Maybe I’m a glutton for punishment, or I’ve got a little too much time on my hands. Or maybe it is a lot of both, but here goes:

I started looking for a (spare) ABS unit for my ‘86 that I could have on hand if ever needed, and I found one that would have been a great deal but it turned out that there was corrosion that rendered the unit suspicious. The seller graciously refunded me. This was a 0 265 200 020 unit.

I did as much research as I could and found several posts here that I used for reference……most notably the posts from mark970 and Tof.

Well, I found a second unit at what I considered a good price and received assurance from the seller that if I opened it up and found that it looked to be scrap, that he would take it back with no qualms. It also came with the complete wiring harness. It turns out that this was a 0 265 200 059 unit.

Here are pics of the unit as I received it:





As you can see it looks really clean, but then that is usually the case with a unit that lives in a sheltered cavity not exposed to the environment.
A few more pics before teardown:


I put the bleeder screws in not knowing how long I was going to leave the unit on the bench. I'm sure it was a waste.





So far it looks promising, so I proceed to open the proverbial can of worms.


I had a quality 14mm hex socket to crack that large bolt loose. Notice the upper casting does not have the two small hex bolts.

No debris or corrosion here.......just a small amount of brake fluid.

All screens have no debris or corrosion showing....all are wet with brake fluid.

After a quick wipe with a cloth.

Bolts removed for motor....broke free nicely. No corrosion here.

The shaft of the motor with the cam lobes look good.

The two 24mm plugs on bottom casting before removal.

Internal view of cavities on bottom casting

Bottom casting motor mounting surface.

Bottom casting solenoid mating surfaces.

Bottom casting piston assembly.

Bottom casting piston assembly.

So far everything looks promising.

It's at this time that I start a conversation via email with Jordan from mtechniqueabs.com. Note: His response times each time were quick.
My first question I asked about the torque setting for the large main bolt. His reply:
150Nm.

My next question I asked if I could use the 059 unit in my '86. His reply:
No worries Ken, so the 059 is used in the newer model cars. 1991 - 1993 or so. It does have different solenoids, valving, flow rate, physical height and some other differences. Can you use it? Yeah... is it going to be correct for the car and the rest of the braking system? No.
Later in our conversations he tells me:
You can install the 059, it will work provided it functions as it should but it is a bit different internally.

It's at this time that I feel like I am pestering this guy.........but I continue.

My next question I asked about the torque setting for the two plugs with the 12mm internal hex head. His reply:
The cam lobe driven opposed pumps hold down plugs are M18x1. Grade unknown. No nominal torque figure is available, I do them to feel. Suffice to say they are very tight.
OK, I can do that.

My next question I asked about the two large star plugs that look like T125 or so…..what sits behind those and if everything else looks good, would there be a good chance that there is no problem behind those? His reply:
Behind the large torx plugs are fluid reservoirs. There is a very low flow rate through these, rather pressure variance. These near always have debris inside as it accumulates steadily in the absence of flowing fluid. Accumulation ranges from gloopy fluid, to outright paste. You can watch this video where I tip a "normal amount of junk" one over and you can see what is typical. Most are at least this bad, if not worse. Mind you the unit pictured here is a 4 channel unit from a big body BMW, but same same... Around 20:55 in video.

My next question I asked if there was a way to disassemble the solenoids or am I asking for trouble there? Or spray brake cleaner through them and verify with 12 volts that they activate? His VERY LONG and DETAILED reply:
Disassembling the solenoids is required, and they are staked closed. You aren't going to get them clean by soaking them or spraying through them. Even a bath of hot solvent in an ultrasonic cleaner does little to disturb the buildup where it matters. The little filters at the inlet and outlet accumulate a small percentage of solids but the buildup occurs inside ten fold. There are also more moving parts inside them than you might think.Each solenoid traveler has 6-10 ball bearings inside of it depending on the solenoid variant that rides on two machined axles. Any pitting on the bearings or the shafts and it can hang up. Same is true of the ID of the solenoid body and the OD of the traveler. Pitting makes them hang up, causing the solenoid to not work.

There are three springs inside the solenoid, any of them can break rendering the solenoid non functional. They can also just wear out / fatigue, making the solenoid not work.

Then there is the valve mechanism itself, which has three unique positions. Passive, pressure hold ( blocks increase of pressure ) and release ( dumps pressure back to reservoir ) The traveler is moved to different positions by a tightly regulated pulsed 12v signal of varied current. One or both switched positions can fail to work with no rhyme or reason to it on an otherwise immaculate looking solenoid even though you'll hear it click when power is applied.

Each end of the traveler seats half of a 2.5mm ball bearing against the finely machined surface on a hardened chamfered valve seat, which directs fluid as commanded. Any corrosion or deformation of any sort to the seat at either end? The solenoid doesn't work, and the kind of imperfections that cause a failure to seal are small enough you can't see or appreciate them with your eyes alone.

Incorrect preload on the solenoid nut, after it's been cut free and removed with a special tool, will cause the traveler to not seal on one or more positions... and you guessed it... not work.

There are so many ways the solenoids can fail, and be rendered scrap. I have bins full of likely bad ones that aren't worth trying to even clean. Easily 750-800 of them if I had to wager a guess.

I test each solenoid on an individual solenoid tester, and then again once installed in a finished pump. Each one is expected to hold closed under a minimum of 600 PSI of hydraulic pressure at the inlet from rest, and then again hold pressure rising from a static 600 PSI input when it is increased to 1000PSI while current is applied. If they pass this test they then need to dump the same pressure instantaneously to zero while also still holding from allowing inlet pressure to rise.

Most solenoids fail the hold test. Many fail the reduce test. Quite a few fail both, and go into bids as scrap... often after hours are spent making them pristine inside and out.

I've been doing this for about four years now. I've invested just shy of $150k into equipment and R&D to make what I do possible through extensive trial and error. Ask Bosch if these units are serviceable, they will unequivocally tell you no. They aren't altogether wrong.

The reality of this is you're more likely to cause a currently operable but old unit to not work at all, than you are to succeed in restoring the unit to full functionality in one go without spare units to get additional parts from and a manner to reliably bench test the unit prior to installing.

Just thought I would post this for others so they don't get the wind sucked out from under their wings like I got.

 

You are brave to try this. I don't want to learn a new operation. I would just send it to Jordan. Dan

 

Oh, I am DEFINITELY NOT tearing the solenoids down.

 

Update:

NEVER EVER SAY NEVER. After speaking to another rebuilder, I decided to tear down the solenoids. After some conversation, he assures me that I should have no problem with this and tells me to use a small Dremel bit to defeat the staking on the solenoid in order to get the nut out without damaging the threads. It was not difficult at all using a lighted 10X magnifying glass along with the Dremel bit.

Once I ground through the staking, I inserted the solenoid into a 3d printed solenoid vice and clamped that into a benchtop vice. Using the special tool and a small cordless impact driver, the nut came out easily.

All three solenoids looked clean.....no sediment, just clean fluid

I also purchased a tool to get the large Torx reservoir plugs removed. I had to use a larger electric impact for this.

These had a little fluid in them and very little of anything as you can see.

 

Ken,

I'm glad you got this sorted without having to spend a bunch of money!

If anyone else is interested in this, I have more tools I can sell, or I can do it for you at about half-price. I also have a couple C4 cores on the shelf now.

-Chris