<?xml:namespace prefix = v ns = "urn:schemas-microsoft-com:vml" /><v:shapetype id=_x0000_t75 path="m@4@5l@4@11@9@11@9@5xe" stroked="f" filled="f" oreferrelative="t" o:spt="75" coordsize="21600,21600">Well I'm back again with the same brake problem. I thought I had the problem ironed out. The wheel cylinders on the right ( accidentally said the left side in the brake section) rear wheel were sticking and not releasing (New cylinders) I ran a hone through them for a long time and finely got them to release. Anyway, I put it all back together and they seemed to work. I took a few test drives and all seemed fine, until yesterday when they locked up again.
Just a recap of all that’s been done to the system.
New master Cylinder
New front shoes
Rebuilt front wheel cylinders
New front rubber and steel brake lines
New multi-vac/hydrovac
New rear wheel cylinders on right side (was having problems with them and fond one to have rust pits so I replaced it)
New rear brake lines, rubber and steel.
Rear shoes and drums are in very good condition.
There is not a proportioning valve<?xml:namespace prefix = o ns = "urn:schemas-microsoft-comfficeffice" /><o></o>
In the beginning I found the rubber line to be blocked or deteriorated so prior to the new installation blew out the steel lines with air. Also I had found the backing plate to have some light ridges worn into the backing plate. The adjusters were also froze up. Someone mentioned that they thought that maybe I may have kinked the lines when I made up new ones, I’m not with out skills and pride myself on doing better than average work and the lines look better than new.
My question is, if the right rear brake was adjusted closer to the drum than the left side could the right lock up and not the left side. And if so, could the problem be in the vac system although its new as well? If this was the case wouldn't I see the problem at other wheels. How would you test the multi-vac for this and what could cause this? <o></o>
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Debris in line acting like a check valve? Defective rubber hose acting like a check valve?

 

Did you have any leaking issues with the wheel cylinders or drum seals. Sounds like oil on the shoes issue. Pressure to both sides of the axle should be the same, unless, like someone said, there's a kink in the line going over there. How about the condtion of the springs that return the shoes in place?

 

Thanks for gettin back to me. I did for get to mention that I had replaced the springs on that wheel. Someone here mentioned that could possibly be the problem. Also as I mentioned all the flexible/rubber lines have been replaced and most of the steel line have been replaced with no kinks. Also the lines that have not been replace have been blown out with air.
If you were thinking that the shoes mite be oil soaked I can't say for sure one way or the other I bought the truck knowing that the brakes needed work. After my Sunday test drive I pulled the truck in the shop and crawled up under the truck to feel how hot the backing plates were and after a very short while maybe a minute, I heard the brakes release.

 

I've always heard that there are check valves in a drum brake system that hold a little bit of pressure in the lines. When doing drum to disc conversions you have to remove these valves. Maybe you have a defective one that is holding too much pressure?

 

Are you sure the adjusters are installed correctly?

 

Unless there is some sort of check valve in the multi-vac/hydrovac, as I mentioned there is not a proportioning valve. As far as the adjusters go, I'm pretty sure they can only be installed one way.
Thanks for your help

 

You are correct, residual check valve. Looks like a rubber duck bill. They are behind the brass 45 degree insert at master cylinder outlet.

 

I'm sure you know but I'll mention them.
Free travel at master cylinder push rod.
Return spring on brake pedal.
Vented cap on master cylinder is clear.

Hydra-vac? I wonder if something could be sticking and not returning as it should. This is a total guess, I've never had a problem like yours BUT new parts are often a problem as we know.

 

Make sure your master cylinder and Hydrovac are correctly matched. There's literally dozens of combinations and usually several for a given model and year. I know on my 51 IHC there were four possible Hydrovacs for that model. It's essential that if the MC has a residual check valve, then the Hydrovac should NOT have one - and vice-versa.

Lots of good info here:

Vacuums & Hydraulics

 

Thanks for all the input. There is not a 45 degree elbow coming off of the master cylinder. However the on thing that come to mind is the length of the push rod. I wonder where I could find out how long it should be. And the multi-vac is it not nothing more than a vacuum chamber with a slave cylinder??? just thinking out load here. I thought I had done everything I could I'm just shooting in the dark now.........

 

Just wanted to keep this going and look for possible answers. I still have not found the problem.....................

 

I was just crawling around under the truck and scratching my head when I saw something that may be a check valve. I’m getting tired of just guessing and having to re-bleed the system not to mention that the wheels and drums are just a little on the heavy side. Coming from the frame mounted multi-vac there is a line at the end of what I would call the slave cylinder, it goes to a junction block and from there the lines separate, two to the front brakes one to and rear brakes and the is also the brake light switch all on this block. Anyway where the line from the vac goes into this block at the frame ( its hard to see because it goes through the frame rail) there is a round fitting going into the distribution block. Anybody have any idea if this mite be a check valve. Several times folks here have mentioned check valves. Would check valve be built into the master cylinder or the Multi –vac???

 

In my 56 f600 the check valve is in the master cyl. and keeps 10lbs of pressure to the wheel cyl. There is no check valve in slave body of the hydrovav unit. I am assuming your 65 f600 would be the same.

 

thanks rustrelic. is it built insde the master? someone here mentioned it was on an elbow at the end ot cylinder I don't see anyting like that.......