‘88 c1500 brake module sounds like it’s broken inside when moved.

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alignman88

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On my 1988 c1500 I took the master cylinder, booster valve, antilock module off to replace the power booster and put new master cylinder on. I usually have the stereo on in the shop but late last night it was very quiet in the garage when I picked up master cylinder with everything still bolted to it. When I picked it up to move it out of my way it sounds like the antilock module is full of sand, and/or very fine glass or metal shavings falling through it. Quick search here and on internet didn’t turn up anything. Has anyone heard of this before? My brakes worked very well when I was driving it regularly and the rear drum system had been completely replaced with all new Wagner parts maybe 7-8 years ago but has sat for the the last 6 years or so. Brakes had never been a concern on this thing, so I am completely baffled as to what’s going on. Don’t really want to delete the rear antilock because the truck always stopped well and in my opinion had good brakes for an OBS.

Tried to attach video so you could hear the sounds of the “falling debris” that got my attention but ran out of talent lol. Phone might need some space cleared up to access and post that video. Will post soon as I am able. Thanks in advance for any insight.
 

alignman88

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I have no idea. Sorry.

What happens if you reinstall, and bleed the thing?
That’s the million dollar question. I’m a good way from having it on the road again so should have it figured out before that. Hard to believe it wasn’t working when parked, always got excellent brake life from front and rears so it’s not like one end was doing all the work. May be the most baffling thing I’ve ran across working on vehicles.
 

DerekTheGreat

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Every single one I've pulled at a yard sounds like it's got an etch-a-sketch in it too. If it isn't triggering the brake light and the RABS works, it's fine. When I was pulling them, it was about eight years ago with my first GMT400. I wasn't sure, so I bought a new one and installed it- made no difference in the performance of the system. My problem originally was the brake light, it was on dimly. Once swapping parts didn't fix the issue, I got a GM electrical troubleshooting manual specific to the truck, followed the steps (which I think ended up having me pull and reinstall the fuse to reset it) and it was back to normal with the old module or new module. Since I paid for the new module, I left that installed (I think.)
 

alignman88

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Every single one I've pulled at a yard sounds like it's got an etch-a-sketch in it too. If it isn't triggering the brake light and the RABS works, it's fine. When I was pulling them, it was about eight years ago with my first GMT400. I wasn't sure, so I bought a new one and installed it- made no difference in the performance of the system. My problem originally was the brake light, it was on dimly. Once swapping parts didn't fix the issue, I got a GM electrical troubleshooting manual specific to the truck, followed the steps (which I think ended up having me pull and reinstall the fuse to reset it) and it was back to normal with the old module or new module. Since I paid for the new module, I left that installed (I think.)
Etch-a-sketch is a great description of the sound! Glad you have ran across it before and thank you for the reply. Hard to believe I couldn’t find anything on this online I spent a fair amount of time yesterday after posting here looking for this exact answer. This forum is a great resource with a awesome community of folks! Thanks again!!!
 
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