24 replies to this topic

[Mini Manannán]

 

 

 

Why the hate for FAM7821?  Is it that they fail often?
.

 
With all the parts and rubber in them, there is more 'slack' in the system to take up and they make the brakes feel more spongy than they could be. The Valve is overly complex for the job that it does, it's big, yet the pipework isn't easy to get at. They are also non-serviceable, though if you really want to, they can be serviced to a degree. When they have issues, they can also be hard to diagnose.
 
There's simpler an better ways of getting the job done than to use one of these monstrosities. The other Valve that was used, though it would seem not in the UK, was the Inertia Valve, 13H7757 with the Tandem Brakes, and from a Hydraulic perspective, these are 'seen' in the system they same way a Pressure Shut Off Valve (like on the early cars) would be.
 
Like Retroman said in another thread, I can't be rid of them fast enough. Complete junk in my books.

What do we put in its place Chris?

 

you can just fit the limiter on the rear as per the single line cars, or an adjustable version.

 

Such as this you mean Nick?: http://www.minispare...assic/MS72.aspx

Sorry, I don't know my way around all the various setups like you do

[nicklouse]

i would say yes. from what i have gleaned (i am fairly sure that is where we got to).

[Pete649]

Thanks for the explanation re the GMC227 Moke Spider.

[Spider]

 

 

 

Why the hate for FAM7821?  Is it that they fail often?
.

 
With all the parts and rubber in them, there is more 'slack' in the system to take up and they make the brakes feel more spongy than they could be. The Valve is overly complex for the job that it does, it's big, yet the pipework isn't easy to get at. They are also non-serviceable, though if you really want to, they can be serviced to a degree. When they have issues, they can also be hard to diagnose.
 
There's simpler an better ways of getting the job done than to use one of these monstrosities. The other Valve that was used, though it would seem not in the UK, was the Inertia Valve, 13H7757 with the Tandem Brakes, and from a Hydraulic perspective, these are 'seen' in the system they same way a Pressure Shut Off Valve (like on the early cars) would be.
 
Like Retroman said in another thread, I can't be rid of them fast enough. Complete junk in my books.

What do we put in its place Chris?

 

you can just fit the limiter on the rear as per the single line cars, or an adjustable version.

 

 

Or my usual favorite, the 13H7757 Inertia Valve

 

 

To fit one of these or the MS72 (or just about any other Valve), plumb the front brakes direct off the Master, run a line from the Master to what ever valve you want to use, then come off the Valve to the Rear Brakes

[gazza82]

Couple of interesting paragraphs on Minispares web site relating to the yellow tag masters ..

 

"Bottom piston does rear brakes - upper piston does front brakes.

Some masters before this were the opposite with bottom doing front and top doing rear.



Ensure the correct DOT4 or DOT5.1 brake fluid is used as these cylinders are not designed to use anything else such as Castrol SRF for racing or any mineral fluid."

 

First part confirms what has been said, but interesting about choice of brake fluids .. I was planning to use 5.1 (Castrol React)

[nicklouse]

not really surprising most seals that were designed for DOT3/4/5.1 (glycol based) do not work with Mineral based fluids.  the Surprise is the mention of SRF as that is described as being OK with all glycol based systems and parts.

https://www.castrol....srf-racing.html

[Ethel]

Couple of points:

 

The yellow tag cylinder's stepped bores create different pressures. The lower outlet moves more fluid at lower pressure, which is ideal to engage the rear brakes with less pedal travel. That allows the smaller upper bore to create more pressure, suiting the harder worked front brakes, while making it a bit less likely the pedal will hit the floor first. 

 

The FAM7821's big advantage is that no pressure in the front circuit means the pressure in the rear circuit won't be restricted. Suffer a front failure using the rear subby pressure valve in its place and pressing the pedal harder won't make any difference.

 

I'm with Spider that an inertia valve is better all round. It senses the weight transfer directly, so only limits the rear braking effort when it's actually needed. You'll stop quicker going up hill and will be less likely to lock up the rear going downhill.

[Pete649]

I'm with Spider that an inertia valve is better all round.

 

I can see why this would be the case but, for the sake of argument, if someone was using the yellow tag master cylinder with non standard callipers and rear cylinders and there was a need to be able to adjust the pressure to the rears would I be right in thinking that you would pretty much have to use the MS72?

Edited by Pete649, 07 September 2018 - 05:31 PM.

[Ethel]

No, Inertia valves are just a heavy ball bearing that runs up a slope, to close a valve, as the car decelerates. To fine tune when it closes just alter the angle of the slope (mounting).

[Spider]

No, Inertia valves are just a heavy ball bearing that runs up a slope, to close a valve, as the car decelerates. To fine tune when it closes just alter the angle of the slope (mounting).

 

That's how I've done them. Not super clear here, but this one I've mounted in the engine bay (for easy access) and is adjustable as Ethal has suggeted. The Bleed Nipple on top is to bleed the air from the valve and plug up a port that's used when rear mounted