Soft Brake pedal 1983 Riviera Convert V6

[kevinfoley]

Hello i need some advice on a soft brake pedal. Last fall i had the rotors and pads replaced .After that The soft pedal started the brake light would come on go off go on go off.

The master looked pretty old. So i parked it for the winter .The weather changed took it for a ride that brake light came on.So i changed the master.Bled the brakes .WTF soft pedal .So i took the new master back exchanged it installed new one after i bench bled it .Bled the whole system still soft. Now when i bled the rears, pump pump pump Hold hardly any fluid would would come out.Then the car sat for another month weather was bad .So now i'm back at it .Last nite before i went home i open the right rear bleeder and left it open so gravity would go to work .A few drips .Now i'm here asking you guys if you have any tricks of the trade. 

Thanks Kevin

[1965rivgs]

There are several possibilities.

It is possible given the quality of aftermarket parts, but not probable given this is the 3rd master, the master is not good. Is the rebuilder a quality rebuilder with a reputation to protect?

It`s possible your technique is not proper but I`m assuming you have the necessary experience to bleed the brakes?

It is possible the proportioning valve is bad and not allowing fluid flow to the rear brakes.

I had a similar problem with an Eldorado of the same vintage with 4 wheel disc brakes. Couldnt get the brakes to bleed out and attain a good pedal. Turned out there was a collapsed rear rubber brake hose which was not allowing the system to flow properly. This is a long shot but was the cure in that particular situation.

  Tom Mooney

[kevinfoley]

Hello Tom thanks for the reply .I had left you a message last winter and you were kind enough to Return my call.The reason i did not return your calls back was i had open heart surgery and now i member of the Zipper Chest Club. I was in storage for a couple months LOL.I put the motor replacement project on my Riviera until next fall that was the reason i was calling .I needed a reliable Trans Rebuilder ,And Turbo Motor Guy ..

Well thank you for the advice i will add you ideas to my forensic investigation of this brake system.

[Seafoam65]

                When we get cars in my shop with a new master cylinder installed that when we bleed we can't get fluid out of the back, it is always a proportioning

valve that  has the piston stuck off to one side. The original problem was probably your master cylinder which you have corrected. The

original problem you had with your master cylinder caused the proportioning valve piston to move off center and now it is stuck in the sludge

inside the valve. This is not uncommon......I had one of these no fluid out the back issues two weeks ago on a car we changed the master

cylinder on. Usually you can get the piston unstuck by stomping on the brake pedal very hard numerous times....Raise your foot way up and

slam it down stomping on the pedal. If you do that enough usually the  piston in the proportioning valve will be jarred loose and move back to the center.

I've never actually had to replace a proportioning valve for this issue, normally you can get them unstuck if you jack with them long enough. You did

not state whether the master cylinder you installed is a reman or new. If it is not new, replace it with a new one. Reman master cylinders are a huge NO NO. As far as the rear brake hose being restricted, yes that will cause no fluid out the back, but the car will have a firm pedal, just no rear brake

actuation. 

Edited May 3, 2017 by Seafoam65 (see edit history)

[1965rivgs]

8 hours ago, Seafoam65 said:

                When we get cars in my shop with a new master cylinder installed that when we bleed we can't get fluid out of the back, it is always a proportioning

valve that  has the piston stuck off to one side. The original problem was probably your master cylinder which you have corrected. The

original problem you had with your master cylinder caused the proportioning valve piston to move off center and now it is stuck in the sludge

inside the valve. This is not uncommon......I had one of these no fluid out the back issues two weeks ago on a car we changed the master

cylinder on. Usually you can get the piston unstuck by stomping on the brake pedal very hard numerous times....Raise your foot way up and

slam it down stomping on the pedal. If you do that enough usually the  piston in the proportioning valve will be jarred loose and move back to the center.

I've never actually had to replace a proportioning valve for this issue, normally you can get them unstuck if you jack with them long enough. You did

not state whether the master cylinder you installed is a reman or new. If it is not new, replace it with a new one. Reman master cylinders are a huge NO NO. As far as the rear brake hose being restricted, yes that will cause no fluid out the back, but the car will have a firm pedal, just no rear brake

actuation. 

Winston,

  My experience with a collapsed brake hose which is restricting fluid flow (not necessarily completely blocking fluid flow) is that the system cannot be properly bleed using standard techniques and therefore produces a soft pedal.

  Tom

[1965rivgs]

19 hours ago, kevinfoley said:

Hello i need some advice on a soft brake pedal. Last fall i had the rotors and pads replaced .After that The soft pedal started the brake light would come on go off go on go off.

The master looked pretty old. So i parked it for the winter .The weather changed took it for a ride that brake light came on.So i changed the master.Bled the brakes .WTF soft pedal .So i took the new master back exchanged it installed new one after i bench bled it .Bled the whole system still soft. Now when i bled the rears, pump pump pump Hold hardly any fluid would would come out.Then the car sat for another month weather was bad .So now i'm back at it .Last nite before i went home i open the right rear bleeder and left it open so gravity would go to work .A few drips .Now i'm here asking you guys if you have any tricks of the trade. 

Thanks Kevin

Kevin,

Just a couple more thoughts....when the brake light comes on it is an indication more fluid is pushing thru one circuit versus the other which is why the piston in the proportioning valve moves off center and trips the brake light. Since installing the last master is your brake light on full time? Or does it come on when you put pressure on the brake pedal? Or is it not on at all now?

If not at all the piston should be centered in the valve. If all the time the piston is off to one side of the valve and may be stuck. If it comes on and goes off that is an indication it is at least free in the valve.

Also, some systems will not gravity bleed well. This can be due to the master being mounted at an extreme angle on the booster trapping air in the master or a brake line with a loop which also traps a column of air, etc...best to use the pedal to encourage positive flow or a power bleeder.

Tom

PS Of course, you have checked for leaks? Especially at the calipers after a pad change?