Pulling under emergency stop - my solution

[ursatz]

I thought I'd post this to let folks know how I fixed a problem with the brakes.

Under emergency stop condidtions - full stomp on the brakes, ABS pulsing - my car pulled horribly to the left and didn't really brake as fast as I needed. I drifted right through an intersection this way.

I thought a caliper needed work, but I belive the solution was to simply bleed and replace the brake fluid.

Here's my theory: There must have been just enough air (or contaminant or whatever) to not notice a problem under normal braking, but enough to be an issue when braking very hard. I'm guessing this caused one brake "circuit" to fail, and since they are DIAGONAL, the car pulled something fierce to the left.

Interestingly, the dummy lights didn't glow -- even more interestingly, they would very occasionally light in hot stop and go traffic, and nothing looked visually out of the norm under the hood. I know there are plenty of folks on this forum who have had this happen to them.

It's my hope that this post helps somebody, or better yet, helps avoid an accident - I got lucky!

[jetman]

As a matter of precaution, I do a quick bleed on my brakes whenever I do an oil change. I have found that our brakes are prone to sponginess and fade quite often without any real reason. I suspect that they heat up pretty bad as compared to other designs.

[RoccoH]

You should change brake fluid every year... (and that's a full bleed!)

Thank god we have stringent road worthiness requirements here... wouldn't want a car running me -or somebody else!- over like that when walking on the curbs.

do you KNOW your brakes work like they should, I mean: have you put your car on a roller brake tester?

[Rodentmaster]

It may be worth noting......


The brakes on the ABS equipped Classic 900's are not designed in the same brake line layout as the NON ABS.

The ABS system is what could be best described as a 'T' layout. That is, down stream from the valve body, the fronts are fed separately whereas the rear is fed a single hydraulic line and once at the rear axle, split between the two rears.

The four lines between master and valve body are simply front/rear pressure and returns, no left or right designation.
The ABS system is a 4 channel sense, 3 channel output design. The fronts are independant but the rears are monitored separately but acted on as one.

[RoccoH]

Rodentmaster is right..

[cdaly]

Also note that for bleeding, you need to run the ABS pump to bleed the rear brakes. Essentially you hook up your bleeder drain hose, switch on the ignition, open the bleed screw and press the brake pedal. Allow the pump to rest and cool for 10 minutes after 1 minute of operation...

[ursatz]

Well, the "T layout" sortof changes my theory a bit, but either way I'm happy to have fully functional brakes.

Bleeding the rears, following the Bentley was a fun experience.

[RoccoH]

Originally Posted by RoccoH

...do you KNOW your brakes work like they should, I mean: have you put your car on a roller brake tester?

.......... (why should I lengthen my message with at least 10 characters... )

[philb]

Originally Posted by ursatz

Well, the "T layout" sortof changes my theory a bit, but either way I'm happy to have fully functional brakes.

Bleeding the rears, following the Bentley was a fun experience.

Well, there could have been air in the line for the front left wheel. I think I had a similar problem. I had an abs problem, ( one of the cv joints had incorrect splines, so abs light and no abs ), and during an emergency stop, the car pulled horribly to the left. Now after sorting the abs, it doesn't pull quite so bad, even though I haven't bled the front. Really need to bleed the front.