Technical Upgrading the master brake cylinder

[nmrmak]

Hey all,

I was contacted by some people that are doing rear disk brake conversions and during some discussions we came to a conclusion that upgrading the master brake cylinder might be a good idea. I've used the search function, but only came up with one thread with a guy doing a barchetta mbc conversion on a cinq. How different would it be for a sei (basically asking if anyone has ever done it here) and do you people know of some mbc that has a larger diameter than the sei's, but the same mounting points?

I've done some quick research, and i found that sei's have a 19.x mm diameter mbc, while the uno turbo has a 22.2 mm mbc, for example, but since i don't have physical access to both parts, i can't know whether it'd be a tough conversion.

If there's anyone here who knows which mbc could go into the sei, please let me know

EDIT: Sorry, Sei 1.1 MPI, without ABS

 

[rallycinq]

Sorry, I went for a twin master cylinder set up with balance bar when I did mine.

Cheers

SPD

 

[nmrmak]

How did it go? What car did you get the setup from and how hard was it to mount?
I used the search, but i don't think i found it anywhere

Edit: any pics?

 

[J333EVO]

We have not changed or seen the need to change the master cylinder on our cars which we have converted to rear disc set up if the master cylinder has been healthy, we did change one that was past its best on the car the yellow turbo Cinq.

In fact the Sei was MOT'd on Wed and the MOT tester remarked on how well balanced and strong the brakes were, the check came back as something like fronts 184 & 188 and rear 96 & 98 (what the measurements are I do not know), IIRC though didn't receive a print out.

Brake pedal travel is perfect and feedback and feel are excellent.

Not saying don't do it, bit it may not be needed

 

[nmrmak]

My mc was in a good condition prior to the conversion, but i have noticed a slight difference in pedal travel/feel (easy to spot because i was "heel and toe-ing" (as much as you can heel and toe in a sei... it's more like "right foot part and left foot part-ing") and the difference is obvious when you do that)

So one explanation could be that the seals are screwed after the bleeding, but i'd prefer the explanation that the cylinders in the rear calipers simply need more braking fluid to operate because of their bigger volume and all. It does make sense that the conversion would increase pedal travel, and it also makes sense that a bigger MC diameter would increase pedal hardness and reduce the travel.

Being pretty sure that i've bled every last drop of air from it (correct order + did it with the calipers unmounted so i could turn the bleeding nipple to the highest point -- even flushed the thing with an extra bottle of brake fluid) i'm tempted to point to the MC and blame it So, just wondering if any bigger ones would fit, like from a UT, Marea or something. This would be so much easier for me if i had access to those parts, i could see right away if the mounting points are the same, the lever and so on.

 

[J333EVO]

On the conversions we have done the brake pedal has become firmer and if anything less travel than before with greatly increased feel as standard I think the cento's have very wooden brakes with little feedback.

The only time we ever had an issue was when fitting old style Punto GT front callipers which made pedal have longer travel and way less feel, later style calipers do not seem to have this issue.

I think someone had fitted another master cyclinder, maybe tricker, someone from over the sea, but can't remember who.

 

[nmrmak]

Well, i'm not rejecting the option that i pushed too hard when bleeding and inverted the seals, that might be possible, but the pedal doesn't drop to the bottom if you know what i mean, it just starts braking later on, almost as if there was air (but there shouldn't be any after everything i've done). I wonder if fitting a larger booster/MC with a larger diameter would increase the braking power/make the pedal firmer/better feel, just as an option. Alternatively, i could get a new MC and see if that helps.

 

[Smiler121]

My setup of UT fronts & PGT rears has seen the same kinda' improvements that J333EVO described once the pads bedded in, car has never seen anything other than the standard Mpi original cylinder :slayer:

I also used braided hoses & black diamond pad materials :devil:

 

[nmrmak]

do braided hoses really make much of a difference? i replaced the last part of the hoses with rubber (but strenghtened) one -- standard brake hose.

 

[randomizered]

I have definitely seen longer travel after the front and rear upgrades.

For me, it's not an issue, they still work damn well, and are easier to control, but if you are used to the pedal height, it would cause an issue. I think a new larger Master Cylinder is the way to go.

