Which master cylinder could I use for an upgrade to my standard M/C on my VR6? It is used for track so lots of hard braking. Would prefer less pedal travel. Heard of people using an audi one for the Mk2. Any help gratefully received.
Quick search on "25mm": http://www.clubgti.com/forum/showthread.php?t=233405 http://www.clubgti.com/forum/showthread.php?t=228680 http://www.clubgti.com/forum/showthread.php?t=218407 http://www.clubgti.com/forum/showthread.php?t=212765
Thanks for that Chris. So, it looks like I can fit the Audi 25mm one, I think. Only issue being I may need different unions on the M/C but as I have redone all the brake lines except the M/C line outs, that's not an issue to change those. Ian
Check the way the m/cyl attaches to the servo. Some have a ball end, I think the VR6 does? Or there were 2 versions over the course of time. If you can do a prelim strip down to see what is on the hidden part of your servo, where servo pushes m/cyl, it might get some early answers before bying up a 25mm Audi item.
Chris the M/C attaches with a ball ended rod. Eddie, use EBC yellows (288mm set up) on normal vented discs. I am aware the EBC's can lead to a bit of a poor pedal feel.
I use DS3000 pads on the same ATE 288mm system. These were bought from Bill B last year and have excellent from cold (regular road use) and when taking part in a track day at Bedford full chat @ 120mph to 90 then to 30mph repeatability could not get the brakes to fade and they remained with a progressive feel. I would suggest that your front biasing is spot on though ( my OE ABS and biasing system is still very functional) and be prepared for high disc wear, dust and squeal. If ever you are at an event and I am there driving the ankor please feel free to take it out for a blast.
Thanks Eddie. I have removed the ABS now to get rid of the rear locking up on track use and causing the ABS to activate all the time. Have put an AP bias lever in to sort front to rear balance. Tried Halfords Racing fluid to see how it is. All works well and done two track days since fitting in the last two weeks. No brake fade on either day, (Oulton and Anglesey Int). Just a long/soft pedal feel which didn't change at all through the days. Took quite a lot of pressure to get the fronts to lock which only happened at lower speeds <40mph
The ABS system is different on early models. The later Teves 20 system the biasing is electronic and automatic. infinity did comment about the 'soft pedal' on mine while the car was stationary.
sorry for resurrecting this thread,but i have a question i have a mk3 vr6,is later car 1997 it is in final stages of r32 conversion,the front brakes have been upgraded to ap 4 pots on 330mm discs the rear calipers are standard mk4 alloy jobs everything else except the master cylcinder has been overhauled, the system has been bled twice the pedal is long but has a firm end point if you pump the brake again it is much stiffer and with a firm end point I am assuming the pedal is longer because of the increased caliper volumes up front and that i probably need to change the M/C is this correct does the RS2 M/c bolt straight on to the VR6 are there any compatibilty problems
I'm assuming the original caliper is Girling54 and the upgrade AP jobbies are CP5200? Girling caliper is 54mm piston bore and AP is 37.3 and 41mm bores, there isn't a massive difference in piston bore are between the two, so pedal length will be a tad longer, theoretically mind, but only around 5% longer. Might be something else causing the pedal issue?
Hi thanks for the reply the calipers are the pro 5000+ series the 5040 callipers for 28 mm discs they are 4 pot the original vr calipers are whatever they where..I went to check in the garage they are indeed girling ate 54 i must admit the piston is very deep i make this total piston area of 22.8 cm sq the ap have 38 mm and 41 mm pistons the total piston area per caliper is 49.5 cm sq, which is nearly double although i dont know the stroke or depth of the bores I should add the original M/C before all the bits were replaced had lain empty for 10 months and the original had done 196,000 miles though it was working sweet as a nut and always had done You are not the first person today to suggest there shouldnt be a large differance and that really an upgrade to the rs2 M/C shouldnt be necessary i had thought initially the m/c might have had its day but the advice I appear to be getting is try rebleeding again this time making sure vag-com is used to bleed the abs unit,it was done by a garage but i will check.If after rebleeding several times do i assume the current m/c has had its day and replace with similar or take the oportunity to go to 25.4 mm m/c.and if so is the rs2 master cylinder a fairly straight swap?
I get different figures on the piston areas, briefly showing below using πr2 Girling 54mm piston 3.14 x (27x27) = 22.89 Total = 22.89 AP Pro 5000+ 38mm piston 3.14 x (19x19) = 11.33 41mm piston 3.14 x (20.5x20.5) = 13.20 Total = 24.53 AP caliper is larger overall and to express the pedal travel change using a ratio relative to the master cylinder piston area; 22mm master cylinder gives ratio of 12.91 to 1 23mm master cylinder gives ratio of 11.81 to 1 To put into perspective; 22mm and orginal Girling calipers 12.05 to 1. AP calipers have increased the ratio (to 12.91 to 1) and therefore the pedal travels further. Fitting the 23mm should produce shorter than standard pedal but with the larger m/c you will produce around 10% less pressure at the pads and will need to push harder on the pedal. A 25.4mm m/c will reduce the pedal travel, ratio of 9.69 to 1 and reduce pressure by 25%, short pedal but push very hard. All theoretical and purely mathematics, I haven't driven cars with these setups and that is perhaps the best source of sound of advice but without actual experience this might help.
Hi Strimmer the vr 6 m/c diameter is 23.8 mm so to go to 25.4 which is the RS2 shouldnt represent such a big change ? will give shorter travel and little more effort ? the areas for the callipers were dragged from AP's site the piston area is 49.5 cm there are 4 pistons the girling 54 is just one piston which is why I quoted the figures how would estimate that would affect measurements the mk4 i thought was 23.8 just like the vr well certainly early mk4 cars
Yes, from 23.8 to 25.4 isn't such a big change, table should display how the pedal ratio and pressure changes happen with the changes to caliper and m/c. Master cylinder Caliper Total caliper piston area square inch Master Cylinder area square inch Foot Pressure lbs Pedal Ratio Servo Assist psi Pressure applied psi M/C ratio to piston Pad Pressure lbs 23.8mm OEM 54mm 7.096 0.689 70.4 5 515 1026 10.3 7277 23.8mm AP 4pot 38/41mm 7.605 0.689 70.4 5 515 1026 11.03 7799 25.4mm AP 4pot 38/41mm 7.605 0.785 70.4 5 452 900 9.69 6847 The Girling 54 is calculated as doubling one side of the caliper, effectively a twin pot. http://www.clubgti.com/forum/showpost.php?p=2009001&postcount=51 http://www.clubgti.com/forum/showthread.php?t=225530&page=5 (posts 117-122) If you're changing your 23.8mm let me know
Hi Strimmer just came across this thread and your others good work! I havent changed the master cylinder yet just trying to get some feel for the car as lots has been changed.when i initially started the pedal had a firm end point and it STOPPED but the response was almost binary with little feel,it seems to be settling down now though I sort of think shorter pedal with more resistance could be the way to go more feel,if i do you are welcome to the M/C but it has done 197,500 miles my problem now is i think the rack although not shot isnt working properly again what do you expect at 197,500!
