When I was at Lime Rock Park a month ago I had a very spongy brake pedal in my second on track session causing to use the exit road instead of turning into Big Bend. I figured it was boiled fluid and so I bled the brakes and went out in the 4th session and the brakes felt a little better but not great. I have bled and bled over the last month yet it has not helped.

Over the last month besides bleeding I have changed the front caliper, all the rubber lines to SS lines, and the master cylinder yet nothing has helped and the brake pedal travels to the floor with little effort. I need any and all suggestions because I'm going out on track Friday and would like to use my brakes.

Thanks

Ryan

 

What brake fluid are you using?

 

Motul RBF600 which I didn't think should boil but it was nearly 95 degrees that day and I was braking fairly hard and thought maybe there was air in the system (not from anything I did but just a thought, there was no air in it though) causing the brakes to get spongy earlier then usual.

 

Did you change your brake pads? I've found after hard use my brake pedal feels soft, even after bleeding, it is most of the time glazed brake pads that is causing a "soft pedal" feeling. I, however, have not used high performance brake pads (yet), so they may be different. That's all I can think of. G'luck figuring it out.

 

Yeah, after the track i switched back to my street pads. I doubt that is it as the pedal actually goes to the floor with little effort. Can it be the booster? Pedal? ABS?

 

bump...really need input here asap, I'm stumped.

 

Sounds typical of a problem with the master cylinder and/or potentially the brake booster.

Which is odd since you said you changed the master. Perhaps an install problem with the master or the booster or connection to the booster.

 

Yeah, I don't think it was an install problem since the problem was there prior to the install. What can the booster issue be? I checked the vacuum line going to it and it was good.

 

How old is the Motul? i.e. when was the last time you did a full flush?

 

A full flush hasn't been done for 2 years but I bleed the brakes every month or so. Do you think a full flush at a shop would be necessary?

 

Probably not. All they will probably do at a shop is put fresh fluid in the reservoir, crack the bleeders and gravity bleed the system. You can do that yourself if your comfortable bleeding your brakes.

Did you bench bleed the master cylinder before installing it?

If the problem was happening before you put in the SS lines, calipers and the new master cylinder. It stands to reason the the brake booster may be having problems.

 

Yes. Motul is is very hygroscopic which is why I don't recommend it unless you have a dedicated track car. You should do a full flush of it once a year or it will absorb a lot of water (and hence boil when it shouldn't).

I would recommend Super ATE. It's not as hygroscopic as Motul so you can run it much longer between full flushes.

 

Motul~
I have just started using that and I have noticed that the brake pedal feels extremely different that before.... the degree of braking became very unusual...
meaning that its either gripping softly or I need to brake harder than before and it will brake more aggressively. Is this the norm with motul brake oils?

 

Interesting comments on the Motul. I'm using ATE Blue. Still the same fluid from 1.5 years ago with some bleeding during that period. I'm overdue for a flush but have been impressed by the resiliency of the fluid overall. Then again, I do live in Cali where it is dry and not humid and rarely rains (compared to this year's monsoons in the NY area).

 

Nice tip, thanks Mahjik.

I have been using Motul RBF600 and have noticed that the firm pedal does not remain long after bleeding the brakes. A complete flush has not been done for a couple years.

Ordering Super ATE blue now.

 

I knew the Motul was quite hygroscopic but I figured it should be fine given the frequency that I bleed it. I'm doubting it is the fluid because of how quickly it came on during the session and that it still is occurring after putting 3 bottles of fluid through the system to flush it the best I could though I will flush it as soon as I can. I'm really starting to suspect the booster but what in it could have fail, I'm not familiar with boosters at all or the problems that could occur.

 

Absolutely, Motul may be one of the best fluids, but it is for racing and needs to be flushed almost daily. I will flush each day on weekend races in the Spec7; it absorbs moisture like a sponge.

A way to pick a street / track day fluid that you don't want to change all the time is to forget the dry boiling point and concentrate on Wet point 1st.

Super ATE is very good fluid lasting a while and by switching between ATE Blue and their Yellow version ("Gold"?? something is its name) you can get a true flush. Some fluids by Boiling Point.

Fluid DOT wet F dry F
Castrol SRF 4 518 590
Motul 600 4 421 585
Neo Super-DOT 4 421 585
SuperBlue ATE 4 392 536
Valvoline Syn 4 333 513
Neo HP 4 311 568
Castrol LMA 4 311 446
Ford 3 290 550
AP-600 3 284 572
Wilwood 570 3 284 570
AP-550 3 284 550
PFC Z-rated 3 284 550

 

I run Motul RBF600 on the track without issue. Right now I have 19 days on it since my last flush(I think I MIGHT of bled them once since then). I highly doubt that is your problem, I guess anything is possible though.

 

At this point I am sure it is not a fluid issue as I have run this fluid for over a year without issue.

 

I have not heard of any real brake booster failure. There is a check valve in the brake booster system which had a recall done to it early in the FD's life. The check valve was located on the turbo/precat side of the engine and would prematurely fail due to the turbo heat. Mazda relocated it to the US driver's side to remove the heat which extends it's lifetime.

You can order the recall kit from Ray for around $20 (IIRC). It's two pre-formed rubber lines with the check valve imbedded into the one for the driver's side.

 

Hmm.. Didn't know that.. Any pics where it relocates to?

Also, I just realized you now have over 24K posts... WOW!

 

Sorry Phil, I don't have any pics. There is a vacuum line that come out of the brake booster, goes to a hard line on the firewall, and then makes a u-turn into the UIM. There are two rubber hoses which connect everything up:

1. From brake booster to the hardline on the firewall
2. From the hardline to the UIM

The check valve moved from rubber hose #2 to to rubber hose #1.

Time flies when you are having fun.

 

Thanks Mahjik I'll give Ray a call now.

 

Did you manage to figure out what the problem was Specter328??
I'm having a similar problem with my brakes. Still pulls the car up, but not till the pedal is near the floor. Makes it impossible to heal/toe.
I've bled the breaks a number of times and have had the master cylinder replaced. I've also had caliper seals replaced.
ABS light is on too, weather or not that is related i don't know.
Any help would be greatly appreciated
cheers

 

Funny you should post tonight, I bled the brakes again today and the pedal felt much better and more air bubbles came out (there was a big issue before that introduced a whole lot of air in the system). I'm going out on track tomorrow so I will know for sure then. If your ABS light is on something else may be happening though.