Master cylinders

[hari3392]

hi,its my first time working on the brakes for our build.my question might sound naive but i wanted to ask whether using dual master cylinders from borrowed car is as good an option as getting/importing a proper branded(eg. a brembo one).

[Dash]

Originally posted by hari3392:
hi,its my first time working on the brakes for our build.my question might sound naive but i wanted to ask whether using dual master cylinders from borrowed car is as good an option as getting/importing a proper branded(eg. a brembo one).

I have no experience dealing with finding a part off a car, but if you go through the calculations, you can find what sizes you will need. Wilwood offers quite a lot of options ( Plus they are pretty cheap ~~$60 per cylinder.) Tilton has some good options as well.

[MCoach]

The first question you must ask is "can you find dual master cylinders on a car?"
Most only have one that has the two ports inline. The bores also tend to be way too large for our uses, unless you design for a 1"+ bore.

[Warpspeed]

A master cylinder is about as simple as it gets, and nothing at all wrong with something from a production car.

Now many late model cars do tend towards having huge caliper pistons and large bore tandem master cylinders. But some older and smaller cars that had drum brakes did come with much smaller master cylinder bores.

Another option worth thinking about might be a couple of clutch master cylinders with a balance bar.

If you find something at a junk yard to try and do some testing with, and if it works, then a fully rebuilt replacement will be as good as new, but cost far less than new.

[MCoach]

Originally posted by Warpspeed:
A master cylinder is about as simple as it gets


Yes, they are relatively simple, but it can also be a major difference in compliance, hysteresis, and feel between different brands and types.

Discuss.

[Warpspeed]

Originally posted by MCoach:
Yes, they are relatively simple, but it can also be a major difference in compliance, hysteresis, and feel between different brands and types.

Discuss.
Compliance, hysteresis, and feel, eh ?

Only part that can possibly do that is the ubiquitous cup seal.
Unlike calipers, there isn't anything inside a master cylinder that can bend or flex under pressure.

[MCoach]

Correct.

And what about spherical mount cylinder vs a bulkhead mount? The bulkhead mounts (almost unanimously used) allow a slight misalignment and can be seen when played with that the shaft isn't locked into to This is because as things rotate, they travel an arc and not a straight line. If you make that arc too large (only several degrees) then it starts to push into the cylinder wall with significant force. The same thing happens with connecting rods and pistons inside an engine. That frictional force leads to hysteresis problems.

The compliance comes in with having a floppy pedal with too much free travel. Worn out Wilwoods immediately come to mind...

Feel? the master cylinders do start to bend under pressure once you start running line pressures high enough for 10" wheels and those tiny calipers. With a poor design, think somewhere in the 1200+ psi range...

My testing shows this and is scary to watch those things actually deflect.

[Warpspeed]

Have to agree, pedal mountings and the master cylinder mounting are critical high stress points, where seeing an alarming amount of relative motion is not all that uncommon.

The master cylinder itself is another matter entirely.
I have yet to see the mounting lugs or bore on a master cylinder casting visibly flex.
It has always been the structure the thing is bolted to that moves around.

None of this is true of calipers, get the best and stiffest calipers you can afford.

[MCoach]

Completely agree on the calipers. Several of the teams that I've talked to have had flexing problems there.

I will have to concede the point that it is usually the attachment points that start to flex and bend first.

[sbrenaman]

Originally posted by MCoach:
Worn out Wilwoods immediately come to mind...


Worth repeating. I've replaced old bulkhead mounted Wilwoods with bulkhead mounted AP's, and have never looked back. There is definitely a quality difference between MC brands. Though, you can't go wrong with AP or Brembo. And Tilton makes great stuff at a more cost-effective price.

[MCoach]

I think Tilton actually offers a discount if you mention you are an SAE team.

AP and Brembo both make amazing products. Certain components, like brakes and helmets are just something you do not settle for cheap on. It makes a very large difference and if the time comes that something bad ever happens, you will be very happy with going with the superior quality product, despite the cost that comes with it.