Dangerous - abs activates upon hitting bump right before turn
03-25-2019, 07:35 PM
#1
Race Director
Thread Starter
Dangerous - abs activates upon hitting bump right before turn
Want to see if anyone else has ran into this.
on my 93, i was slowing down for a 270 deg downhill highway on ramp.
right before the ramp was a bump. When i hit bump abs activated making brakes useless for a second before the 270 deg turn
is this normal?
on my 93, i was slowing down for a 270 deg downhill highway on ramp.
right before the ramp was a bump. When i hit bump abs activated making brakes useless for a second before the 270 deg turn
is this normal?
03-25-2019, 07:38 PM
#2
Team Owner
Pro Mechanic
If your wheel left the asphalt for a split second...which it obviously did, then yeah, it's normal. The brakes weren't useless...but their effectiveness at that moment (at least for that one or two tires) was reduced.
How's your shocks? And tire pressure?
How's your shocks? And tire pressure?
03-25-2019, 07:53 PM
#3
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Yes this is normal and in fact is described by Dave McLellan in Corvette From The Inside. When they were developing ABS for the C4 there was initially a 1-second lag before the abs system would allow the brakes to be reapplied. This was put in the system to overcome issues when the left side of the car was on a different type of road surface than the right side (think ice patch). However during testing it was discovered that if the brakes were applied and then the car hit a bump and went airborne the ABS system would prevent the brakes from being reapplied for that full second. He says that Bosch was able to reduce the lag to a half-second which must seem like a long time when you hit a bump at say 100mph.
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RtStuf (03-26-2019)
03-25-2019, 10:35 PM
#4
Race Director
Thread Starter
Yes this is normal and in fact is described by Dave McLellan in Corvette From The Inside. When they were developing ABS for the C4 there was initially a 1-second lag before the abs system would allow the brakes to be reapplied. This was put in the system to overcome issues when the left side of the car was on a different type of road surface than the right side (think ice patch). However during testing it was discovered that if the brakes were applied and then the car hit a bump and went airborne the ABS system would prevent the brakes from being reapplied for that full second. He says that Bosch was able to reduce the lag to a half-second which must seem like a long time when you hit a bump at say 100mph.
i seem to remember hearing the abs/asr systems were optimized again in the 95 and up model year
03-25-2019, 10:37 PM
#5
Race Director
Thread Starter
bilstein z51 shocks (installed in 2002 so perhaps they are old?)
stock vert front springs
stiffer z07 rear spring
del alium control arm bushings
z07 front sway bar with heim end links
banski rear end heim joint suspension
Last edited by dizwiz24; 03-25-2019 at 10:38 PM.
03-25-2019, 10:46 PM
#6
Team Owner
Pro Mechanic
34 lbs is way too high, IMO. The 'Vette isn't heavy and has a big (wide) tire. Don't need a lot of pressure.
03-26-2019, 08:02 PM
#7
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I did go back and look but the book does not give any definitive answer as to when the 1/2 second lag went into effect. It indicates that it took in excess of a year as Bosch needed to go through a winter cycle with their testing.
Black Book indicated that 86 was the 1st year for the Bosch ABS system so perhaps 87 or 88.
The only other thing I find in the Black Book is mention that 1990 had "improved ABS and Yaw control" so perhaps it was not until 1990.
ASR first became standard in 1992 this was also a Bosch system that does interact with the brake system.
The next mention isn't until 1995 when it indicates that all 95 vettes Except ZR1 came standard with the latest ABS/ASR-5 while the ZR1 retained the ABS/ ASR-2S.
03-26-2019, 08:25 PM
#8
Safety Car
Personally I think 32-34 lbs should be in the ballpark but you need to confirm it's right for your car.
Hope that helps.
03-26-2019, 09:06 PM
#9
Race Director
Thread Starter
I did go back and look but the book does not give any definitive answer as to when the 1/2 second lag went into effect. It indicates that it took in excess of a year as Bosch needed to go through a winter cycle with their testing.
Black Book indicated that 86 was the 1st year for the Bosch ABS system so perhaps 87 or 88.
The only other thing I find in the Black Book is mention that 1990 had "improved ABS and Yaw control" so perhaps it was not until 1990.
ASR first became standard in 1992 this was also a Bosch system that does interact with the brake system.
The next mention isn't until 1995 when it indicates that all 95 vettes Except ZR1 came standard with the latest ABS/ASR-5 while the ZR1 retained the ABS/ ASR-2S.
Black Book indicated that 86 was the 1st year for the Bosch ABS system so perhaps 87 or 88.
The only other thing I find in the Black Book is mention that 1990 had "improved ABS and Yaw control" so perhaps it was not until 1990.
ASR first became standard in 1992 this was also a Bosch system that does interact with the brake system.
The next mention isn't until 1995 when it indicates that all 95 vettes Except ZR1 came standard with the latest ABS/ASR-5 while the ZR1 retained the ABS/ ASR-2S.
didnt know whether itd be worth it or pita.
also dont know if intertwined with 93 ecm - at that point if i need new ecm itd be too much of a pita
03-28-2019, 11:19 AM
#11
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So very true. For normal street driving, about 30psi (cold) is about ideal. Go any higher and you being to lose traction earlier. I've experienced this myself, with near disastrous results.