OT but hopefully interesting: single to dual brake line conversion Options

[Tdskip]

So I need to get this thing ready for a charity event and that includes new brake lines. I converted it to a two line, split front and rear, brake system for safety purposes but haven’t finish3s the hard lines yet.

I’m thinking having a proportioning valve in the system so I can adjust the front/rear bias would be a good idea but am not sure how to plumb that.

I have a conventional mid ‘90s Toyota dual M/C now.

Figured our racers here have dealt with that so thought I’d ask. For those that have done this where did you put the valve? I’ve seen two types - one where both lines from fhe MC go to a combination valve and splitter (pictured below, just an example I haven’t ordered this yet or decided to go this way) OR a set up where only the rear line goes through the valve.

Thanks in advance for any ideas and coaching.

[Tdskip]

Example of the rear circuit located valve

[Tdskip]

OK -to close this out and in case anyone was curious, OK to do rear only.

[Tbrown4x4]

(IMG:style_emoticons/default/confused24.gif)

[Steve]

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I don’t get it either... you already have a redundant master cylinder that separates the front from the rear and an emergency brake. Why go further than that?

[Tbrown4x4]

I assumed 914, but it must be for a Land Cruiser.

To add to the confusion, your combo valve diagram is the type with a proportioning valve inside already. (Hence the term "combo")

I'm not sure how well adding a second adjustable valve would work. You're only trying to prevent rear brake lock up under HARD braking.

[Tdskip]

Sorry if that was confusing but I was asking about the FJ40 Cruiser (which is why the picture of the rig and I put OT in the title of the post)

Guys who build race cars, like some of the people here, will often ditch factor stiff for more control and include these sort of proportioning valves so I thought there may be someone who would offer up their experience.

The last picture if not my Cruiser, but an example of how they can be set up.

@TBrown4x4 - this thing is lifted and had a short wheel base so I do need to sure the rear doesn’t come around on me.

Thanks.

[davep]

I guess the basic thing is that all 914 came with the dual circuit design, and have the proportioning valve in the rear. So really of interest to teeners is an adjustable proportioning valve (been around for decades) or deleting the valve.

[Superhawk996]

Just a quick word of advice from a former automotive brake engineer.

Race cars with bias valves are great for the track . . . not really a good idea for the street.

On track, too much rear brake and the car starts to get loose (i.e oversteer) but you have a skilled driver (hopefully (IMG:style_emoticons/default/biggrin.gif) ) sort of expecting it and plenty of runoff if he wasn't. On the track loads are more or less known, surface grip is more or less known, weather is known.

On the street grip is unknown, dry pavement, wet pavement, snow? New tires or nearly worn out tires?

On street loads are unknown (Frunk full tank of gas or empty)? Luggage in Frunk? Or, maybe you loaded the trunk with depleted uranium? Who knows & it varies trip to trip. These extra loads will dramatically affect how much bias you can put on the rear.

You have no opportunity on the street to "tune" the system for that day without risking your life.

More than likely, you'll end up setting it "safe" with way more bias to the front to keep things stable. Then you're giving up whatever you potentially could have gotten out of the rear with a proper proportioning valve.

No easy advice off the cuff on picking proper (fixed) proportioning valve without writing a dissertation. Use OEM is your best bet.

Side note: Diagonal split isn't out of the question and might be safer for your application. If you've ever driven a vehicle with both fronts failed, it's an eye opening experience.

In your FJ40 example, if you over bias the front on a front/rear split and then do fail the front circuit, you'll find you basically have no brakes. Short wheel base (FJ40, Jeep CJ) and high Cg will only make this exponentially worse.