Jump to content

Brake issues...still


Recommended Posts

Alright, so here's the NEW brake setup on the corvette:

 

AP racing 4 piston rear calipers

AP racing 6 piston front calipers

Alcon individual master cylinders

 

Calipers are all matched to each other, master cylinders matched to caliper sizes (alcon did the math). I blew out all the lines prior to installing all the calipers.

 

SO, we went to TWS with the car this weekend. The brakes do work and the pedal does have modulation now, which is good. But the brakes don't work WELL. After two sessions of bedding in the pads, I really thought these brakes would be just crazy good. They feel like they're just sliding through the pad, as if they were fadded or over heated. Also, the resivoirs blow fluid out all over the damn place. So, SOMETHING is up. Also after the two sessions, the rear brakes are barely working, as the rotor is barely wiped clean.

 

So after all was said and done, we threw a rod clean through the side of the LS6 block, so our weekend ended short.

 

Here are my thoughts:

 

1st: I'm going to redo the brake lines on the car. Possibly something is kinked. I don't have any air in the lines, so nothing seems to be leaking.

 

2nd: I think that the pads that came with the calipers, suck.

 

3rd: The resivoir cap vents are not working, so the resivoir is building pressure and blowing crap everywhere.

 

What do you think? I'm really quite stumped again. The back brakes aren't doing anything IMO, so thats why the car won't stop. But why wouldn't they work? EVERYTHING IS 100% NEW.

Link to comment
Share on other sites

Man I'm sorry. What vette is this?

 

Other than pads I don't think we have had issues...

 

Keep thinking of things to add sorry... Are you running a bias?

 

See it happened again... I know he added ducts to help cool the brakes. Do you have ducts?

Link to comment
Share on other sites

Try softer pads. Sounds as if they are just too hard and all the heat they develop is going to the fluid rather than the rotors. When you boil the fluid it comes out the reservoirs.

If the backs aren't working at all the car will lock the fronts and pitch sideways very easily.

Don't know what else there is besides the kinked lines - but a kinked line would stop em from clamping at all. If they are clamping and still not making stop friction then I highly suspect the pads.

Link to comment
Share on other sites

Wilwood Calipers (like W6) , Wilwood Rotors and Wilwood Pads (Second to the most aggressive)

 

Says that on the vettes the front do most all the work. Have you tried putting it on the lift and run it a little then hit the brakes? He thinking they are grabbing but as you have stated on the course they arent grabbing like you'd like.

Link to comment
Share on other sites

Get a heat indicator paint kit. Apply all three colors to the rotor, the caliper and even the hub. without running your cooling fans, start with a 405 and change upward until you are in the middle of the heat range on the indicators. Once you have the base line of acceptable stopping power in mid temp range - run with the fans and increase the pads until you loose consistancy in release and feel, then back down one. AP pads are 405 being the softest and 401 being the hardest. The 405 starts dropping co-efficient drastically at about 550 degrees- the 401 noticeably at about 400deg. Big difference. Many folks over engineer and think if works on 5000 lb NASCAR - it must work even better on a 2800 hot rod. The hard pad may not even be reaching 400 degrees - but gets there too fast! Always start soft and go up from there - never hard and come down! I would rather use a soft pad and change them more often than use a hard one and have no brakes at 600deg.

 

Your fans are not to force the temp down during a braking event but rather just to speed up the cooling cycle between braking events. I have seen some folks use some sort of insulator pad between the pad and caliper to help reduce boil.

 

I always take what the driver says as the bottom line, but also have to back it up with something physics related. You yourself said it best - "They feel like they're just sliding through the pad, as if they were fadded or over heated." - theres the feeling... "Also, the resivoirs blow fluid out all over the damn place." - there's your physical indicator, the boiling fluid.

 

Brake fluid, no matter how we try to keep it uncontaminated will always draw some moisture as the vents allow it in with the air (I would imagine that with the humidity in Texas it would be worse than what we saw in So Cal desert), that moisture becomes steam as soon as the pedal is released - remember that just like on a radiator, pressure raises the boiling point. As soon as you come off the brakes the pressure is gone and the water molecules in the fluid at the caliper, explode into steam and your reservoirs puke like a sailor after too much rum.

Link to comment
Share on other sites

This is just a long shot but check all your "Flares". I've seen them distorted and block the opening at the fitting. They didnt leak but they restricted the flow. I've also seen bad fittings too. You might have some debris stuck in one too.

