AdFab Brake lines?

[Matt S.]

Most all 4x4 OEM rigs I can think of have 2 front brake lines and 1 rear/split. I have seen competition vehicles with single brake line per axle split to each wheel. What I am trying to figure out is why we all run 2 front brake lines? Besides the single most obvious reason that the failure of that one line would be a "disater", why should I not look into doing this? If I am able to run my new hard/soft lines in such a way were I will not have to worry about breaking one, it is sounding pretty good. I know that the proportioning valve may need some changing around, possibly getting one aftermarket (adjustable).

I have to build all new hard lines ANYWAYS. This is the only reason I am looking at this option. I want to put all new brake lines on this MJ and need to start figuring this stuff out.

 

[JeepFreak21]

...Besides the single most obvious reason that the failure of that one line would be a "disater"...

Even with the conventional system, if you lose 1 line, don't you lose pressure to the whole system? Isn't that why you see people vice-gripping the end of a broken line, so at least you could continue with the rest of the brakes working?
Billy

 

[5-90]

The brake pressure is split - that's why the master cylinder has two pistons. It should be split front/rear, so if you lose, say, the rear line - you still have brakes up front (and vice versa.) You'll still lose fluid, but it's not a total disaster straight away.

The reason for the two flexible hoses up front and one in the rear is fairly simple - articulation. The rear axle has a hardline that runs from end to end, and is screwed directly into the wheel cylinders. The flexible line runs from the chassis to the axle - which allows for motion of the axle relative to the chassis. If you had a vehicle with IRS, you would need two flexible lines in the rear - one directly to each wheel (since the wheels move relative to the drive axle.)

Up front, each wheel can move relative to the chassis (steering,) so two flexible lines are required. Even with SLA front ends, you have to allow the wheels to steer - with IFS, the need is even greater.

You can probably put flexible lines on the rear wheel cylinders, but if the wheels don't move relative to the axle, there's no point. A hardline would be more durable than a hose, so a hardline is used.

If you're really worried about it, you can install "line locks" that you actuate manually (with, say, a cable to the dash panel) directly off of the master cylinder. That will allow you to "shut off" half of the brake system. I'd want to go a step further and have it be a "switching valve" - and then run the other hose to either the master cylinder reservoir or to the other brake system - no sense in risking a master cylinder rebuild if you don't have to. "Deadheading" a cylinder like that can result in seal rupture, which is always a pain to fix...







IFS - Independent Front Suspension
IRS - Independent Rear Suspension (or that Satanist Internal Revenue Service)
SLA - Solid Live Axle

 

[vetteboy]

The master cylinder only has two outlets, so the front line is T'd somewhere. Whether it happens at the axle or the ABS pump/distribution block doesn't really matter as far as performance is concerned. Even with an OEM setup, the failure of a single left or right line would cause a loss of pressure in the whole front circuit.

Some older trucks came OEM with a single front line...the Dodge 60 in my build is one example. I actually used a factory front line for it, and routed the line down the upper link...

I've got a whole bunch of downtravel with this rig, and I didn't want huge (and custom!) soft lines in each wheelwell. So I sourced all OEM brakelines and minimized the softline length as much as I could...rear is similar except they run down the lower links:

(had to do that for the cutting brakes)

The short soft lines from the body are rear lines from a 1985 Plymouth Reliant K, the lines to the rear caliper are 1979 Chevy Cavalier front hoses, and the softlines on the front axle are all OEM for that axle (1982 Dodge D60).

Works great, now I just need to find a master cylinder that fits and has enough flow...