Weird Brake Problem
04-15-2012, 02:49 AM
#1
Burning Brakes
Thread Starter
Weird Brake Problem
Car is an '89 S4 5 speed.
At our autocross today, as I was pulling up to the grid for my next to last run, it felt like the brakes were applying them selves - felt kinda like the e-brake on. Stepped on the pedal and it felt a bit low, but returned to normal on the second pump.
We had a high speed slalom with heavy braking as we turned into a skidpad type section. As I exited the slalom and nailed the brakes to slow for the turn in to the skid pad, the pedal went to the floor! I threw it sideways and slid to a stop, killing many cones.
As I crept back to the start/finish, the brakes seemed to return to normal. The drive home from our autocross site (about 20 miles) was uneventful and the brakes seemed to function as normal.
I don't know if it's related, but about two weeks ago I came out to find a puddle of brake fluid under the car. It was wet and appeared to have leaked from the grommets where the reservoir plugs into the M/C . I sprayed everything off with brakeclean and ordered new grommets. The car, however, has not leaked another drop - even though I never installed the new grommets.
The level has stayed constant at about a quarter inch below the max mark.
This was only the second that time I've autocrossed this car. The first time (last season) after my last run I noticed that there were a few droplets of brake fluid on top of the fender which had, apparently, been blown through the vents in the reservoir cap. I managed to clean it off before it cased any serious harm.
So, what do you guys think? The sensation that the brakes were applying themselves makes me think power booster - or is it the M/C? Judging from the under- hood condition, this car seems to have a history of blowing brake fluid or brake fluid vapor through the vents in the reservoir cap.
James
At our autocross today, as I was pulling up to the grid for my next to last run, it felt like the brakes were applying them selves - felt kinda like the e-brake on. Stepped on the pedal and it felt a bit low, but returned to normal on the second pump.
We had a high speed slalom with heavy braking as we turned into a skidpad type section. As I exited the slalom and nailed the brakes to slow for the turn in to the skid pad, the pedal went to the floor! I threw it sideways and slid to a stop, killing many cones.
As I crept back to the start/finish, the brakes seemed to return to normal. The drive home from our autocross site (about 20 miles) was uneventful and the brakes seemed to function as normal.
I don't know if it's related, but about two weeks ago I came out to find a puddle of brake fluid under the car. It was wet and appeared to have leaked from the grommets where the reservoir plugs into the M/C . I sprayed everything off with brakeclean and ordered new grommets. The car, however, has not leaked another drop - even though I never installed the new grommets.
The level has stayed constant at about a quarter inch below the max mark.
This was only the second that time I've autocrossed this car. The first time (last season) after my last run I noticed that there were a few droplets of brake fluid on top of the fender which had, apparently, been blown through the vents in the reservoir cap. I managed to clean it off before it cased any serious harm.
So, what do you guys think? The sensation that the brakes were applying themselves makes me think power booster - or is it the M/C? Judging from the under- hood condition, this car seems to have a history of blowing brake fluid or brake fluid vapor through the vents in the reservoir cap.
James
04-15-2012, 09:23 AM
#2
Nordschleife Master
From your description I suspect "brake fade" where the fluid, or water in the fluid, boils. This could be caused by a dragging caliper. Maybe you've a few problems in there.
The first thing to do is jack each corner and see if the brakes are dragging.
The second thing is to flush the brake system and put in a DOT4 grade brake fluid. Like many tracksters I use the ATE blue and gold brake fluids; alternating colors to see flushing results. That might be enough.
The first thing to do is jack each corner and see if the brakes are dragging.
The second thing is to flush the brake system and put in a DOT4 grade brake fluid. Like many tracksters I use the ATE blue and gold brake fluids; alternating colors to see flushing results. That might be enough.
04-15-2012, 10:01 AM
#3
Pro
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Personally I would replace the MC as well as the 4 flex lines going from frame to calipers and then completely flush all lines replacing with Dot 4 per GlenL's recommendation. Pedal all the way to the floor is symptomatic of MC failure, no matter how it got there. It could be caused by boiling fluid but that is not so likely since you have other symptoms like a puddle under the car....when parked....
04-15-2012, 01:15 PM
#4
Team Owner
replace the MC ,
use ATE super blue racing fluid .
The MC is rusted where the grommets for the tank sit,
and thus will never seal properly even if new grommets are fitted.
. If your DE or racing a new MC should be one of the first things thats installed .
use ATE super blue racing fluid .
The MC is rusted where the grommets for the tank sit,
and thus will never seal properly even if new grommets are fitted.
. If your DE or racing a new MC should be one of the first things thats installed .
04-15-2012, 01:55 PM
#5
Rennlist Member
Sounds a lot like mine, the brake would start dragging and then let go and be fine for a while, very unpredictable.. It was the MC. No problems since replacing it.