RABS valve bypass. A completely different take.

Selahdoor

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Everyone has their favorite method of bypassing the rabs valve. Plenty of pics and explanation available here, too.

I am going to suggest that you use the valve itself to bypass the valve. And no, I don't mean what everyone on the net suggests, by taking out that spring. You'll see in a minute.

I took the rabs valve off of my truck, and took it apart, to see if I could figure out how it works.

First, here is the valve, removed from the truck. You take out three bolts, disconnect the brake lines, and it'll fall right off, into your hands.
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Now let's take the big nut off the end. What you will find is a spring and a piston. (The blue part inside, in the pic.) Most people just suggest that you take that spring out and yer good to go. But it will easily begin to leak out the big nut, if you do that.
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Now, one way that I might suggest that you could bypass the way this valve works is to maybe push the piston in there, tight. Fill it with epoxy. Keep filling that chamber with epoxy. And maybe drop a few washers in there for good luck. Put the big nut back on, with epoxy, as well.

That will almost completely make the valve a bypass. There WILL be just a tiny bit of a pulse in the line, however, due to the rest of how the valve works. For that, pic number three.
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Ok, this is the valve taken in half. You take out the four allen head screws, and it will pop in half like this.

What is in the screw cap to the top left is a spring, a copper washer, and a plunger. Those go into the tube you see in the top half of the valve body. The plunger goes in, pointy end first, then the spring sits in the recess on the back end of the plunger, and the copper washer sits in there, over the spring.

In the end of that tube you can see a tiny hole. The pointy end of the plunger has a ball bearing, that seals that hole up. The spring and the copper washer, hold it in place, and keeps the teeny hole sealed up.

Until the coil is given power by the rabs control module. Then the plunger is pulled up away from the teeny hole, and brake fluid then flows out of the valve body, through the grooves on the side of the plunger, and out that teeny hole. Where it pushes that blue plunger out against that spring.

The control modules 'oscilates' the power to that coil, and that oscilates the amount of power going to the rear brakes. Or it just leaves it open, and no power will go to your rear brakes until you pump them again. But they are counting on you not pumping the brakes in an emergency stop. That's why they made the ABS in the first place. I grew up without ABS. I naturally pump my brakes in an emergency. I don't need the abs to save me from myself. In fact, the thing has nearly killed me a few times. That's why I am deleting it.

Ok, let's get to the coil side of the valve.
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Now what you are looking at, is the center of the passage that the brake fluid comes through. This is AFTER I drilled out the sintered bronze piece that was in the center bore. (A filter of sorts?)

Now all you have to do at this point is to drill that hole out to the right size, use a bottoming tap, and then plug that hole with whatever plug you have that matches your bottoming tap. I'd suggest you use epoxy to glue that plug in, as well.

Now, if there are no other passages inside that half of the valve body, you have essentially just used the valve itself, to become exactly the same bypss as my collection of brass has become. (In this thread: https://www.oilburners.net/threads/rabs-delete.86314/post-1086980)

You don't even have to put the two halves of the valve body back together. (You can, if you want it to LOOK like you still have the rabs on there, and it looks like it's working. LOL)
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The rabs has three bolts holding it on. Luckily one of the three, is in this half of the rabs valve body. Just use that one bolt to bolt it back in place, replace the brake lines on it. Bleed the brakes, and yer good to go.

This is just my suggested way of using the valve and not having to do a bunch of plumbing. Do this at your own risk.
 

Selahdoor

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I suppose an even easier way to make it a bypass might be to just cut the two wires going to that coil. Then it won't pull the plunger away from the teeny hole.

I just think there is a chance that it will develop a leak, anyway. And I suspect that particular leak may be the reason these valves screw up in the first place. Working coil or not. (Slowly sinking pedal. Or brakes locked partially on, after release.)
 

quickster

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Nice write up. I will bookmark this one for when I have the time to fix mine. Which is soon. I was looking at mine and it seemed wet where the wires go into the unit itself. Any way brake fluid can get through o the wiring?
 

Selahdoor

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Nice write up. I will bookmark this one for when I have the time to fix mine. Which is soon. I was looking at mine and it seemed wet where the wires go into the unit itself. Any way brake fluid can get through o the wiring?

Sorry it took me a while to realize there was a question here.

Here is a pic of the valve, taken apart.

The green line points to the O-ring that is inside there. It is supposed to seal in the bore that the other end of the green line points to.

I believe this O-ring commonly leaks. If that leaks then brake fluid gets into the entire area that I have penciled in red. Once it gets in there is it natural that it will follow the wires out. (Where the straight red line is.)
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Just the cheesy nature of the way this valve is made, is plenty good enough reason to delete or bypass it somehow. It's no wonder that people replace this with a new one, and have the same problems 18 months later.
 

quickster

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That's right with the leaking. My valve is leaking, or always wet where the wires exit the valve. Going with the brass fitting setup when I get the time. I'm just going to replace the one line that with the large nut on it to the 3/8x24(?) so they are both the same. Mount it, then I'm done.
 

franklin2

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It's just too easy to take the valve out and couple the in and out brake line together with a coupler like this. It's all I had to do to my 89.

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quickster

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But for me, and probably a bunch of other guys I have two different size fittings. If that was the case I would have used a rubber brake line with two female ends. I think it's 1/2 in and 3/8. Pipe.
 

Selahdoor

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It's 1/2 - 20 inverted flare, to 3/8 -24 inverted flare. If you can find the right fitting, that's great. I built a bypass out of several fittings that accomplished the same thing.

I also went and had a short flexible brake hose made with those two fitting sizes.

It's not that difficult to bypass the RABS.

I didn't start this thread to show the fastest easiest way to bypass the RABS. I started it to show a way to use the RABS itself as a way to bypass the system. Do it right, put it back in, and no inspector will know the difference.
 

quickster

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Who gets these old things inspected? LOL. They are exempt I thought. I never had any of my trucks inspected.
 

chillman88

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Who gets these old things inspected? LOL. They are exempt I thought. I never had any of my trucks inspected.

We have to pass safety around here but stuff like ABS/Air bags/traction control are all exempt. Basically seat belts, lights, tires, and making sure nothing is broken badly like ball joints or frame rot. That's about all on these old beasts thankfully.
 

quickster

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When you're old like me you tend to self inspect --a lot. If I stay in the house I end up having to do chores. So I spend my time under or over my truck. Rolling around under the truck is relaxing.
 

franklin2

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franklin2, do you have a link for that coupler and or part number. Thanks,that just seems to easy!
I didn't have the two different sized lines, so possibly one of my lines has been replaced with a standard 3/16 line and fitting. It's been awhile ago, I remember taking the abs out, I might have replace the lines when I was doing it.

Here is the standard 3/16 coupler on both sides (3/8-24 threads on both sides)

Dorman 785-310D

If you indeed have a 1/2-20 nut on one of the lines, you can buy this 1/2-20 flare coupler

And then put this adapter in one side to adapt down to the 3/8-24 size.
 

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