Choosing the right master cylinder(MC)

[Brett]

There was a discussion going on about servo(power assist)brakes. Whether or not are cars need them.

I sat back and listened to the discussion but it was all personal opinion, no facts. Nothing to back up what anyone was saying.

So out of curiosity I did a search on the topic (servo vs manual operated brakes)

Found alot of good info on the subject and they were all saying the same thing about the matter.

Here is one web site( I think they should know what their talking about) that seems to cover most of the the questions about brakes.

https://www.motor.com/magazine-summa...der-selection/

[Phill]

I sat back and listened to the discussion but it was all personal opinion, no facts. Nothing to back up what anyone was saying.

I can easily lock my front brakes up under heavy braking even though there is no servo fitted. That's not an opinion, that's a fact..

The addition of a servo alone wouldn't prevent it, merely make it more easily achieved. The stopping power would not be improved without making other changes such as a brake bias valve, or changing the cars weight distribution , or wheels and tyres, or improving the frontal downforce. These aren't opinions, these are based on reasoning.

[Supanovakit]

That’s a really interesting article as I was thinking of changing the rear drums to disc, and never thought about the fluid displacement and different requirement for drum/drum, disc/drum, disc/disc. Actually it makes total sense.
Thanks for that.


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[steve]

Don't be to hard on people offering personal opinions, I've asked questions during my build and I'm happy to hear opinions (unsubstantiated or otherwise), it's then up to me as the OP to go away and do the research before making a decision on what to buy, or what to do.
I read the article you linked to and it was informative.

[islandman]

The stopping power would not be improved without making other changes such as a brake bias valve,

Phil, From the articles I've read they all pretty much state that when changing from drums to disks, adding servo's etc.. a brake bias valve is a must. So yes the servo will help, but you have to fit and adjust the bias valve / bar too.

[Peter]

A very informative article. Thanks Brett. The paragraph I found interesting was,

" When you get right down to it, master cylinder selection is a trial-and-error process. Pedal feel and what's comfortable for the individual driver will dictate the final choices.".

Aside from those with standard VW pedal setup with a single dual cylinder, which rather limits choice, it relates mostly to those with twin or triple master pedal boxes, (which usually come with a bias bar)

Driving conditions also play a part. In my case it would be mostly stop start, heavy holiday traffic and then blasts down the toll road around Puerta Banus to beat the jams in the summer. wet greasy roads in the winter so hard to avoid lock ups, meaning I need a lot of 'feel' as well as stopping power when needed. Twin 3/4" masters with a dash adjustable balance bar with 4 pot vented discs and rear disc conversion seems to fit the bill as I can apply just enough in traffic without 'cooking' the brakes or slam them on when a dick head pulls out in front, (as with my recent BMW E30 shunt that has standard disc front drum rear)..

The Wilwood site has some very technical suggestions and formula.

Someone who does mostly highway driving would need different setup to someone who drives mostly in city. But as it says above, each unto heir own.

[Spacenut]

I can easily lock my front brakes up under heavy braking even though there is no servo fitted. That's not an opinion, that's a fact.

That is a very common problem on the Nova, due to the change in weight bias when removing the Beetle shell and shifting the fuel and passengers towards the back of the car. I believe both VW single and dual-circuit brakes are split front and rear - the easiest way to stop the fronts locking too early is to put an adjustable pressure restriction valve in the front brake circuit and reduce the front brake pressure until the front brakes just lock when you stamp on the anchors. This effectively restores the optimum brake bias.

I wouldn't recommend servo assistance until the brake bias is correct. The Lancia Monte Carlo was a salutary lesson in that respect

Lauren

[islandman]

The Lancia Monte Carlo was a salutary lesson in that respect

Lauren

I didn't understand the relevance of that reference till I did a quick google..... https://www.lanciamontecarlo.net/Mon...al_Brakes.html

[Peter]

I don't use Google, my wife knows everything, she says.

Aside from that, it bares out what I said about brakes, going 3/4" on the 8 cylinders of the Wilwood set up means a little more travel but a better feel, If I went for 7/8" I would reduce travel but also loose feel.

My BMW has a big straight 6 up front but discs at the rear so I still get lock-ups on the front as the rears are bloody useless, other than on the ITV brake tester thank heavens. I could fit discs (E36) to rear and increase bias but that would destroy its classic status.