Hi all I have a 1996 Mk3 16V 2.0 that I use for trackdays only. I am focussing on handling, weight reduction and brakes before working out what to do about more power. This is meant to be a cheap (relatively speaking) hobby but I am serious about improving my driving. In my quest, I am unsatisfied with the brake pedal feel and travel with the current system. I have braided hoses, Mintex F-series pads, good discs and RB600 fluid (fully flushed). Having felt a few racing brake systems, that is what I want from the pedal feel and travel. I don't like the ABS, and want to develop my cadence braking, so that has to go. This is in fact the first question in this thread. I understand the ABS system balances braking force front/rear automatically, and realise when I remove it I need to fit a bias adjuster. In order to keep costs low-ish, I would like to avoid a pedal box if at all possible. When I remove the ABS I understand I will need to obtain a non-ABS booster (from a US forum, I believe this is what we call a servo). The question is whether there is a way for me to determine the right booster (if indeed there are any variants). I understand from TPS there are many different servos and don't know where to start. Equally, I don't want to buy new if I can help it. However if there is a real benefit to buying new, I might consider it. I appreciate any help you have the time to give me. Thanks all for a great forum. Yossarian
Could you not fit the servo/master cylinder from a late mk2 golf? 16v G60 etc? The actual brakes themselves are the same so you know they're compatible.. Remember though, that if you're comparing your pedal travel to that of a racecar that the racecar probably won't have a servo so the pedal travel/feel will be very different..
If it's for track only, I'd bin the servo and run a direct master cylinder. Saves weight and better feel, if you get the sizing right. You will need a bias valve too.
The trouble is with that is that unless you increase the output from the servo to suit then fitting a larger master cylinder will reduce your braking force..
Cheers guys. I like the idea of binning the servo altogether and going direct. Mike, how would I know what size m/c I need to get for a direct setup please? Cheers Yossarian
I'd suggest 17 - 19mm. See the thread where Mike and myself discussed this recently.. http://www.clubgti.com/showthread.php?260590-Master-cylinder-and-servo-advice&p=2254649#post2254649
Somewhere round that size is where I'd guess... depends on the size of the brake calipers and how much fluid they need. Old 911s with no servo use a 19mm M/Cyl, IIRC, but the pedal is a bit hard and dead. Too big and the pedal is really hard. Too small and the pedal gets close to the floor before you've got full brakes on, as you're not shifting enough fluid. Cars with servos normally use a bigger bore than the same setup without. I heard there was an old polo M/C which might be up to the job. Not sure on details though. Google is quite helpful on the subject as well... http://www.locostbuilders.co.uk/viewthread.php?tid=12195 "Use a mastercylinder size that is suitable for non servo use and a pedal ratio of between 4.5 to 1 and 5.0 to 1 and everthing is fine. No need to change the caliper (they were oversized for the book donnor Escort). An easy to find mastercylinder design for use without a servo is one from a base model 1980s VW Polo or Golf it is a 19mm (3/4" bore., cars with servos use mastercylinders with a bore 22.2mm (7/8" or bigger. Using a smaller mastercylinder bore reduces pedal effort. " I bought Jon Olds' Mk1 Golf Rally car which IIRC has a 0.625(16mm) or 0.675"(17mm) - I'll check which one - master cylinder, no servo and Willwood 4 pot calipers, which gives great braking and brilliant feel. The direct mount cylinder costs a lot less money than a pedal box (which is absolutely fine if you have the budget and want the extra adjustability it gives you). First time I drove it hard was in the pouring rain round Llandow, and the braking feel was just awesome... no unplanned lock-ups at all - even when on the brakes riding over wet kerbs into the chicane, I could control the braking to keep it all stable and in a straight line. The calipers are going on my trackday car shortly (Mk2 Scirocco), and I'll be adopting a similar setup for the master cylinder, to bin the servo and linkage in the A1 chassis, which I'm guessing will save around 8-10kg. The other advantage of binning the servo and linkage, is that it'll give me the chance to weld a brace bar between the front struts, and stiffen up the front end of the car, so I'll put some of the weight back, but it'll be doing something useful.
Yup - 914/4 and very early 911 had 17mm, which is probably beetle carry-over, as per your post on the other thread. 914/6 and later 911 without servo had 19mm.
Never do that! you will hit the floor without having begin to brake ! Just try to know the actual brake MC diameter and fit a larger, I can imagin that with the ABS, you must have a 22.2 or 23.8 mm mc, (7/8 or 15/16 inch), try the upper model: 23.8 or 25.4 mm, you will have less pedal travel, with a little bit more effort, do not touch the mastervac. If you have some doubts, look at the video of my Gr4 Oettinger, one can see the pedal travel: I had G60 brakes with the original 22.2 mm mc, found the pedal travel too long and replaced it with a 23.8 model.
