Dual chamber MC question

I've been thinking about upgrading the stock single chamber MC on my 3A to a dual one using Herm's kit. But I've been wondering, is a proportioning valve necessary (or a good idea)? :? I've searched the threads, and none of them mention using one. I would think that the rears would lock right up when the brakes are applied since there is barely any weight back there.

 

Mine don't lock up, but if you really hammer down on the pedal they do, but then so do the front from what can tell

 

I'm using 10"ers out of a '66 CJ5.


While doing some more searching about installing Herms kit, I found this on the 3B page:

But like w3srl said, he's been fine for 6 years.

 

There's a lot of variability whether you need a proportioning valve or not. I suspect Steve's is cranked wide open because of the small rear brakes. Less likely to lock up. When I had discs on the front and 11" drums on the rear I didn't have one, still don't with disc/disc but probably should have one as the rear locks up just slightly before the front. I have run into some conversions I've done that did need one on the rear though or they would lock up. I'd try it without first. You can always add it if needed.

 

I'm running disc/disc on the 3B and installed a Wilwood unit below the dash. It did make a difference and I suppose you could even change the bias based on loading, but something I have never found necessay. To me, it's not worth having to rebleed the brakes a second time if you put it together without it and then find you probably need it. Not a big expense.

 

Piratejack.net sells adjustable proportioning valves on ebay, they go for cheaper than their website. Mine should be here any day, and with shipping to Canada it was still cheaper than their list price. They can be hard to contact by phone but an ebay purchase is easy.

I have rear drums and front rotors, and it's 50/50 which ones lock up first. Since I drive on ice and mud I want the fronts to always lock up first.

edit: I just went to power brakes from manual, with the manual brakes they never really locked up, so it may not be an issue anyway.

 

Alright, thanks Gents for the input. I think I'm going to put the dual chamber MC in without it and see. I want to be able to push the brakes when towing my trailer and know I'll be safer when I stop... Hopefully.

 

I finished putting the dual MC in today, but I have another question. How far should my pedal move? It stops at about 1" before the floor board and is solid. There is no air in the system and the brakes are all properly adjusted. With the old single one, the pedal moved about 1" before it got solid.

 

Did you bench bleed your master cyl. before you installed it?

 

Yep. The pedal doesn't feel spongy at all.

 

While I was eating breakfast, I came up with an idea. I took the return spring off to see if there was any free play with the push rod. Yep, there was about 1". Solved that and now it is much much better.

 

Smart little wipper snapper an't you! Nice Job.

 

Just curious on a couple of things. I also have his dual res. MC and discs up front with the 11 inch drum rears.
1) did you have to shorten the rod from the brake pedal to the MC? My first one was cut and welded together to make it shorter. I felt this mod a little unsafe. I then tracked down some used rods (both ends) and cut one down the threaded one to the right size and threaded it all the way to the eyelet. Now it fits without any welding and is just as strong. I got that idea from someone else who did it this way.

2) I have semimetallic pads up front but will be switching to organic. I read and was told that organic pads are for manual brakes whereas all others are for boosted brakes. They say with organics you can stop much better.

3) I run a proportioning valve in my set up. Seems to be working great for me.

Paul