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914World.com _ 914World Garage _ Brake Fade?

Posted by: Trevorg7 Aug 5 2005, 09:13 AM

Nothing like your brake peddle hitting the floor while exiting the freeway at 65 to get your heart started in the morning.

So, north bound 280 exiting to 92 and my brake peddle hits the floor !

I manage not to hit anyone and coast to a surface street. After limping down the street a bit, 10 mins, the brake peddle came back and I was able to stop again.

Was this brake fade? Seems unsafe to drive home but????

I've done all brakes in the past three months and bleed the brakes. Could it have been just a bubble I missed or pure brake fade?

Thoughts?

Thanks

T

Posted by: VegasRacer Aug 5 2005, 09:20 AM

'Brake Fade' occurs from heat buildup due to repeated or prolonged brake application. If your brakes were just suddenly gone for some other reason, you have a different serious problem that needs to be addressed.

Posted by: Trevorg7 Aug 5 2005, 09:28 AM

Good point. I was a freeway speed for 30 mins with minimal or no braking.

Further analysis; no obvious leaks and the brake fluid reservoir is at the same level it was two weeks ago.

T

Posted by: Mueller Aug 5 2005, 09:28 AM

bad mastercylinder??

any leaks @ the fittings?

I had a line come loose on my car once...luckly I was just driving down my street..

Posted by: goose2 Aug 5 2005, 09:35 AM

sounds like a master cylinder problem to me

Posted by: mihai914 Aug 5 2005, 09:36 AM

Also add a sticking piston or rear brake pads too tight.

Posted by: Trevorg7 Aug 5 2005, 09:43 AM

Great feedback guys....so.....questions...

would a bad mastercylinder 'fade' but come back and work functionally; again, no leaks present?

If a caliper was dragging, it would cause excesive heat therefore fadding, true?

T

Posted by: seanery Aug 5 2005, 09:47 AM

a dragging caliper would most likely cause a pulling feeling, too

Posted by: Porsche Rescue Aug 5 2005, 10:11 AM

I don't think "fade" applies at all to your experience. The pedal does not go to the floor with fade. It simply requires more pedal pressure while achieving less braking. Since you did not overheat the system you can also eliminate "boiling" the fluid as the cause. You lost hydraulic pressure for some reason. Chase down the problem before doing any more driving. Next time could have a different ending.

Posted by: goose2 Aug 5 2005, 10:12 AM

If a piston is sticking, you will feel it when coasting to a stop...will feel like you are applying the brakes (which you are, in effect). This could cause heat build up and fade, but only on that caliper...unless it gets hot enough to boil the fluid. Feel the wheel hubs after a drive and see if any are heating up...another telltale for sticking calipers. If a master cylinder seal is giving up, it CAN allow the pedal to go to the floor by letting the fluid bypass the seal without an external leak. This is kinda rare, but I've seen it happen. I'd check everything (look under the carpet by the M/C for wet spots) , rebleed the system, make sure my insurance was paid up, and try again.

Jim's right about "fade"....wrong symptoms.

Posted by: bondo Aug 5 2005, 10:22 AM

I'd say if you can't find anything wrong, replace the master cylinder anyways. If it happens again before you get to that, try pumping the pedal. It may give you some braking back.

Posted by: ArtechnikA Aug 5 2005, 10:31 AM

QUOTE (Trevorg7 @ Aug 5 2005, 11:43 AM)
would a bad mastercylinder 'fade' but come back and work functionally; again, no leaks present?

yes.

usually right before it 'fades' once and for all.

corrosion deep in the bore can lead to roughness that chews up the piston seals. most of the time (until ultimate failure) they'll work okay. now and then a corocion crater may line up with a bit of chewed seal and you get an internal leak. no fluid leaves the MC, but neither did any get pressurised.

there have been about a billion and six discussions about whether you should use a 17mm or 19mm MC; a search will turn up many discussions, all of which turn out the same way. (i.e. - pick one)

i wouldn't wait long on this. this weekend is not too soon. get at least 2 quarts of whatever brake fluid you want to run - Ate Gold or Super Blue is a safe choice, or Valvoline SynPower, for instance.

Posted by: ! Aug 5 2005, 10:38 AM

Most likely the MC, also I would consider that in conjunction with contaminated fluid. When was the last time THAT was changed, Hmmmm? Water entrained in the old nasty crappy fluid that hasn't been changed since the Nixon administration will corrode a cylinder.....

Another item....the pedal board...got one? Sometimes people leave those out and the brake pedal will bottom out due to "fade" or when bleeding brakes or from a leak will cause the piston to bottom out/go past the point of design....not gud.

Brakes....they do a body GUD....

Posted by: URY914 Aug 5 2005, 10:39 AM

BTW, a MC change is a PITA.

P

Posted by: Dr. Roger Aug 5 2005, 10:41 AM

You did not mention weather nor not you could recover some pedal when pumping it.

