Hey guys, I need to tap into the knowledge of all you smart people and figure out what is all part of an ABS system maintenance/cleaning for my 89'

Quickly...I bought a very well preserved (and running) 89' ZF Z51 late last year. It had sat for 10 years so I knew I'd be fixing many things as the car loosened up.

The fun begins this year and already I had a really hard time with the brakes (I had issues with them last year when I bought the car, the brakes were sticky and not functioning propely). I removed all 4 corners to powdercoat and install SST hoses. Once I got to the bleeding part (which I've done many times in the past) it was so erratic. It would bleed normal, then nothing. Later try again and 3 of 4 would go, then nothing...not even the previous 3. It didnt feel like an air bubble scenario to me not to mention I probably wasted about 2qrt of fluid as a result of sucking it back out of the reservoirs because of constant "floaters" (i also had to clean the reservoirs after the initial sucking out because the bottoms were all black sediment). I also noticed upon removal and rebuilding that the front calipers were all rusty on the inside (the rears looked good). I also noticed that the front calipers don't exactly match...however they are both OE PBR J55's but I think at least one of them was a rebuilt/replacement (the pistons in one of them was also coated, not chrome and the casting was modified for some reason...I'll attach a photo if anybody has a clue as to why they would machine a caliper with a radius on the front).

So I guess the question is this...I have the ABS unit out of the car (I had fluid in the joints prior to the unit so I'm going to assume with all the rust and floaters I saw, the screens in the unit are clogged)...I plan to at a minimum blow out the lines at each corner prior to re-installing the ABS...but what should be done with the master cyclinder/power booster? is this the time to remove and clean/purge or is this a don't fix what ain't broke scenario? I've never been this deep into the ABS but it's good to learn since every C4 I've owned has had ABS issues at some point in ownership...plus I already have the unit broke open, this might be the best time for a deep clean???

Thanks in advance

 

Since you have it this far apart-and you say it had rust and "floaters"-yup it would be well worth it to go ahead and rebuild the master cylinder now too. It would suck not to and have crap come out of it later and start plugging things up again. As for the machining of a caliper-it's usually done to clear the inside of a wheel.

 

Thanks for all of the useful input! Is there anything special to know about the MC removal? how about removing the power booster?

 

Relevant reading...

https://www.corvetteforum.com/forums...issaembly.html

 

Thaks for this link, this is a great thread!

 

Lies-within (mtechniqueauto.com)

Might want to look at some of the before pictures from this rebuilder. Backflushing will not clean it out. Dan

 

Thank you!

 

Here is a message I got from the owner of the company I linked to. Dan


Good morning Dan,


So the C4 Corvette came with many different ABS pumps over the production range. The earlier cars have the Bosch ABS2 units well represented on my website that I routinely rebuild. These went into the cars until the end of 1991, where there were replaced but the Bosch ABS2U/S units. These were for all intents the same unit from a function and internals standpoint, in simplified castings which were essentially extruded aluminum billet. I believe these were the result of steam lined production and tightened production costs as the forging of the original unit were likely more expensive to manufacture and machine.


In 1995 again the C4 saw an update, to the Bosch 5.0 hydraulic modulator which brough the control electronics onboard the pump which did in time create a whole array of new and interesting failures.


More to the point though, manually or power bleeding fluid through the pumps will exchange the fluid sitting in all of the main passageways and in the solenoid valve areas. The volume of flow really isn't sufficient to dislodge schmoo buildup from any surface, the fine mesh filters included.


Using a scan tool to activate the DC motor will help drive fluid out of the storage reservoirs and aid in the exchange of that fluid with fresh. This fluid only sees flow during an ABS event, when the ECU is requesting a pressure increase after it has already dumped inlet pressure back to the master. It is very hard to exchange the fluid under any normal use because there is so little volume of flow, its all static pressure changes that do the work.


Bleeding routines in scan tools usually cycle the pump and each solenoid, but the main intention is to jiggle free air cavitation as tiny bubbles like to cling to surfaces inside the pump which creates a rubbish pedal feel.


The primary failure mode on Bosch 2 and 2U/S units is internal coking blocking flow and or immobilizing moving parts. On the Bosch 5.0 units those generally suffer from control unit failures more than anything else. I have not yet rebuilt a 5.0 but I can tell you the early 5.0 units did share some of limited internal designs with the legacy units and they would be susceptible to the same buildup related failures overtime with enough neglect to routine fluid services.


Feel free to share my response on CorvetteForum with all that may benefit from it.

 

I'll have to read that more thoroughly when I get home but this seems like a golden nugget of information, thanks for sharing that!