Link to comment
Share on other sites

one problem that is sometimes overlooked with corvette 4 piston calipers is that they can be installed upside down on some years, left caliper on the right, right caliper on the left, leaving your brake bleeders on the bottom of the caliper rather than the top creating an air pocket in the top cylinder. just something to check out.... make sure the bleeder is on top or they will never work right

Link to comment
Share on other sites

bishop,

 

That's great advice and thank you for the numbers. I think you're correct, the pads just aren't doing anything. I'm amazed that we could be overheating the fluid. The reservoir is mounted inside the cockpit, about two feet from the master cylinders. We're using the Castrol SRF brake fluid, which is pretty much the best money can buy. I personally think the caps aren't venting, which is why I'm blowing fluid everywhere. But the I believe the pads are my culprit for the non stopping issue.

 

4cylfordz - nothing on this car is stock, its all AP racing. But thanks for the info anyway, you're right, if those bleeders are upside down, nothing works.

Link to comment
Share on other sites

"I'm amazed that we could be overheating the fluid. The reservoir is mounted inside the cockpit, about two feet from the master cylinders."

 

From the Article Here:

"The pad material and rotor configuration must be compatible at operating temperatures. Rotors act like radiators when it comes to brake system heat absorption, so it is important to match rotor characteristics to friction material characteristics. For example, radically increasing rotor size might require a less aggressive, lower-temperature friction compound, because the huge rotors are so efficient in radiating heat that the original friction compound never reaches proper operating temperature.

 

Friction can be generated by forcing the brake pads mechanically against the spinning rotor (abrasive friction) as well as via the transferring of a thin layer of brake pad material to the rotor face as temperatures rise (adherent friction). Depending on the pad and rotor formulation, the resulting transfer layer can greatly improve overall µ. Race pads are often specifically designed to maximize the effects of this transfer film technology, generating higher friction and a lower wear rate. If your race pads are generating significant adherent friction, the rotors actually get thicker with use.

 

Most street pads can also establish a transfer layer, but to gain maximum benefit if changing pad compounds, first lightly burnish (or wear-mate) the rotors to wipe away the original (and likely incompatible) transfer layer. Drive your car around town at moderate speeds while braking moderately. Most manufacturers strongly caution against turning new or used rotors in a brake lathe-it does more harm than good."

 

From this - if your transfer layer is acting as an insulator - the only place the heat has to go is straight thru the pad, plunger and to the fluid. It does not matter where the reservoir is (as long as it's higher than the M\C). Also I have found that 75-80% is good on the res - doesn't need topped off.

Link to comment
Share on other sites

This is a matched set from AP correct? I know on the z06 it is a matched Wilwood set. I think they called and said here is the race application. What do we need and $xxxx.xx later they were on...

 

Man, what an issue. Have you tried a basic flow test to determine volume of fluid released? If you know all the air is out you should be able to open the fitting (I would use a bigger syringe to bleed the hose into) empty it each time and write down the volume. Your fronts should be close and your backs should be close. You said pressures are good so this will answer whether you are moving fluid or not...

Link to comment
Share on other sites

I was just thinking. Do you have room for a screw on inline type regulator? I know many people use them as a poormans bias. I have seen them room on the front only. Maybe you could use one for the front in addition to existing front/back bias?

 

Also, have you tried blowwing out the lines? I'll go back and re-read but I don't remember seing where you said you did?

 

Mark

Link to comment
Share on other sites

I was just thinking. Do you have room for a screw on inline type regulator? I know many people use them as a poormans bias. I have seen them room on the front only. Maybe you could use one for the front in addition to existing front/back bias?

 

Also, have you tried blowwing out the lines? I'll go back and re-read but I don't remember seing where you said you did?

 

Mark

 

Mark,

 

Yeah, I blew out the lines before we put on the new master cylinders. I had another racer call me yesterday and tell me something I though was smart. He asked if my pads were on the rotor (which, they are within 1/16-1/32nd of an inch). He said they had encountered a problem in the past from the rotor shaking/vibrating/expanding while going down the speedway straights, causing just enough friction to heat the pads and boil the fluid. Once they got on the brakes hard, the fluid was already too hot. I thought that made perfect sense. Additionally, I think the pads should have more room, not only for drag purposes, but also so they can build some pressure and volume prior to hitting the rotor. So perhaps I just need to mill my pads down some???

 

Thoughts?

Link to comment
Share on other sites

1/16 - 1/32 is ideal - as long as you have it on BOTH sides.

