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Discussion Starter #1
Small back story.. Picked up a "cheap" 2000 M5 around this time last year needing some TLC. Been busy with work etc and the car has been sitting most of this year with occasional runs down the road to try to keep everything operational. I think the car was also sitting several months or a year or two before I bought it. Been working a few less hours the past couple of weeks and got some time on the car to try and get it ready for state insp'. To the meat & potatoes...

Worked on the brakes this week. Found right (pass) rear side caliper not working as evidenced by the rust not being cleaned off the right rear disc when I went to bed in the new to the car pads I just put on the front brakes. Figured OK got a seized caliper. Pulled caliper off and put a piece of wood where the pads were, and pumped the brake pedal to try and pop the piston out, didn't even move?! (This has worked for me before with cars from up north with salt corrosion ect). So I pulled the caliper off, put some compressed air in the brake line hole and the piston shot out without any resistance (not seized)...

So tried to pump the brake pedal with the caliper off, nothing comes out of the right rear brake line, even with the engine on for the booster and standing on the brake pedal full weight.. nothing. Pedal feel is still firm. The line to the right rear is blocked somewhere, or a valve in the ABS pump is stuck closed? I have a feeling it maybe some valve in the ABS hydraulic pump?

Did a search but didn't really find anything similar, only one post about no fluid pressure at a front caliper, but their pedal had no pressure either, mine does and the rest of the brakes work fine. Wanted to see if anyone had a similar problem? Or if anyone knows where there's a schematic of the brake system even?
 

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First thing you need to do is find the line that feeds that caliper at the ABS module. With a helper pushing on the brake pedal open the line just as if it was a bleed screw. If you can't figure out which line it is do all four and if you get fluid from all then it is the line.
 

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Discussion Starter #3
Thanks, that was actually going to be my next thing to try when I get time off. I was out of time for this week when I got to this point. Was maybe going to go backwards from the soft line to the caliper one joint at a time toward the ABS module, testing for fluid pressure. Or even taking it for a spirited spin on a wet day and trying to activate the DSC & ABS, with the hopes of unsticking a valve in the ABS module?

Was hoping to find a similar story (& solution) on here as I have with almost all prior issues on the E39 chassis. I noticed one of the jack points is kinda pushed up into the body, wondering even if someone jacked the car up in the wrong place and crimped the line LOL.
 

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It is more than likely a crushed line or one that rotted on the inside and plugged. The ABS relieves pressure from a line it does not block it. I would suggest you do not drive this car until you sort this. Likely it is a line failure and the line could fail and release all brake pressure, relieving you of all brakes.
 

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Discussion Starter #5 (Edited)
Yeah it's not a daily driver or a driver of any kind at the moment. State inspection has been out since 2009 by the prior owner and it's been sitting mostly since I bought it a year ago. I've only driven it late at night just to keep the lifters oiled up etc around the country roads where I live maybe once every 2 months (I live in the sticks). And I won't be driving it around any traffic until I know I can rely on the brakes. If what ever is stopping the fluid flow breaks loose internally, I now have big pocket of air in the rear caliper I took apart to worry about suddenly imparing brake performance. (Unable to bleed due to the lack of fluid flow)

It's a southern car so not much corrosion/rust on it underneath. But it's always possible moisture got into the fluid somehow and line is rotting inside out. Prior owner's maint looks to have been lacking to say the least.
 

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Discussion Starter #6 (Edited)
Sailor, you made a comment about greasing/not greasing caliper slide pins in relation to summer or winter driving? Do you remember what thread that was in? When doing the rear brakes on this car I noticed the pins where slightly gummed up with old grease.
 

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It was gzig5 thread. You are not suppose to grease them. I do but clean them out regularly. If you search that topic you will find links to many pages explaining why not to grease.
 

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Could be the flexible hose that's collapsed, they fo that sonetimes but I would have expected a tiny bit to come through. There are short flexible hoses that 'feed' the rear wheels located just after the abs unit and are exposed to some engine heat, these too could have collapsed and failed. Might not be a bad thing to replace all six flexible hoses anyway...
As you've mentioned, opening each union at a time is a sensible method.
I hope you get this sorted easily.
 

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if its not the flexible hoses or crimped hardline, then I would assume ABS hydraulic module. I posted about it for my front driver caliper. I rebuilt all calipers, replaced all lines with ECS exact fits and to no success was I able to unclog the hydraulic module. Activated with INPA and DIS with no success. I ended up replacing the hydraulic module from clemster and bleeding with DIS and motive power bleeder. good luck.

Fixing these cars are never ending... Good thing they give never ending happiness!
 

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To OP, EASIEST way to know if there's a clog line is to unplug the line from that culprit caliper, attach a clear tube and bottle to the detached brake line and start pumping your brake pedal. If there isn't any fluid coming out, its either a clogged ABS hydraulic module, or clink in the line. After that, detach the correct line from the ABS module, attach a bottle of brake fluid to the line and apply vacuum on the opposite end. DO NOT APPLY COMPRESSED AIR, don't ask me why..:mad:.. If the brake fluid flows through the entire line, your culprit is the ABS hydraulic module. If that's the case, don't bother to fix it, just replace it with a quality used piece from clemster. If not, replace your line. Either way, you'll need DIS to properly bleed the ABS module as it is no longer a contained system. Good luck.
 

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Discussion Starter #12 (Edited)
To OP, EASIEST way to know if there's a clog line is to unplug the line from that culprit caliper, attach a clear tube and bottle to the detached brake line and start pumping your brake pedal. If there isn't any fluid coming out, its either a clogged ABS hydraulic module, or clink in the line. After that, detach the correct line from the ABS module, attach a bottle of brake fluid to the line and apply vacuum on the opposite end. DO NOT APPLY COMPRESSED AIR, don't ask me why..:mad:.. If the brake fluid flows through the entire line, your culprit is the ABS hydraulic module. If that's the case, don't bother to fix it, just replace it with a quality used piece from clemster. If not, replace your line. Either way, you'll need DIS to properly bleed the ABS module as it is no longer a contained system. Good luck.
Thanks to everyone for the input and pointers. I'll be trying some of these things out when I next get time to work on it, hopefully later this week.

Mofoaka, I already did up to the point of taking the line off the caliper and trying to squirt fluid into a clear bottle, not even a drip came out, even tried with the engine on to run the booster, stood on the pedal and pumped it hard, nothing! My next thing to do will be to trace the line back to the abs module and start working my way back and see where the fluid stops.

I read some of your post, didn't get time to read it all yet. Looks like an adventure LOL. Your post was the only one that came up kinda similar to my issue or initial symptoms. I'll be referring back to it when I start digging deeper into this, it's already been helpful. Yeah I do need to get DIS. I need to get some of the more advanced diagnostic S/W now, but need to get a working laptop first. Having a couple of these cars in need of TLC I'm going beyond the scope of the Peake reader now.. And already have bought a few things off Clemster so he'll be the first to hear if I need an ABS unit.
 
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