proportioning valve... bad ? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

sactoC10 · 09-12-2003, 01:02 PM

OK,

The more I think about it, the more I realize that there are three areas that could be causing my brakes to stick...

Screwed up-old and deteriorating brake lines (maybe this is it).

Bad master cylinder (but I don't think so).

Screwed up proportioning valve (leaning more this way).

Here's my problem. I have new spindles, new pads, new fluid and yet the first couple stops are fine, but the following ones get worse and worse until both front brakes feel VERY tight. If the truck sits for a while, the brakes will be fine for another 2-3 presses of the pedal... then everything is stiff again.

What are the thoughts out there, proportioning valve, or lines?

JT

smokekiki · 09-12-2003, 01:17 PM

I would change the lines first.When I changed mine they where around 40.00.

Primed67 · 09-12-2003, 01:21 PM

Are your brakes sticking all around or just in the front?
Do you have disc brakes in the front? If so your calipers may be bad. If they have gotten real hot sometimes it will warp the piston and cause the brakes to drag or lock up. Also how old are your brake lines? I don't think they are the cause of your problem but if they are craked or worn they need to be replaced.

sactoC10 · 09-12-2003, 02:02 PM

Great... a fourth option, yikes.

I am hesitant to go with the caliper option at this point, since when they've gotten tight I've simply babied it home and was never more than 2-3 miles from home. Yet I'm not sure how hot they'd have to be to get warped. And really, the calipers looked to be in very good shape when I took everything apart.

OK, more to investigate.

sactoC10 · 09-12-2003, 02:04 PM

My guess is (even though the ball joints and many other parts have been serviced or replaced) the brake lines are 32 years old. They look old, not cracked...but old.

Woody · 09-12-2003, 02:13 PM

I think (dangerous I know) that I have read about that kind of problem and it was the linkage rod not allowing the master cyc to return all the way. Like you held the brakes part way down. This kept the fluid from returning to the master cyc.

sactoC10 · 09-12-2003, 02:17 PM

YES, that is exactly what the problem feels like.

It is as if the fluid is not returning to the master cyclinder, but simply pumping to the front brakes...continually. Then, when the truck sits for a while, the fluid just "migrates" slowly back to where it is supposed to be.

What linkage rod are you talking about? Is it something IN the master cyclinder? Should I get a rebuild kti for the MC?

boraxman · 09-12-2003, 03:05 PM

Yikes, cant wait to see what kind of problems I will encounter when im done with my DB conversion

So far lets see used 72 master/booster, will it function?(lines dont fit prop valve), 72 spindles(I already know i'll be doing ball joints and tie rod ends). Wait everyone made it sound so easy

sactoC10 · 09-14-2003, 10:34 AM

My problem is not yet resolved. I put the new brake lines in which was a good thing to do. I do not sense the valve is the issue...master cylinder is my next matter to explore.

Boraxman- I spoke to a friend who converted the drums on the front of his old chevelle to disc. He picked up a prop valve from and old nova or something similar at a wrecking yard, bolted it in and had no problem.

Imagine that!

Locutus · 09-14-2003, 04:13 PM

You did replace all the rubber lines? Sometimes they collapse inside, but they look good on the outside. My Sub lines collapsed and it would feel like the brakes weren't releasing in the front. The line lets fluid thru so your brakes work when you press but when you release the pressure the line collapse inside and it acts like a oneway valve. It does bleed down over time.

Mike

Don Smith · 09-14-2003, 11:00 PM

Master cylinders for drum brakes have residual pressure check valves in the outlet ports. Disc brake should not have the check valves in the front outlet. Check valve could cause tight brakes.

Ed ke6bnl · 09-15-2003, 07:52 AM

Quote:

Originally posted by Don Smith
Master cylinders for drum brakes have residual pressure check valves in the outlet ports. Disc brake should not have the check valves in the front outlet. Check valve could cause tight brakes.

We had my boys truck up on stands and then realized the front brake discs were not releasing, we wrote in on this board and they suggested we check the master for a check valve and it was still in there we removed it and it worked correctly. Ed ke6bnl

09-12-2003, 01:02 PM	#1
sactoC10 71 DELUX Join Date: Sep 2003 Location: Northern CA / Sac Posts: 1,056	proportioning valve... bad ? OK, The more I think about it, the more I realize that there are three areas that could be causing my brakes to stick... Screwed up-old and deteriorating brake lines (maybe this is it). Bad master cylinder (but I don't think so). Screwed up proportioning valve (leaning more this way). Here's my problem. I have new spindles, new pads, new fluid and yet the first couple stops are fine, but the following ones get worse and worse until both front brakes feel VERY tight. If the truck sits for a while, the brakes will be fine for another 2-3 presses of the pedal... then everything is stiff again. What are the thoughts out there, proportioning valve, or lines? JT

