ABS Master Cylinder / Pump Assembly

[brokencase]

Hmmm..

Something is different here. The connections on the bottom of my ABS unit are different from yours.

I will see if I can post a picture.

[brokencase]

Mine is a little different. I wonder why you have that thicker adapter in the middle.

[brokencase]

Speedway Motors has this compact universal booster/master with a 1 inch bore.
Booster is 7 inches in diameter and overall mounted length is 11.875"

https://www.speedwaymotors.com/Dual-7-I ... ,5084.html

This is worth reading...

BoosterChart.gif (37.92 KiB) Viewed 4536 times

The only down side is you would have to get the master rebuild kit from them should you ever need it.

However the nice thing is that it has a simple threaded rod on the pedal side which makes it easier to interface to the Scorpio pedal mount.

Their universal boosters all have a 3.38" x 3.38" bolt square. I'll have to measure the pattern on the Scorpio.

I believe the Mustang booster is a dual diaphragm type. The Mustang one may be more compact and the master is definitely lighter aluminum.

[Fresh Air Inspector]

Hello Brokencase,

Interesting that your centre brake line connection is so different. The female threaded fitting in the ABS housing also appears to be larger in diameter than mine. My car is from Spring 1988 production - the driver's door was replaced by the original owner due a parking lot incident. The idiots at the body shop didn't transfer the VIN sticker. I don't believe mine has had any ABS repair done - the service history does not indicate this, but you never know. However, the connection set-up on mine seems overly complex, leading one to surmise it has been worked on. The good news for you is your brake line set up (3 lines), is the same as mine meaning the Mustang (or similar), master cylinder should work (assuming the threaded fittings are the same).

Have you been able to determine if the Mustang master cylinder has the same brake line orientation as the Scorpio (front to back; LF, rear, RF)?

The Speedway Motors info on brake boosters is very useful. I would prefer to stick to a Mustang or similar servo / master cylinder set-up as it ensures a reasonable parts supply down the road. I take it that you are leaning towards a 1" bore master cylinder?

I will probably dive into this modification over the winter when the car is off the road. My thoughts on the pedal push rod is to reuse the one from the Scorpio assuming it is the correct length. If too long I may be able to shorten the end that contacts the piston. If too short, cutting the push rod, threading the ends and inserting an internally threaded sleeve with lock nuts would allow one to adjust the length.

Need to start looking around for a Mustang servo / master cylinder assembly. Fingers crossed.

[brokencase]

I've been looking for an inexpensive used booster with master cylinder from a Mustang but no luck.

The ones at RockAuto all want a core charge.

So I have been exploring the universal alternatives. I think this is a better way to go since they are newly manufactured and are not rebuilt.
In addition, they have ports on either side of the master that provide flexibility as well as the threaded pedal rod.

This is an very affordable and compact option...
https://www.ebay.com/itm/142998969080

Best option I have found so far.

I'm not too concerned about availability of rebuild kit. If it last 80-100k miles I'll be fine. In fact I'll probably be dead by then.
I think the master cylinder on my Explorer lasted around 80k.

1" bore is what the Scorpio has.

Don't think the Scorpio bolt pattern on the firewall is the 3-3/8" that is typical. I think the Mustang is 3-3/8" also.
This could present some problems. Naturally new holes must be drilled. Need to look the firewall area over on the inside and make sure nothing is in the way.

[brokencase]

Just wondering why there are only 3 brake lines coming out of the ABS. Is it the case that only the fronts are independently "pulsed" and the rears are tied together on one line? Or is there another line that we do not see?

I should probably look at the Helms manual.

[brokencase]

Another interesting alternative...

https://www.ebay.com/itm/191402810713

Includes the the proportioning valve. Many of these universal kit claim "Corvette style" master cylinder. So perhaps that is an indication of where to get a rebuild kit from.

[Ed Lijewski]

Just wondering why there are only 3 brake lines coming out of the ABS. Is it the case that only the fronts are independently "pulsed" and the rears are tied together on one line? Or is there another line that we do not see?

I should probably look at the Helms manual.

XR (basis for the Scorpio) has three lines.

Helms? Helms??? Instead of the Ford SM?

YMMV

[Fresh Air Inspector]

Hello Brokencase,

Interesting links, what I would miss is a 'see through' reservoir along with the level sensor. Those two items make a 'quick check under the hood' so much easier. A did a lengthy search on Ebay, Amazon and Summit and all have listings galore but very few have brake line fittings on the 'passenger' side of the master cylinder.

Agree that going the 'rebuilt' route via RockAuto or ?? is not the best route, I would prefer a 'new' item although that may end up meaning 'made in China' .