Some great information here, thanks. I hadn't caught that thread despite searching Mickey, so thanks. Mike, I'd only searched for mk3, so the locost link didn't come up - serves me right for being too specific! Billb, first of all great driving, that car and the race looks like a lot of fun. Can I clarify though please? Are you suggesting to keep the servo and just increase the Master cylinder size instead? I still want to get rid of the ABS - unless you really think I am looking in the wrong place for a solution. After your comments, I think you're suggesting I may be better off changing the M/C for a non-ABS, but larger one and leaving the servo (is that Mastervac?) alone. Your pedal travel looks ideal, still allowing for heel/toe (a technique I am trying to develop, but am having difficulty with the current pedal travel/feel), something like that would be really good. Cheers chaps
By the way Jager, given Bill's comments that may be an interesting option. I've followed that thread and the links within it. I clearly have some more research to do before I put my hand in my pocket. Cheers
It's a Golf one, no ABS, with Servo and a Audi 100 24 mm MC which fits "plug & play". From the Golf3 I just know it must be 280 mm discs with 54 mm callipers, like the G60 or the Ibiza 2.0 16V, with the same rear discs & callipers (just 5 holes). I'd have to see for the fitting of a specific non-ABS mc., this will also request an adjustable limiting valve for the rear brakes About the 17/19 mm mc you spoke about, they can be fitted in a pedal box, but you need one for front and another one for the rear! Just read on the homologation form that the ABS MC is a 23.8 mm (22.2 w/o ABS). so you can try in a first step , to remove the ABS, I suppose the MC has at least 2 or 3 outputs to connect directly. Maybe not quite legal on open roads???
Thanks Billb. Interesting that my MC is so large, thank you very much for researching this. I have been doing some more research on this approach and the 25mm mc from an RS2 looks promising. I understand I would need to swap the servo for this mc. From what I have read the ABS servo has an odd mc fitment. I also understand, and quite possibly this is where a little knowledge can be dangerous, the fitment of the pedal linkage to the servo is a ball and socket type. The question is whether an RS2 servo has this fitment. D any of you guys know? Does this sound like a good approach? Or can I keep it more simple? Thanks Yossarian
Bill, I think you've either quoted the wrong thing or completly misunderstood what myself and Mike H are talking about. The use of a 17mm or 19mm master cylinder is for use in applications without the servo fitted. VW themselves fitted 17mm master cylinders to mk1's without servo's (i.e fitted directly to the pedal) It all comes down to mechanical advantage. The master cylinder is simply part of a lever. Increasing master cylinder diameter will reduce pedal travel but at the expense of mechanical advantage. Personally I've run a genuine VW 17mm master cylinder (no servo) and then replaced it with an ATE 19mm master cylinder (no servo) then replace that with a HRP pedal box that runs a 14mm master cylinder for the front and a 16mm for the rear (again, no servo).. I've always run sans servo because I prefer the pedal feel for toe/heel work and (rarely) left foot braking.
I think we're at cross purposes, and Bill is talking about setups that still use a servo. I had to look up 'mechanical advantage' on wikipedia, so here's the link for anyone else in the same boat. http://en.wikipedia.org/wiki/Mechanical_advantage I think for a lightweight track, race or sports car, it's fine to run without a servo, provided the system is all sized correctly. Once you get over a ton or so, at a bit of a guess, then you need bigger and bigger brake calipers that displace more fluid, the required volume for the master cylinder to push gets bigger, so the master cylinder bore gets bigger, and the pedal needs progressively heavier shove to get enough braking force. Not being an engineer, there are probably other factors that I'm not taking into account, but I think as a rule of thumb, it's about right.
This is great stuff chaps, it is becoming clearer all the time. I really appreciate your patience with me and your continued assistance. Mickey, I've seen some of your very early posts and noticed at one stage you made bias boxes - and to some acclaim by all accounts! The more I research this and re-read all the responses here, the more inclined I am to go with the original suggestion of direct MC without servo (binning the ABS too). With that in mind I've been looking around at MCs and the other options cited and for the price of MCs and a non-ABS servo, it's close to a bulkhead-mounted bias box (c. 200 inc. real Girlings). Given that with one of those the work is done, provided I get the MC sizes correct. Time for more research... One last hurdle is the pedal linkage which being a ball and socket arrangement is going to impossible to find something out of the box to fit. Some of the suppliers I've spoken to about the bias boxes have suggested drilling into the pedal, fitting a clevis/rose joint and linking that way. Given these are my brakes, and I often hurtle into corners and brake very late I want to get this part right. Do these people sound right to you guys? Would drilling into the pedal metal weaken the structure in any way? BTW, I get all my kicks from braking and cornering because the acceleration in the damn car is so slow Thanks all!
