Man-A-Fre Dual Master Cylinder on 4-drum '67- Need confirmation.

[65swb45]

It's not a question of needing more or less fluid.
It is simply that a smaller slave piston has less force, or a larger slave piston makes more force.
The opposite is true for the master bore size.

Going down in wheel cylinder size reduces the amount of braking force for a given pedal force.

Jim,

This is something that I would like to explore a little more with you, and whoever else cares to chime in, for the benefit of all. Disclaimer: my mechanical sense is based solely on inductive and deductive logic. IOW, I have never formally studied this.

Logic tells me that a larger bore master cylinder will move more fluid per inch of pedal travel than a small one. Using exaggeration for emphasis, a 10" bore moving one inch will move more fluid than a 1" bore moving one inch.

Likewise, all things being equal, a smaller bore "slave" as you use the term will respond faster than a larger one. That dynamic is confused in the pre-81 Landcruisers because front drum cylinders only utilize one piston, while the rears use two. So using a 1" front and a nominal 7/8" for the rear, the effective braking is still slower in the rear, because it requires the movement of fluid equivalent to a 1-3/4" single piston. And that is how Toyota's estimation of appropriate bias is achieved.

Under my system of logic, your comment on brake force has to proceed from a deductive universe comprised of disc brake calipers. Where the piston applies DIRECT force to the friction material, i.e. the brake pad, I would completely agree that the "larger slave piston makes more force." But where the piston does not transfer pressure directly, and that pressure is made across a uniformly sized intermediate part, the head of a wheel cylinder piston, to me the size of the piston cannot directly affect the force, only the rate at which the force is applied.

 

[Spike Strip]

@ntsqd

 

[FJ40Jim]

Your understanding of speed in a hydraulic system is spot on.

But there is a direct inverse relationship between speed and force. The very small distance traveled by a slave wheel cylinder makes speed in the brake system moot. The force applied to the brake pad or brake shoes is important.

As a though experiment, imagine the 1" bore slave mentioned above. We'll bend the math and say it has a piston area of 1 in². Now apply force to the brake pedal to develop 100psi. The 1" piston will be pushing outward with 100# of force.
For the experiment part, now change the slave piston to one that is 10 in². If the system is pressurized to the same 100psi, the force at the piston is 1,000#. For a given pedal displacement, the larger slave will only move one tenth the distance, but with 10x the developed force.

One of the more complex aspects of drums is the self-servo effect, which can mean there is not a perfectly linear relationship between developed hydraulic force and braking force. But there is still a definite relationship.

For more info I recommed the "Automotive Brake Systems" textbook, by Robert Bosch, gmbh, published by SAE.

 

[wngrog]

Good stuff. I’m still lost but learning.

 

[FJ40Jim]

So, if I wanted the fronts to take most
Of the load for my never to be loaded down Long wheelbase 45 pickup I should have done 1 1/8” front and 7/8” rear.

I'm not gonna dig through the parts book to see what the stock bore sizes are, but if the goal is to shift brake bias to the front, then either make the front cylinders larger, or rear cylinders smaller.

 

[FJ40Jim]

Does larger tires effect the factory setting? Also suspension mods?

Larger tires reduce brake effectiveness for two reasons.
Mainly because the larger tire increase the leverage of the tire, or decreases the brake force developed at the contact patch.
Secondarily, a larger wheel&tire package is a larger flywheel and at highway speed it can add up to quite a bit more energy to be absorbed by the brakes.

A vehicle that is taller and has softer suspension will tend to weight transfer more to the front end under hard braking, so will tend to unload & lock up the rears sooner.

 

[bb67tlc]

Saga continues... So talking to Man-A-Fre (asking about returning the kit), they say that because the Aisin stock dual MC is setup for front disk/rear drum you'd need a proportioning valve for that on my 4 drums, but it doesn't sound like you guys (or Mark in particular) see it that way... with experience to prove it. Not sure what to do. It worked for 50 years with the single master, and I've got a new one of those! But I'd rather be safe than stock (within reason). I've got a while to figure this out- here's what was happening today... ripping out the rusty bits. One wheel down. (no, that's not me- my little welding experience told me to avoid trying this at home).

