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Tech Spam thread - because 1/4" BSP gets 5 hand spans to the jiggawatt


Roman

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Brake master cylinders, I want a new one.

Current one looks a bit passed it, 2-300k on the clock. I have changed the front brakes to something bigger, but the calipers are spec'd to work fine on stock master.

The question. How much different will a 19.05mm bore (current. marked as 3/4) be to a 20.6mm bore (Rockauto available, marked as 13/16)? Doesn't seem like too much difference to me on the face of it, but keen to know what the go is.

I could get mine rebuilt (potentially, I don't know this for sure, but figure by the time I pay for that, I could have a new one and just slap it in. If the bore diameter difference isn't going to upset things.

TIA

 

Reason i'm looking at Rockauto first is it doesn't seem like the sort of thing people will stock here. 

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The bigger master will be great, you will end up with a very slightly firmer and higher initial bite point on the pedal, both of which are good in my opinion. 

Don't worry about the increase in pedal effort in a car with factory pedal ratio and a booster. 

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If the existing one just needs seals then it would be cheap to repair, less than $50.

If it's got a pitted bore then it gets a bit more expensive to fix, you'd need to bore it out and put in a sleeve to bring it back to factory spec, or just overbore it.

/Got pics of your old one? I wonder how similar it is to Starlet ones.

 

Also, this would be an expensive thing to screw up, or even get right for that matter:

 

 

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Oh yeah cheers, will wait for this lockdown thing to sort itself and give them a call, see what they got / what they can do with mine potentially. Not in a hurry to get it sorted, so may as well try all local options.

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1 hour ago, Bling said:

Brake master cylinders, I want a new one.

Current one looks a bit passed it, 2-300k on the clock. I have changed the front brakes to something bigger, but the calipers are spec'd to work fine on stock master.

The question. How much different will a 19.05mm bore (current. marked as 3/4) be to a 20.6mm bore (Rockauto available, marked as 13/16)? Doesn't seem like too much difference to me on the face of it, but keen to know what the go is.

I could get mine rebuilt (potentially, I don't know this for sure, but figure by the time I pay for that, I could have a new one and just slap it in. If the bore diameter difference isn't going to upset things.

TIA

 

Reason i'm looking at Rockauto first is it doesn't seem like the sort of thing people will stock here. 

Finally located your build thread,  (love your sheet metal work by the way; being very average with bodywork I'd take my lathe over a hammer and dolly any day!).

The difference between 3/4" and 13/16" is close to a 17% increase in bore size, i.e. swept displacement. As a rule of thumb you'd notice a harder pedal requiring more pressure but with less  movement, in some applications not an issue but in others it could be a problem.

It looks like you've chosen Dynalite calipers (?) for the front; they are a great value for money caliper and are aimed at street upgrades where in most cases the standard master-cylinder and rear brakes can be retained without compromising pedal travel/effort and most importantly brake bias. Good choice, interested to know what rotors are you running with them? Remember that a Mastervac style brake servo doesn't know what it's attached to, all it does is look at the linear compression on a synthetic reaction disk and adjust the amount of pedal assistance accordingly, rule of thumb is always a larger m/cyl = more pedal effort. 

My advice would be to look at retaining the 3/4" Master if at all possible, rule number one with brake mods has always been to only change one thing at a time. If due to economics or availability then take a leap of faith with the 13/16" but it will be a considerable change. 

Cool car, hockey stick mirrors rock! 

Edited to say I re-read you thread and picked up on the rotors.

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Just now, sr2 said:

The difference between 3/4" and 13/16" is close to a 17% increase in bore size, i.e. swept displacement. As a rule of thumb you'd notice a harder pedal requiring more pressure but with less  movement, in some applications not an issue but in others it could be a problem. 

 

If you were looking at a pedal box setup or a clutch master /slave combo I would be suggesting retaining the factory size..

But as a road car is designed to be driven by many different groups, factor this in, a fraile elderly woman should be able to provide sufficient pedal effort to bring the car to a halt..

You will not need the legs of a power lifter to get the car to pull up with a small increase in master diameter, especially with a booster, if you were to be deleting the booster once again you would need be far more careful about master cylinder diameter. 

I run minimum 1 inch master - ideally 1 1/16 on a variety of my cars, my mx5, my old evo, the civic. This is an awesome upgrade if you enjoy a bit of spirited driving. 

It inspires so much confidence when the brake pedal is right there without anything in the way of soft or dead travel. 

 

Edit: I think the one on my starlet is off a late 90s camry, was a straight bolt on to the factory Starlet booster. 

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Just now, mjrstar said:

If you were looking at a pedal box setup or a clutch master /slave combo I would be suggesting retaining the factory size..

But as a road car is designed to be driven by many different groups, factor this in, a fraile elderly woman should be able to provide sufficient pedal effort to bring the car to a halt..

You will not need the legs of a power lifter to get the car to pull up with a small increase in master diameter, especially with a booster, if you were to be deleting the booster once again you would need be far more careful about master cylinder diameter. 

I run minimum 1 inch master - ideally 1 1/16 on a variety of my cars, my mx5, my old evo, the civic. This is an awesome upgrade if you enjoy a bit of spirited driving. 

It inspires so much confidence when the brake pedal is right there without anything in the way of soft or dead travel. 

 

Edit: I think the one on my starlet is off a late 90s camry, was a straight bolt on to the factory Starlet booster. 

If you have an issue with too much pedal travel fitting a larger diameter master-cylinder is simply a shortcut fix to address the symptom rather than the underlying problem.

If I may reiterate my previous post a Mastervac  servo does not know what its connected to,  a 17%  increase in foot pressure will be noticeable.

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For sure, you do notice the difference, it will require a touch more pedal effort but not to the point that you need both feet to stop the car.. 

The deadband in the pedal does exist as you first apply pressure to bring the pads up to the discs, minimising this is all good (in my opinion).. 

 

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Just now, mjrstar said:

For sure, you do notice the difference, it will require a touch more pedal effort but not to the point that you need both feet to stop the car.. 

The deadband in the pedal does exist as you first apply pressure to bring the pads up to the discs, minimising this is all good (in my opinion).. 

 

We probably need to agree to disagree on this one, I'm not sure what you mean by 'deadband'; if there is excessive pedal travel surely it should be addressed - not just disguised by fitting a larger diameter master cylinder?

I originally worked for PBR in Australia in the late 70's and then set up booster repair centers and trained staff for APPCO Brake and clutch in the 80"s. After moving to more lucrative forms of employment I've spent over 25 years building and running competition cars and have been involved in designing and setting up and testing brake systems in multiple cars. Over all those years I have never seen an increase in master-cylinder displacement being touted as an improve all remedy?  

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