Home page
SPONSOR AD SPONSOR AD

Topic: 1977 Proportioning Valve

in Forum: C3 Engines, Driveline and Handling


1977 Proportioning Valve

Posted: 11/8/07 2:20pm Message 1 of 12
Former Member
Send PM
Toledo, OH - USA
Joined: 2/22/2007
Posts: 175
Vette(s): 1977 auto.L48 383 stroker
I am having problems getting pressure back on the brake pedal after bleeding the brakes.  Can this be caused by a bad proportioning valve and if so what do i need to do from here.  Thanks for all the help. I am stranded and need a life vest!


SPONSOR AD:: (Our Sponsors help support C3VR)

1977 Proportioning Valve

Posted: 11/8/07 6:17pm Message 2 of 12
Former Member
Send PM
Charleston AFB, SC - USA
Joined: 10/31/2007
Posts: 111
Vette(s): 1979 Cream Beige Coupe w/383 & 700R4
From my experience it tends to be air in the lines. These cars are a b!*ch to bleed properly. You need to also bleed them weird, which the order is: drivers back, pass back, drivers front, pass front.
 
I had a ton of problems with mine, and I'm going to just get a pressure bleeder.
 
As for the valve, you should be able to just slam on the brakes really really hard to center the valve if it was actually offset. If it was actually bad I'm not sure, I wouldn't think it could really do anything besides only give you braking in front or back instead of both if it was bad though? Well, unless it was leaking, but you would see that.
 
Hope that helps any, and good luck.
 
-Josh
Sarge812007-11-09 19:23:19


1977 Proportioning Valve

Posted: 11/8/07 8:16pm Message 3 of 12
Profile Pic
Lifetime MemberLifetime Member
Moderator
Send PM
Duncanville, TX - USA
Joined: 11/8/2003
Posts: 20225
Vette(s): #1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas
Did you have a good pedal before? Did you replace anything, like pads, or calipers?
If so, then you prolly do have some air in the system.

The p-valve can flop to one end if the brakes are not bled properly. If it does, you will only have brakes on one end or the other...front or rear. It will normally re-set itself if you do hit the pedal fairly hard, quickly. Does your "Brake" light come on? If it comes on when you press the pedal, but then goes back off, there is air in the system, or the master may be bad, or have air in it.



Joel Adams
C3VR Lifetime Member #56    

My Link


(click for Texas-sized view!)
             NCRS

"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

1977 Proportioning Valve

Posted: 11/9/07 5:29am Message 4 of 12
Former Member
Send PM
Toledo, OH - USA
Joined: 2/22/2007
Posts: 175
Vette(s): 1977 auto.L48 383 stroker
I did have low pedal before but that was because I found out my right front caliper was leaking.  I replaced both front calipers and hoses on it and put new pads on the front.  I did not bleed the brakes in the sequence as described above.  The proportioning valve does appear to be leaking so I will try to bleed the brakes again in the proper manner.  Thank you for all of your help, I appreciate it!


1977 Proportioning Valve

Posted: 11/9/07 6:55am Message 5 of 12
Profile Pic
Standard Member
Send PM
Florence, KY - USA
Joined: 9/9/2007
Posts: 143
Vette(s): 1977 Coupe; yellow, 4 speed, one option car with original engine
For what it's worth I recently replaced a trailing arm assembly and when replacing the caliper, (with my son in the car as the brake pedal management assistant), I first tried to pump up the brakes and open the valve to let the air out and basically got nowhere. What worked for me was to open the valve on the downward movement of the pedal then close the valve for the upward pedal travel. Took a few strokes and trips to the master cylinder to add fluid but now the pedal is solid and the brakes are good.


current
1977 Coupe
 
gone but not forgotten
1996 Grand Sport
1984 coupe 
1974 coupe
1964 roadster

1977 Proportioning Valve

Posted: 11/9/07 7:34am Message 6 of 12
Profile Pic
Lifetime MemberLifetime Member
Moderator
Send PM
Duncanville, TX - USA
Joined: 11/8/2003
Posts: 20225
Vette(s): #1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas
"Pumping" the brake pedal really only aerates the brake fluid...not a good thing when trying to bleed them!
With the pedal up, open the bleeder screw, then press the pedal down. Once it is all the way down, close the bleeder, and release the pedal slowly.(same method as described above). This works the best, is you have to manually bleed them with the pedal.
Tapping on the caliper with a plastic, or rubber mallet will also help dislodge any air bubbles stuck to the calipers, especially on the rears.
Of course, a pressure bleeder is the absolute best way, but not everyone has one. They are getting cheaper now, tho, so they are a bit more affordable, and well worth the investment for anyone with a Corvette with discs.

I have to say, my sequence for bleeding is not the same as Josh's...the normal procedure is:
RR-LR-RF-LF...you want to bleed the furtherest caliper from the master first. This lessens the chance of having trapped air in the crossover line, that may wind up just floating from one side to the other, and never really getting out.


