination valve after the master, you may need to center it and the instructions to do that will be in the FSM

Thanks.
The MC is bench bled.
I am going to go the old-fashioned method of bleeding once my wife gets back to town.
What's the combination valve? I've never heard of that before

 

[pbcanney]

It's very high miles. It's hard for me to get up there and look (I'm 6'3 and flexibility is not my strongpoint). I'm gonna try and see if that may be the issue.
Thanks for the reply.

I'm 5' 6" and have a hard time under the dash.

I just changed the booster / mc on mine. Getting the pin through the clevis/pedal was a painful experience. I removed the driver seat and used a couple of throw pillows to level the area where my back was with my feet in the behind the seats area.

My wag is the system needs to be bled the old fashioned 2 man way. BUT, if one caliper was worn out......... I'd be looking at the others.

I've always replaced brakes / parts / calipers at least 2 at a time anyways. Fluid will follow the path of least resistance.

I think the combination valve Hib is referring to is the brass valve the mc is connected to on the frame by the 2 steel lines coming out of the mc.

 

[White75]

I'm 5' 6" and have a hard time under the dash.

I just changed the booster / mc on mine. Getting the pin through the clevis/pedal was a painful experience. I removed the driver seat and used a couple of throw pillows to level the area where my back was with my feet in the behind the seats area.

My wag is the system needs to be bled the old fashioned 2 man way. BUT, if one caliper was worn out......... I'd be looking at the others.

I've always replaced brakes / parts / calipers at least 2 at a time anyways. Fluid will follow the path of least resistance.

I think the combination valve Hib is referring to is the brass valve the mc is connected to on the frame by the 2 steel lines coming out of the mc.

Yes, that clevis pin is a *****! I haven't even gotten the clip back on in case I need to remove the booster or pedal assembly. I'll have to get my wife to take a picture of me when I'm under there again. My legs are either hanging out of the door (killing my back) or vertical (t-top is off for this very reason
I know the block your talking about now. I'll see what centering it means. Doesn't look like it's been moved in 30 years

 

[pbcanney]

I feel your pain. look at this idiot

Yes, that clevis pin is a *****! I haven't even gotten the clip back on in case I need to remove the booster or pedal assembly. I'll have to get my wife to take a picture of me when I'm under there again. My legs are either hanging out of the door (killing my back) or vertical (t-top is off for this very reason
I know the block your talking about now. I'll see what centering it means. Doesn't look like it's been moved in 30 years

 

[MikeMc71]

I feel your pain, when doing major work under the dash I:

1) Remove the steering wheel

2) remove the seat

3) throw pillows is a must

4) sleep there, so I don't have to get in and out of the f*%$#@* thing at night.

5) Pay someone to hand me tools

6) See a chiropractor when my wife and son finally pry my body out

and I'm only 5'8"..........................good luck, M8!!!

 

[White75]

I feel your pain. look at this idiot

That's just about the way I'm positioned

 

[thesurvivor]

Hey Hib.....why can't these brakes be vacuum bled? I admit it didn't work on my '73, while gravity bleeding did. Why is that?

 

[White75]

Latest update:
I installed speed bleeders on all calipers (6 total) and manually bled the brakes. I got no air and a touch of pressure in the pedal but it still goes to the floor. Cranked up the vette (that only took 2 cranks!) just to see and the pedal went all the way to the floor. I am completly flabbergasted at this point. I am just about ready to take it to a shop and get someone to professionally look at it because I have exhausted my knowledge. I checked all the lines and fittings and there is no leaks whatsover. I went so far as to look at the vacuum lines as well!
Any clues to my next steps. After hearing it run and growl I really want to get it out on the road

 

[Hib Halverson]

Hey Hib.....why can't these brakes be vacuum bled? I admit it didn't work on my '73, while gravity bleeding did. Why is that?

The piston seal system in the C2/C3 disc brake system is only marginally capable of sealing when there's a negative pressure differential, ie: when the pressure behind the pistons (a vacuum) is lower than atmospheric. In most cases, applying a vacuum to the brake calipers sucks air past the piston seals and into the caliper.

Of course, that defeats the purpose of bleeding by introducing more air into the system than was there to begin with.

 

[Hib Halverson]

Latest update:
I installed speed bleeders on all calipers (6 total) and manually bled the brakes. (snip)
Any clues to my next steps. After hearing it run and growl I really want to get it out on the road

Ok. The master has been bench bled. Now, take the speed bleeders out and either pressure bleed the system or manually (foot) bleed the system.

Also, in what condition are the piston bores in the calipers on the car? New? used? If used, how old and how often had the fluid been changed? If new, are they stainless sleeved?

 

[White75]

Ok. The master has been bench bled. Now, take the speed bleeders out and either pressure bleed the system or manually (foot) bleed the system.

Also, in what condition are the piston bores in the calipers on the car? New? used? If used, how old and how often had the fluid been changed? If new, are they stainless sleeved?

Everything is bled now. I got good, clear, bubble- free fluid out of all 6 ports using the foot method with no speed bleeders. Pedal is still going to the floor and not coming all the way up. The good news is that the fluid is flowing so there is pressure somewhere in the system.

The pistons are brand new rebuilds, stainless sleeved but no o-ringed. I checked for leaks too and didn't see any.