FIRE in the wheel-well!

[Nadine UK GTS]

I was racing my '97, done a lot of R&D and work re using my OE brakes, as can't aford to go 18" rims and Daves big brakes yet... (this is what works for me: Cone cool ducting, Porsche air deflectors, Roe Ti pistons, SRF fluid, PF 01 pads, 2-piece aero-rotors, wheel-well cut outs, rear Tom 40mm caliper mod) anyway...highspeed braking..and unfortunatly still running with race damaged bent frame putting camber/caster out on front wheel, causing uneven brake forces through fronts...heat melted front ball-joint rubbers, grease ignited...flames were leaping from wheel-well; I've never moved so damn fast to put out fire, YIKES, not nice seeing my Beloved on fire, grabbed drinks bottle off bystander to pour on flames!

Until I can save the readies to have my frame jigged out, does anyone know at what temp does grease ignite, and would synthetic grease withstand higher temps pre-ignition? I'm going to replace ball-j boots and make up heat shields for them, would this maybe enough to get me by? I don't want to be a firewoman again!

 

[Tom F&L GoR]

Hi Nadine,

Grease can be oversimplified as being additized oil in a chemical sponge. The type of material used to hold the oil varies (lithium, sodium, etc), the type of base oil used (mineral or synthetic) and the formulation of additives (extreme pressure, for high or low speeds, etc.)

The Flash Point is when the vapors from the product, when mixed with air, will ignite with an external source but not continue to burn. This value is typically used for transportation safety requirements and also as a quick evaluation for contamination (since a small amount of gasoline, for instance, will greatly lower the flash point of an oil.)

The Fire Point is when the vapors can be ignited, but the product continues to burn, and this temperature is somewhat higher.

The Auto-Ignition temperature is that when the product will ignite without an ignition source. (Diesel fuel)

Grease has a dropping point at which the thickener stucture breaks down and the grease runs. From a machinery point this means the lubricant is moving away from that which needs to be lubricated. Even when cooled, the the grease may not be satisfactory for lubricating the parts. The better grease is one in which the thickener tolerates a higher temperature, moreso than the base oil. A good grease can have a good thickener and still use mineral base oils.

Flash point therefore isn't typically a grease spec and we can only estimate from the flash point of the oil itself when it gets runny. Also, the additives used are produced and delivered diluted in mineral oil, so even a "full synthetic" product has 5-10% mineral oil. And from the discussion above, this "contamination" lowers flash and fire points.

A mineral oil flash point can be as low as 200C, that of a similar viscosity synthetic perhaps 30C higher. The fire point of each would be 20C-30C above their flash point. The auto-ignition temperature is a different property, though. Gasoline has a low flash (-45C), but high auto ignition temperature (280C, it has a high octane rating); diesel has a high flash (170 C) but low auto ignition temperature (250C, so it has a high cetane rating.)

So what do you want to look for? A lithium or lithium complex grease, high dropping point, and then finally one with a high base oil viscosity at 100C. Naturally, Mobil makes such a grease under their Mobil 1 branding.

All numbers quoted are approximate.

 

[Janni]

And yes- heat shields will help immensely - when running our 96's at Viper Days - Henry made some heat shields and the ball joints boots survived quite well.

I have a set that I would be happy to send you, Nadine - race proven and ready to go. Lightweight aluminum - attach with cable ties. Can either send direct or through Chuck.

Just let me know.

(Tom seems to have the types of grease thing pretty well covered)

 

[GTS Dean]

I was racing my '97, done a lot of R&D and work re using my OE brakes, as can't aford to go 18" rims and Daves big brakes yet... (this is what works for me: Cone cool ducting, Porsche air deflectors, Roe Ti pistons, SRF fluid, PF 01 pads, 2-piece aero-rotors, wheel-well cut outs, rear Tom 40mm caliper mod) anyway...highspeed braking..and unfortunatly still running with race damaged bent frame putting camber/caster out on front wheel, causing uneven brake forces through fronts...heat melted front ball-joint rubbers, grease ignited...flames were leaping from wheel-well; I've never moved so damn fast to put out fire, YIKES, not nice seeing my Beloved on fire, grabbed drinks bottle off bystander to pour on flames!

I'm going to replace ball-j boots and make up heat shields for them, would this maybe enough to get me by? I don't want to be a firewoman again!

Nadine,

Your mods (except for forced air ducting) are almost exactly as on my car, as are the problems - just short of catching fire. The one thing I would say is that until you get some heat shielding to protect the ball joint boots, you HAVE TO keep them replaced with fresh ones. With such an aggressive friction compound, your rotors can easily see 1300F. Try at every opportunity to keep air moving through the wheel wells after a hard session at the track. Drive at a very modest pace on the cool-down lap and don't be in a hurry to park in your pit stall. I usually putt around the paddock at 15-30 mph (whatever is reasonably safe) until the engine temps have returned to normal. By then, your brakes should be good too. Heat soak is a killer for Vipers.

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[GR8_ASP]

A heat shield is the answer as indicated above a few times. A single wall heat shield properly located can reuce the radiated temperature by 50 percent. I have a graph somewhere which shows single, double and insulated double wall heat shielding. And memory (not as good as it used to be) is that single wall shielding provides about a 50 percent reduction in radiated energy. That should be more than adequate for the ball joints. I believe comp coupes come with them.

 

[Neil - UK]

I beleive *** missed the cool down lap and came into the pit garage, I saw it happen there was an initial flash of light,then nothing, about 5 seconds later small flames started hovering above the drivers side front disc, they didnt seem to get any bigger a bit worrying for a few moments until some water was found

 

[Nadine UK GTS]

Thanks Tom, I just about kept with you there...interesting, thanks for the education.

Janni, you are too kind, I would love the shields please, would save me time, even if just to take patterns off them if needed back; would be much quicker than me starting design from scratch. Best if you send to me direct I'll pm you address, I'll of course cover postage etc; is there something nice I can send you in return from UK perhaps?

Dean your Porsche air deflectors look about as chewed up as mine by the inner wheel! LOL

I did do some track cool off, and always roll car about in pits so rotors don't hot spot. New lesson learned though!

 

[Janni]

I'll get these out to you this weekend!

 

[GTS Dean]

***,

Not just chewed up, but you can clearly see the upper right corner is melted, along with the tie rod end boot - with grease drooling down the knuckle. Look carefully at the brake pad below the wheel stud at the 4 o'clock position. BrakeMan #4 paint charred ash white. Those Ti pistons really help!

People were all abuzz that my brake rotors were glowing red-hot in the strong sunshine.

 

[Nadine UK GTS]

Dean, you too have nice brown color caliper lettering, don't expect Dodge produced them with the lettering in mind as a heat temp indicator though!

Neil got this pic of my rotors glowing in the daylight if you look carefully!