ABS rear brake circuit lockout

alicrozier · Post by **alicrozier** » Thu Aug 03, 2006 1:28 pm

Anyone experienced the rear brake circuit lockout on the ABS? I managed to activate it in the wet at Spa (braking for the Bus Stop).

The explanation from Lotus (I have a letter) is that in extreme circumstances of weight transfer the system activates a solenoid valve which locks out the rear system leaving you with just front brakes.

The symptoms I experienced are the pedal going solid (caused I guess buy the reduced volume and short lines to the front) and reduced braking for a given force.

(also asked on SELCOK and Exiges.com)
http://forums.seloc.org/viewthread.php? ... pid2297341

Rich H · Post by **Rich H** » Thu Aug 03, 2006 1:38 pm

Why would you want to loose control of braking at the rear and shunt all the power to the front reducing sensitivity?

Did it go suddenly or was it progressive?

Rich

alicrozier · Post by **alicrozier** » Thu Aug 03, 2006 2:00 pm

RICHARDHUMBLE wrote:Why would you want to loose control of braking at the rear and shunt all the power to the front reducing sensitivity?

Did it go suddenly or was it progressive?

Rich

I believe as a nanny measure to prevent too much rear braking and instability.

Kicked in suddenly as in 'click'

....

Rich H · Post by **Rich H** » Thu Aug 03, 2006 2:10 pm

Nanny measure on a lightweight semi-race car that upsets braking at critical moments?

Good idea

NOT!

Andy G · Post by **Andy G** » Thu Aug 03, 2006 2:21 pm

thats a truely "special" system!

FFS

robin · Post by **robin** » Sat Aug 05, 2006 12:28 pm

RICHARDHUMBLE wrote:Nanny measure on a lightweight semi-race car that upsets braking at critical moments?

Good idea

NOT!

Well the theory is relatively simple - when cornering you don't generally pull on the handbrake - why? Because applying the rear brakes to the point of blocking causes the car to swap ends.

Now the ABS can sort this out for you, but usually only once the car is destabalised. When there is no weight over the rear wheels, the amount of effective braking they can do is naff all, and so the ECU will turn them off speculatively during the moment of high weight transfer to prevent you getting into trouble in the first place.

Ali - ask them for a test that will demonstrate this function at relatively low speeds so we can be sure the system engages and then check the pedal feel. If it's the same, fair enough. If it isn't then they can go back and look for other problems (or tell us that we're not trying hard enough, again).

Cheers,
Robin