Rear brakes locking up... - The 1947 - Present Chevrolet & GMC Truck Message Board Network

smoked68 · 09-29-2010, 12:24 PM

I have just replaced the brake booster, master cyl, and prop valve on my 68 c-10. It is doing the same as it was before I changed everything. Back brakes will lock and slide, especially on wet pavement. I have discs in front drums in back. New calipers front and new cyls. in back. There is no air in the lines and the kit was bought from early classics with everything needed and for a disc drum set up. Any ideas?? Oh they release and work normal when off the brakes, the backs are just grabbing harder than the frnts.. Thanks, Mike

71tahoe · 09-29-2010, 12:34 PM

My rears would lock up because of brake fluid on the shoes. If the rear cylinders have leaked, you may need to replace the shoes. Could also be over adjusted.

68gmsee · 09-29-2010, 01:36 PM

Prop valve may the one for all drum brakes but best thing to do is probably to purchase an adjustable prop valve. That way you can adjust them for maximum stopping front and rear.

It's possible they may be grabby but if everything is new and looks good then a prop valve is what you will need. I don't believe overadjusting is causing the problem unless you have them so tight that the wheel won't turn. Adjust them so they barely rub on the drum without preventing it from turning.

forgot: a good article to read. http://www.chevyhiperformance.com/te...lve/index.html

ChevLoRay · 09-29-2010, 01:53 PM

I think the proportioning valve is the answer, too. I also have ECE disc/drum setup. My rears were locking before the conversion, but it can be because of a leaking axle seal that gets oil on the shoes (I know, but it is what happens) or the wheel cylinder leaking brake fluid onto the lining of the shoe, but that has also been suggested.

If all those parts are new, and you have all new hardware, my thinking is that the Proportioning valve is the right place to start.

smoked68 · 09-29-2010, 03:44 PM

Thanks for the info. Yeah Ive looked no grease or brake fluid on the drums... so I guess Ill go with an adj prop valve. Ok so where do I get one??

68gmsee · 09-29-2010, 05:38 PM

Jegs is a good start but there are others. Probably need to do a search unless someone knows of another place to get one.

Be sure and look through this article.

http://www.chevyhiperformance.com/te...lve/index.html"]http://www.chevyhiperformance.com/te...lve/index.html[/URL]

LostMy65 · 12-15-2010, 04:32 AM

Any recommendation on which adjustable proportioning valve to buy?
baer, etc.

There is quite a selection and prices to choose from:
http://www.jegs.com/webapp/wcs/store...+proportioning
http://www.summitracing.com/search/?...justable&dds=1

cdowns · 12-15-2010, 07:39 AM

you might have proper proportioning valve but hooked up backwards???

cardreams · 07-04-2011, 03:33 PM

have same problem on my truck 1970 power brakes and drums all around how do u know if the proportioning valve is hooked up backwards????

cdowns · 07-04-2011, 05:31 PM

Quote:

Originally Posted by cardreams

have same problem on my truck 1970 power brakes and drums all around how do u know if the proportioning valve is hooked up backwards????

drum brake systems do not have a proportioning valve// they have a distribution block

cardreams · 07-04-2011, 10:50 PM

Quote:

Originally Posted by cdowns

drum brake systems do not have a proportioning valve// they have a distribution block

ok can u but them on backwards????

fastwillie 696969 · 07-05-2011, 02:03 AM

got pics of the rear brakes and drums ? and when you did the rear brakes did you use any lube on the backin plates? how did you adjust the drums by turning by hand or measure the drums and adjust the brakes.
i would like to see the brakes ,how about the e brake cable rusty stickin >> ?

68gmsee · 07-05-2011, 09:38 AM

Be aware that someone may have added power brakes from a newer truck with disk brakes so it is possible to have a prop valve. I did that on my 69 with all drums and it worked fine.

09-29-2010, 12:24 PM	#1
smoked68 Registered User Join Date: Oct 2006 Location: Rock Hill, SC Posts: 421	Rear brakes locking up... I have just replaced the brake booster, master cyl, and prop valve on my 68 c-10. It is doing the same as it was before I changed everything. Back brakes will lock and slide, especially on wet pavement. I have discs in front drums in back. New calipers front and new cyls. in back. There is no air in the lines and the kit was bought from early classics with everything needed and for a disc drum set up. Any ideas?? Oh they release and work normal when off the brakes, the backs are just grabbing harder than the frnts.. Thanks, Mike __________________ 1968 chevy shortbed, Dark Shadow Gray 4 bolt 383 Stroker,Weiand Super Charger, disc brakes, 9 inch, 391 gear, 20" Eagle wheels, muncie 4 speed/ Hurst shifter, 4/7 drop, Hedman midlengths, 3 inch exhaust w/ 2 chamber flows. 1966 Mustang with 306 roller, c-4, 9 inch Detroit locker rear. 1965 Fastback Mustang w/347 stroker, top loader 4spd, 9 inch detroit locker. 1966 Mustang coup, 306 roller, c4, 9 inch. 65 Cobra, 427, T6oo, 9inch, of course. First gen Hayabusa, airbox mod and running 2 exhaust cams.. Zoom Zoom Zoom

09-29-2010, 12:34 PM	#2
71tahoe Registered User Join Date: May 2006 Location: Jonesboro, AR Posts: 916	Re: Rear brakes locking up... My rears would lock up because of brake fluid on the shoes. If the rear cylinders have leaked, you may need to replace the shoes. Could also be over adjusted.

