No Rear Brakes with lots of troubleshooting need help!! - The 1947 - Present Chevrolet & GMC Truck Message Board Network

NPilot1975 · 03-18-2007, 09:27 PM

OK, I was driving my truck the last 2 weeks as my daily driver. I was suspect of my rear brakes and finally jacked it up this weekend to see if they were working and they weren't. First I tried the obvious and rebled all 4 brakes, with neg results. Then, I used CPP and some comments from the board and tried to reset the combination valve, still no rear brakes. At this point, I am not sure what else to try another than a new master cylinder. Attached below is a photo of my current setup. Is it the right one for disc front and drum rear? Thanx for any help.

KFreddy · 03-18-2007, 09:53 PM

With disc all around you can ditch the combination valve but you will need to add and use a proporting valve for front/rear bias adjustment...

NPilot1975 · 03-19-2007, 10:10 AM

Is there a way tell if the MC is good without taking it off? I had the lid off, if the brakes were pumped there was a jet of fluid that would come up in each bowl (not out of the bowl but above the surface of the fluid.) I was told this is not good. I get fluid at all four corners, but the front discs work and the rear drums have nothing. I am assuming MC or Combo Valve????

JimKshortstep4x4 · 03-19-2007, 07:24 PM

I would suggest taking the line to the rear off of the prop valve and try bleeding it there first. If no fluid comes through it is the prop valve or the MC.
To eliminate the prop valveas a problem bleed the rear of the MC only.

All of the Master Cylinders that I have seen have the fluid stream up when depressing the brake pedal.

Sometimes bleeding the rear brakes can take forever so if the MC and prop valve check out, just keep bleeding the rear.

Jim

GREASEMONKEY72 · 03-19-2007, 07:42 PM

one another thing to think about is the wheel cylenders

goodluck

PanelDeland · 03-19-2007, 08:49 PM

If you don't have a good stream of brake fluid at the rear wheels(if it dribbles rather than squirts) You could have a collapsed hose on the rear.You may still get some fluid but it may not be enough to actuate the shoes.

RANDY COX · 03-19-2007, 08:51 PM

Check the rear end rubber line (on the differential) if it's old and drie rotted it will collaps and thus no fluid,will pass through.Hope this helps.

RANDY COX · 03-19-2007, 08:54 PM

Oops,Paneldeland beat me to it,wouldn't hurt to check.

**oldgold70c10** · 03-19-2007, 08:54 PM

When I did my rears I didn't just bleed them, I used one of those mityvac pumps and actually flushed all the old fluid and lines out. It took several refills of the master cylinder before the fluid didn't come out black and full of stuff: a good reason for changing the hoses- they rot from the inside too, and they are 30+ years old.

NPilot1975 · 03-19-2007, 11:40 PM

Thanx for all the comments. I may try to bleed the back again, although it seems to have pretty good stream when bleeding. I completely rebuilt the rear brakes 5000 miles ago and they look like they haven't been working at all. The shoes still look new. The combo valve is tripped and I can't get it to center, could that indicate a MC problem?

JimKshortstep4x4 · 03-20-2007, 05:30 AM

Are you saying that you cannot get fluid past the prop valve?

If the valve is tripped and you cannot center it, there may be a leak in the rear. If it is tripped, you can usually get fluid by if you pump the brakes very lightly.

Power bleeding as mentioned is a very good way to go.

Jim

A.P. · 03-20-2007, 02:11 PM

NPilot1975
I recently fixed my truck's brake problems and it was similiar like yours. My front brakes would lock easily and the rears would not assist. It turned out to be my prop valve was stuck.

03-18-2007, 09:27 PM	#1
NPilot1975 Senior Member Join Date: Aug 2002 Location: Plymouth, MA Posts: 891	No Rear Brakes with lots of troubleshooting need help!! OK, I was driving my truck the last 2 weeks as my daily driver. I was suspect of my rear brakes and finally jacked it up this weekend to see if they were working and they weren't. First I tried the obvious and rebled all 4 brakes, with neg results. Then, I used CPP and some comments from the board and tried to reset the combination valve, still no rear brakes. At this point, I am not sure what else to try another than a new master cylinder. Attached below is a photo of my current setup. Is it the right one for disc front and drum rear? Thanx for any help. Attached Images __________________ 1972 Blazer body...need to get a thread started for the rest of the story Last edited by NPilot1975; 03-18-2007 at 10:04 PM.

03-18-2007, 09:53 PM	#2
KFreddy Active Member Join Date: Apr 2005 Location: Miami, Florida Posts: 286	Re: No Rear Brakes with lots of troubleshooting need help!! With disc all around you can ditch the combination valve but you will need to add and use a proporting valve for front/rear bias adjustment...

03-19-2007, 10:10 AM	#3
NPilot1975 Senior Member Join Date: Aug 2002 Location: Plymouth, MA Posts: 891	Re: No Rear Brakes with lots of troubleshooting need help!! Is there a way tell if the MC is good without taking it off? I had the lid off, if the brakes were pumped there was a jet of fluid that would come up in each bowl (not out of the bowl but above the surface of the fluid.) I was told this is not good. I get fluid at all four corners, but the front discs work and the rear drums have nothing. I am assuming MC or Combo Valve???? __________________ 1972 Blazer body...need to get a thread started for the rest of the story Last edited by NPilot1975; 03-19-2007 at 10:14 AM.

