Master Cylinder Upgrade Part Numbers

[ratdude747]

Working on a brake repair/upgrade for my 1984 using a later model (Bricknose/Aeronose) master cylinder. Right now I'm getting my butt kicked when it comes to brake bleeding (Long story short: Vacuum bleeders suck, waiting on a pressure bleeder to come in). In the mean time though, I do have some information to share.

First off, Raybestos makes a new master cylinder for the later application that includes the residual pressure valve, the reservoir, and the reservoir level sensor, specifically MC39634:

As of this writing RockAuto has them for $33 before tax and shipping (no core)... which pending testing, is a great deal.

One thing I plan to (eventually) do is wire the reservoir level sensor into the brake warning circuit (parallel to the existing proportioning valve switch). The connector to do this is Motorcraft WPT-446; I de-pinned the center terminal (which on my pigtail was double wired) and used the outer two pins. The third pin is tied to one of the outer pins; this is used on later model vehicles to tell the ABS controller if some twit has unplugged the sensor to bypass a low level condition (which the ABS controller needs to know about; activating ABS with a brake line failure is a great way to make a bad situation worse!).

Before going this route, I didn't know the Raybestos MCs came with all the trimmings (RockAuto's pictures showed there not being a residual pressure valve) so I opted for a used eBay Ford unit... which was a complete loss. Nothing worked... it was seized on arrival and the front brake circuit wouldn't bench bleed. Also, the reservoir sensor was toast... more on that below.

If one needs to replace one of these reservoir sensors: you'll read online the only fix is to replace the entire MC (or the reservoir at least). Not technically true, as there are two options:

1. Find an NOS sensor. It's Motorcraft E6DZ-2L414-A, usually found on ebay for around $70 (way more expensive than a Raybestos MC with a new sensor, but if you're a purist dead set on a new sensor, that's the way you'd need to go)

2. Rebuild the sensor. The sensor is merely a potted reed switch; through some hacking away, I was able to dissect my faulty sensor (which seemed to have a bad solder joint, but I broke the switch tube):

A better way to do this may be to boil the sensor in a pot of water; the potting compound loses it's adhesion and softens with just a little heat, which would probably allow one to yank the tray out of the tube and pick off the compound without cutting or scorching anything. I made the mistake of using a MAPP torch on mine to soften the compound... even lightly used, it melted the plastic tray.

The switch tube I used to repair mine is a 14mmx2mm 0.55A unit:

If I were to use this switch, I'd pot it with some hot glue... but since I have a new one (that works great), I'll use that instead!

Master cylinder installed (I had to ditch the line bracket and re-bend the lines as the front and rear brake circuit positions are switched):

Now if I can get the darn things to bleed...

[Gary Lewis]

Thanks for the info, Larry!

And when the pressure bleeder gets in you'll be amazed at how easy it is to bleed brakes with the new master cylinder.

[85lebaront2]

Thanks for the info, Larry!

And when the pressure bleeder gets in you'll be amazed at how easy it is to bleed brakes with the new master cylinder.

I had an attractive helper when I did Darth's.

[Gary Lewis]

I had an attractive helper when I did Darth's.

Yes, you did!

[ratdude747]

Updates!

First, According to RockAuto pictures, Motorcraft BRMC63 is also a new complete MC with all the trimmings. $69 per... if the Raybestos one ends up being a fail, that'll be my plan C (as I'm already on plan B!).

Second, the pressure bleeder came in... worked great. Used the HF vacuum bleeder for a catch bottle... also worked great (if not overkill )

I now have a working brake pedal... but sadly no better than the old one I removed. Guess it wasn't faulty... and my brakes just suck a bit (then again, I'm comparing it to a lighter newer 1995 ranger with dual piston (stock!) calipers )

I also was able to wire in the level switch. Originally I was planning to splice it near the Proportioning valve switch, but due to access issues I only got far enough to cut back some of the harness tape.

Better idea: Turns out the needed connections (Brake Warning light: Pink/White; Ground: Black) are in an exposed section of harness right below the brake booster, allowing for a location to splice into:

Throughout the process I did several electrical tests to confirm I had the correct wires, culminating in a "shove the float and see the light" test that passed with flying colors.

All assembled (now this morning):

Sadly I must have had a leak or spill I wasn't aware of... bye bye paint on the bottom of the brake booster :

Not sure how to fix that. I'd prefer not to pull it again... and all I have is spray primer and paint (and painting it in place isn't practical for hopefully obvious reasons). Can't be much worse than it's unpainted form?

Yeah, I suck at anything paint and body related.

Would I do this again? Only if I blew a master cylinder... which I though I did, so it's a yes?

[Gary Lewis]

Updates!

