Rear brakes locking up...

[smoked68]

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]

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]

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]

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]

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]

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]

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]

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

[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????

[cdowns]

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]

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]

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]

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.