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Kenny Z.
Kenny Z., Ford Senior Master Tech
Category: Ford
Satisfied Customers: 5235
Experience:  Auto Trans, Drivability and Electrical Specialist
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89 F250: with rear only ABS...control valve

Resolved Question:

I have a 89 F250 with rear only ABS. Is there a quick test that can be used to check the proportional valve and ABS control valve?
Submitted: 8 years ago.
Category: Ford
Expert:  Kenny Z. replied 8 years ago.
Do you have the codes or do you need to know how to get the codes?
Customer: replied 8 years ago.
Reply to KenZ's Post: There are no codes showing on the panel and I don't know how to get them?
Expert:  Kenny Z. replied 8 years ago.
Is the abs or brake light on?
Customer: replied 8 years ago.
Reply to KenZ's Post: I just double check the abs warning light again. When I turn the key on the light comes on and goes off in 2 seconds. As far as I know the light is working.
Expert:  Kenny Z. replied 8 years ago.

Ok, If the light is proves out and then stays off then you are done testing the ABS.If there was a fault in the system the light would come back on and glow steady or flash.The only way to test the proportioning valve is to take off the lines and check flow but I would wait to try that. Did you check the wheel cylinders to see if the pistons are frozen by pushing the shoes back and forth against the cylinder.If not can you crack open the bleeder and see if you have any fluid flow there while pressing the pedal? Let me know....I am clicking on answer now in case you find the problem with those steps.Let me know either way and good luck.

Customer: replied 8 years ago.
I did a complete brake job on the rear in including the wheel cylinders about 6 months ago before this problem came up. When I bled the brakes I got full flow at all bleeder valves. Including this time after I replaced the master cylinder. There is no air in the system. When I apply the brake peddle it feels like its hitting a brick wall. It feels like something is not allowing break pressure to be applied to the breaks.
Expert:  Kenny Z. replied 8 years ago.
If there is some flow at both of the rear wheel cylinders it must not be much.Can you jack up the rear end and see how much pressure is really getting there by brake torquing it and seeing if it has enough pressure to hold the wheels?If it cant hold the wheels then you will have to find it trial and error starting with rabs valve then the proportioning valve.It does not make sense to me that you have flow and the cylinders move freely but wont stop the rear wheels......Did you check the booster by chance?
Customer: replied 8 years ago.
The booster checked out ok. Is there a specification on how much volume of brake fluid there should be on each pump on the brake peddle at the wheel cylinders, abs control valve, and proportional valve so I can measure it.
Expert:  Kenny Z. replied 8 years ago.
No there is no published rate that I know of.I can say from experience that one full pedal travel is probably around an ounce.You could crack a line at the master and give it a pump and use that amount for reference.
Customer: replied 8 years ago.
Is there a pressure specification at the wheel cylinders, abs control valve, and proportional valve ? If so I think a simple pressure gauge could be installed into the system at each point.
Expert:  Kenny Z. replied 8 years ago.
Looking everywhere I have access not coming up with any specs for brake pressure
Customer: replied 8 years ago.
Have you ever tried a pressure gauge if so should the pressure be the same at all points with the engine running or not or does it matter?
Expert:  Kenny Z. replied 8 years ago.
the pressure will be higher with the engine running because the booster is involved.If you use the same format for each test it should be consistant.i.e.engine running trying to use the same pressure on the pedal each time.
Customer: replied 8 years ago.
Well I still feel like I'm back to square one but I will try your suggestions. With your experience is there a known problem with this 89 F250 braking system. If so witch componets fail the most.
Expert:  Kenny Z. replied 8 years ago.
No not for that problem did you try what I said about lifting rear end and seeing if they hold while brake torquing?How did you check the booster?
Customer: replied 8 years ago.
The brake torquing failed. On the brake booster I started the engine, ran it for 1 to 2 minutes and turned it off and depressed the peddle slowly three times and after the third time the peddle staid above the first two pumps. I also depressed the peddle turned off the engine and held the peddle down for 30 seconds with no change in peddle travel.
Expert:  Kenny Z. replied 8 years ago.
sounds like either the rabs or proportioning valve is stuck.could be either one.To test the booster you want to pump it up with the engine off till at highest point then start engine with foot still on pedal,it should drop significantly 1" or more.If it drops it is good.Thats not your problem anyways.
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