09-12-2003, 01:17 PM	#2
smokekiki Mike Join Date: Jan 2003 Location: west chester pa Posts: 2,474	I would change the lines first.When I changed mine they where around 40.00. __________________ 70'c/10, 71 suburban4x4 402bb, 72suburban 4/6 drop, 72k/5 4x4 blazer 4" lift 35 tires

09-12-2003, 01:21 PM	#3
Primed67 Registered User Join Date: Sep 2003 Location: Tyler Posts: 575	Are your brakes sticking all around or just in the front? Do you have disc brakes in the front? If so your calipers may be bad. If they have gotten real hot sometimes it will warp the piston and cause the brakes to drag or lock up. Also how old are your brake lines? I don't think they are the cause of your problem but if they are craked or worn they need to be replaced. __________________ 1969 Chevrolet SWB Stepside 1959 Chevrolet apache * Sold 1967 Prostreet Chevy SWB Fleetside *Sold 2014 1/2 ton Crew Cab Chevrolet 4x4

09-12-2003, 03:05 PM	#8
boraxman Keepin an eye out Join Date: Feb 2003 Location: So.Cal Posts: 3,921	Yikes, cant wait to see what kind of problems I will encounter when im done with my DB conversionSo far lets see used 72 master/booster, will it function?(lines dont fit prop valve), 72 spindles(I already know i'll be doing ball joints and tie rod ends). Wait everyone made it sound so easy __________________ 1970 Chevy C10 SWB 5.3 1996 Toyota Tacoma SR5 4x4 2007 Vespa GTS 250 Scooter ZIP 91351

09-14-2003, 10:34 AM	#9
sactoC10 71 DELUX Join Date: Sep 2003 Location: Northern CA / Sac Posts: 1,056	probably not valve... My problem is not yet resolved. I put the new brake lines in which was a good thing to do. I do not sense the valve is the issue...master cylinder is my next matter to explore. Boraxman- I spoke to a friend who converted the drums on the front of his old chevelle to disc. He picked up a prop valve from and old nova or something similar at a wrecking yard, bolted it in and had no problem. Imagine that!

09-12-2003, 02:02 PM	#4
sactoC10 71 DELUX Join Date: Sep 2003 Location: Northern CA / Sac Posts: 1,056	Great... a fourth option, yikes. I am hesitant to go with the caliper option at this point, since when they've gotten tight I've simply babied it home and was never more than 2-3 miles from home. Yet I'm not sure how hot they'd have to be to get warped. And really, the calipers looked to be in very good shape when I took everything apart. OK, more to investigate.

09-12-2003, 02:04 PM	#5
sactoC10 71 DELUX Join Date: Sep 2003 Location: Northern CA / Sac Posts: 1,056	My guess is (even though the ball joints and many other parts have been serviced or replaced) the brake lines are 32 years old. They look old, not cracked...but old.

09-12-2003, 02:13 PM	#6
Woody Registered User Join Date: Feb 2000 Location: Georgetown, KY, USA Posts: 631	I think (dangerous I know) that I have read about that kind of problem and it was the linkage rod not allowing the master cyc to return all the way. Like you held the brakes part way down. This kept the fluid from returning to the master cyc.

09-12-2003, 02:17 PM	#7
sactoC10 71 DELUX Join Date: Sep 2003 Location: Northern CA / Sac Posts: 1,056	YES, that is exactly what the problem feels like. It is as if the fluid is not returning to the master cyclinder, but simply pumping to the front brakes...continually. Then, when the truck sits for a while, the fluid just "migrates" slowly back to where it is supposed to be. What linkage rod are you talking about? Is it something IN the master cyclinder? Should I get a rebuild kti for the MC?

09-14-2003, 04:13 PM	#10
Locutus Registered User Join Date: Jan 2003 Location: Santa Fe, Texas Posts: 250	You did replace all the rubber lines? Sometimes they collapse inside, but they look good on the outside. My Sub lines collapsed and it would feel like the brakes weren't releasing in the front. The line lets fluid thru so your brakes work when you press but when you release the pressure the line collapse inside and it acts like a oneway valve. It does bleed down over time. Mike

09-14-2003, 11:00 PM	#11
Don Smith Registered User Join Date: Jul 2000 Location: Hampton, Ga, USA Posts: 217	Master cylinders for drum brakes have residual pressure check valves in the outlet ports. Disc brake should not have the check valves in the front outlet. Check valve could cause tight brakes. __________________ 68 Short Stepside, 350, quadrajet, 700r4, 3:73 posi, power front discs, HEI, Factory Air, Tilt, Tach, accelerator cable instead of rod, sway bar. 96 Impala SS 97 Monte Carlo

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