It’s maybe a conversation we should have one to one, but my thinking was more about the actual amount of caliper piston travel, regardless of fluid pressure, that should be allowed for. But maybe that’s not the right way to think about it, and I’m receptive to being told so. What I do know is that (by simple mathematical calculation) for a particular MC diameter that I’m using the max caliper piston movement will be 0.5mm. I don’t drive the car so it’s not my safety as risk, but is 0.5mm likely to be sufficient - assume AP 4pots.
You cant just remove the servo and abs without designing a complete new system with a master cylinder specced for a non servo system. The master cylinder diameter and stroke will depend on the volume of the caliper bores.
You will need a BPV fitting in the system so you can adjust the brake balance for different circuits and track conditions. Best go to a race engineering company who will advise.
Actually, what I’ve found is that whilst it’s relatively easy to work around the servo removal, the biggest design constraint is the OE brake pedal ratio. It’s just over 3 and could really do with being as much as 5 or 6 ie more in line with what you find with pedal box arrangements.
plip,
As someone who has raced both Supercup cars and others, I would advise that pad knock off after running curbs can be significant to the point that if you haven’t tapped the pedal with your left foot before the next corner, then undesirable smells may come from your race suit. In addition, just if the Jump In part is not working you will get a long pedal and also if using a certain well known make of brakes, which we found go spongy when hot, you can find a very unhappy car. Take the servo away and you are likely to have either a very hard pedal that you find very difficult to modulate or travel so long you can’t heal and toe. Even on a light kit car with tandem master cylinders we have to advise any driver about the heavy weight of the brake pedal before they drove it.
That’s interesting, although with three separate NCs all with OE calipers, and pushed pretty hard on track, knock off has never been an issue.
Hi Robbie and all who have started this post.
We have stripped a NC to track use. ABS no longer working and wiring to rear disconnected, and fused both 30 and 40 amp taken out. At a very wet Blyton yesterday we were having brake balance issues. Seemingly back snatching ( EBC yellow rear carbotec front). Does the ABS pump hydraulically control bias, if so will putting the fuses back in re engage? My uneducated brain tells me it can only control the bias from the electronic information from the wheels, so now of no value.
Thanks guys
Would also fitting a proportion valve on rear circuit add to being able to increase balance.
If Nick looks at this ,would it benefit softening pad selection
The simplest way forward would be to try a really low friction rear pad. But it rear lockup continues, adding a proportioning valve will give you the ability to reduce rear brake pressure.
On my car we went a step further and removed the servo and added a twin master cylinder setup, but I wouldn’t necessarily recommend it lol
Thanks we had talked about doing that. Have you removed the pump or is the pump still helping you
Mike
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The abs unit is removed. I’m afraid we never tried the setup with it physically still in situ, but my feeling is that it makes no difference in terms of any pressure limiting capabilities whether present or not.
I have this nagging feeling that it doesn’t, I went to put the fuses back in yesterday which would have proved that but was talked out of it. Hence asking you guys. Don’t know when I’ll get the next chance now.
If you have fitted a proportional valve in have you got a picture of the set up. Which one have you used.
Thanks for your time
Mike
We went for a Tilton in this instance, but the AP version does exactly the same job.
It took me a long time to understand exactly what a prop valve does. They often seem to be termed “bias” valves, and to an extent they do change the front/rear distribution of brake pressure (at the calipers), but they only do this once a certain rear brake pressure (generated within the MC and then transmitted, unaltered,to the calipers) has been achieved. But then, depending on the position of the prop valve lever, once a particular rear brake pressure has been achieved, any further increase in pressure (at the MC) will only partially be transmitted to the calipers. With both the Tilton and the AP valves, I think it’s reckoned that it increases at around half the rate of increase prior to reaching the threshold set by the lever position.
In another car that I have an association with we have brake pressure sensors in both front and rear circuits that measure actual pressures reaching the calipers. From observing these pressures we could see at what pressure the rear brakes would be most likely to lock up. And then the prop valve lever could be set to position which matched that value.
In terms of numbers, we found we could achieve up to around 80bar of pressure in the fronts, and with no intervention from the prop valve, the rear pressures would reach around 60bar. But beyond around 45bar the rears would tend to lock up (but fronts were still ok at 80bar). So we set the prop valve to setting 3 (AP valve in this instance) and the 80:60 split became more like 80:40. Of course, those values could have been adjusted via a different pedal box balance bar position, or different pads or tyres etc etc, but driver feedback suggested that the way we dealt with the rear lockup situation, in this instance, was to their liking, so we’ve stuck with it.
Back to the MX5, and prior to removing the servo, we actually found that front lockup was our biggest challenge. But at this time we had already elected to use really low friction pads in the rear. Various front pads were tried, including XP8s, but we ended up with Yellow Stuff, and they seemed ok, although shortly after we went to the servo delete delete setup and from AP calipers - which I don’t recommend lol.
Wow thanks for this information and time.
Rob does lean on brakes, we have previously had problems with yellows not holding up, he had a almost new set collapse at Oulton Park. We then tried Blue in front and yellows in rear, much much better but we still found them fading after around 20 laps. We did have a full working ABS system in the car but he was switching it off. You will probably realise the step up with Carbon Loran pads, they are in a different league, we understand that you need less in rear so have stuck with yellows, hoping for a balance. This was the first time we had run in wet, and Rob lost all confidence in braking.
We have always struggled a little with balance on rear and now taken ABS out we were looking any way at a proportional valve. We were thinking of taking the pump out but need to be sure we are not creating any more problems, and weather the pump in but not connected was exasperating it.
Modern cars far to complex today
Have you fitted braided lines from the MC? I’m asking as I’ve not worked on brake lines it may make it simpler.
