ABS Master Cylinder / Pump Assembly

[Fresh Air Inspector]

Hello All,

I've been through a number of threads and found the 'theories' somewhat confusing.

Background
When I bought our Scorpio the brake / ABS light took awhile to extinguish (~25 seconds), after start up (after sitting overnight). After about a month of driving the brake / ABS light would come on occasionally when the brakes were applied. This became a regular occurrence soon afterwards. During this time I also noticed that the brake fluid reservoir would 'fill up' about 4cm (1.75"), above the Max line whenever the car was parked overnight. I assumed this is normal when the system is shut down.

I took a gamble and replaced the Accumulator with a good used one. This solved the brake / ABS light issue while braking. The brake fluid reservoir filling up overnight remained the same.

Current Situation
A few days ago I noticed the pump relay under the dash 'chattering' when stopped with my foot on the brake pedal. This morning I did a few tests and it still takes ~25 seconds to extinguish both lights after start up (sitting overnight). I can push on the brake pedal 3 or 4 times before the pump relay kicks in. If I keep my foot on the brake pedal the pump relay will begin to chatter.

I'm debating whether to replace the Accumulator with a new one or replace the complete master cylinder / pump assembly with a 'remanufactured unit? I know it is an expensive part but brakes are a critical component that shouldn't create questions.

Has anyone ever converted a Scorpio to a 'standard' brake servo / master cylinder set like the European 'non-ABS' cars? I recognize that this will negate the ABS system but to me that is a small price to pay for a significantly less complex brake system.

Looking forward to the feedback.

[brokencase]

It takes my ABS light about 20-25 seconds to go out after starting up and when it has been sitting a while. I believe this is typical.

Rubber parts for the master cylinder portion are available from Frenkit. However it is my understanding that attempting to rebuilt the ABS portion is not advisable.

viewtopic.php?f=29&t=32539

I have been fortunate in that the only problems I have run into in the past have been frayed wires to the ABS sensors causing intermittent connection. In this case the light will come on after hitting bumps and applying the brake. The ABS is then disabled until the ignition is cycled.
It is usually the front right sensor that fails because it is toward the rough side of the road. Replacement of the sensor/cable resolves the issue.

Given how old the cars are, I think it is important to flush the brake fluid on the Scorpio at 2 year intervals.

I have a collection of Teeves ABS troubleshooting docs I have collected over the years and will place on mediafire for you here...

https://www.mediafire.com/file/luurozy9 ... f.zip/file

Have not heard of anyone converting the master cylinder. But many have just disabled the ABS functionality and disabled the ABS light on the dash.

[brokencase]

Now that I think about it your suggestion is intriguing. I don't like bastardizing things, but the repair/replace of the ABS unit is expensive.

I think I can count on one hand where I actually had the ABS kick in during emergency stop situations...and as it gets long in tooth I don't drive it in the snow and I try to avoid the rain.

There must be some master cylinder (with associated power brake booster) that could be substituted from some other vehicle.
Indeed...swapping parts from other vehicles to keep a Merkur going is a topic that Brad (DPDISXR4Ti) and I most adore...

At most we are talking about a custom control rod and very likely some custom brake line fabrication.

Could something like this be adapted? Not sure. Booster might hit the shock tower. Perhaps best to hit the junk yards and pick up some potential candidates.
Below is 89 Ford Ranger. There is a slight angle as it attaches to the firewall, but one could 3d print a wedge adaptor to keep it level.

89rangerboostmast.jpg (19.64 KiB) Viewed 11105 times

It makes you wonder...did Ford have a standard bolt pattern for the booster into the firewall? I see 4 bolts on the ABS unit!

ScorpABS.jpg (273.82 KiB) Viewed 11103 times

FreshAirInspector - You're going to have to be the guinea pig on this one. My ABS works and I have worked out a Chinese Ford Transit ABS sensor substitution, Take the torch and find out what you can...

[Fresh Air Inspector]

Hello Brokencase,

Appreciate the detailed response and the ZIP file - lots of interesting information especially the 'translated' Polish document.

I may try a 'new' accumulator to see if that solves the relay chatter issue. If it doesn't, I'll have a good spare. According to one of the documents you provided it has a lifespan of 5 - 8 years, unless I misunderstood the text. In theory this could be true as that component is definitely worked hard, mind you Citroen suspension spheres as well as the British Leyland Hydrolastic spheres use the same principal and live quite long.

Your rationale on replacing the current master cylinder set up with a 'standard' one is the same as mine. The Scorpio Mk1 was sold in Europe without ABS but from what I have found the master cylinder is a '2 bolt' mounting so that one is probably out. The picture of the Ranger assembly is interesting but I see two potential problems; the servo housing is quite 'thick' which may cause clearance issues plus the Ranger is a disc / drum set-up, don't know if the pressure to the rear brakes would be correct, plus how would you measure it?

I'll have a close look at my spare Volvo 940 master cylinder set-up. The servo housing is a slim design with a small outside diameter plus it is set up for 4 wheel disc brakes.

Need to make a trip to the local 'pick and pull' to see what is available. For me it will be a few weeks before I will have the time - hopefully the snow and cold won't be too much of an issue.

