Brake Master Cylinder Dilemma

Joined
Jun 30, 2022
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4
Location
Los Angeles, CA
Gentlemen,
I am confronted by a problem with my brake master cylinder.
The Vehicle/The Facts = 1977, BJ40, from Honduras, tandem master cylinder, 1 1/8" bore, two top plastic reservoirs, side brake line entry points, bottom safety light switches, standard 4 bolt mount, with vacuum booster, NO PROPORTIONING VALVE, JUST TWO SEPARATE CIRCUITS FRONT/REAR. drum brakes in the front and rear (Note: The vehicle is NOT factory original and seems to have been assembled out of parts on hand.)
2. In looking for a brake master cylinder, the dual factory standard units for the U.S. seem to have a 7/8" bore (i.e. - Rock Auto rebuild kit - won't work because my cylinder has 1 1/8" bore) - so - I am looking for a new master cylinder. Specter has one, but is 1 1/4" bore, and I suspect that this one would give me less pedal travel and require more pressure. Consequently, the only similar bore would be from an FJ45 (truck version) from Canada - correct?
3. Because this old car is such a mongrel, I suspect that the correct factory master cylinder may have had a different bore diameter (i.e. - I found that the wheel cylinders were all mismatched with different bore diameters- problem now corrected with NAPA parts). So - would anyone know, with certainty, what bore diameter a master cylinder, for a BJ40 in Honduras would have had for the 1977 model year?
4. Because this old car is such a mongrel already, I am wondering if a 1 1/8" bore, American master cylinder could be adapted to work? The 4 bolt mount would have to be adapted to a two bolt mount, and the brake lines would have to be adapted for American flare nuts - but......... It might work, or it might open up Pandora's box. (Think "practicality" rather than "factory Toyota officiality")
Has anyone ever side-stepped Toyota's master cylinder with success, or is this idea a disasterous failure in the making?
 

73FJ40

After another night of rust removal!
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My '73 FJ40 has drum brakes all around. the front wheel cylinders are 1 1/4" bore, single acting (one cup seal), two on each wheel. The rear wheel cylinders are 7/8" bore, double acting (two cup seals) two on each wheel.

If your wheel cylinder dimensions match mine, then I think a dual MC for 70 - 74 FJ40 would work, as far as volume output from MC to the 8 wheel cylinders. I've never had my MC apart, so I can't tell you the bore. I'm sure a search here would enlighten you.

If your configuration is different, this of course doesn't necessarily apply.
 
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Victoria, BC
The only reason id use an American M/C is if I was also swapping in a matching booster. I can & has been done. I would suggest using a stock M/C from a pre 75 Toyota Landcruiser, no proportioning valve needed given you are running four wheel drums.

I personally prefer 4 wheel discs, a 80 series Booster & M/C, and an adjustable proportioning valve. Given what you've done already, I'd run the drums at least for now. I'd at least convert the fronts if they ever need to be redone. Rear discs are very nice, but not nearly as big a difference as front discs. There is a good reason 75+ Landcruisers in North America have front discs. They don't need adjustment and in my experience last 5 times as long as drum brakes (100k miles on the first set of front pads).
 
Joined
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Messages
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Location
Los Angeles, CA
My '73 FJ40 has drum brakes all around. the front wheel cylinders are 1 1/4" bore, single acting (one cup seal), two on each wheel. The rear wheel cylinders are 7/8" bore, double acting (two cup seals) two on each wheel.

If your wheel cylinder dimensions match mine, then I think a dual MC for 70 - 74 FJ40 would work, as far as volume output from MC to the 8 wheel cylinders. I've never had my MC apart, so I can't tell you the bore. I'm sure a search here would enlighten you.

If your configuration is different, this of course doesn't necessarily apply.
Thank you for the information and your insights. As far as the wheel cylinder bore sizes, I have lost track. This old car has been sitting for five years since I replaced the wheel cylinders with NAPA parts, so I would have to dig in there and have a look to be sure. I do remember the "two wheel cylinder set up in the front," and the "one wheel cylinder in the rear," but beyond that, my memory has faded. I have "heard" that the non-U.S. export cars often retained the older parts and configurations, so I would not be a bit surprised to find out that you are right about the parts from a "previous model year" being used in this old car. I will have to dig a bit deeper, but I do appreciate your input and your insights. Thank you!
 
Joined
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Messages
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Location
Los Angeles, CA
The only reason id use an American M/C is if I was also swapping in a matching booster. I can & has been done. I would suggest using a stock M/C from a pre 75 Toyota Landcruiser, no proportioning valve needed given you are running four wheel drums.

I personally prefer 4 wheel discs, a 80 series Booster & M/C, and an adjustable proportioning valve. Given what you've done already, I'd run the drums at least for now. I'd at least convert the fronts if they ever need to be redone. Rear discs are very nice, but not nearly as big a difference as front discs. There is a good reason 75+ Landcruisers in North America have front discs. They don't need adjustment and in my experience last 5 times as long as drum brakes (100k miles on the first set of front pads).
Bikersmurf:
Thank you for your insights and suggestion, and I will take them to heart as I go forward. I am still trying to find out what the "correct" or at least the "common" bore size was for the master cylinder. The 1 1/8" MC bore that I have just does not seem correct for this car, and my brief research tells me that it was the MC used on the Land Cruiser with the truck bed behind the cab, which may have had larger diameter wheel cylinders for its drum brakes. I suspect that you are correct about the pre-'75 MC being the correct one, given that this old thing has no proportioning valve, just two circuits, with drum brakes on all four corners. I appreciate your insights and will doubtless benefit from you experience with disc brakes. I have worked with discs and drums on other cars, and discs are far easier to deal with as a rule. Let me "beat a few more bushes" and then I will have a fairly clear picture of what I need to do to address this problem. For the moment, I think your "pre-'75 MC" takes the nod, and this has been the consensus of two others also. Much obliged to all!
 
Joined
Jan 22, 2007
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Alva, Fl.
Look at BMA Auto parts--they have OEM (maybe NOS) parts--your brake master from them(it's an ADvics--a branded subsidiary of AISIN, costs $200+---you can get cheaper(yes CHEAPER) for <$100--I put in a new Advics master almost 15 yrs ago--no issues--I can't complain(Toyota no longer has this master(470210) available)
 
Joined
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Los Angeles, CA
sggoat -

I will do as you suggest and take a peek at BMA Auto Parts. They are new to me, so it will be both enlightening and interesting. Thank you!
 

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