03-19-2007, 07:24 PM	#4
JimKshortstep4x4 Senior Member Join Date: Jul 2001 Location: Muskegon,MI,USA Posts: 6,026	Re: No Rear Brakes with lots of troubleshooting need help!! I would suggest taking the line to the rear off of the prop valve and try bleeding it there first. If no fluid comes through it is the prop valve or the MC. To eliminate the prop valveas a problem bleed the rear of the MC only. All of the Master Cylinders that I have seen have the fluid stream up when depressing the brake pedal. Sometimes bleeding the rear brakes can take forever so if the MC and prop valve check out, just keep bleeding the rear. Jim __________________ 1971 Shortbox step side 4x4, 350 sbc, 3:07 rear end 1965 Impala SS 400 sbc, Muncie rock crusher 1966 Impala SS 396 bbc, TH 400 1969 El Camino, 350 sbc, TH 350 1971 Snowplow built on a Blazer frame 1972 GMC Short bed, stepside, TH 400, 427 BBC

03-19-2007, 07:42 PM	#5
GREASEMONKEY72 Registered User Join Date: Aug 2006 Location: Bakersfield,CA Posts: 7,893	Re: No Rear Brakes with lots of troubleshooting need help!! one another thing to think about is the wheel cylenders goodluck __________________ -steven Alte Seele S.S. "Allison" '72 C/10 LWB 350SB/TH350 - DD PITBULL IS NOT A CRIME

03-19-2007, 08:49 PM	#6
PanelDeland I am a Referee of life. Join Date: Jun 2000 Location: Greensboro N.C. Posts: 13,993	Re: No Rear Brakes with lots of troubleshooting need help!! If you don't have a good stream of brake fluid at the rear wheels(if it dribbles rather than squirts) You could have a collapsed hose on the rear.You may still get some fluid but it may not be enough to actuate the shoes. __________________ The 47-present Chevrolet and GMC Truck Message Board Network,it's owners,moderators,members,and associates of any type should not be held responsible for my opinion. You can't fix stupid,not even with duct tape. "My appearance is due to the fact that "GOD" does punish you for having too much fun!" Barrett-Jackson has perfected alchemy,they make rust into gold! "You can lead a horse to water but you can't saddle a duck" "Cleverly disguised as a 'Responsible Adult' "Sometimes your Knight in shining armor is just a retard in tinfoil"

03-19-2007, 08:51 PM	#7
RANDY COX Registered User Join Date: Mar 2001 Location: RADFORD, VA Posts: 2,651	Re: No Rear Brakes with lots of troubleshooting need help!! Check the rear end rubber line (on the differential) if it's old and drie rotted it will collaps and thus no fluid,will pass through.Hope this helps. __________________ 1964 BBC 402 4x4

03-19-2007, 08:54 PM	#8
RANDY COX Registered User Join Date: Mar 2001 Location: RADFORD, VA Posts: 2,651	Re: No Rear Brakes with lots of troubleshooting need help!! Oops,Paneldeland beat me to it,wouldn't hurt to check. __________________ 1964 BBC 402 4x4

03-19-2007, 08:54 PM	#9
oldgold70c10 Who's got steelies? Join Date: Feb 2006 Location: Morrison, Oklahoma Posts: 1,026	Re: No Rear Brakes with lots of troubleshooting need help!! When I did my rears I didn't just bleed them, I used one of those mityvac pumps and actually flushed all the old fluid and lines out. It took several refills of the master cylinder before the fluid didn't come out black and full of stuff: a good reason for changing the hoses- they rot from the inside too, and they are 30+ years old. __________________ 1969 C10 LWB W/ 250 I6 & 3spd 1970 C10 with '67 small window cab, 68 front end, blue; 305/TH350, 3.08 limited slip rear end, manual brakes, power steering; & 4-wheel drums-My daily driver. 1975 Chevelle Malibu Classic Coupe 350/th350 mint green 1970 C20 Suburban 350/700R4 4.10 gearing green & white 1978 Big 10 Silverado 350/th350, working ac, 2 tone blue-My summer daily driver 1983 GMC 1500 Sierra 305/SM465 2.73 rear end How to add a trip odometer to your 67-72 stock speedometer How to rebuild your Q-Jet My Truck Page My Youtube Channel

03-19-2007, 11:40 PM	#10
NPilot1975 Senior Member Join Date: Aug 2002 Location: Plymouth, MA Posts: 891	Re: No Rear Brakes with lots of troubleshooting need help!! Thanx for all the comments. I may try to bleed the back again, although it seems to have pretty good stream when bleeding. I completely rebuilt the rear brakes 5000 miles ago and they look like they haven't been working at all. The shoes still look new. The combo valve is tripped and I can't get it to center, could that indicate a MC problem? __________________ 1972 Blazer body...need to get a thread started for the rest of the story

03-20-2007, 05:30 AM	#11
JimKshortstep4x4 Senior Member Join Date: Jul 2001 Location: Muskegon,MI,USA Posts: 6,026	Re: No Rear Brakes with lots of troubleshooting need help!! Are you saying that you cannot get fluid past the prop valve? If the valve is tripped and you cannot center it, there may be a leak in the rear. If it is tripped, you can usually get fluid by if you pump the brakes very lightly. Power bleeding as mentioned is a very good way to go. Jim __________________ 1971 Shortbox step side 4x4, 350 sbc, 3:07 rear end 1965 Impala SS 400 sbc, Muncie rock crusher 1966 Impala SS 396 bbc, TH 400 1969 El Camino, 350 sbc, TH 350 1971 Snowplow built on a Blazer frame 1972 GMC Short bed, stepside, TH 400, 427 BBC

03-20-2007, 02:11 PM	#12
A.P. Black 72 Chevy Join Date: May 2002 Location: Los Angeles, California Posts: 662	Re: No Rear Brakes with lots of troubleshooting need help!! NPilot1975 I recently fixed my truck's brake problems and it was similiar like yours. My front brakes would lock easily and the rears would not assist. It turned out to be my prop valve was stuck. __________________ 72 Chevy, SWB, 350engine, TH400



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