Looks like the current 'servo / master cylinder' criteria is;
1. 1" bore
2. 7 or 8" diameter dual diaphragm servo
3. brake line ports on the passenger side

Need to figure out the fitting thread sizes, I don't relish the idea of having to fabricate 'adapter lines'. Don't know about you but I have a 50/50 track record with making my own brake line flares (bubble or double). Mind you I've been using standard steel, need to try Cunifer [tm] (cooper-nickel). Much more malleable and completely rust proof.

Regarding your question 'why 3 brake line ports'. On some ABS equipped vehicles with independent rear suspension (or solid rear axle), there is only one brake line to the rear of the vehicle. A 'T' fitting splits the feed to the two rear wheels. When the ABS system is called into action (assuming a 4 wheel skid), the solenoids for each front wheel and the one for the rear wheels start to pulse modulating the pressure to all the calipers.

My Volvo 940 is rear wheel drive (solid axle), with a 'locker' rear axle. The differential housing has a sensor for the ring gear that provides the speed signal for the speedometer but it also provides the rear wheel signal for the ABS system. It also has a single rear brake line with a 'T' fitting to direct the brake fluid to the two rear calipers.

As mentioned, the Ford SM has a very good diagram in section 12 (Brakes), page 29-2.

BTW I found another picture of a Scorpio ABS Master Cylinder / Pump Assembly from a 1989 model and it also has the same large fitting as mine. Wonder what the rationale is for that? If I do end up swapping out mine I'll pull the fitting apart - almost looks like a check valve of sorts.

Hope it helps.

[Fresh Air Inspector]

Hello Brokencase,

I spoke too soon.

The picture of the late 80's Mustang servo / master cylinder is our best bet at this point. From what I can see it has the following benefits;

1. dual diaphragm servo (probably 8").

2. provision for three brake lines (based on the video you included, the orientation is the same as the Scorpio; F R F).

3. it takes the 'plug in see through' reservoir which may even accept the Scorpio cap and level sensor.

Looks like the 1" bore master cylinder used in the '93 Cobra version (according to the Maximum Motorsports website), is a good point of reference for our application. It has the three brake line fittings, plus the fittings for the front brakes are on the passenger side of the master cylinder.

[Ed Lijewski]

A 'T' fitting splits the feed to the two rear wheels. When the ABS system is called into action (assuming a 4 wheel skid), the solenoids for each front wheel and the one for the rear wheels start to pulse modulating the pressure to all the calipers.

Assume a one front wheel skid and the system pulses only the braking for that wheel, so steering capability although lessened remains. Rear wheels on Scorpio vintage ABS have no steering capability. Thus two lines front, and one line with a T rear.

YMMV

[brokencase]

If you go with the Mustang setup you will have to get the brake proportioning valve that goes along with it. This valve has to be for a front/rear disc brake car.

If I were to do this I would make up my own junction block out of aluminum that interfaces to the Scorpio brake lines. You then make whatever short lines are needed to interface from the junction block to the brake proportioning valve and master cylinder.

Here is a Ford style proportioning valve.

https://www.npdlink.com/attachments/2b0 ... iagram.pdf

[Ed Lijewski]

If you go with the Mustang setup you will have to get the brake proportioning valve that goes along with it. This valve has to be for a front/rear disc brake car.

If I were to do this I would make up my own junction block out of aluminum that interfaces to the Scorpio brake lines. You then make whatever short lines are needed to interface from the junction block to the brake proportioning valve and master cylinder.

Here is a Ford style proportioning valve.

https://www.npdlink.com/attachments/2b0 ... iagram.pdf

FWIW XR guys who replace OE rear drum brakes with disc brakes typically (almost all from what I can tell) remove the OE XR proportioning valve.

YMMV

[brokencase]

Here is another way to do it...

Use the 1" cobra mustang master (or the universal unit I posted earlier) with two output ports.

Get one of these...
https://www.jegs.com/i/JEGS/555/63025/10002/-1

Less expensive version,,
https://www.ebay.com/itm/203014472472

Then get two 90 degree elbows to get the two side ports pointed downwards as I have indicated in this modified diagram from their install manual.
Use whatever adapters needed to interface to the Scorpio lines. You then just have to make two short lines to go to the master cylinder.
This way you won't have to modify the existing brake lines. This leaves you the option to return to ABS if desired.

Adapters for metric to SAE are available for the brake lines.

jegblock1.jpg (45.34 KiB) Viewed 4512 times

Good discussion on proportion valves..
https://www.motortrend.com/how-to/71398 ... ing-valve/

[brokencase]

Helms? Helms??? Instead of the Ford SM?

YMMV

MMDV - I guess I am the only one around here who knows that Helm is the distributor for the factory manuals.