Brake pedal issue BMW 325 track car

[ryan2022]

Hi guys, I'm posting this for a good friend of mine back home. He's been running this season at Mosport and Watkins Glen and has been having a brake pedal issue...possibly stemming from boiling brake fluid or air in the system.

After a 20 lap session , the pedal is very spongy despite a fresh bleed with motul dot4

The pads are new hawk hp+.

The car has 120k miles on it and were wondering about wheels bearing' brake booster or the calipers. It's only seen 100 Miles or so of track time in total.

Once the brakes are bled again it feels fine...then another session has them spongy again. The calipers aren't dragging....although something is tripping the cars stability control to the point where it's intrusive.

Any thoughts are appreciated.

 

[bdcardinal]

What are the brake temps? Any brake cooling added to the car?

 

[Nick1994]

Is this a 1984 or a 2006 BMW 325?

 

[ryan2022]

I guess that would help!

It's a 2003 325i sedan.

No cooling upgrades although we've talked about ducting

 

[bdcardinal]

I would do ducting, I am sure someone makes a kit to add a bracket to the front uprights. I have had them on all my Mustangs.

 

[bdcardinal]

I just checked and Turner Motorsports does, but they are really proud of them.

 

[Ojustracing]

20 Laps at WGI/Mosport? at what pace?? Aprox 2 min laps? is 40 min. Sessions are how long? I would say brake ducts mandatory.

 

[MCompact]

Brake ducting and check the condition of the rubber lines- better yet, replace them with SS braided lines.

 

[bdcardinal]

Originally Posted By: MCompact
Brake ducting and check the condition of the rubber lines- better yet, replace them with SS braided lines.


Absolutely. Does the car still have the OEM calipers? Also what wheels are on it? A wheel that is more of a solid face will increase brake temps as well.

 

[ryan2022]

Thanks guys, all good suggestions. He is running the OEM 17" sport package wheel. He's currently looking for something lighter over the winter.

We talked about ducting as well, but I think the plans are caliper rebuilds, brake lines and possibly a look at the master cylinder.

Thanks again for the replies. I'll pass this along.

 

[ryan2022]

p.s. The session may not have been quite that long, but I know they were longish runs. He's an experienced driver and pushes the car hard.

I think the stock hardware can handle it, but it may be time to replace some items.

 

[Ojustracing]

Ryan
My 3265lb street car needs brake cooling after just 3 laps(fast/heavy braking track). Boiling the brake fluid at speed can get bad really quick. Once you pick up the pace enough the limitations of the stock equipment become very apparent. I still feel he will need aux brake cooling.

 

[RooflessVW]

I've been wanting to post on this. What fluid are you using?

You're boiling the fluid in your calipers, and you need to focus on heat management.

 

[oliver88]

We use Endless RF650 in all of our race cars...Firm pedal, no way you can roast it....Factory fill on the Porsche 991 Cups and RSR....Been running in in the 996 cup with some massive brake temps...never a problem...put it in a troublesome 944, end of fade/sponge issues...Obviously it will not correct a mechanical issue but it eliminates fluid issues and you can take that variable out of the troubleshooting equation !