Milling the pads will increase the amount of fluid in the caliper at rest - more fluid takes longer to boil, so in that aspect it makes sense. As far as building volume before hitting the rotor - that would only apply to the first time you step on the pedal as in pump in or bleeding. After that they will only relax to a slight drag (would be nice if there WAS some sort of return spring - but that would defeat constant self adjustment). You should have almost a 1/4 inch clearance (or more with used pads) when the caliper plunger is pressed all the way back.

In fact a mech that I used to work with forgot to pump in (or even bleed) the brakes on a 78 vette after a wheel bearing job - he popped the gas to back out of the shop and when he came down on the pedal it went all the way to the floor with no effect. He paniced and missed the emer brake and stopped about three inches into the side of another customer's camaro costing over 7500 in damage. It took two more pumps before the pads hit rotor.

Make sure the calipers are centered - as in not rubbing on the fluid side for one sided hydraulics! To accomplish this you can shim the caliper, the caliper mounting bracket or in extreme cases (like when something - spindle or wheel etc - prevents you from being in center (not recommended - but then neither are the abuses of racing).

 

You are running vented rotors and not solids - right?

Link to comment
Share on other sites

I was just thinking. Do you have room for a screw on inline type regulator? I know many people use them as a poormans bias. I have seen them room on the front only. Maybe you could use one for the front in addition to existing front/back bias?

 

Also, have you tried blowwing out the lines? I'll go back and re-read but I don't remember seing where you said you did?

 

Mark

 

Mark,

 

Yeah, I blew out the lines before we put on the new master cylinders. I had another racer call me yesterday and tell me something I though was smart. He asked if my pads were on the rotor (which, they are within 1/16-1/32nd of an inch). He said they had encountered a problem in the past from the rotor shaking/vibrating/expanding while going down the speedway straights, causing just enough friction to heat the pads and boil the fluid. Once they got on the brakes hard, the fluid was already too hot. I thought that made perfect sense. Additionally, I think the pads should have more room, not only for drag purposes, but also so they can build some pressure and volume prior to hitting the rotor. So perhaps I just need to mill my pads down some???

 

Thoughts?

 

Here is something else I just thought of along those lines. I had an issue on my Pro Truck where the face of the axle(flat surface) where the back of the rotor hit was bent from contact. As the rotor went around you could see the caliper move(from rotor hitting pads). (It was extremely noticeable.) Have you verified the shafts to be true? Would cause same affect as you discribed.

 

Also, Mr. Bishop is dead on when he mentions centering. We always forget those basics and that is a good place to look... (Nick I need a thumbs up iconic) post-1147-1272930863.gif

Link to comment
Share on other sites

  • 2 months later...

Good Lord, it was the brake lines...UGH. We were using the stock lines, but flared into "T" joints, then run to a single master cylinder. The M/C couldn't supply the volume and pressure for both lines running to the rear and the two large lines running to the front. Now that I have one line to the rear with a split and one line to the front with a split, they seem to be working... But only around here at the shop. TWS this weekend.

 

Fingers crossed.

Link to comment
Share on other sites

They started out pretty lame, but were getting better. I think we were sent some street pads (we just used what we were sent from stillen). Then 8 minutes into our FIRST practice, our brand new GM performance parts LS6 blew up.

 

I'm getting tired of this.

 

When you have a chance PM me this week. I will get you a couple of numbers. You may already have one as he does some of the NASA stuff. The other number will be for the guy who crewchiefs the car.

 

Anyways, sorry to hear the news.

 

Mark

Link to comment
Share on other sites

Yeah, we were bummed. This guy just has the worst luck, I swear. That engine should have gone for 1 1/2 seasons, easy. Its was a BONE STOCK, GM built motor. I'm anxious to pull it apart and see what let go. It should be warrantied, which is good. I'm just worn out with the car, it seems like we show up to the track with a 100% clean, prepped, well built race car and within an hour, its disintegrating.

Link to comment
Share on other sites

I just came across this thread or I would have replied eariler, but the issues your talking about with the brakes really sound as if you have a master that has too small a bore. A car that uses very little rear brake will still stop badly if it has almost no rear brake. Working with formula cars we where amazed at how often the manufacturers math was wrong. As far as the LS6 blowing up again, gotta love that union labor!

Link to comment
Share on other sites

Archived

This topic is now archived and is closed to further replies.

×
×
  • Create New...