M939 ABS Module Pics

Just bought a new replacement ABS ECU from SUPRMAN after over-volting mine from shutting off both dash switches at the same time. I don't think a proper design should be able to self-destruct, but whatever.

Thought I would throw up a few pics of the new module, prior to install. The module is sealed, with a Gortex vent (passes air but not water). It also has a grounding strap which connects through a mounting bolt.

If you are looking for your ABS module, it looks something like this, and has a pneumatic valve on it, located above the intermediate axle, I think. I honestly have not went under to replace it yet. I want to resolve the over-volt issue first by changing the alternator, or applying in line suppression to the module, before I install this new unit. Old module was blowing 15A fuse as soon as battery switch was flipped on. ABS light on solid. Was working perfectly before this event.

I just put a 27SI on my NHC250. The stock pulley didn't fit the shaft, went with a slightly smaller pulley diameter for the alternator to excite at idle.

I think you have a bad main ground.
Here's my reason.
I put a battery cutout switch on a truck and killed the main ground wire to battery.
Every time I forget to turn that cut off on and turn trucks main power switch on dash it will pop and blow the fuse on my radio.
Check some grounds

I have done it a couple of times and turned battery switch off first. Or left battery switch on for a week.
Never has been a problem

When you go to install, try to access the module from the "top", couple of easy screws and you are there. Don't try to undo the whole assembly below, that would be torture. I did have the benefit of not having a bed on when I pulled one from Glen. With every one I've seen there has been some grease on the pins, maybe dialectric , I haven't checked the TM, but someone might pipe up with what they actually did before you install it. I've pulled two and they both had it.

Coffey1 said:

I have done it a couple of times and turned battery switch off first. Or left battery switch on for a week.
Never has been a problem

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I'll check the ground to frame connection(s). Ground to engine is perfect, as truck cranks very fast. It looks like my ABS module sustained several over-volt shut downs before finally failing. Also seems to be a lot of the main cause of failure of these. It is probably just what happens, or most of those trucks have weak grounds also? When you shut your truck down now, if you do the wrong switch sequence, does it drive your voltage gauge high? I guess don't do it just to answer the question, but have you noticed?

therooster2001 said:

When you go to install, try to access the module from the "top", couple of easy screws and you are there. Don't try to undo the whole assembly below, that would be torture. I did have the benefit of not having a bed on when I pulled one from Glen. With every one I've seen there has been some grease on the pins, maybe dialectric , I haven't checked the TM, but someone might pipe up with what they actually did before you install it. I've pulled two and they both had it.

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Thanks for the experience.

The HUlk said:

I just put a 27SI on my NHC250. The stock pulley didn't fit the shaft, went with a slightly smaller pulley diameter for the alternator to excite at idle.

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Is it a genuine Delco unit, or a Chinese clone? How much was it and where did you get it? I'm trying to track these things. Will have Delco Remy cast into the rear if genuine. Will say nothing and cost under $200 if Chinese (I have a source as low as $89). Also, the stock military 60A alternator actually spits out about 63 amps at idle, I measured mine a month or so ago. Are you saying your alternator would not even generate a charge at idle, or you were just hoping for even more so went with a smaller pulley? How does your volt gauge now act if you shut the truck down in the wrong switch order (don't try it, but have you noticed)?

74M35A2 said:

Is it a genuine Delco unit, or a Chinese clone? How much was it and where did you get it? I'm trying to track these things. Will have Delco Remy cast into the rear if genuine. Will say nothing and cost under $200 if Chinese (I have a source as low as $89). Also, the stock military 60A alternator actually spits out about 63 amps at idle, I measured mine a month or so ago. Are you saying your alternator would not even generate a charge at idle, or you were just hoping for even more so went with a smaller pulley? How does your volt gauge now act if you shut the truck down in the wrong switch order (don't try it, but have you noticed)?

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My replacement alternator would not self-excite at idle so no, just starting the truck up would not charge. I have put several single wire units on MVs and a backhoe and you have to bump the RPMs up after starting to get the alternator to start working.

Mine is a $109 unit from the place I have purchased 3 others from. Unfortunately I just found out two days ago mine isn't charging but that could be a Chinese quality problem. I only know it isn't working, I have not worked to why yet. My Chinese unit came with the test papers showing it would put out 80 AMPs at speed.

Jim (The Hulk) you must drill out the military pulley to get it to fit the civi alternator but your way works too.

The abs module has a big diode across the power inputs to protect against reverse polarity. This diode has a bad habit of shorting out.

No I've never seen the voltage spike whether I shut down right or wrong.

74M35A2 said:

Is it a genuine Delco unit, or a Chinese clone? How much was it and where did you get it? I'm trying to track these things. Will have Delco Remy cast into the rear if genuine. Will say nothing and cost under $200 if Chinese (I have a source as low as $89). Also, the stock military 60A alternator actually spits out about 63 amps at idle, I measured mine a month or so ago. Are you saying your alternator would not even generate a charge at idle, or you were just hoping for even more so went with a smaller pulley? How does your volt gauge now act if you shut the truck down in the wrong switch order (don't try it, but have you noticed)?

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Mine is a clone branded WAI and is 65A 24V. I got it from a local shop for $165. Probly paid too much but I figure having a local person to deal with if there are problems is worth paying for. The alternator will not charge at all using the stock pulley at idle as the RPM's are to low. The voltage guage reads in the yellow area which is nominal battery voltage only at idle. After increasing engine speed about 100 RPM or so the voltage gage jumps up to the green area above nominal battery voltage. I have not tried the improper shut down and never noticed the volt guage when I did previously using the stock alt. I believe when improper shutdown occurs using the stock alt, the voltage reference the alternator uses to determine charge output drops to zero causing the alternator to go into full charge mode. This may cause a voltage spike potentially damaging the alternator, regulator, batteries, brake module, etc. That problem should not occur with self excitng alternators such as the one wire 27SI I installed.

swbradley1 said:

Jim (The Hulk) you must drill out the military pulley to get it to fit the civi alternator but your way works too.

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Steve, using the stock pulley drilled out would still leave me with no charging at idle like you are experiencing. More reason to get a smaller diameter pulley that fits the shaft. Not charging at idle may put more load on the alternator when at higher RPMs trying to top off batteries that don't get charged enough if that makes sense.

The HUlk said:

Steve, using the stock pulley drilled out would still leave me with no charging at idle like you are experiencing. More reason to get a smaller diameter pulley that fits the shaft. Not charging at idle may put more load on the alternator when at higher RPMs trying to top off batteries that don't get charged enough if that makes sense.

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Correct, I only said that about drilling because that is what almost everyone does. I hope you kept the part number or link to the pulley you used because I might want to try it sometime.

swbradley1 said:

Correct, I only said that about drilling because that is what almost everyone does. I hope you kept the part number or link to the pulley you used because I might want to try it sometime.

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Gotcha Steve. The pulley was one the local shop had laying around, no package or markings. I have yet to install it and will collect some dimensional info as well as confirm the results to post soon.