distrobution/proportioning block drum/drum vs disk/drum

[dablack00]

Ok guys. I have done disk swaps before. I just finished one on my 68 cougar. It was drum/drum and I got a disk/drum distibution block out of a 70 cougar w/ disk brakes and plumbed up some wilwood disks up front.

Now for my question. Why do you have to swap distribution blocks? Are there valves inside? I thought a master cylinder would control the risidual pressure that is needed for disk (10 psi) vs drum (3or4 psi). What is going on there.

The reason I ask is I would like to swap on some disk brakes from a 73-79 truck, but I don't want to swap out the distribution block. I was hoping I could just get some residual pressure valves from wilwood and put them in.

thanks
Austin

[Leadfoot]

There is two different stories about this one.

One is you may trip the prorp valve.
And the other one I never listen to. Personally I done tonnes of these conversions And the only time this happens it when you bleed the brakes and mash the pedal real hard, when bleeding the back. so just take it easy when you are bleeding brakes. You don't need to change it at all.
But make sure you use a disk brake master cylinder.

[dablack00]

Wow. That is what I think too. I always use a pressure bleeder so I never even touch the pedal. I'm going to get the new master and swap the complete disk brake Ibeam assemblies.

thanks
Austin

[FORDification]

I completely disagree....when converting from drum to disc brakes, you absolutely need the prop valve for better front/rear balancing. A proportioning valve (which, incidentally, is also application-specific) has two valves in it. One is a shuttle valve that separates the front and rear brake pressure circuits, and activates the pressure warning switch. The second is a pressure metering valve for the rear brakes, to reduce hydraulic pressure to the rear drums, preventing rear wheel lockup.

Here's some reading on the subject:

http://www.stoptech.com/tech_info/wp_pr ... lves.shtml

[fordman]

i have to agree with kieth.

[dablack00]

I have decided that since I don't want to get into everything yet, I will wait until I do. My pedal is going to the floor and I have a leak somewhere. My truck has been sitting for three years and it finally has the new engine and trans it deserves. I will fix the leak, put on new wheel cylinders, soft lines and master cylinder. I already have new shoes.

thanks
Austin

[binder56jd]

Keith- good read- thanks- jd

[Leadfoot]

I think I need to clear something up. There is book smarts, than there is working/applied mechanics. Both are some what right, Personally I go with
the true points about mechanics, not all what you read in 100 percent correct. tech. stuff changes so try to keep up.

all the prop. valve on these trucks really dose Keith is cut the lowest pressure line right off so it won't leak all the pressure off and you can still stop with With either your front or back brakes, not both. & it also lights up a warning light when that happens. So you know and get it fixed.

They don't meter the rears at all to stop rear tire lock-up. Thats A fairy tail. I live were It snows so if this was true I would of crashed my truck every winter. Sorry that doesn't happen.

I bet the rear tires are locking up because the rear shoes were adjusted to tight.

The only one that really meters the rears Is mounted over the rear end
And has a arm that links down to the rear end. These one really were just meant for different weight loads, and In Fancy ones could Help in Heavy braking stoping the rear from locking because of weight transfer.
With out ABS on the front these would be pointless, and front tires would all ready be locked on These old trucks. Now do you see my point.

I lived at a race way, took lots of schooling on mechanics, and built race vehicles. I work on all the latest vehicles prof. Do you think I would mess around with unsafe brakes, The hole reason I became a mechanic is cause I got a bad brake job on my first car a 1967 cougar, the brakes went and I hit a tree. I know what loosing a loved vehicle is about. Brakes are the most important thing period.

[Leadfoot]

them there words are fighting words, no hard feeling ay!

[dablack00]

I don't think anyone here would take what you said with any hard feelings. I get what you are saying.

I have a 68 cougar that had manual drums all the way around. I put on a power booster and an aluminum master from a 93 mustang. I also added a wilwood disk brake kit. When I went to bleed the system, the front bled great, but the rears wouldn't flow anything. I pulled the drum and the rear shoes looked brand new. Those brakes haven't worked in a long time. I assume that the line is clogged. I tried it as is and the brakes are great. WAY better than the manual drums. I only drive the car back and forth to work so it doesn't really matter, but I will fix it in the future.

As for the truck, I'm sure it would work without the special disk/drum proportioning valve. That being said, the factory didn't change it for fun. The different one is there for a reason. I'm still not sure what I want to do. I work on my own alot and bleeding brakes is a problem. I have a motive pressure bleeder that works great, but I have to use a master w/ the screw off top. The only masters like that, are modern disk/drum masters.

thanks
Austin