top

Brake Fade or something else

Post new topic Reply to topic trackscotland.co.uk Forum Index | Technical Goto page 1, 2, 3, 4  Next   Page 1 of 4

Thu Apr 07, 2016 9:38 am PostPost subject: Brake Fade or something else
AK
Site Admin


Joined: 27 Nov 2006
Posts: 20094
Location: Aberdeen

Reply with quote

update...

with the rears checked and tested last weekend I'm now almost positive that my braking issues are just upfront.

Over time they just get worse... and the rears remain as efficient.

Qualy - great
race 1 - starting to get worse
race 2 - crap, but still good enough.... just have to press like a hero.

A bleed normally sorts it out... so to me at least... this means there is either air getting in (fluid bled doesnt suggest air), or the fluid is getting too hot. Sadly I didnt have time to bleed between R1 and R2 :/

Fluid - RBF660
lines - all braided
pads - Carbotech XP12

I need to get some temp paint for the caliper and discs as I'm sure my braking isnt getting them to > than RBF660 temps. Fee's car has a mirror setup, and no issues. I know I brake with more vigour than Fee, but its for shorter spells.

MS - replaced
booster - replaced
one way valve - replaced
calipers/discs - replaced for larger

Tangents - there are no signs of oil/grease on the inside of the caliper or wheel, so sure its not just being lubed!

Any other pearls of wisdom?
_________________
Impreza Race Car - SLS/SMRC
Mini Race Car - SMRC
911 - 1981 Air Cooled 3.0
500 - 1969 Fiat 500 L
Toureg 262 RLine
Track Scotland
Back to top
View user's profile Send private message
 
Thu Apr 07, 2016 9:56 am PostPost subject:
HummuH
SMRC S&S Rep


Joined: 05 Jan 2012
Posts: 2417
Location: Sniffing petrol

Reply with quote

What fluid does Fee use?

Personally, I'd remortgage and flush through with Castrol SRF and see how that fairs. I know if you look at the specs it appears other fluids may be better but it is by far and away the most stable fluid I've ever used.

I think I've got some AP Racing temp stickers if you want to see what caliper temps are like at SLS?
_________________
MD Racing
SMRC Sports & Saloons Facebook Page
Back to top
View user's profile Send private message
 
Thu Apr 07, 2016 9:58 am PostPost subject:
David Long
established user


Joined: 15 Mar 2009
Posts: 797
Location: Cumbernauld

Reply with quote

It sounds like a brake compound issue to me, but it might be worth stripping one of the calipers and check for any pick-up in the bores. They could be getting tight when hot. I would also try hard pumping (when cold and stationary) to see if it has the same effect as the bleeding.
_________________
R600 Dubaru
website
PB @ KH
Duratec in Detail
Back to top
View user's profile Send private message Visit poster's website
 
Thu Apr 07, 2016 10:07 am PostPost subject:
Steve H
user


Joined: 19 Aug 2014
Posts: 266

Reply with quote

is it a soft pedal or loss of braking force with hard pedal?

Soft pedal - brake fluid overheating.

Loss of braking force with hard pedal - brake pad matrix unstable at the temperatures being generated and gas being generated as matrix brakes down.

You should only get air in the system by allowing the fluid reservoir level to drop.
Back to top
View user's profile Send private message
 
Thu Apr 07, 2016 10:08 am PostPost subject:
AK
Site Admin


Joined: 27 Nov 2006
Posts: 20094
Location: Aberdeen

Reply with quote

popping the pistons and giving them a polish, flushing with SRF - all good ideas

Fee uses same RBF660

Temp stickers would be great! ta
_________________
Impreza Race Car - SLS/SMRC
Mini Race Car - SMRC
911 - 1981 Air Cooled 3.0
500 - 1969 Fiat 500 L
Toureg 262 RLine
Track Scotland
Back to top
View user's profile Send private message
 
Thu Apr 07, 2016 10:10 am PostPost subject:
AK
Site Admin


Joined: 27 Nov 2006
Posts: 20094
Location: Aberdeen

Reply with quote

Steve H wrote:
is it a soft pedal or loss of braking force with hard pedal?

Soft pedal - brake fluid overheating.

Loss of braking force with hard pedal - brake pad matrix unstable at the temperatures being generated and gas being generated as matrix brakes down.

You should only get air in the system by allowing the fluid reservoir level to drop.


longer pedal, but feels hard enough when I'm pushing on it...

i.e travel feels longer and more force is required to stop

I'd think if it was pads it wouldnt simply get better with a bleed
_________________
Impreza Race Car - SLS/SMRC
Mini Race Car - SMRC
911 - 1981 Air Cooled 3.0
500 - 1969 Fiat 500 L
Toureg 262 RLine
Track Scotland
Back to top
View user's profile Send private message
 
Thu Apr 07, 2016 11:25 am PostPost subject:
Steve H
user


Joined: 19 Aug 2014
Posts: 266

Reply with quote

Agreed, sounds more like fluid instability at temperatures to me. Bleeding the brakes after every quali / race / etc is an easy and quick fix. Do you have ducting to cool the brakes?

If it is the pad matrix breaking down you wouldn't get a longer pedal. As the matrix breaks down and releases gas it provides a cushion between the pad and the disc which effectively pushes the pad off the surface of the disc. You would also notice the structure of the pad breaking down over time rather than just wearing out.

