Hi guys

Just recently (finally) got my Nissan brakes on the front of my Superbug. I've been driving for a few days now & have bled the system at least 5 times. I still have a very spongey pedal. it pulls the car up very very well, but the pedal feels very wrong to me, I'm used to a very high hard pedal.
I'm thinking that the 19mm m/c isn't up to the task of pushing 4 pot calipers with 40mm pistons.
So, I just went a picked up a Kombi m/c which is 24mm, but before I go pulling everything apart, do u think that it's just still air in the lines?
Should I have the system proffesionally bled by a brake shop , as apposed to the traditional method?

With regards to the Kombi m/c, there a few differences. There is a shaft where the brake pedal rod would go, I suppose it just goes inside as per the Kombi?, no need to cut it off? There is no thread on the flange of the m/c so longer bolts with nuts will be needed, no drama, the fittings are also slightly tilted, but they look as though they will all still fit up nicely.

There are many guys overseas that are running huge porsche brakes with the standard 19mm m/c.

Any advice would be most appreciatted as the nationals sprint is on next week & I really want this sorted

regards
Jak

Hi Jak

I think the tube is to go inside the booster. The only problem i can see is the that the bolt holes may be out of index.

944s used a stepped M/C, 23 & 19 I think, so see how the Kombi one goes.

Steve

Nice looking brakes Jak. I was told of a trick for bikes (always seem to have spongy & vague feel after a flush); once you've bled the system, zip tie the lever down overnight. Can't see any reason why you couldn't try something similar on your bug?!

where are your bleeders make sure they are on top of the calliper.

yep the bleeders are on top.

I'm going to stick with the standard m/c & put some k's on it this week, make sure everything beds in nicely. Then I'll try again.

regards
Jak

Hi Jak

My limited experience with brakes was the single pot 944 callipers on my 1302. I found that the standard front callipers felt great with the 944 rear callipers and the standard 1302 m/c. However as soon as I fitted the front callipers the pedal felt spongy and had a lot of travel, no matter how many times I bled the system.

I decided to fit the matching 944 m/c (the stepped 23 front, 19mm rear one) and the pedal instantly felt much better. I came to the conclusion that the 1302 m/c didn't have the volume to move the front callipers without a lot of travel.

The 944 m/c may also be a good option for your setup as the rear callipers would be connected to the 19mm side of the m/c so that side of your setup would not change.

Cheers
Jeremy

Hi Jeremy

What size are the pistons in the single pot 944s

Steve

Thanks for that Jeremy. What modifications were needed to install the 944 master cylinder?
If u could email me a pic of it installed that would be great
regards
Jak

Jak , I have just finished the brake up grade on the 75 L bug circut car . I have a Willwood 4 piston caliper on each wheel and these calipers have 4 x 45mm pistons each . I have fitted a 22mm Kombi master cylinder and the pedal is good . I have mounted the cylinder using the std beetle rubber plugs and angled plastic outlets which are connected to the std late reservoir with the std braided hose all of the way . I have also fitted a Willwood poportioning valve to adjust the bias . All of the pressure side of the system is assembled by myself using all stainless steel braided lines and stainless fittings all from speedflow . The braking capacity of this is dangerously effective , ROD.

Hi Rod

Your car looks great, myself and other people organizing the Supersprint at the VW Nationals really appreciate the time and effort everyone has made to attend this event.

Steve

Thanks for that info Rod. Did u have any difficulty with regards to the tube on the Kombi master cylinder binding on the brake rod? or does the 22mm unit not have that like the 24mm Kombi m/c?
regards
Jak

So if those Nissan 4 pots are 40mm each piston then you've basically doubled the surface area of a std bug caliper and as the m/c has a stroke of less than half an inch I think it fair to say you are not able to shift enough fluid to make the pedal go hard.
Doing the maths your nissan calipers have a total surface area of 5026mm2. The 19mm m/c has a surface area of 226mm2. Times this by 15mm of piston stroke and you get 3390mm3 of fluid moved. So not even enough to move the pistons 1mm. i think my maths is correct but anyone wish to say otherwise is fine by me
With the bus m/c you may well need a pressure regulator for the rears tho. Vauxhall, GM, in the UK used to use these niffy regulators that screwed into the m/c for the rear brakes. The spring rating inside the regulator limited the pressure allowed to the rears. Bloody useful they were

Hi

With brake hydraulics your not actually moving fluid as you would say with a hydraulic ram, your applying pressure against a fixed object.

