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7.3L IDI Diesels (Not Power Strokes) Technical discussion of topics related to vehicles powered by the 7.3 Liter In-Direct Injection Navistar engines.

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Old 07-29-2009, 02:07 PM   #31 (permalink)
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Hi everybody,

I found this great article about the RABS valve that I thought somebody here might find useful. It gives diagnostic tips and everything.

The Fading Bronco Brake Pedal
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Old 11-25-2009, 04:29 PM   #32 (permalink)
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RABS Valve

Wow thats a neat trick to test the RABS Valve. I will try tomorrow and thanks! This 1994 F 350 owner was ready to park this sucker and forget about it! I'll let you know the results tomorrow! Also what are the possibilities for the guy it didn't work for, a bad EH valve or bad Antilock brake module?

Another way to test the Master cylinder I heard is disconnect the back brake line from the cylinder, plug it up somehow, and see if they work. Is this a good idea? How do you plug up a brake line?

Thanks
Bill
New Jersey
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Old 11-26-2009, 04:38 AM   #33 (permalink)
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it's usually the seals of the valve inside the HCU that go bad and allow fluid to leak past them, not the electronic control module under the dash. I originally did the spring mod for faster recovery times when brake pedal is released, not to fix a sinking pedal. As far as plugging the lines, yes you can do it, just unbolt the lines from the master cylinder and install a suitable solid plug in their place.
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Old 11-28-2009, 06:24 PM   #34 (permalink)
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Hard to believe I started this thread over a year ago and Im still dealing with brake issues. I used MLSC's trick with the spring modification to the RABS valve. This was a good short term solution as it got me down the road towing my trailer to Grand Canyon and back. Now it seems I have a wheel cylinder leaking at the right rear and possibly an axle seal as things are really wet in there. Im thinking its time to replace the shoe set and both wheel cylinders.. make sure everything is correct.. even turn the drums.
Maybe then I will consider replacing that expensive RABS valve? I dont know.
Would be nice to get this brake issue solved correctly once and for all. I have learned how to be very gentle on the brake pedal but now its not really driveable. Do I have to get that valve from the Ford dealer? are there other sources out there?

Thanks Vinnie
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Old 11-28-2009, 06:37 PM   #35 (permalink)
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Hey vinnie, FWIW Kragens on-line shows a RABS valve assembly. About $150.00
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Old 11-28-2009, 08:11 PM   #36 (permalink)
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Quote:
Originally Posted by chuckster57 View Post
Hey vinnie, FWIW Kragens on-line shows a RABS valve assembly. About $150.00

Really? So then it is available in the aftermarket... ok
I think for that price im just going to do it and bleed the entire system at that time. Thanks for checking around Chuck..


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Old 11-28-2009, 10:14 PM   #37 (permalink)
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I have been reading a few threads about these Rabs valves. Has anyone here bypassed the valve and if so what were the results. Obviously there will no longer be ABS braking to the rear but are the braking pressures correct to the rear wheels? Will you have normal braking or will you wear out either the fronts or rears quicker? If ford designed this system into the truck you cant always just bypass it and expect things to work like a standard pickup. Does someone have this experience out there and could comment one way or another?

Thanks Vinnie
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Old 11-29-2009, 04:50 AM   #38 (permalink)
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I've driven my truck 255K miles and never thought the abs was any good at all - I can't even feel a pulsation like I do with other vehicles. Point is, why not remove it and replace with a splice in the brake lines?
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Old 11-29-2009, 09:52 AM   #39 (permalink)
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Has anyone replaced their vacuum pump?? It was a simple solution for my 1994 turbo IDI. The breaks went to the floor and had similar symptoms. If you try this make sure you use a power steering pulley puller. The vacuum pump is 100 dollars at autozone.
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Old 11-29-2009, 05:00 PM   #40 (permalink)
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I found this quote from MLSC..

We've been discussing that topic over at FTE for a while now, and someone brought up an excellent point - RABS-equipped trucks do not have a proportioning valve, they rely on the RABS to back off the line pressure when the rear wheels can't handle it and start locking up. If you bypass or disable the RABS you're now supplying the rear brakes with full line pressure all the time, meaning they will lock up so easy it's scary. Non-RABS trucks tackle the issue with a proportioning valve that reduce the pressure to the rear brakes, and often a load-sensor on the rear axle to drop the pressure even more when there's little to no weight in the bed. So the correct way elliminate the RABS would be to either install a proportioning valve for a similar GVWR non-ABS truck (requires modification to the front lines as well), or install an aftermarket brake-bias valve between the master cylinder and the rear axle.

I actually ran in that issue with my old Chevy truck, it was a shortbed stepside truck that even with full tank and me and a passenger was still under 4000 lbs, yet the brakes were powered by a 1-ton hydroboost system (both booster and master cylinder), and to top it off my tires were mismatched front to back as well (32x10.5 fronts, 33x12.5 rears) - I used a Willwood manual brake-bias valve to sort out this mess, it took me a while to get it right but in the end the decel was so good it could throw you in the windshield and still not lock up any tires.

So keep that in mind when you go about shutting off the RABS, unless you do something to reduce the line pressure when you run empty your truck will be very much unsafe on low-traction surfaces like wet pavement or snow.
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Thankyou.

That was what I was looking for. Good information.
Im going to check on the exact price for the part or maybe try the proportioning valve.
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Old 12-02-2009, 09:56 PM   #41 (permalink)
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It's beginning to look alot like Christmas...

Here's what Santa brought me this year... not too exciting but practical i guess.. a set of fleet rated brake shoes.. turned drums.. wheel cylinders.. one inner hub seal.. complete new spring kits.. AND A NEW RABS VALVE!

I will report back once finished..
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Last edited by vlamica; 04-09-2011 at 08:19 PM.
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Old 12-02-2009, 11:03 PM   #42 (permalink)
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Looks like your gonna be busy for a bit...Watch out for the storm forecast for this weekend.
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Old 12-02-2009, 11:31 PM   #43 (permalink)
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I just scanned this thread and it makes me want to pull out my hair.
I have a 7.3 truck, but it is an 85 so it has a proportioning valve.
I have a leaky axle seal so I don't really know how my brakes will work or if the valve is good but here is my point.
I believe I started a thread about this a while back and didn't get much response if any.
It's a given that everyone here is her because they are a do it yourselfer.
Has anyone tried installing a manual brake proportioning valve?
I will do it in a second when finances and time allows, it just seems so much simpler.
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Old 12-03-2009, 08:23 AM   #44 (permalink)
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other valves that work

I heard the Dodge valve will work on the Ford.
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Old 12-03-2009, 01:56 PM   #45 (permalink)
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So do you mean a Dodge load sensing valve or did they have a manual proportioning valve?

I misspoke below when I said mine had a proportioning valve, I suppose it may have one also, but I meant to say load sensing valve.

Thanks for the reply, I just like simpler remedies and had seen an ad for a manual valve at a local auto parts store and hoped someone had tried one before.

Of course it would take a little getting used to, but seems like it would be so much more simpler and reliable.
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