 

I had sent him an email asking if normal flushing actually flushes the ABS unit. There was not an agreement on this forum. I figured he would know. Knowing now that the ABS unit costs 1200 bucks to rebuild I flush every two years. If you look at the before pictures you will see some rust. Rust happens when there is water in the fluid. You mentioned rust in your caliper. I am not trying to spend your money but if my brakes were not working correctly, If I had rust in the caliper, If I saw floating crap in the master, and if I already had the ABS unit removed I would not think twice about sending it in for a rebuild. I am not connected to this company in any way. Dan EDIT: I wonder how hard it would have been for Bosch to put fine filters on the inlets in a manner that allowed them to be removed and cleaned without pulling the unit. Sure would have been nice. EDIT2: It also would have been nice to have a way to push a couple of buttons in some special way that allowed the ABS go into an internal flushing program maybe an hour long in a manner that did not burn up the pump. This to be done before regular flushing.

 

I just rebuilt the entire unit, upper and lower sections. I have not installed it yet to see if it works

The screens were full of rust so I feel that I didn't go through this for nothing!

I did the upper half before I realized the dirty filters mean the dirt is in the lower half...not a big deal, I was able to do the lower half without removing anything from the upper half other than a couple bolts to disconnect the motor.

 

Nice, You are obviously more skilled than the average C4 owner. Dan

 

Well as nice as that is to hear I'm simply learning as I go...just like I do all my projects

Thanks for the kind words , the email you shared also helped a lot, in fact I purchased a Snap-On MT2500 with the ABS cartridge so I'll also be learning how to use that to cycle the solenoids.
Regarding the link shared in this thread, I def used that as a guide!!! that post is excellent as well.

I'll have the full video up on my youtube channel shortly after the install is complete.

I'll get this into the car SOON...top priority today is to replace the rack-n-pinion from my 87' that I had to rip out for a warranty exchange.

 

This is a great! Props to you for diving into this.

 

I have to say, this wasn't the can of worms that I was expecting. The inside of this is fairly simple...I didnt need any "special" tools. It did require a 12mm hex socket that I had but found that I clearly need to upgraded from the Harbor Freight variety as it started to round the main bolt and I will purchase a 15/16" 6-point impact socket (i like them thick) so I don't use a regular 12-point craftsman socket...other than that just your normal tools. Lots of micro-fiber rags and an assortment of brushes (nylon, brass and steel all got used) and I coated all o-rings and plastic parts with fresh brake fluid just prior to reassembly.

As you can see from the photos, I simply had rust in my pump, if floated around and clogged the screens but I had no build-up or "packed valves" in the lower half so my situation was a simple cleaning...not a rebuild (i'll consider myself lucky).

 

Excellent info here.

Did you reuse the original seals or source fresh ones?

 

I dug into my unit because I had a very hard time bleeding the brakes after buying a car that sat for 10 years. It was also obvious that at least one of the front calipers was replaced and I believe thats when the rust was allowed to get into the system. I noticed rust on both front calipers but none in the rears...

I didnt replace a single thing...the only thing I didn't do that the person in the "pictured link" did was I did not dissameble the lower pistons/valves at all (I dissambled the lower half, I just didnt break each valves down further, I just cleaned them with brake cleaner and a brush and then soaked them in brake fluid)...my lower unit looked perfectly fine so I went with the "don't fix it if it aint broke" mentallity. All the o-rings looked good. I was really surprised that there was no "main" gasket...one very large bolts holds the two halves together, compressing each solenoid into it's pocket sealed off by a small gasket. Each solenoid has it's own gasket/o-ring but they looked fine.
The lower unit valve assemblies also had small o-rings but I left them alone. I'll be installing it this weekend so we'll see

 

Excellent to know, the fluid in the new to me C4 is gross to say the least and booster is bad too. I plan to start in on the booster after injector swap.

I have R4S Porterfield pads for it, SS lines, and need to acquire 13" front brake stuff once driveable. Life with old cars!

 

Sounds FUN

I'll be doing the booster and MC as well, at least at the minimum maintenance level required (assuming things check out) however the MC does need to be cleaned. I'm still working on the ABS, I had some issues assembling it, I damaged 2 o-rings in one of the solenoids (I noticed one was a little sloppy but I tried...) and wouldn't you know it, out of the 3 different metric o-ring sets I have, neither one is in my inventory so I'll be making a trip to Grainger this week.
Meanwhile, everything is soaking in brake fluid since this could be a 2 week break while I gather parts. I'll also draw up a cheat-sheet for people if they want to manually cycle a solenoid for whatever reason (if they dont have an old school scan tool).

 

Where's Booger when you need him? Poke-poke-poke...shake-shake-shake....