It is on my list of things to try, but I haven't got round to it yet, so i have no help. I have only read the thread that you have

Kristian

 

[arc]

i wouldnt bother upgrading the MC, or fitting braided hoses unless there was something wrong with the hoses you already have (ie leaking)

 

[nmrmak]

@arc: they're not leaking, it's just that after what i'm sure is a good system flush and bleed, i still get a little longer travel until it starts to brake (but when it does, it's good)

Any one of you tried driving a Golf V after a Sei? Once you fly through the windshield after braking for the first few times, you'll accept that there's a huge difference between the brakes. I just want to come nearer to that.

@kritip: well, we could make a joint effort then and see if we can find an MC that would fit I'm pretty serious about doing the conversion, it's just that i simply don't have access to all the parts (and i can't go to the scrappy and start comparing MCs, they'll kick me out -- they're usually in the "buy it or go away" mood over here)

EDIT: Yes, it could be a sign my MC is going maybe and that i just need a new one, but how can i know for sure if there aren't any major internal leaks?

 

[arc]

Any one of you tried driving a Golf V after a Sei? Once you fly through the windshield after braking for the first few times, you'll accept that there's a huge difference between the brakes. I just want to come nearer to that.

thats just over-asistance on the servo, not good brakes. any new(er) car does that. i was driving my dads 56 plate passat the other day, and that does it. very snappy on the pedal but when trying to shave a deecnt amount of speed off - the brakes were poor compared to mine.

 

[nmrmak]

okay, that is true, i'll agree with that. Dad's Golf mkV has a longer stopping distance from the same speed than my sei with the mushy brakes. Sure, you have to calc in the weight difference, but the golf has much wider tires + abs (which isn't much of an assistance either). The stopping power is good, the modulation is good, but the point at which the car starts braking is not. Now that i'm thinking about it, i could just probably install a 1-2mm spacer between the MC and the servo and it would bring the pedal up (what a bodge that would be )

 

[rallycinq]

Now that i'm thinking about it, i could just probably install a 1-2mm spacer between the MC and the servo and it would bring the pedal up (what a bodge that would be )

Not a bodge at all, if done properly. Which side of the car do you sit on to drive?

Cheers

SPD

 

[nmrmak]

Left side, opposite to what you're used to in the UK (assuming you're from UK)

 

[rallycinq]

Left side, opposite to what you're used to in the UK (assuming you're from UK)

Correct assumption, I knew you were from the continent, your english is far to good to be from the UK.

Done properly there is nothing to stop you either extending the action of the pedal or the connection between the servo and MC.

Cheers

SPD

 

[nmrmak]

Thanks

I'd have to be careful if using a spacer, if it's too thick the brakes will stick all the time and that's definitely not good

Maybe, just maybe, i should try sourcing a new MC and fitting it to see if it makes any difference. If there's no difference, no worries, the old one was 5-6 years old anyway And i can alyways put a spacer on that if still needed. I'll have to see what the prices are like first.

And i still can't get the idea of using a larger bore MC out of my head

 

[J333EVO]

I'm in agreement with Arc, I dislike the newer VAG stuff, the brakes are truely aweful, way way over servo'd, and then wilt when pushing on, a friend of mine back in Glasgow was a manager of a EuroRentaCar branch and we "test" drove loads of new cars and VAG stuff really stood out as being the worst, though many modern cars are pretty poor, found the brakes on the new 500 to be nearly as bad.

For me its because modern cars are built for people who can't really drive or to be more fair have no real interest in it, everything is like a switch, the brakes are a switch with little modualtion because the ABS will sort it out if you over do it, the fly-by-wire throttle only allows as much power as ECU (ABS, ESP and any other stupid thing they come up with) works out if tyres can trasmit the power, so even stamping on it would be modulated by ECU not the driver, you can't left foot brake because as soon as brake pedal pressed the throttle is lifted (on fly-by-wire), yes all in it has made cars safer but at the detrement of making teh drivers poorer as they drive feeling way to safe knowing car will sort it out, Sat morning rant over lol

 

[Smiler121]

I haven't got a go in it yet but my friend has just bought a 1.2 (3 cylinder!!!) Polo & is describing the brakes to be extremely sharp compared to his instructors car, with very little modulation & his Dad who has driven loads of cars agrees - I am glad that VAG products got mentioned here!!!