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So, anybody ever heard of this brake issue?

shady

shady

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I'm working on a buddies 05 chevy cavalier. It has a weird 2 input/4 output proportional valve.
It had an issue with the proportioning valve that was keeping the fluid from putting pressure to the passenger rear wheel. Unfortunately though, that prop valve seems to be discontinued.
He said 'Just make it stop.' so we took the odd 4 way prop valve out and installed T's. Intending to add a cheap aftermarket prop valve before the rear T.
Went to bleed the brakes (car off of course) using my pressure bleeder.
When you open the rear bleeders, fluid shoots out. All air is out, all is good. But when you crack the fronts, fluid/air suck INTO the calipers from the hose and catch bottle lol.
never seen anything like it, and beings the system was just wide open installing T's,... HOW is there a vacuum on it at all. lol. Car was never started.
and the pressure bleeder still has pressure...:dunno:
Other funny part is, if you open a front bleeder, and push the pedal you can get the flow to go out like it should SLOWLY. And remember the rears are good.
But when you try the actual brakes , (fronts still have air, and a weird vacuum), the fronts will grab the discs, and the rear brakes don't apply at all:doah:

I bought a new master for it, assuming its shot. But figured I'd tell others about the craziness I'm dealing with lol.
 
Is the master not supposed to pull vacuum when you release the brakes? Best guess is there was some residual negative pressure in there when you cracked the front. In any case, I think replacing the master is the best idea here, and if you can get your buddy to pitch for it, install an aftermarket prop valve wherever you can..
 
I opened the bleeders on both sides, a bunch. This was happening without even touching the pedal. Never did even out lol. And, it had a bunch of pressure on from the pressure bleeder.
I'm thinking about just opening them and leave em that way to see what happens lol.
 
I just looked up the procedure on AllData for this car and it's quite the bleeding procedure. This one also has the scan tool bleed procedure. I'm sure it's your abs stuff that is giving you issues.
 

Attachments

  • Hydraulic Brake System Bleeding (Pressure) (Brake Bleeding) - ALLDATA Repair.pdf
    147.1 KB · Views: 1
  • ABS Automated Bleed Procedure (Brake Bleeding) - ALLDATA Repair.pdf
    204.7 KB · Views: 1
Sound like exactly what I did, except the cross bleeding. Right rear, then left front. I did the old school, RR-LR-RF-LF.
No ABS on this car
 
Some cars have a electric assist module which is why they have a bleed procedure that requires a scan tool. Not sure if this is one but if it has any kind of OBD2 you should look into what data you might be able to read with a scan tool and if it is registering brake info anywhere then that may be your tell-tale sign.
 
No. This one amazingly, being an 05, was straight up standard old school brakes. Only thing that made it different than our square bodies is it had a 6 port prop valve. 2 in, 4 out. The shop they had taken it to for brake work said the prop valve was bad. It's not made anymore I guess. I sure couldn't find one either :dunno:.
Dude brought it to me and asked if I could make it stop.
I loosened the lines at the prop valve and only had fluid coming out of 3 of the outs when the pedal was pushed. So I removed the prop valve and installed T's. Then tried to bleed it and craziness ensued.
Changed the master and it bled right out no issues and stops awesome. Even at a fast panic stop.
Tried it on gravel to see if the rears locked before the fronts, and the fronts locked first.
Told the dude what I did and gave it back to him.

The only thing I can think of making that vacuum on the front calipers is the pressure bleeding through the master to the rears when I bled them, created that vacuum on the fronts due to the Venturi effect leaking by seals in the master. Otherwise, that part still baffles me lol. Because I still had full pressure on the reservoir, and the front bleeders were sucking in.:dunno::screwy:

Out of my hair now. It's the dudes late 20's sons car. Not his only one. And supposedly he's going to try and sell or trade it off.
Told him I could re try the prop valve. But id have to buy adapters, since I had to change the thread parts and reflare everything installing the T's. He said he wasn't putting another dime in it and just wanted it out of his hair too. Lol.
Guess his son had a nice Mitsubishi he traded off recently for $100 at a dealership:doah:, and kept this POS.
 
It was definitely a proportioning valve that was removed right? My only thought was that if someone removed the balance valve that shuts off the front or rear when a line blows then bleeding the back may cause a vaccuum in the front because the front and rear are no longer isolated. Maybe it was a combination balance balance and prop valve?
 
That's a big possibility. But it's out and not going back in lol. Maybe we couldn't find it because it was called a balance valve.
Either way, it wasn't working.
 
picture of valve you removed ?? Is called dual diagonal brake system. many fwd cars are using this system.
 
shady said:
I'm working on a buddies 05 chevy cavalier. It has a weird 2 input/4 output proportional valve.
It had an issue with the proportioning valve that was keeping the fluid from putting pressure to the passenger rear wheel. Unfortunately though, that prop valve seems to be discontinued.
He said 'Just make it stop.' so we took the odd 4 way prop valve out and installed T's. Intending to add a cheap aftermarket prop valve before the rear T.
Went to bleed the brakes (car off of course) using my pressure bleeder.
When you open the rear bleeders, fluid shoots out. All air is out, all is good. But when you crack the fronts, fluid/air suck INTO the calipers from the hose and catch bottle lol.
never seen anything like it, and beings the system was just wide open installing T's,... HOW is there a vacuum on it at all. lol. Car was never started.
and the pressure bleeder still has pressure...:dunno:
Other funny part is, if you open a front bleeder, and push the pedal you can get the flow to go out like it should SLOWLY. And remember the rears are good.
But when you try the actual brakes , (fronts still have air, and a weird vacuum), the fronts will grab the discs, and the rear brakes don't apply at all:doah:

I bought a new master for it, assuming its shot. But figured I'd tell others about the craziness I'm dealing with lol.
Click to expand...
Did i see that correctly: 2005? With ABS ?
 
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