My car (96 Ghibli Open Cup) has an unusual braking setup that I'm about to make some modification to. see http://www.ferrarichat.com/forum/showthread.php?t=106237 for details. It has 3 proportioning valves. As was recommended on that thread I'm going to be using some brake pressure testing equipment to: 1. Document the current configuration. 2. Help me with calibrating the changes. I will be removing the engine compartment mounted rear bias adjustment and moving that to cockpit. I may also remove the individual rear wheel bias valves as well. This is a 3 channel Bosch ABS system. So here are my questions: I've seen several types of equipment for measuring the pressure. One system inserts in the caliper replacing a pad. I'm not sure if this will properly engage all the pistons with out some kind of plate in there as well. Seems like it would be useful for detecting caliper problems though. I do a lot of work alone so a system with a stop point/recording function is important. The system that slips in the caliper does that. The others I've seen connect by replacing the bleed screw. I have the big Brembo racing calipers so I assume I'd need a particular adapter. This would involve bleeding before and after each test as well? I'm going to be installing something like a Tilton proportioning valve and it seems to me that a single meter mounted in the dash would allow me to check the front rear bias once I know what settings I like. Or, do I really need 2 meters? Isn't just maximum pedal pressure and a look at one meter good enough? Currently the car wears the front pads and rotors and I'm still on the original rears with very little wear after 1,800 km of track. It's a front engined car, think M3 size/weight/power. I don't race, just club track events and any suggestions on which brands/models of equipment would great as well. Thanks for any input. Bob S.
You have 3 channel ABS. ABS is a giant proportioning valve. Your extra valves will do nothing. If you delete the ABS then you can change the valves. You do not need to go through all the issues with pressures. You are not changing overall brake pressures unless you change your master or calipers etc.. If so you need to re-engineer the system not start at brake pressures. Volumes/piston areas of the calipers need to be matched to the master output. If you are just dumping the ABS and adding porportioning valves you do not need to knwo presures and pressure will got give you any usable info as to how to set the valves. You will find a gross position for the valves then fine tune as track and car conditions change. Exactly what are you trying to achieve?
yup! VE wrote: :"That is like nothing I have ever seen. The 3 channel ABS is 2 front and a rear circuit I believe. It is an early gen ABS, and does not have ECU feedback loop adjustment of the type I mentioned earlier. The adjustable prop valve in the engine bay is not of a type I have ever seen before. The rear appears to have load sensitive prop valves installed. I assume the lever is attached to a suspension member at some point and changes the brake pressure with ride height. But why one at each wheel...I dont know. This is the most unique setup i have ever seen. It would seem that the rear is reducing pressure dynamically as the suspension travels, which is not a bad thing. The only thing i can say is that I am a bit stumped by the whole setup. I have never seen anything like it." Well everything I said still applies. I do not know your car or system but in general It is not so outlandish a design. I am not a pro but you need two PV's with diagonal split systems which this is likely one. The ABS is very crude and 3 channel means two front wheel sensors 1 rear sensor for both wheels. Two load sensing PV's (1 per wheel) are also seen and works with split systems. In the front somewhere is a pressure differential valve for the split. So here is my guess. I think this was a way for Maser to simulate 4 wheel ABS as in vary the pressures at all wheels VS Front rear as the car turned-in. Where these cars raced where trail braking into corners was the way to drive them? There you would see braking in turns and differential pressures left rear to right rear yes? That would help inside rear traction on turn-in. Also, such a system would help on bumpy tracks with lots of camber change in the track surface. Where were these raced? What he said about using the pressure guages makes sence to see what the system is doing now but that assumes it if still functioning well before you can decide that how it is now is as designed then. Maser if very bad with Electromechanical and mechanical systems as far as durability. They think of great things and execute badly. I am not sure if the pai readings are going to tell you alot because the true info you need is what happens at threshold braking with the ABS coming on. Since it is a PV too that will effect ultimate brake psi I would think. Also, any mods like stiffer springs, roll bar changes etc. have just change how the package works together due to the LSPV at eachrear wheel. It sounds like Maser tried to get trick vs going to true 4 wheel ABS. The only way for you to get true control IMO is to gut out the ABS and redesign the entire system with new master sized to the calipers with F/R PV. Otherwise you will need to think like a Maser tech and figure it out. Maybe several bottles of wine will help.
"So here are my questions: I've seen several types of equipment for measuring the pressure. One system inserts in the caliper replacing a pad. I'm not sure if this will properly engage all the pistons with out some kind of plate in there as well. Seems like it would be useful for detecting caliper problems though. I do a lot of work alone so a system with a stop point/recording function is important. The system that slips in the caliper does that. The others I've seen connect by replacing the bleed screw. I have the big Brembo racing calipers so I assume I'd need a particular adapter. This would involve bleeding before and after each test as well?" yup. and this system is better more accurate and will screw into the generic metric bleed screw with little fanfare or hunting for parts. "I'm going to be installing something like a Tilton proportioning valve and it seems to me that a single meter mounted in the dash would allow me to check the front rear bias once I know what settings I like. Or, do I really need 2 meters? Isn't just maximum pedal pressure and a look at one meter good enough?" ???? you need to meter each wheel at differeing ride heights to see what the LSPV is doing to the static pressures.
Not sure where to start with you Billybob but let's try this. I was not asking for advice as to how to modify the braking system. I already received some conservative advice from a brake systems engineer and it was from free of cheap shots at my car. So I'm going to start with that. In stock from, which this car is far from, it had the 3 channel abs system and a pair of rear proportioning valves. I assume they added the front engine compartment mounted one for a reason. I agree that they probably didn't approach this with best method but the budget was limited. My start will be to replace the engine compartment unit with a cockpit one so that I can experiment on the track. Your statements about the with the abs system the valves will do nothing is absurd. This is a very simple abs system. I'm not really sure why I'm responding to it but I guess you just hit the wrong button. So let's move on ... I would also like to be able to document how the two rear valves work for the following reason. This is a stiffly strung car and it is very different from the street car and as such I think the amount of rear suspension movement make be far less than that of the street car. It just may be that these two valves are totally inappropriate now for the given amount and position of rear suspension movement. That's one of the things I'm hoping to learn. That is why I want the input on the tools. I may well eliminate the abs system once I've documented and tried adjusting the system I have. My original questions remain unanswered. Bob S.
