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Old August 3rd, 2014, 01:58 PM
meatblanket's Avatar
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Mike Simpson
1955 86 1986 ExMOD 110
Join Date: Apr 2010
Location: Golden CO USA
Posts: 520
Brake problems

This is on my 1986 Exmod 110, power brakes, disk brakes in front with non-vented rotors, drums in rear.

Here is what's wrong:
1) Excessive pedal travel
2) Brake warning light comes on if I hit the brakes hard
3) Brake will "pump up" to normal level in about 3 strokes
4) Back brakes only lock up in panic braking, front brakes ineffective
5) Sharp jab on the pedal gives resistance up high briefly, then vanishes and seems like only the rear brakes are working.

Here's what I've done so far, in the order I did it:
1) Adjusted rear brakes, bled brakes
2) Replaced master cylinder, bled brakes
3) Replaced front pads, bled brakes
4) Bled brakes

None of this has made any difference. What else can I do? I was sure that the master cylinder was the culprit, since it feels like I'm just not getting sufficient line pressure to the front. But it wasn't. Could the pdwa valve cause this problem? Calipers? It doesn't pull to one side.

The pdwa valve in this truck per the military supplemental parts catalog is NRC6515.

I've found this thing plumbed into the line going to the rear brakes. It's bolted to the inside of the right frame member. Anyone know what this is? The rear brakes are working fine so I doubt this is contributing to my issue, but I don't see it showing up in the parts manual.


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Old August 4th, 2014, 07:10 PM
Capt Milks's Avatar
Capt Milks
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Defender V-8, Defender 2.25
Join Date: Oct 2004
Location: United States
Posts: 1,716
Might be a bad brake booster. have you checked the check vales operation on the booster? Checked the booster hose?

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Old August 4th, 2014, 08:22 PM
BostonAndy's Avatar
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Moose :: 1985 110
Join Date: May 2012
Location: Maine
Posts: 341
I'm having similar problems after driving through flooded roads last week. No warning lamp (if I have one) and no reproducible brake lock ups (probably a different issue). My gut feeling is the boost or vac pump.
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Old August 4th, 2014, 08:35 PM
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John B.
1991 Defender 90, 200TDI
Site Team
Join Date: Sep 2003
Location: Calgary
Posts: 7,890
When you changed the pads, did you check that all 4 pistons were free? They tend to seize up over time.

Check that the hub bearings are not loose. That is a normal reason for needing to pump them up.

Did you use an OE branded master cylinder and pads?

As above, have you checked the booster?
Pissing people off on the "net" since 1983.

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Old August 4th, 2014, 09:45 PM
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Jafir Elkurd
Flaky Green 198something ex-mod 90
Join Date: Jan 2013
Location: Centerton, AR
Posts: 1,558
Originally Posted by meatblanket View Post

The pdwa valve in this truck per the military supplemental parts catalog is NRC6515.
Looks like you've got NRC8215 instead. Googling it suggests it was on some disc/drum setups, but microcat says it's for vented front disc/solid rear disc.
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Old August 4th, 2014, 10:01 PM
Rocky's Avatar
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72 + D1 drivetrain
Join Date: Sep 2006
Location: Colonies
Posts: 7,534
Looks like cut off brake lines above what you have. Any other make do fixes in the brake system?

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