A brake system is a thermodynamic system which requires a change in energy to slow the car down - i.e. it changes kinetic energy into heat and noise.
Back to top
View user's profile Send private message
 
Thu Apr 07, 2016 11:41 am PostPost subject:
AK
Site Admin


Joined: 27 Nov 2006
Posts: 20094
Location: Aberdeen

Reply with quote

no ducting, and this is an area i'll look to address today. new bumper fitting today, so will open the ducts like on Fee's... but having nothing to duct with to the brakes just yet
_________________
Impreza Race Car - SLS/SMRC
Mini Race Car - SMRC
911 - 1981 Air Cooled 3.0
500 - 1969 Fiat 500 L
Toureg 262 RLine
Track Scotland
Back to top
View user's profile Send private message
 
Thu Apr 07, 2016 12:11 pm PostPost subject:
HummuH
SMRC S&S Rep


Joined: 05 Jan 2012
Posts: 2417
Location: Sniffing petrol

Reply with quote

AK wrote:
no ducting, and this is an area i'll look to address today. new bumper fitting today, so will open the ducts like on Fee's... but having nothing to duct with to the brakes just yet


Unless you get the feed very close to the disc face there's very little benefit to brake ducts other than ramming excess air into the arches.

However, I'd think there would be an off the shelf bracket option for Imprezas to allow ducting close to the disc.

Like this:


_________________
MD Racing
SMRC Sports & Saloons Facebook Page
Back to top
View user's profile Send private message
 
Fri Apr 08, 2016 6:15 am PostPost subject:
Ibiza125
established user


Joined: 14 Jul 2009
Posts: 570
Location: Ellon, Sunny Scotland

Reply with quote

Have you still got ABS Adam? Could be a barsteward to get all the air out of it?
_________________
Toyota Supra A90
200SX S14
Ford Fiesta ST150
Peugeot 205 STDT
Back to top
View user's profile Send private message Send e-mail Visit poster's website MSN Messenger
 
Fri Apr 08, 2016 7:21 am PostPost subject:
AK
Site Admin


Joined: 27 Nov 2006
Posts: 20094
Location: Aberdeen

Reply with quote

car never had ABS... bare bones TypeR version
_________________
Impreza Race Car - SLS/SMRC
Mini Race Car - SMRC
911 - 1981 Air Cooled 3.0
500 - 1969 Fiat 500 L
Toureg 262 RLine
Track Scotland
Back to top
View user's profile Send private message
 
Fri Apr 08, 2016 8:19 am PostPost subject:
foz01
WankR
WankR


Joined: 10 Feb 2008
Posts: 1322
Location: Location, Location.

Reply with quote

How much meat is on the discs and pads? Carbotech pads on our Evo were brilliant, k-sports and with 20laps they never deteriorated..
_________________
Motorsport Exige Project Thread
Back to top
View user's profile Send private message
 
Fri Apr 08, 2016 8:33 am PostPost subject:
nefarious
user


Joined: 02 Nov 2008
Posts: 222

Reply with quote

I've had a slightly similar problem on the Westfield, which uses Ford Cossie/XR4x4 calipers on the back.
They're known for trapping air, and what tends to happen is they appear to bleed fine (i.e. no bubbles), but you never get the pedal 100% hard. When they get proper hot (e.g. in my case, when the hub nut is coming loose and the disc is fouling the pads and overheating them), the pedal gets longer and longer.
For me, the solution was a) to fix the cause of the overheating and b) bleed the system, take the calipers off the hubs, mount them upside down, bleed, return them to the right way up, bleed again. Only had to be done once, and ever since, I've just bled normally and everything's OK.

As a general point, those laser pyrometers (30 for Maplin) are very useful for diagnosing brake problems. Do a couple of straight-line runs and take disc temps all round - any asymmetries or crazy high numbers will point you in the right direction for sticky pistons, brake bias problems, or in my case, a wobbly hub.
_________________
Strong Broo Racing
Back to top
View user's profile Send private message
 
Fri Apr 08, 2016 8:46 am PostPost subject:
alistairolsen
established user


Joined: 16 Nov 2007
Posts: 715

Reply with quote

Does a bleed sort it out, or does bleeding the brakes take coincidentally long enough to allow the pads too cool a little and hence it feels better?

Have you tried borrowing Fees car to see if the issue is the difference in driving style? If her car is fine with you driving then there has to be a difference between the cars.

If there was air in the system IMHO it would feel crap all the time, your issue sounds temp related.
Back to top
View user's profile Send private message
 
Fri Apr 08, 2016 10:51 am PostPost subject:
Fee
Site Admin


Joined: 27 Nov 2006
Posts: 3606
Location: Antartica

Reply with quote

alistairolsen wrote:
Does a bleed sort it out, or does bleeding the brakes take coincidentally long enough to allow the pads too cool a little and hence it feels better?

Have you tried borrowing Fees car to see if the issue is the difference in driving style? If her car is fine with you driving then there has to be a difference between the cars.

If there was air in the system IMHO it would feel crap all the time, your issue sounds temp related.


Do you really think I'd let Adam use my car for a whole SMRC race? Shocked
Have you not seen what he does to them!?

I think you are right though
I've never had an issue with my brakes, BUT I am a lot less aggressive on them. My set up works for me, but that doesn't necessarily mean the same set up would work for Adam.
10-12 laps (if he gets that many) of hard use of the brakes may need a better / different set up
_________________
2010 Time Attack AWD Club Challenge Champion
2013 Rolly Polly Champion

R32 GTR: TimeAttack - Track Scotland
Back to top
View user's profile Send private message Send e-mail
 
Post new topic Reply to topic trackscotland.co.uk Forum Index | Technical Goto page 1, 2, 3, 4  Next   Page 1 of 4

View previous topic
View next topic
Display posts from previous:   




You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum