Does anyone have any braking questions.
07-09-2015, 09:42 PM
#62
Drifting
For those with the early version [97 to 00?], I've raced for two years on my 99 with the abs computer disconnected. I run ww H pads on the sl6 caliper up from (7420 mm pad and stock rotor size) and stock rear calipers with ebc yellow pads. The rears would lock up if I ran the same pad compound front to rear.
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07-10-2015, 02:05 AM
#63
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Jim,
I think Ben's answer above is more accurate about the rear brake bias defaulting to more front heavy setting when the fuse is pulled, I've always looked at it as the rear brakes being "shut off" when in reality it's just a system that is already front biased becomes even more front biased.
Now it seems like there is a difference in opinion as to what happens when the fuse is pulled, I believe that the system becomes more front heavy and limits rear braking. Bill on the previous page believes that there is no rear bias at all and it will make the rear lock up first.
I think Ben's answer above is more accurate about the rear brake bias defaulting to more front heavy setting when the fuse is pulled, I've always looked at it as the rear brakes being "shut off" when in reality it's just a system that is already front biased becomes even more front biased.
Now it seems like there is a difference in opinion as to what happens when the fuse is pulled, I believe that the system becomes more front heavy and limits rear braking. Bill on the previous page believes that there is no rear bias at all and it will make the rear lock up first.
Pressure Hold
The EBCM closes the inlet valve and keeps the outlet valve closed in order to isolate the system when wheel slip occurs. This holds the pressure steady on the brake so that the hydraulic pressure does not increase or decrease.
Pressure Decrease
The EBCM decreases the pressure to individual wheels during a deceleration when wheel slip occurs. The inlet valve is closed and the outlet valve is opened. The excess fluid is stored in the accumulator until the return pump can return the fluid to the master cylinder.
Pressure Increase
The EBCM increases the pressure to individual wheels during a deceleration in order to reduce the speed of the wheel. The inlet valve is opened and the outlet valve is closed. The increased pressure is delivered from the master cylinder. (This means the pressure comes from the driver's foot on the brake pedal and no where else).
When the fuse is pulled that kills the power to the EBCM and it can't modulate the fluid pressure at any of the wheels. It can't do a pressure hold, a pressure decrease or a pressure increase. Since there is no mechanical proportioning valve and the EBCM can't limit the brake pressure being applied to the brakes you get maximum pressure at the rear brakes. There is no way the pressure is reduced at the rear wheels when the fuse is pulled you basically have a straight path through the BPMV to the brake cylinders.
Bill
07-10-2015, 09:38 AM
#64
Right now we are just guessing and I need to stop that. Guessing gets people killed in brake world. All we know is that the pressure changes with the ABS power line pulled. I cannot say what that line pressure does while unpowered and during a dynamic stop. I would need to see some data logging before changing my mind. For the time being we are going to recommend leave the abs fuse it in.
Please don’t just say “the rear would lock” explain where you are getting lock up. Are you experiencing rear lock in the straights, corner entry. Do the rears lock while off the brakes?
For those with the early version [97 to 00?], I've raced for two years on my 99 with the abs computer disconnected. I run ww H pads on the sl6 caliper up from (7420 mm pad and stock rotor size) and stock rear calipers with ebc yellow pads. The rears would lock up if I ran the same pad compound front to rear.
07-10-2015, 09:46 AM
#65
Drifting
I would get minor rear wheel lock on longer, hard, straight line braking zones. It was never severe enough to cause stability issues and honestly if it wasn't for other driver videos and some tire smoke, I wouldn't have noticed. Keep in mind I have the earlier system, so I was answering the question for people with that system.
07-10-2015, 09:48 AM
#66
I would get minor rear wheel lock on longer, hard, straight line braking zones. It was never severe enough to cause stability issues and honestly if it wasn't for other driver videos and some tire smoke, I wouldn't have noticed. Keep in mind I have the earlier system, so I was answering the question for people with that system.
07-10-2015, 02:09 PM
#67
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St. Jude Donor '03-'04-'05-'06-'07-'08-'09-'10-'11-'12-'13
I am getting spinning of the tires on the rear rims under braking. This has occurred with two different sets and sizes of rims. One setup was with aftermarket Z06 repro 18x12 wheels with GTI Compound Continental Slicks mounted and the other was with CCW 18x13 wheels with Hoosier A6s mounted. There is less spinning of the tires on the CCWs but there is still some.
Typically this is due to tire pressure. So on your first couple laps, pressures are low and the bite is high so you can move the tire. Our TransAm cars and ALMS car could move the front tires almost one full revolution and the rears almost 3/4 of the way around. Now the rear was generally on acceleration and the fronts moved under braking.
It would be hard, but not impossible to move the rears under braking.
Next time the tires are off the wheels, you probably need to blast the old rubber off the wheel, and you can do a few things. If there is a shop near by sometimes they can knurl the bead seats on the wheels, or have them blast the wheels there with a media blaster so they are not smooth. This can help as well.
07-10-2015, 03:25 PM
#68
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Typically this is due to tire pressure. So on your first couple laps, pressures are low and the bite is high so you can move the tire. Our TransAm cars and ALMS car could move the front tires almost one full revolution and the rears almost 3/4 of the way around. Now the rear was generally on acceleration and the fronts moved under braking.
It would be hard, but not impossible to move the rears under braking.
Next time the tires are off the wheels, you probably need to blast the old rubber off the wheel, and you can do a few things. If there is a shop near by sometimes they can knurl the bead seats on the wheels, or have them blast the wheels there with a media blaster so they are not smooth. This can help as well.
It would be hard, but not impossible to move the rears under braking.
Next time the tires are off the wheels, you probably need to blast the old rubber off the wheel, and you can do a few things. If there is a shop near by sometimes they can knurl the bead seats on the wheels, or have them blast the wheels there with a media blaster so they are not smooth. This can help as well.
Thanks for the insight and suggestions. I hadn't thought about tire pressure.
Bill
07-10-2015, 03:26 PM
#69
Melting Slicks
In a 01+ C5 my experience has also been rear lockup tendency with the abs fuse pulled. I have setup 2 cars without ABS, my 99 C5 FRC and a 2002 C5Z. Both of them are using Wilwood rear proportioning valves to control rear line pressure. And on the 2002 we measured line pressures front and rear before and after making changes to see the effects. Both cars are dialed in without ABS now and brake great. My 99 has a switch on the dash that can activate or de-activate the abs fuse as desired. Thanks to Jeff Ritter and Joel for educating me last year on brake setup. This thread is also full of great info! 
07-10-2015, 03:31 PM
#70
Melting Slicks
Tires spinning on rims is quite common. Fronts usually spin slightly under braking and rears under acceleration. Having race tires mounted by a race shop or at the track will minimize or eliminate this compared to your typical neighborhood tire shop that soaps up the tire and rim to assist mounting.
07-10-2015, 03:55 PM
#71
Race Director
Tires spinning on rims is quite common. Fronts usually spin slightly under braking and rears under acceleration. Having race tires mounted by a race shop or at the track will minimize or eliminate this compared to your typical neighborhood tire shop that soaps up the tire and rim to assist mounting.
My Discount Tire shop uses "Euro Paste" which is like the "soap" you mention. Mine usually move from a couple of degrees to as much as 180 degrees the first event. Front more than rear. I may get them rebalanced and then they are pretty stable from there on. My guess is the paste gradually dries up.
07-10-2015, 04:14 PM
#72
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St. Jude Donor '03-'04-'05-'06-'07-'08-'09-'10-'11-'12-'13
Yeah...all of the race guys at the track side service typically use some sort of paste/grease/soap....so I don't think a 'race tire' place is going to be much different than the factory tire guys at the tracks with us at the Pro races.
That being said, most of the race wheels either use some sort of knurl/blasted finish/or different bead.
The BBS wheels have almost a 'grip' tape band around them.
Our new ZR7 wheels we are doing for the Corvette's have a blasted finish on the beads on those to help it to stick.
That being said, most of the race wheels either use some sort of knurl/blasted finish/or different bead.
The BBS wheels have almost a 'grip' tape band around them.
Our new ZR7 wheels we are doing for the Corvette's have a blasted finish on the beads on those to help it to stick.
07-10-2015, 04:16 PM
#74
Drifting
I plan on putting in the proportioning valve soon and trying to run the same compound all around (so I can be just like Bill!).
07-11-2015, 08:03 AM
#75
Burning Brakes
Here's a question for you. I have a 2002 Z06 which is a dedicated race car (NASA ST-2). I run Stoptech ST-60 front and ST-40 rear. I've never been happy with the long pedal from the stock master cylinder after the upgrade so recently I upgraded to a truck master cylinder with a 1 3/8 piston (stock is 1"). As expected the pedal is insanely hard and I'm still trying to decide if I want to keep it or not. I chose this MC because it was the same one used in the DRM unit. The only reason I didn't choose the DRM unit is because the include a proportioning valve under the hood. I intend to plumb a proportioning valve into the cockpit where I feel it's more useful. My question is this: given the fact that the Z06 has proportioning built in through the ABS unit, will the use of a separate proportioning valve BEFORE the ABS unit help pedal feel (softening it up a bit)? Do you even recommend it since there is dynamic proportioning built into the ABS unit?
07-11-2015, 04:57 PM
#77
Burning Brakes
Thanks Ben. I was trying to locate something around that size but gave up and went with the 1 3/8" unit (GMC 3500 HD application). On this unit I have in there now I had to cut off the tube nuts and install 1/2"-20 ones. Do you know what size threads yours uses? What are you running your car? Do you have a proportioning valve?
07-11-2015, 11:09 PM
#78
How can one find out the m/c bore sizes of various gm vehicles? I have been searching for a few years simply trying to find out the size of the stock m/c on my '99 C5 and this is the first time I have ever seen a size mentioned. Going up to a 1-1/16" or even 1-1/8" would make for a preferable pedal in my case.
07-12-2015, 12:44 AM
#79
Also, is it the case that some pads, like PFC01's, get abrasive if the rotor temp is not high enough?
I am running AP 355 J-Hooks up front with block-off (quantum) spindle ducts. The rotors are doing way better than anything I have had to date, but would not mind extending their life further if possible.
07-12-2015, 08:53 AM
#80
Safety Car
I searched parts catalogs (I think maybe the Dorman encyclopedia) to find something that would work. I don't think there is a 1 1/16" that will work but I could be wrong.
The 1 1/8" uses metric tube nuts, one size is shared with the C5 but it is for the wrong braking circuit. I think Hoses & Fittings, etc (they location I used is in California) could make a short adapter tube, or just make new ez bend hard lines with the proper ends.
On the 1 1/8 MC, I think you will also need to swap over the C5 reservoir (easy, just held in place by a pin).
The 1 1/8" uses metric tube nuts, one size is shared with the C5 but it is for the wrong braking circuit. I think Hoses & Fittings, etc (they location I used is in California) could make a short adapter tube, or just make new ez bend hard lines with the proper ends.
On the 1 1/8 MC, I think you will also need to swap over the C5 reservoir (easy, just held in place by a pin).