Joel Adams
C3VR Lifetime Member #56    

My Link


(click for Texas-sized view!)
             NCRS

"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

1977 Proportioning Valve

Posted: 11/9/07 8:22am Message 7 of 12
Profile Pic
Former Member
Send PM
Badin Lake, NC - USA
Joined: 4/21/2004
Posts: 101
Vette(s): 1979 Red L-48 Corvette with Doeskin interior, 3-speed automatic, 3.55 rear; 1986 L-98 Coupe, 4+3 Manual - Satin Black and Purple (SCCA TT/Hillclimb Car); 1993 White LT-1 Coupe, Black Interior, 6-speed
I used the same sequence Joel recommended and it worked fine.  I had the wife pump the brakes and I did the bleed screw management.  You need to close the valve before you let the pedal up to keep air out of the system.  I have a pressure bleeder, but have done just as well with the 4.99 brake bleed kit at autozone.  Little tygon plastic hose and bottle with a  magnet that make it easy.  I like the clear tubing as I can see the color of fluid and check for bubbles/debris in the system.
 
I just replaced all 4 calipers and went to SS lines. Big difference.  BTW - one other thing I noticed on mine was the lack of power boost after a few quick stops - turned out to be two problems.  One was the power boost check valve (6.99 at NAPA - or free from any other GM vehicle) which was leaking and then my 79 had a brake vacuum "filter" which acts like a vacuum restrictor.  You don't need it and so I tossed it in the trash.  Brakes worked fine after that.  It is my understanding from a GM specialist that a number of late 70s GM cars had these filter/restrictors to assist in keeping the vacuum level up in the intake manifold.  In any case, the car runs great without it, and the brakes work like they should. 



C3: 1979 Corvette Coupe, Auto, L-48, Red/Doeskin (my wife's fave);
C4s: 1986 C4 coupe (SCCA road race car), satin black, 4+3, Z51 package, L-98;  & 1993 C4 coupe, white, 6-speed, LT-1.

1977 Proportioning Valve

Posted: 11/9/07 10:25am Message 8 of 12
Former Member
Send PM
Charleston AFB, SC - USA
Joined: 10/31/2007
Posts: 111
Vette(s): 1979 Cream Beige Coupe w/383 & 700R4
[QUOTE=Adams' Apple]I have to say, my sequence for bleeding is not the same as Josh's...the normal procedure is:
RR-LR-RF-LF...you want to bleed the furtherest caliper from the master first. This lessens the chance of having trapped air in the crossover line, that may wind up just floating from one side to the other, and never really getting out.[/QUOTE]
 
Ah. See I got my bleed order from another poster here who said the service manual said the rd, rp, fd, fp order. I'd probably listen to Adams', he knows a lot more about these things than I do :P
 
[QUOTE=sfindlan]my 79 had a brake vacuum "filter" which acts like a vacuum restrictor.  You don't need it and so I tossed it in the trash.  Brakes worked fine after that.  It is my understanding from a GM specialist that a number of late 70s GM cars had these filter/restrictors to assist in keeping the vacuum level up in the intake manifold.  In any case, the car runs great without it, and the brakes work like they should.  [/QUOTE]
 
Hrm, what's this filter look like? I have a 79 as well and would like to know if it can improve pedal feel!
defsegx2007-11-09 10:28:00


1977 Proportioning Valve

Posted: 11/9/07 11:06am Message 9 of 12
Profile Pic
Lifetime MemberLifetime Member
Moderator
Send PM
Duncanville, TX - USA
Joined: 11/8/2003
Posts: 20225
Vette(s): #1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas
[QUOTE=defsegx]Ah. See I got my bleed order from another poster here who said the service manual said the rd, rp, fd, fp order. I'd probably listen to Adams', he knows a lot more about these things than I do [/QUOTE]

Well now...I don't know about that...

Perhaps the person that posted the other method is from Australia, or somewhere else that drives on the wrong side of the roads...


Joel Adams
C3VR Lifetime Member #56    

My Link


(click for Texas-sized view!)
             NCRS

"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

1977 Proportioning Valve

Posted: 11/9/07 2:58pm Message 10 of 12
Former Member
Send PM
Yelm, WA - USA
Joined: 7/12/2007
Posts: 356
Vette(s): 1979 L82 4 speed Scat 383 crank 190 cc Procomp Aluminum Heads 202 160 stainless valves GM Powder metal rods Speedpro H860CP Hypereutectic pistons 280 cam hydralic HEI Pro comp 1.6 roller rockers Mighty Demon 750 Sanderson CC1AP Hedders.
[QUOTE=sfindlan]I just replaced all 4 calipers and went to SS lines. Big difference.[/QUOTE] 
 
Did you replace the rubber with SS and the hard lines too? I am looking at my making or buying new hard lines for mine. Since I got 4 new calipers I'm a little concerned about using the old hard lines as they aint too pretty. 
79rebuild2007-11-09 15:00:35


in Forum: C3 Engines, Driveline and Handling


SPONSOR AD: (Our Sponsors help support C3VR)