Pistons in my front Brembos are 37.5 mm & 26 mm
37.5 / 2 = 18.75 x 18.75 = 351.5625 x 3.1416 = 1104.46875

26 / 2 = 13 x 13 = 169 x 3.1416 = 530.9304 so total area is 3270.7983 for one caliper, I used these with a stock MC

Type 3/4 calipers 42 mm
42 / 2 = 21 x 21 = 441 x 3.1416 = 1385.4456 x 2 = 2770.8912

Beetle calipers 40 mm
40 / 2 = 20 x 20 = 400 x 3.1416 = 1256.64 total is 2513.28

Steve

Hiya,

It is pressure but only once any slack within the system has been taken up. The brake pads aren't tight up against the piston or disc so fluid needs to be moved to make the pads contact the disc. Once the pads contact the disc then pressure begins to be applied and anything that can expand will take more fluid to fill the gap before the pressure can increase again.
So if you have used most of the m/c stroke to take up the slack then you have little travel left with which to increase the caliper piston pressure. Hence feeling spongey.
Your setup of 3270 lies within the fluid pushed by the m/c of 3390.
Or think of it another way. By how much would a piston 1 metre across move using the bug m/c. Neglecting friction losses the piston would move but only by hundreths of a millimetre. So the pistons need to be matched to allow sufficient fluid to be moved to allow pressure to be applied.

Jak , the cylinder that I used has the front snout on it and it was not necessary to remove it . I did however have to lengthen the pushrod a little as the piston sits further away from the pedal . There is not a problem if you want to remove the snout as it will do nothing in a beetle , ROD.

Hi Jak

Sorry for the slow reply - I hardly get onto the forums lately, I ended up selling the car due to escalating costs of repairing our leaky home!

Fitting up the 944 m/c
I used the standard 1302 holes with long bolts (no studs on the m/c). This put the m/c on a tilt which meant that one of the ports for the front circuit (it has two for the front and one for the rear) is very close to the brace that runs under the spare wheel well. I gave my brace a whack with a hammer and a punch and this moved it out of the way. I ran 2 new front lines- one to each side for the front, although I have heard of people just using one port and blocking the other successfully - which means you can using the existing brake pipes.

For the rear the existing pipe isn't long enough - so the trick is to use a T piece and use the 3 port of the T piece for the brake light sensor - or maybe use the second front port - might need to check the pressure of the system and make sure it turns on quickly enough.

I used the standard pedal rod on the brake pedal, but lost the rubber dust boot that covered the m/c as it doesn't fit the Porsche one.

And the next trick was the plumbing for the reservoir - use the rubber bungs that come with the Porsche m/c and find the plastic fittings from a 70's BMW 7 series (pick a part is your freind as these fit the Porsche bungs and the VW hose. The standard VW plastic fittings for the m/c are too small in the Porsche bungs and the VW bungs are too small for the Porsche m/c.

I can't find any photos at the moment, but I'll keep looking I'm sure I had some of it fitted.

Steve - From memory the single pot calliper piston sizes are 36mm rear and 54mm front.

Here is an old thread where I obviously had more time on my hands!!!
http://www.germanlook.net/forums/showthread.php?t=4595 

I wondered when you'd be wanting more brakes for that Subi monster your running

Cheers
Jeremy

Hi Jeremy

Did you use the stock bug rear brake T piece? I needed to lengthen a fitting on my old 1302 and I used a short line from a bug strut and the rear T piece with 2 lines into it and a brake light switch to fill the 3rd hole.

Shame you had to sell your car.

Steve

Just a quick update on the brakes, I did the Nationals supersprint with the standard 19mm MC, they were awesome, didn't run out of brakes all day & didn't lock a wheel all day which was a first on both counts.
I bought a new 24mm MC which I had planned on installing, but before I did, I rebled the brakes on the weekend & had big spurt of air come out of both front calipers!, needless to say the pedal has come up quite a way, almost to the spot where it was before. It's still not quite as hard a pedal as before but I actually like it better, after most track days I would have a sore right calf muscle from the brakes, but now the pedal has much much more modulation & it requires much less effort to put the brakes on than before.
So it now has Ford Falcon rear brakes, Nissan R32 fronts & standard 19mm MC.
regards
Jak

Hi

Thats great news, and this is with 40mm x 8 pistons, wow.

Steve

Jak i'm running BA falcon brakes on the front of my kombi with standard kombi MC. at first i thought i should get the BA master cylinder as well cos the brakes felt softer but now i really like it and have so much more braking power

old thread, but relevant for me currently
Jak have you tried putting the kombi mc in? im toying with installing one but with a hydraulic clutch, see economy stimulus on here or hydraulic clutch thread on germanlook if you can

also, rod if you read this, could you throw a pic up of the mc mounted in your L showing what holes are pointing where?

Thanks guys

I won't be putting the Kombi MC on as I'm really happy with the standard one now. Since getting all the air out of the brakes the pedal feel is fantastic. I'm very happy with the brakes.
regards
Jak