Newer style master cylinder types

[Lima Delta]

Looking at getting a new bricknose era master cylinder.
Napa is listing a few different units for a '91 F250.

One specifies over 7000lb GVW, one under 7000lb GVW, one unspecified all with different NAPA part numbers.
My bullnose is an under 7000lb GVW 4x4 so it has the dual piston calipers, but I don't know enough about the bricknose F250 4x4 brake options.
Does it really matter which cylinder I get?
I assume the master for the heavier trucks has a bigger bore but it should still fit, no?
Would there be any detrimental effect to installing "larger" unit if it fits?

Thanks!

[Gary Lewis]

That's a hard question to answer as there is no solid info on which to base one's response.  But, I think it best to keep the master matched to your truck in order to get the best balance in braking front/rear as well as "feel" in the pedal.

In your case our page at Documentation/Driveline/Brakes says that your truck with a GVW of less than 8500 lbs would take master cylinder E4TZ 2140-A.  But apparently in '87 the federal requirements changed and the break between light duty and heavy duty trucks became 7000 lbs instead of 8500 lbs.  And that page shows that a 1987 - 1989 F250 with less than 7000 lbs GVW takes a E7TZ 2140-C.  But since my Master Parts Catalog quits at 1989 that's as far as I can tell on that page.

But our page at Documentation/Interchange goes much later, and it shows that the E7TZ 2140-C master was used at least until 1992.  So that's the one I'd go with.

As for fit, there was a change in stud width between the lighter duty masters and HD masters, so I think you'd be safer getting the LD F250 master.

[Lima Delta]

Thanks Gary, very helpful!
Part number E7TZ 2140-C does cross reference to one of the napa masters I was looking at.

[Rembrant]

I'm a big fan of this swap! I did it both Bullnoses. On my '84, I even wired in the float switch so that my Brake warning light in the cluster would illuminate of the fluid got low. I put the same master in my '80 Bullnose, but it was a used one and the float switch was bad in it, so I didn't bother wiring that one in. They worked fine for me (on my little lightweight half tons)

[Gary Lewis]

Yup, me too.  Although my master cylinder doesn't have the float so there was nothing to connect, electrically.

[Lima Delta]

Cory, yes, I thought of that thread where you described your swap last night after I pulled the master out of one of my parts trucks. I was hoping for a quick replacement with that part, but after emptying it the bottom of the reservoirs were full of rusty goo and didn't inspire much confidence. I think I'd prefer aluminum!
If I remember correctly, you removed the factory proportioning valve as well?
Does the switch on these newer masters provide an warning that there's a pressure imbalance between circuits as well, or just a low fluid warning?

[Rembrant]

Hey Lima,

Ya, I removed the prop valve on both of the trucks I swapped. The switch in the F150 masters is just a float, nothing more...so it only knows if the level is low.

[Lima Delta]

Well, for better or worse I have a new master cylinder on order.
Try as I might I could find one with the residual pressure valve included. Nor can I find any listing for any parts by that name.
Any chance anyone has a part number for that? Ahem, Gary, cough cough...

[Lima Delta]

Or alternatively, since I plan to use the existing brake valve, does anyone know what size/pitch thread the residual valve on these master cylinders use?
There must be a way to adapt a brake line to the MC without using the valve?

[Rembrant]

Lima Delta wrote

Or alternatively, since I plan to use the existing brake valve, does anyone know what size/pitch thread the residual valve on these master cylinders use?
There must be a way to adapt a brake line to the MC without using the valve?

 
The fitting is quite big, and it seals with an O-ring, but I don't what size it is, sorry. I had a spare valve here for the longest time, but it went away with a bunch of parts that I sold. Some of the aftermarket replacement masters come with them. The one new one I bought did not, so I grabbed a couple of them at the junkyard.

[Lima Delta]

Rembrant wrote

 
The fitting is quite big, and it seals with an O-ring, but I don't what size it is, sorry. I had a spare valve here for the longest time, but it went away with a bunch of parts that I sold. Some of the aftermarket replacement masters come with them. The one new one I bought did not, so I grabbed a couple of them at the junkyard.

I was thinking an inverted flare bushing of some kind...

Anyway, I guess I'll phone around tomorrow to see about a used part. I never hold out much hope for finding anything at the scrap yards around here lol