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Brakes - Rear working then not working


texana55

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We put rear disc brakes on Lauren's car. In the heat, she was doing fine, and then just after the half way point in the race she suddenly developed a terrible push coming into turn 1&2. I didn't think thre same was happening in 3&4. She drives with 2 feet, so I figured maybe she was just riding the brake some and jabing it too hard coming into the turn. I could see the wheels cut left and the car going straight up the track. I figured since it was dry slick she was locking it up. So, that was the heat.

 

Feature started out, the car was fine, turning well, staying up with the pack, etc, etc. Somewhere near the last few laps of the feature there was a caution. Right after that caution, here comes the same problem instantly. She went into the turn, the wheels are cut to the left and straight she goes.

So, i decided it wasn't her I don't think. I think for some reason the back brakes instantly quit working and that is the push.

 

So, my question is has anyone ever seen this. Could there be some small debris in the system and it instantly voids the back brakes from getting pressure. this was just very weird the way it happened. It's Sunday morning and I haven't gone outside yet, but will be checking the rear reservoir real well to see if anything is maybe floating in there, but I really doubt it since it was new and clean.

 

Would appreciate any ideas.

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Maybe too much rear brake. If using stock master cylinder it has a built in residual valve for rear drum brakes and it may not be releasing enough. been there and had similar problem

 

if it was too much rear brake and we're on dirt, wouldn't that normally cause it to want to get real loose coming into the turn, like when cars have bias and they adjust it for more rear brake, doesn't that loosen it up and want to bring the back around quicker? We can't run any adjustment so it is a stock aproach to equal pressure coming out. But, real puzzled...

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Was she running the car faster the 2nd half of the race? Did she tell you if she was using the brakes alot throughout the race? Obviously alot of cautions in the race so it should have been fairly cool. What kind of pedal soft, hard, etc. As much info as possible even if it sounds not needed.

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its tough to tell with kids...I know...the information i get back is usually not helpfull...lol Here is what I would ask...she might be able to tell you if the car was acting like it was not slowing as much...but...think about this...even with no brakes...the car should have still turned...she might have had to let off a little sooner....but I know from experiance...if I lose confidence in the car..I start messing up...so if she went in one time to hard and pushed...from that lap on... she might have been thinking...the car is messing up...all the while it could have been her....these kind of problems are tough...lol I cant think of any issue that would make the rear stop working instantly...then work again. and on what 01 said...I am pretty sure he meant that if the residual valve was holding pressure on the disks then the brakes would have gotton hot and faded. SO..I would look at both...car and driver...lol good luck....but..for the record...She is doing amazing....she really does have talent...just tell her she has to be flexible....sometimes she has to do the work too...the car cant do it all...if she has to drive without depending on the brakes...she can...(as long as it will still stop for a wreck..lol) But..I also think..if its not fun stop...(even though i dont) its not fun driving a car you dont trust...so she probably did the right thing....JMO AJ

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This sounds alot like what we faught at edna running super stock. As the race went on our rear breaks would actually lock down the rear calipers. The rotors would start glowing then car would tighten up then start pushing. Pissing me off because we were already at a disadvantage running out of class. After several things we found the stock rubber Y connector on top of the rearend was bad. It never leaked fluid but it did push air thus not retracting the pads. Alot of people reuse this part and tie in the new lines to it. Try changing that as well.

Edited by Danielsen Motorsports
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Sorry, I was away from the forums a few days on business trip. Thanks all for the input / help. I am going to take the car to practice on Sunday and see if I can repeat any of the problems with the old man in the car. AJ, I truly appreciate your words. I think you also hit a key point that I will have to work with her on understanding when the car starts doing something different, as the driver, she may have to do something different also to make it react differently.

 

I think in that feature if she would have stuck it out she may have gotten something back out o fit. But, we had talked before the start and I told her if the car became a problem where she felt she was a danger to others it was ok to get off the track and salvage others cars as well as ours. It was disappointing as she had been working her way up, and it was near the end. I think in the future, I will tell her to just drop back, play with the car on some different techniques and salvage a finish. You are so right AJ on being able to communicate with the young drivers as to how difficult that is. I guess it is just the learning process we go thru together. Still having lots of fun each night and building on that bond....

 

Thanks again, everyone!!

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CHECK TO MAKE SURE THE ROTORS ARE NOT PUSHING HTE CALIPERS IN U WILL HAVE GOOD PEDAL SITTING BUT AS SOON AS U ROLL OR PICKUP SPEED IT WILL PUSH IN THE CALIPER AND U HAVE TO MAKE UP THE FLUID THAT HAS BEEN PUSHED INTO THE RESEVOIR KINDA LIKE WHEN U PUT PADS ON JUST A THOUGHT

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  • 3 weeks later...

Dunno if this helps or not but check anything rubber @ the y on the year end and see if it collapses. I have heard before of one brake of one wheel at a time having the collapsing problem with rubber lines even on steel braided lines... This may be totally different but ya never know... Only way I know to check is have someone pumpup the breaks and see if the line swells which would mean the line is soft and prone to collapse... Just something to check... I have heard of guys switching to all steel line throughout the system to prevent this from happening... Hope that helps...

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