 

[4x4veteran]

Larger tires reduce brake effectiveness for two reasons.
Mainly because the larger tire increase the leverage of the tire, or decreases the brake force developed at the contact patch.
Secondarily, a larger wheel&tire package is a larger flywheel and at highway speed it can add up to quite a bit more energy to be absorbed by the brakes.

A vehicle that is taller and has softer suspension will tend to weight transfer more to the front end under hard braking, so will tend to unload & lock up the rears sooner.

So a PV is not useless in some instances.

Some of my hobby cars have been Fiats.
The sedans have a PV with an arm that adjusts for extra weight as the car is lowered by carrying a load.

Many of the Land Cruisers out there have over size tires, heavier springs, springs over axle, lift kits, engine swaps that change weight distribution and more that the stock brake setup was not designed for.

These valves should be taken in consideration when modifying the Land Cruiser.

 

[wngrog]

Not worthless. Especially since I bought all new cylinders (not cheap) all 1”

Doing this over I would have done 1 1/8” front and 7/8” rear with my early single circuit master.

Since I’ve alrealdy done the 1” all around a $70 CityRacer proportion valve and a $40 brake line from Rainman to splice it into my 9mm like is the cheapest option.

 

[FJ40Jim]

Yes, a PV may be necessary where the system brake bias is incorrect.
A couple of examples: a popular modification is replacing drums with big disc brakes on the rear of an FJ40. Experience shows that a PV in the rear line will be needed to dial down the effectiveness of the overly large GM disc brakes.
Another popular mod is increasing the front calipers to the 4R or even the Tundra caliper. A PV will be needed in the front line to dial down the effectiveness of the larger calipers.

 

[FJ40Jim]

Saga continues... So talking to Man-A-Fre (asking about returning the kit), they say that because the Aisin stock dual MC is setup for front disk/rear drum you'd need a proportioning valve for that on my 4 drums

Oh, my head is starting to hurt, The stupid is very strong in this statement.

The stock single circuit drum MC is 1" bore, no proportioning, no RPV.
Changing that to a dual outlet 1" bore MC, no proportioning, no RPV. changes nothing hydraulically.
X amount of pedal pressure produces Y amount of braking in both cases.

The Aisin MC shown in post #10 is no different from the Wilwood MC, except it is easier to buy, has M10 ports and is cheaper.

 

[wngrog]

Saga continues... So talking to Man-A-Fre (asking about returning the kit), they say that because the Aisin stock dual MC is setup for front disk/rear drum you'd need a proportioning valve for that on my 4 drums, but it doesn't sound like you guys (or Mark in particular) see it that way... with experience to prove it. Not sure what to do. It worked for 50 years with the single master, and I've got a new one of those! But I'd rather be safe than stock (within reason). I've got a while to figure this out- here's what was happening today... ripping out the rusty bits. One wheel down. (no, that's not me- my little welding experience told me to avoid trying this at home).

View attachment 1697661

The only reason I went down the road of rebuilding this 4 wheel drum with single master is because my truck is ball and claw so it would need an entire housing swap and my engine bay and truck are mostly stock and keeping it that way is my goal

 

[bb67tlc]

[QUOTE="
Changing that to a dual outlet 1" bore MC, no proportioning, no RPV. changes nothing hydraulically.
X amount of pedal pressure produces Y amount of braking in both cases.[/QUOTE]

That's what I would think. Jeesh, I'll go Aisin.
Thanks All!

 

[ntsqd]

Oh, my head is starting to hurt, The stupid is very strong in this statement.

AMEN!!!

Though a drum brake RPV (NOT a Proportioning valve!) may be required or desired if not required. These simply keep the drum's retracting springs from being too good at their job.

