Is it normal your brake feels somewhat spongee afeter a lapping day? Mine feels this way after last lapping day. Would a simple brake fluid flush fix this? TIA

 

Normal? Sort of. Common, yes. Good, no.

Flush the fluid. A bleed would likely get rid of the sponginess, but a flush is better.

Come to think of it, you might be better off bleeding the brakes and then doing a flush right before your next lapping day. Fresh quality fluid is the best safeguard against a spongey pedal.

Relatively-fresh brake pads also help; the thicker pad can insulate a little of the heat from getting into the caliper, and from there into the fluid.

--DD

 

Thanks Dave, that means I have two weeks...

 

Doing a track day on Dot 3 brake fluid (normal street car stuff) will very likely result in boiling, which causes sponginess due to the vapor being able to compress in the lines. Typically, bleeding the lines will get the vapor out and return your pedal feel, however, the next time you get them hot the same thing will happen. Even if you flush the system with the same fluid, you'll likely exceed the boiling point again the next time out. If you want a more permanent solution, switch to a brake fluid with a higher boiling temp. I found that the Valvoline Dot 4+ synthetic stuff is pretty good and CHEEP at only like $6/qt. There are also lots of other good synthetics out there that would meet your needs. Another cause of spongy pedal feel can be the stock rubber lines flexing. When the rubber gets hot, it expands under pressure. SS brake lines are made to prevent this symptom and are generaly a good idea if your car sees a lot of track days.

- Scott

 

Definately use a different brake fluid than typical DOT 3. My personal recommendation is ATE Super blue (they also make an amber colored fluid to make flushing the fuids easier). I and many other people use this on their racecars and it only costs $15 per bottle which will be more than enough to flush your car's brake system. The process of flushing the fluids is very simple to do, buy you'll need a helper, piece of tubing to go over the bleeder valve, a plastic bottle, and if getting crazy a piece of wire to hold it near the bleeder valve.

 

ATE Super Blue and Typ 200 are good fluids. Motul is supposed to be better--but it is even more hygroscopic (sucks water in from anywhere it can find it) so you may have to replace it more frequently. It's also $$$.

If budget is important, but you still want fresh fluid every track weekend (recommended, BTW), Ford Heavy Duty fluid is supposed to be good inexpensive stuff.

--DD

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Dave_Darling &raquo;</TD></TR><TR><TD CLASS="quote">ATE Super Blue and Typ 200 are good fluids. Motul is supposed to be better--but it is even more hygroscopic (sucks water in from anywhere it can find it) so you may have to replace it more frequently.</TD></TR></TABLE>

Not true. Motul is not more hygroscopic than most other fluids. In fact, the "wet boiling point" of the Motul 600 RBF fluid (its boiling point after it has absorbed moisture) is still significantly higher than the ATE fluids.

There are a few fluids that are less hygroscopic than others - notably the superexpensive Castrol SRF - but that is much less of a consideration for track folks, who tend to flush our fluid fairly often so we're usually using pretty fresh fluid - than for people who don't do much driving and whose cars sit for extended periods of time (e.g. classic car collectors). As long as you change your fluid fairly regularly - I make sure mine has been changed in the previous 6-8 months any time my car is out on the track, and my Motul fluid has never boiled - the dry boiling point (when the fluid is fresh) is much more important than the wet one.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Dave_Darling &raquo;</TD></TR><TR><TD CLASS="quote">It's also $$$.</TD></TR></TABLE>

Motul generally runs around $15 for a half liter bottle. That means it's around $30 or so for a full flush on our cars. That's a small price to pay for greater protection against boilover and fade.

You'll find the most recent complete list of brake fluids, including their boiling points and prices, in this topic.

 

Thank you for all the advice. The fluid I use is Motul already and they are four months old. Maybe I didn't flush it right the first time?

 

I would just bleed it...