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| damien89 | Brake fade is back with the warm summer temps! Got a question | ||
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Guru
 
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Hi guys, haven't posted in a while so here goes,
Yesterday gave the vette a bit of a run then came to an empty area and used the brakes a bit heavy for three times in succestion so that the abs pump would work a bit. After 2 mins of leaving the area driving at 30 mph the brake pedal almost sank all the way to the floor. If i pump it twice it comes back up but then goes down again if i push it after 5 seconds. Then after 5 miles the pedal started to get the normal feel again?! Just a recap this vette has had new front calipers, new master cylinder, new hawk pads and new fluid in the last 2 years and it has just done 1000miles approximattelly. One thing i noticed is while braking is that the vette dived a lot at the front, i know that their is a brake bias spring that i can change to change the bias. What i'm thinking is could the front brakes are getting hot because of the front bias issue? Secondly, the brake fluid it has is delphi lockheed dot4 which has a wet boiling point of 163oC, after doing some research yesterday i found that their brake fluids with a wet boiling point of 200oC + Should i start by changing the fluid to a better one or was it a case of me overcooking the brakes? |
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Posted on: 2012/6/11 6:59
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| BillH | Re: Brake fade is back with the warm summer temps! Got a question | ||
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The Stig Moderator
 
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3 hard stops won't boil the fluid. I dought it would even if you were slowing from 120 down to 5 mph.
Now, you could boil the fluid if the rear brakes aren't working correctly. The pedal going to the floor could be a couple things = Master Cyl. Booster - check it for any cracks and check all the vacuum connections. It's also possible that when you activated the ABS that you introcuced some pad "knock back", the caliper pistons got pushed back into the calipers a bit and needed those pumps to return to their normal position, wheel bearings with a bit of play can cause this too. (It's a common problem on C5's with hard braking). My 92 did this twice when I first bought it with the stock pads and it never did it again, supprising. Did you bed in the Hawks per their instructions? So, I'd check the Booster, check the wheel bearings. I'd also find a safe place and see if you can make this happen again. The bias spring - yea, the performance spring works well, BUT it's not the cure for your current situation. you have to find out if your current brakes are working correctly. The diving at the front may be more noticeable just because you put the Hawks on. It also may be worn out shocks. You can "bench test" the bias by putting the car on jackstands. have someone slowly depress the brake pedal (engine running) while you spin the front wheel. Keep turning the front wheel until your helper's pedal pressure makes it just stop (you can no longer spin it). Then go to the rear tire, it should be hard to spin but may turn a little bit. If it spins easier, there may be a problem there. It's best to lay on your back and pull down on the tires. Do it from the same position on the tire front & rear. If you change the fluid, I'd recommend Castrol LMA. It's on the shelf at the car parts stores, costs the same as the other fluids and has a 311 wet boil. I run it with my Hawks. Good luck. |
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Posted on: 2012/6/11 14:20
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| damien89 | Re: Brake fade is back with the warm summer temps! Got a question | ||
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Thanks for the response Bill,
I will try to answer your questions, If after 5 miles the brake pedal returned to its normal position/feel will it still be a booster issue/crack somewhere, or would it keep doing the symptom if it was the booster? As for the pads bedding i did a few stops from 60mph then let the brakes cool by driving and using the brakes as least as possible if i remember correctly. I have never checked the wheel bearings but i don't think that they have much play in them as the vette only has 20500miles. As for brake fluid i was thinking more like Motul rbf600 or Castrol react srf. The castrol lma is almost the same spec as the one i'm using in regards to the dry/wet boiling points. Could it be that because this vette sits in a garage most of the time in winter it absorbs moisture alot more then other cars which are used? As for the bias issue i have hawk hp on the front and the normal semi metallic pads on the rear, could this be another thing to cause this problem? Anyone have any other opinions? |
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Posted on: 2012/6/11 16:21
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| BillH | Re: Brake fade is back with the warm summer temps! Got a question | ||
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The Stig Moderator
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Quote: damien89 wrote: As for the pads bedding i did a few stops from 60mph then let the brakes cool by driving and using the brakes as least as possible if i remember correctly. That's probably not enough, you need to smell the pads and then let them cool. Bedding in the pads - 3 stops 30mph to 5 (do not totally stop the car), 5 stops 60 to 5 with medium pedal pressure, 2 stops from 80 to 5 with heavy pedal pressure. then stay off the brakes until you can park it. If the brakes are still hot, move the car 1 foot every minute 5 or 6 times (helps the rotors). |
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Posted on: 2012/6/11 16:34
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| damien89 | Re: Brake fade is back with the warm summer temps! Got a question | ||
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Quote:
Thanks for the quick reply will try ordering the pads and see how it goes. |
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Posted on: 2012/6/11 16:42
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| damien89 | Re: Brake fade is back with the warm summer temps! Got a question | ||
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I have a question, what difference does it make if the pad have been bedded in or not? Does it contribute to my problem?
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Posted on: 2012/6/13 4:31
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| bogus | Re: Brake fade is back with the warm summer temps! Got a question | ||
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Grand Imperial Pooh-Bah
 
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pad bedding will help with better force transfer and heat removal.
I am willing to bet you have a master cylinder failing. Check the area where the master meets the booster. if it's weeping, time for something new. |
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Posted on: 2012/6/13 4:45
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| damien89 | Re: Brake fade is back with the warm summer temps! Got a question | ||
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Quote:
Thanks bogus |
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Posted on: 2012/6/13 8:36
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| BillH | Re: Brake fade is back with the warm summer temps! Got a question | ||
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The Stig Moderator
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Quote:
Only the bias issue, NOT the low pedal. Most people incorrectly think that brake pads ride and clamp on the steel rotor. They do not, they clamp to an adherent layer of brake pad material deposited there by propper bedding. BTW, before you install the new rears, clean your discs. Use Scotchbrite abd lotsa brakeclean. The 2 inch pads and a drill work best but it can be done by hand. And it can be done with the discs on the car. |
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Posted on: 2012/6/13 13:09
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| damien89 | Re: Brake fade is back with the warm summer temps! Got a question | ||
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Quote:
Lets forget the bias issue for a moment, but i cant understand why the pedal almost went to the floor then after 5 miles it came back to normal, My intuition tells me that their is something related to heat, first thing that comes to mind is the brake fluid, because if it was the pads the pedal would remain firm but i would have no brakes, the last time my mechanic changed the fluid was by filling the reservoirs with then letting the fluid out of each wheel by gravity instead of removing the old fluid and filling the system and bleeding it. Could some of the old fluid remained in the system and affect the boiling point? |
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Posted on: 2012/6/13 16:14
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| BillH | Re: Brake fade is back with the warm summer temps! Got a question | ||
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The Stig Moderator
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Quote:
Not to the point that it would affect anything. However, after hearing about the rear pads, it's slightly possible that the lack of grip with those pads caused the fronts to overwork and boil the fluid. I've had this happen on racecars with 2 master cyls. where the rear bias was incorrectly adjusted and the fronts were doing all the work. This problem ia not due to underpreforming brake fluid. You still need to do all the checks on the m/c and booster. And you need to change the rear pads. Good Luck |
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Posted on: 2012/6/13 17:33
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