First, According to RockAuto pictures, Motorcraft BRMC63 is also a new complete MC with all the trimmings. $69 per... if the Raybestos one ends up being a fail, that'll be my plan C (as I'm already on plan B!).

Second, the pressure bleeder came in... worked great. Used the HF vacuum bleeder for a catch bottle... also worked great (if not overkill )

I now have a working brake pedal... but sadly no better than the old one I removed. Guess it wasn't faulty... and my brakes just suck a bit (then again, I'm comparing it to a lighter newer 1995 ranger with dual piston (stock!) calipers )

I also was able to wire in the level switch. Originally I was planning to splice it near the Proportioning valve switch, but due to access issues I only got far enough to cut back some of the harness tape.

Better idea: Turns out the needed connections (Brake Warning light: Pink/White; Ground: Black) are in an exposed section of harness right below the brake booster, allowing for a location to splice into:

Throughout the process I did several electrical tests to confirm I had the correct wires, culminating in a "shove the float and see the light" test that passed with flying colors.

All assembled (now this morning):

Sadly I must have had a leak or spill I wasn't aware of... bye bye paint on the bottom of the brake booster :

Not sure how to fix that. I'd prefer not to pull it again... and all I have is spray primer and paint (and painting it in place isn't practical for hopefully obvious reasons). Can't be much worse than it's unpainted form?

Yeah, I suck at anything paint and body related.

Would I do this again? Only if I blew a master cylinder... which I though I did, so it's a yes?

Good job, Larry! (In spite of the spill.)

Thanks for documenting it, including the part numbers, as others are sure to want to follow in your steps.

[ratdude747]

Good job, Larry! (In spite of the spill.)

Thanks for documenting it, including the part numbers, as others are sure to want to follow in your steps.

One other oddity I came across (in retrospect):

The wires in the harness I tapped appeared to be striped (and in looking at the full resolution of the pics, is indeed striped)... not dotted like other places on the truck (radio power/illumination wiring, etc.). I didn't think the change had been made yet. Is 1984 a transition year?

[Gary Lewis]

One other oddity I came across (in retrospect):

The wires in the harness I tapped appeared to be striped (and in looking at the full resolution of the pics, is indeed striped)... not dotted like other places on the truck (radio power/illumination wiring, etc.). I didn't think the change had been made yet. Is 1984 a transition year?

1985 appears to be the transition year. Stripes had been used prior - in addition to dots and hashes. Ford just eliminated the dots and hashes for 1986.

[ratdude747]

Updates!

First, According to RockAuto pictures, Motorcraft BRMC63 is also a new complete MC with all the trimmings. $69 per... if the Raybestos one ends up being a fail, that'll be my plan C (as I'm already on plan B!).

Second, the pressure bleeder came in... worked great. Used the HF vacuum bleeder for a catch bottle... also worked great (if not overkill )

I now have a working brake pedal... but sadly no better than the old one I removed. Guess it wasn't faulty... and my brakes just suck a bit (then again, I'm comparing it to a lighter newer 1995 ranger with dual piston (stock!) calipers )

I also was able to wire in the level switch. Originally I was planning to splice it near the Proportioning valve switch, but due to access issues I only got far enough to cut back some of the harness tape.

Better idea: Turns out the needed connections (Brake Warning light: Pink/White; Ground: Black) are in an exposed section of harness right below the brake booster, allowing for a location to splice into:

Throughout the process I did several electrical tests to confirm I had the correct wires, culminating in a "shove the float and see the light" test that passed with flying colors.

All assembled (now this morning):

Sadly I must have had a leak or spill I wasn't aware of... bye bye paint on the bottom of the brake booster :

Not sure how to fix that. I'd prefer not to pull it again... and all I have is spray primer and paint (and painting it in place isn't practical for hopefully obvious reasons). Can't be much worse than it's unpainted form?

Yeah, I suck at anything paint and body related.

Would I do this again? Only if I blew a master cylinder... which I though I did, so it's a yes?

The good news: I found the source of the spilled brake fluid... And doubly confirmed that the reservoir switch works.

The bad news: the good news is because my rear brake line didn't seat/seal right and was barfing fluid everywhere! I also was away from home... So I limped to the local Menards and got a wrench and fluid. Thankfully it seems that loosening and retightening the fitting did the trick.

[Gary Lewis]

The good news: I found the source of the spilled brake fluid... And doubly confirmed that the reservoir switch works.

The bad news: the good news is because my rear brake line didn't seat/seal right and was barfing fluid everywhere! I also was away from home... So I limped to the local Menards and got a wrench and fluid. Thankfully it seems that loosening and retightening the fitting did the trick.

I think the good news easily outweighs the bad news. Congrat's!