Also you did not mention if you reset rear caliper pad clearance.

Also you didn't mention if you bled your proportioning valve.

Is the master cylinder mounting points rusted?

All of these can give the results you experienced.

Best regards,
Official member of "914club Brain Trust".

Posted by: trekkor Aug 5 2005, 10:43 AM

I had true brake fade at Streets of Willow during our WCC track day.

Conditions: Fast driving ( 65-100 mph ) and HARD braking every 10-20 seconds for 10-12 minutes straight.

Add to this older stock brake pads and very old, water contaminated brake fluid.

The older pads means harder, longer brake application. More heat.
When the calipers get boiling hot after about 9 minutes the water in the brake fluid starts to boil and vaporize creating bubbles ( liquid turning into a gas ) in the system.

The pedal gets softer and softer until you have no brakes. Not fun.

As soon as I detected ANY loss of braking power, I went back to the pits, right away.

Bleeding the brakes ( purging the air out of the calipers ) gives you brakes, but only until they heat up again.

A few of us experienced this.

Solution is to flush the old fluid out at regular intervals, not waiting for symtoms of fade.
My SS lines and race pads didn't hurt either.

KT

Posted by: Rough_Rider Aug 5 2005, 10:46 AM

Check your lug nust, Seriously....
If any are loose the rotor can wobble ever so slightly. This backs the pistons into their bores. Pumping the pedal brings them back into place.

Also check your rotors for warpage, this causes the same effect.

Posted by: Trevorg7 Aug 5 2005, 12:16 PM

Thank you all for the info.

To answer more questions; pumping did not bring them back right away. fluid changed < 6 months ago. As the brakes 'came back' pumping did help. Not too sure on the rest of the stuff.

I'm at my office in San Mateo; shop recomendations? as I dont feel good about the 40 mile drive home in the current situation.

HPH is 5 miles away. Are there others?

T

Posted by: Travis Neff Aug 5 2005, 01:29 PM

I had a sticky front caliper and there was just the slightest pull when driving straight, as the car was driven longer the pads in contact with the rotors got hotter and hotter. A few slow stops (street light to street light) you could feel the pedal get lower and lower - like one or maybe two applications - then nothing. It only pulled right before it all gave way under braking.

It may be a MC or a leak, but it could be like you describe as a dragging caliper. Easy check is to put your hand over each wheel, if you have a draggin caliper(s) that wheel will be freaking hot.

Posted by: trekkor Aug 5 2005, 01:37 PM

HPH is where many of us take our cars if we do not have time to/ want to/ know how to, do it ourselves.

Rich has worked on literally 1000's of 914's for over 30 years...Where else will you find that kind of experience?

KT

Posted by: Dave_Darling Aug 5 2005, 04:07 PM

QUOTE (Porsche Rescue @ Aug 5 2005, 08:11 AM)
The pedal does not go to the floor with fade. It simply requires more pedal pressure while achieving less braking.

There are actuall two kinds of phenomenon that get called "brake fade". The kind you describe here is "pad fade", where the pads simply get too hot to grab the rotor. The pedal stays nice and firm, but the car does not slow at all.

The second kind is "pedal fade"--and that generally happens when you boil the brake fluid. The brakes get more and more soggy, until the pedal just goes straight to the floor and you don't slow down at all.

You can make the second come back by pumping the pedal. Not so the first kind.

I agree that this occurrence isn't one of those.

--DD

Posted by: Trevorg7 Aug 5 2005, 05:42 PM

Thanks again for all the advice.

I've 'paid' Rich at HPH a visting and we believe the cluprit is the left rear caliper. Need new roaters in the rear too.

~$1k for one new caliper, two roaters, pads, DOT steel brake lines, fluids/flush. Seems like a lot but it is what it is.

T

Posted by: ! Aug 5 2005, 05:53 PM

Ouch.....I have a set of rear calipers....early ones... and some rotors if you wanna tow it home and fix it yerself...

Posted by: trekkor Aug 5 2005, 07:03 PM

When you factor in cost of parts, and labor not to mention actually making a profit as a business, it sounds like about 4-5 hours shop time to me.

You could rebuild the caliper yourself and buy all the parts.
Question is: how long will it take you and are you able to do the work yourself/ have the space/ have the tools?

Just asking...

KT

Posted by: Trevorg7 Aug 9 2005, 10:14 AM

I got my car back today. Please do not mistake my 'paid' comment as a condemnation of HPH; $1500 bills are always a shock unless, of course, that was my mortgage payment then I would be happy...I digress. In the short amount of time I've worked with HPH Rich has been great.

So the culprit was a sticking left rear caliper. The cause was the emergency brake and the caliper fried, warped the pads and boiled the fluid.

New caliper, roaters, DOT steel braided brake lines...other misc brake parts, and some other maintenance work to replace a transmission seal and I'm on the road.

Thanks

T