20 replies to this topic

[Aridgerunner]

Is there not a clue in the thread size if the ports? The tube and flare sizes are standard but the tube nuts are delibarately not in some cases to help avoid getting them wrong.
Your valve surely is a PRV, not a PDWA?
Just leaving work now, I will be back later with the correct info unless someone beats me to it.

There are no clues with this car. Nothing is as it was when it left the factory. PRV or PDWA, I don't know. All I know is it is an FAM7821.

Looking forward to hearing from ya.

[Spider]

That Master Cylinder cannot be used in a split diagonal set up, so as Nick has already suggested, I think there's some re-plumbing to be done.

 

The Yellow Tag M/C as a stepped bore, so you'll end up with different brake hydraulic pressures from one side of each axle to the other, and this will give different braking from one side to the other. Pretty ugly!

 

With the pipework you have already, I don't think it will be too hard to do.

 

The FAM 7821 is a PRV (Pressure Reducing Valve). Personally, I don't rate them at all, but can be used.

[tiger99]

The FAM7821 is indeed metric threaded, so please take care as it is sometimes possible to mix them up with UNF threads, with a severe risk of failure. It is definitely a PRV.

 

Now I assume that your car is left hand drive, so the PRV is not located in the same place as I would expect. However although the pipes are different shapes, the ports get connected up the same way. First to define LEFT and RIGHT, they are in anything that I do used relative to the way the driver, in the seat, sees things when looking forwards. So you have radiator on the left, clutch on the right.

 

The PRV is bolted to the bulkhead with the pressed sheet metal end, a sort of dome that covers the spring, pointing to the right, towards the clutch end, the big hex nut on the other end pointing to the radiator. The ports pointing downwards are outlets to the brakes, those pointing upwards are inlets from the master cylinder.

 

The bottom port nearest to the radiator side goes to the rear brakes, which as you will have found, runs down between the bulkhead and subframe, along under the floor, to a T piece on the rear subframe. The port nearest the clutch side goes to the front brakes, but I am not sure how it is run in your case.

 

Now to the bit where it gets tricky. Your master cylinder should be GMC227 (I assume you do not have a servo). The larger, lower port is M12 and goes to the REAR brakes, via the PRV port directly above the rear outlet. The other M10 port goes to the front, via the remaining PRV port.

 

The following link will help, but please be aware that the picture is for right hand drive. That makes no difference to which port is connected where, but looks different.

 

http://www.minimania...linder___GMC227

 

I advise a careful road test to ensure that the rears are not locking, just in case something is crossed, which would be dangerous as your front brakes, which do almost all the work, would be seriously pressure limited.

[Aridgerunner]

Tiger, thanks for the very thorough description and information. I definetley have some re-routing of the pipes to do. I may have to make some custom pipes but I've done that many times in the past on other cars. I will be sure to double check all threads before before trying to insert any fittings.

As noted earlier the car has 7.5" rotors and drum rear brakes. What bore rear wheel cylinder should I use?

As for a test drive, that's a long way off in the future. I'm rebuilding this car from the sills up and when I get tired of welding I work on other stuff, like brakes. Once I get the brake system installed to where I'm comfortable it will all come back out, along with engine and sub-frame so that area can be properly repaired and painted.

Thanks to everyone that has replied. You guys are great.

[Spider]

When plumbing up the Yellow Tag Master Cylinder, the Front Brakes are plumbed off the top port and the Rears from the lower port. This is important as they have a stepped bore.

 

As noted earlier the car has 7.5" rotors and drum rear brakes. What bore rear wheel cylinder should I use?
 

 

If you are going to fit the FAM7821, you'd be safe with 5/8" Rear Wheel Cylinders.

[Aridgerunner]

Thanks again. I'll be sure to use the 5/8" bore.