In the meantime I will re-read all the documents you provided plus go through the Ford documentation and see what else is online.

[PeterP11c]

In the lifetime of my Scorpio, which is over 29 years, I went through 2 complete sets of ABS pump assembly including the accumulator. The combination ABS yellow light and Brake red light always stay on the longest time after ignition. No matter what the condition of the ABS system, these two take about 20 plus seconds to go out. The brake pedal chattering happens intermittently and I couldn't figure it out, so got used to it. On the top of things, I get the brake pad yellow light flash for 15 seconds on first start, must be a sensor somewhere but it is another mystery to me. BTW, if you need some Polish translation, don't hesitate to reach out.

[Ed Lijewski]

Re the pump relay chattering it's also possible the relay is failing, or the pressure switch is failing.

Noah Boehm modified a Scorpio ABS MC unit to delete the ABS valve section with a cut off plate machined from aluminum stock (I think). I don't know if he's installed and road tested the unit on his XR yet but he's verified that with that plate there are no leaks.

YMMV

[my8950]

See photo

[brokencase]

Regarding that mod...

Correct me if I'm wrong but is it not the case that when ABS fails (or this mod) you are left with just basic, non-power assisted brakes?

This is (and at least my) motivation for finding a master/booster from another vehicle that could be adapted.

FreshAirInspector - I would not worry too much about whether the car had rear drums or not. Front/Rear distribution is usually accommodated via the sizing of the brake surfaces. If worst comes to worst you could put in an adjustable distribution valve.

[brokencase]

Late 80's mustang booster seems to have a smaller diameter booster...ported on opposite side...

mustangboost.jpg (22.95 KiB) Viewed 11076 times

[Ed Lijewski]

Regarding that mod...

Correct me if I'm wrong but is it not the case that when ABS fails (or this mod) you are left with just basic, non-power assisted brakes?

If the ABS yellow MIL is illuminated signaling a fault in the ABS system boosted/power braking remains functional.

Noah will confirm but I assume removing the ABS valving module via his block off plate leaves boosted/power braking functional.

YMMV

[brokencase]

I don't thinks so Ed. You disable the ABS as Noah did, you disable boosted braking. All you have left is the master cylinder.

[brokencase]

This video tells a lot about the fox body master cylinder.
https://www.youtube.com/watch?v=ewBTATu3Iy8

Looks like the 93 Cobra master cylinder is better suited to the Scorpio.
Scorpio is 1" bore as is the Cobra. Cobra had rear discs.

https://www.maximummotorsports.com/1-19 ... -C528.aspx

I think it would be worth going to the junkyard and picking up booster/master just to check fitment.

[brokencase]

I took a look under the hood of the Scorpio today and I think the Mustang master/booster would fit. But I can't be certain unless I get a hold of one.
The master reservoir may bump into the fuel lines but they could be bent forward slightly.

Here is how I would do it. You have four separate lines going into the ABS, one for each wheel.

I would make (or purchase) a manifold block to tie the rear lines together and the front lines together. You don't want to cut the original lines.
You then run the two separate lines for front and back into the Mustang master cylinder. Optionally (and probably recommended) is a brake proportioning valve on the rear circuit.

[Fresh Air Inspector]

Hello Peter,

Appreciate the offer to translate Polish - the 'mediafire' link that Brokencase included in his Tue. Nov. 16 post has a number of documents. The largest is a Polish to English translation. Overall it is quite well done, a few words are incorrect and the text in any image remains in Polish. Nonetheless it is an excellent document.

Hello Ed,

I would be hesitant to disable the ABS side only without knowing the exact impact. What I like about where this thread is going is the discussion on replacing the complete ABS / Master Cylinder assembly. For some (many?) of us, installing a 'standard' vacuum servo / master cylinder dramatically simplifies the complexity of our vehicles.

Hello Brokencase,
Great reference material on the master cylinders especially the bore diameter info. I agree that the Mustang unit is a good possibility. It appears that the servo is about 20cm (8"), in diameter which should fit. A quick check of my Volvo 940 indicates that the total length of the servo plus the master cylinder is about 35cm (~14"). It uses a servo about 20cm (8") in diameter and roughly the same depth as the Mustang unit. At 35cm (~14"), overall length it touches the fuel lines which, as you pointed out, can easily be moved out of the way.

I had a close look at the brake lines on the underside of the Scorpio master cylinder (see picture below), and compared these to what is in the shop manual (see page 12-29-2). The front brake line goes to the LF, the middle line to both rear wheels and the rear most line to the RF. I assume that the male threaded fitting (10mm), used in the Scorpio would thread into the Mustang master cylinder, this would allow the both front brake lines to easily connect. It is difficult to see in the picture below that although the middle fitting is quite large, it 'appears' that the end that threads into the master cylinder is the same as the other two. If that is the case, it will make connecting the Mustang master cylinder much easier. Also, the YouTube video about the Fox body master cylinder you just posted shows the three brake line connections.

The challenge for me is finding a used Mustang master cylinder assembly - the yards here crush older vehicles not long after arrival. Wish me luck.

Hope it helps.

[Fresh Air Inspector]

Doh!! Forgot the picture in my previous post!

Brake Line Connections - 2R.jpg (271.19 KiB) Viewed 11038 times