As Jim pointed out in a previous post, the speed at which parts move in a brake system is never a concern or design criteria, only the force multiplication or division based in the relative piston sizes.

Yes, a PV may be necessary where the system brake bias is incorrect.
A couple of examples: a popular modification is replacing drums with big disc brakes on the rear of an FJ40. Experience shows that a PV in the rear line will be needed to dial down the effectiveness of the overly large GM disc brakes.
Another popular mod is increasing the front calipers to the 4R or even the Tundra caliper. A PV will be needed in the front line to dial down the effectiveness of the larger calipers.

Silly, isn't it? Spend all of that time and effort increasing something only to have to dial it back down because of a myopic single part view rather than system-wide view.

 

[wngrog]

Well. I’ve found this thread anything but silly.

It’s good to see what some say then have others come in with true experience and knowledge and help this of us that don’t understand or are doing it wrong.

This is a very misunderstood system and the very best thing to do if you are keeping it stock is to do exactly what Toyota did back when it was built. They are smart dudes.

Sure you can always improve old Systems for improved safety and redundancy but if you want to get it right the first time copy the OEM.

 

[ntsqd]

I meant specifically doing something like putting those huge GM calipers on the rear, and then having to use a Proportioning Valve ("PV" or "P-Valve") to nearly turn them off or the rear brakes lock up way, way too easily.

Residual Pressure Valves ("RPV") don't keep the drums from locking up too easily. They keep the drum brake shoe retraction springs from pulling the shoes too far away from the drum. Prevents that seat-gripping pucker when the pedal goes to the floor the first time, only to become firm brakes on the second pump.

If you are using a disc-drum m/c on a 4 wheel drum system you do not need to worry about any RPV that might be in the m/c's disc outlet. Though you will probably need to add a drum RPV to that circuit.

If you are using a disc-disc m/c on anything with drums you will probably want the 10 psi RPV in the drum or drums circuit(s), and it should be in that circuit as close to the m/c as is reasonably possible. No exotic means, just somewhere close to the port on the m/c. The OEM's build them into the m/c for their convenience, not because they absolutely have to be located there.

As Jim mentioned, hydraulic brake bias or balance in 4 drum systems is done with juggling different size wheel cylinders. The front cylinders should be larger than the rear cylinders. The smaller rear cylinders reduce the apply force on the shoes reducing rear brake effectiveness to the point where they won't lock-up in the worst case situation.

Get any ideas about the speed at which things move out of your head. This isn't a factor in brake system design or use. It all moves fast enough that this is of no concern. Sometimes things move too fast in brakes and there are components that deliberately slow them down, but those are not common.

 

[cuencanolenny]

The stock drum brakes are correctly 'proportioned' by the factory, i.e. the rears are not as effective as the fronts, so there is no need for a PV on 4 wheel drum trucks.

Thanks to you all. Some five years ago I bought a "kit" for my '70 which included shoes, springs, cylinders and master cylinder. I sourced new drums from the USA at the same time. I knew that the listing for the cylinders stated that Toyota no longer made them and that all cylinders were 1 1/8" diameter. While I never took the master cylinder apart, just from the size of the casting I don't see how it could have been any larger than 5/8" bore. Adjusting shoes until they drag still requires two pumps to get it stopping. Hated it. So now I'm going to do my '79 which has FJ45 drums, the 295mm X 3" units, the rears are "normal." I followed what the fellow said at the top of this thread and went to Man-A-Fre, however, the only master cylinder they showed is similar to the one I have, single reservoir type. It does not list a bore diameter. I find a Raybestos unit that lists 7/8" bore. From what I have gleaned from the comments here, a larger bore would be better, but how to find it? Raybestos specifically lists the bores for the various wheel cylinders required, 1" fronts and 7/8" rears. Please advise as locally in Ecuador I can get no specifics, just $99 per wheel cylinder and supposedly made in Japan.

 

[FJ40Jim]

76-later USA MC is 7/8 bore.
E-75 MC is 1" bore.