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Mixing DOT4 fluids?

Sesshomurai

Couple questions.

1) Is it ok to top off the brake fluid a little if it is down a bit in the reservoir? at the track
2) Is it ok (but not advisable I know) to mix DOT 4 fluid "brands" if need be?

thanks.
 
darreng505 said:
Couple questions.

1) Is it ok to top off the brake fluid a little if it is down a bit in the reservoir? at the track
2) Is it ok (but not advisable I know) to mix DOT 4 fluid "brands" if need be?

thanks.

1) Certainly, but our reservoir caps don't seal very well. Most of us run them somewhere between the top of the reservoir and the seam in the middle. If you run it full on track, it will likely seep through the cap and brake fluid is not nice to paint. The other consideration is when using track pads you will wear them down quickly. When you swap your full depth street pads back on you need to make sure you leave some room in the reservoir when you are pushing the pistons back in to the caliper.

2) Generally yes. You should read the manufacturers instructions on the bottle, but all the fluids I have used say they mix with other DOT 4s. If you mix fluids with different boiling points (DOT 3 and 4 for example), the fluid wil take on the property of the lower boiling point fluid.
 

Sesshomurai

Thanks for the tips sir.

I've now logged 4 track days in the past 9 calendar days. I'm bushed! My stock Pirellis are now toast.
Got new tires and pads on the way.

Even though this is off topic (I don't want to spam the board too much), are there any other post-track days(4)
maintenance items I should consider doing? The oil is fresh still (2 weeks old). I believe there is DOT4
brake fluid in there already....
 

Grant 302

basic and well known psychic
I'd change the oil after 4 track days...the oil isn't 'new' anymore! :D The only other thing I'd check at this point would be your pads and rotors. I think the rest of the fluids would go at least double the track days.

I think the stock brake fluid is DOT3, and I wouldn't worry about mixing with different brand fluids aside from the issues that Gary mentions. For the first flush though, to get out all the original fluid, I used cheaper DOT4 to flush the system then used Motul immediately after that. That's only a cost consideration because I'd hate to flush with something that's $20/bottle...
 

Sesshomurai

Thanks Grant.

Oh, one thing that did come up -- I was locked out of 3rd gear coming down from 5th at 135mph, braking super hard before a turn and trying to get into 3.
A shop pro guy I spoke to after coincidentally mentioned getting the trans cooler scoop to avoid those kind of gearing issues. It was my 3rd run of the day so the tranny was
very worked.

Should I consider changing the tran fluid at all? He said it turns to mush when it overheats and causes shifting issues. Not sure how knowledgeable he was, but more than me.
 

Grant 302

basic and well known psychic
I can't imagine trying to drop from 5th to 3rd directly on the track. It's risky for over-revving the engine and could kill the synchro if you're making the shift too early and aren't double clutching.

What speed were you trying to make the shift to 3rd?
 

Sesshomurai

Grant 302 said:
I can't imagine trying to drop from 5th to 3rd directly on the track. It's risky for over-revving the engine and could kill the synchro if you're making the shift too early and aren't double clutching.

What speed were you trying to make the shift to 3rd?

At first I was trying this (5->3), and breaking hard down to about 40-50mph and got into 3rd ok a couple times, but hopped the wheels slightly once and next lap went into 4th, then 3rd which worked better for me.
My instructor didn't have a problem going from 5th to 3rd if I had the correct speed, but the deceleration was so fast, timing the gear shift was tricky for me still.
 
IIRC FR told someone here to change diff and trans fluid at 12 hours of track time.

Bleed the brakes at least, flush would probably be better.

3rd lock out doesn't seem to be cured by the scoop, I get it on the street with spirited driving and the scoop. Try applying very slight right pressure when going into gear, the centering doesn't seem to get it right on 3rd when hot (at least on mine) but applying slight right pressure usually gets it in. I usually push with my palm straight forward after allowing it to center, but on this car it just doesn't work. In 4 years of tracking several other cars I have never missed 3rd in any of the other cars so I don't think it is an issue with my shifting style, but rather something with the shifter. Confirmed this weekend in my Spec E30, not a single shifting issue. Another thing, though it would seem unrelated, is pump the clutch a lot between sessions to cycle the fluid and bleed it. My trans shifts much better with a freshly bled clutch. Though I did have a fluid leak at one caliper so that might have been part of my issue, I haven't had it to the track or driven it hard since Ford replaced the caliper.
 

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