09-29-2010, 01:36 PM	#3
68gmsee Active Member Join Date: Jul 2007 Location: Centrally located between Houston, Austin and Waco. BCS area. Posts: 7,947	Re: Rear brakes locking up... Prop valve may the one for all drum brakes but best thing to do is probably to purchase an adjustable prop valve. That way you can adjust them for maximum stopping front and rear. It's possible they may be grabby but if everything is new and looks good then a prop valve is what you will need. I don't believe overadjusting is causing the problem unless you have them so tight that the wheel won't turn. Adjust them so they barely rub on the drum without preventing it from turning. forgot: a good article to read. http://www.chevyhiperformance.com/te...lve/index.html Last edited by 68gmsee; 09-29-2010 at 01:37 PM.

09-29-2010, 01:53 PM	#4
ChevLoRay Old Skool Club Join Date: Jun 2001 Location: Benton, AR "The Heart of Arkansas" Posts: 10,880	Re: Rear brakes locking up... I think the proportioning valve is the answer, too. I also have ECE disc/drum setup. My rears were locking before the conversion, but it can be because of a leaking axle seal that gets oil on the shoes (I know, but it is what happens) or the wheel cylinder leaking brake fluid onto the lining of the shoe, but that has also been suggested. If all those parts are new, and you have all new hardware, my thinking is that the Proportioning valve is the right place to start. __________________ Member Nr. 2770 '96 GMC Sportside; 4.3/SLT - Daily driven....constantly needs washed. '69 C-10 SWB; 350/TH400 - in limbo The older I get, the better I was.

09-29-2010, 03:44 PM	#5
smoked68 Registered User Join Date: Oct 2006 Location: Rock Hill, SC Posts: 421	Re: Rear brakes locking up... Thanks for the info. Yeah Ive looked no grease or brake fluid on the drums... so I guess Ill go with an adj prop valve. Ok so where do I get one?? __________________ 1968 chevy shortbed, Dark Shadow Gray 4 bolt 383 Stroker,Weiand Super Charger, disc brakes, 9 inch, 391 gear, 20" Eagle wheels, muncie 4 speed/ Hurst shifter, 4/7 drop, Hedman midlengths, 3 inch exhaust w/ 2 chamber flows. 1966 Mustang with 306 roller, c-4, 9 inch Detroit locker rear. 1965 Fastback Mustang w/347 stroker, top loader 4spd, 9 inch detroit locker. 1966 Mustang coup, 306 roller, c4, 9 inch. 65 Cobra, 427, T6oo, 9inch, of course. First gen Hayabusa, airbox mod and running 2 exhaust cams.. Zoom Zoom Zoom

09-29-2010, 05:38 PM	#6
68gmsee Active Member Join Date: Jul 2007 Location: Centrally located between Houston, Austin and Waco. BCS area. Posts: 7,947	Re: Rear brakes locking up... Jegs is a good start but there are others. Probably need to do a search unless someone knows of another place to get one. Be sure and look through this article. http://www.chevyhiperformance.com/te...lve/index.html"]http://www.chevyhiperformance.com/te...lve/index.html[/URL] Last edited by 68gmsee; 09-29-2010 at 05:43 PM.

12-15-2010, 04:32 AM	#7
LostMy65 But Found Her 25yrs Later! Join Date: Oct 2010 Location: Oregon City, Oregon Posts: 10,530	Re: Rear brakes locking up... Any recommendation on which adjustable proportioning valve to buy? baer, etc. There is quite a selection and prices to choose from: http://www.jegs.com/webapp/wcs/store...+proportioning http://www.summitracing.com/search/?...justable&dds=1 __________________ I lost my 65 - Found it 25 years later: http://67-72chevytrucks.com/vboard/s...d.php?t=426650 66 C20 Service Truck: http://67-72chevytrucks.com/vboard/s...d.php?t=428035 Last edited by LostMy65; 12-15-2010 at 04:41 AM.

12-15-2010, 07:39 AM	#8
cdowns Senior Member Join Date: Jan 2003 Location: daytonabeach Posts: 22,956	Re: Rear brakes locking up... you might have proper proportioning valve but hooked up backwards??? __________________ 71c-10 350/2004r/4:11 lowered3/4 longbed/dead by hurricane MEANING OF DEATH::::: SOMEBODY ELSE GETS YOUR STUFF DONT BELIEVE EVERYTHING YOU THINK TAKE MY ADVISE;I DON'T USE IT ANYWAY

07-04-2011, 03:33 PM	#9
cardreams Registered User Join Date: Dec 2008 Location: kingston ont Canada Posts: 443	Re: Rear brakes locking up... have same problem on my truck 1970 power brakes and drums all around how do u know if the proportioning valve is hooked up backwards????

07-05-2011, 02:03 AM	#12
fastwillie 696969 ~Rest In Peace~ Join Date: May 2005 Location: CALIFORNIA NOR CAL Posts: 9,707	Re: Rear brakes locking up... got pics of the rear brakes and drums ? and when you did the rear brakes did you use any lube on the backin plates? how did you adjust the drums by turning by hand or measure the drums and adjust the brakes. i would like to see the brakes ,how about the e brake cable rusty stickin >> ? __________________ is it fast ? it has a lighting bolt donut? B___H please, I can remove 90% of your so called "beauty" with a kleenex

07-05-2011, 09:38 AM	#13
68gmsee Active Member Join Date: Jul 2007 Location: Centrally located between Houston, Austin and Waco. BCS area. Posts: 7,947	Re: Rear brakes locking up... Be aware that someone may have added power brakes from a newer truck with disk brakes so it is possible to have a prop valve. I did that on my 69 with all drums and it worked fine.



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