Mike
Yes, braided flexi hoses throughout.
Driver style seems to make a huge difference to perceptions about pad performance. We have a lot of experience, covering many different vehicles, of the various compounds in the Carbotech range and have huge respect for their capabilities. By contrast, we’d never ever advocate anything remotely associated with EBC products. That said, we reluctantly followed a recommendation to tryYellow Stuff and they not only suited driver preference in terms of pedal feel and retardations levels, but also lasted really well.
When it comes to brakes, more so than almost any other aspect of car performance, there really don’t seem to be hard and fast answers/ solutions.
Again thinking of the cars systems. If we remove the ABS pump, as it’ seems to be of no value to the system now all sensors have been removed/ disconnected, we simply split MC lines front and back putting in a proportional valve in the rear line?
My fear is the ABS pump will be in some way connected to another system that will bite us?
I have as stated pulled the identified fuses, so what other than hydrologic could it be? ( probably stop me opening the glove box:roll_eyes:
)
Re pads Rob raced karts in the dry we used to use the hardest pads they were like a switch on or off🙄 much softer ones in wet. We are still in very much of a learning curve with the car, so will have to try a different pad selection in wet may be. It’s been a big step with the carbon pads, but he does like them. Fluid is another topic, bought a job lot of EBC, it’s almost gone now so will experiment. So many different views again on this😂
Did you have your lines made to order or generic lengths? Yes and the next question where.
Thanks again
Mike
On removing the abs, the only issue we encountered, if you can even call it that, was the abs dash light stayed on permanently. But even this can be sorted by someone who knows their way round the ecu.
Maybe in some way also connected with the abs removal is that at some point we lost any read out from the speedo. Perhaps that’s to do with the wheel speed sensor info no longer being picked up via the abs unit, but we had a lot of other wiring removed at the same time, so can’t be sure. However, I have seen many videos of Supercup racing and don’t think any of the cars have working speedos.
In terms of brake lines, there was until relatively recently a company that made a braided brake line kits specific to fit a car with abs removed. And I believe they supplied multiple sets to some of the MX5 specialists. So it might be worth while making a call to someone like Paul Sheard Racing. Failing that, I’m sure a company like Corten- Miller in Lincolnshire could sort something out for you based on our car which will be with them next week.
On brake fluid, any decent Dot 4 fluid will be just fine.
Hi funnily we have just lost Speedo as well. Would appreciate a cost on the lines a big help. You don’t by any chance have a picture of how they piped in the removal of the ABS pump.
From your in car pictures did you bring a line in to valve and then back out to engine bay to pick up rear lines. Again not sure how to plumb in. My servo has 2 lines into ABS pump and within the pump it splits it into the dual circuits. We would have to simplify front rear and again assuming either or would do.
What series does the car run in? Rob would like to complete in endurance series 2022. We are hoping to get a full series of the Javelin sprint in next year, have been involved this year but only 1 event due to COVID. The car is not to MSA regs at moment it was supposed to be for fun but🙈
So will progress the build as funds become available.
My co-owner sorted the brake lines and I’m afraid I honestly don’t know how much they cost. But don’t think it was a massive amount.
The pic shows the two outlets from the OE master cylinder, one of which gets split into two almost immediately for both front brakes and the other goes through the firewall and hooks into the proportioning valve. The single pipe then goes to the end of the transmission tunnel where is then gets split into two for both rears. All very simple.
When we set out on modding the car we were mainly thinking in terms of having fun at trackdays rather than with any race series in mind. But we ended up doing a lot more than originally planned - 980kgs, full cage, all new Superpro bushes, KW Race 2-way coilovers, AP front brakes, servo delete, Quaife rear diff, 3.5 engine and gearbox, uprated clutch, plumbed in extinguisher, heavily revised electrics and so on and so on.
And then in April 2019 we decided to have a run up to Scotland and just for fun entered a round of Super Lap Scotland thinking we should easily be able to get round Knockhill in under 1min. Not so easy at all!!! So we had to have another go at the next round , and then the next and the next, and eventually did make the breakthrough and a bit more on top. This year the car hasn’t turned a wheel, but I’m hoping we can do a few trackdays over the winter months.
Thanks for the information and pics it is as I hoped. Be great if they get me a cost On the lines for doing as you have.
Hopefully going to see someone Thursday they want to see the car before they give me a cost for doing it. You guys seem to have planned it well, I’m sure I could do that. Hope you get a chance to get out in the car and have some fun. We are locked in again with COVID so think that’s it for us.
Rob has a YouTube channel “ J AND S MX5” there are some of our days on that.
We are both great full for people like you and the mx5 community for your help and advice
Mike
Late to the party as always but just wanted to say a massive thanks plip for all the advice you’ve been giving the old man here. I have next to no idea what you’re both talking about with servos and hoses, but if the end result is I can hit the brake pedal without locking the back wheels up i’ll be a happy bunny! 
It was really very tricky slowing the car down in Blyton earlier on in the week in the wet, I found myself having to brake very gently and very early for the corners or face a screechy sideways trip into the run-off area. The cones are my friends, I am not aiming for them, honest. 
No problem, I’m glad if our experiences are of some help to others.
Do you do any data logging when on track? If so, it would be interesting to know what kind of braking G forces you are achieving right now and then compare to where that might be by comparison with where we’ve now reached. Based on data gathered over many years from a large range of cars we set what I thought was a fairly conservative goal of around -1.3 g on decent semi-slicks and near to -1.5g on slicks. But in practice we’ve struggled to see more than -1.1g even on slicks, and quite frankly I think we’ve probably exhausted possible solutions without reaching out into the realms of aero. But if you’re currently seeing a more regular -0.8 to-0.9g max then you can at least be assured that more is possible.