Smoke! Fire!

[jac1976]

Please help me to figure out what went or what I did wrong.

1973.5 911T converted to a single battery setup. Now has a Deka ETX30L AGM battery.
I have not driven the car in 4-5 days and the temps here in San Antonio have dipped close to freezing, but nothing arctic.

Hooked up the jumper cables with the negative on the Porsche attached to the right shock tower.

Gave it some time and cranked. The motor continued to attempt to turn over a number of times after I turned the key to the off position...

Now, SMOKE! Pulled the cable from the shock tower and looked under the car to find a green flame just inside the right front wheel being fed by brake fluid.

Moreover, it seems the battery in my Tahoe may have gotten a bit warm, as the plastic conduits that were in contact with the battery have melted in places.

Any ideas?

Thanks and Merry Christmas!

[darrin]

your experience sounds like what would happen if you reversed polarity on one end (i.e. you accidentally attached the tahoe's positive terminal to your shock tower and the tahoe's negative terminal to your battery's positive terminal).

[jac1976]

I agree. But all was connected correctly. Double and triple checked.

[74-911]

Originally Posted by jac1976

1973.5 911T converted to a single battery setup. Now has a Deka ETX30L AGM battery.
I have not driven the car in 4-5 days and the temps here in San Antonio have dipped close to freezing, but nothing arctic.

Drove the car 4-5 days ago and it needed a jump?? Could an internal short in the AGM battery reverse the polarity somehow ?? just a WAG...

[Ronnie's.930]

Originally Posted by jac1976

I agree. But all was connected correctly. Double and triple checked.

Which of the two cars were you trying to jump (you don't mention that), and how were the jumper cables connected? I can't picture what you mean in your first post where you say that the negative on the Porsche was attached to the shock tower.

[jac1976]

Jumping the Porsche from the Tahoe. Connected as follows:
Porsche +
Tahoe +
Tahoe -
Porsche shock tower

[Ronnie's.930]

Very strange - so enough heat was generated in the vicinity of a brake hose to actually rupture it?

Where specifically on the strut tower did you connect the negative cable?

[hdrockerroller]

The part that is of interest is that it continued to turn over after you turned the key off. This sounds like the ignition switch broke. Maybe it shorted and drew so much current that it started the fire. I recently had to change the ignition switch on my 83 911SC, but I didn't have that symptom. Food for thought anyway, btw I'm near san antonio in helotes so whenever I end up completely stumped i haul it to jones autowerk.

[jac1976]

Thanks for all the input, still trying to figure this one out. Hdrockerroller- after scratching my head for a while, I gave Kathy a call. May have it hauled over to Iota as they have got the car back on the road for me.

[jac1976]

Very strange - so enough heat was generated in the vicinity of a brake hose to actually rupture it?

Where specifically on the strut tower did you connect the negative cable?

The main bolt. Should I have used on of the two smaller bolts? Have not gotten back in to look closely at where exactly the leak is. I can see where the fluid is dripping off the line, but not sure if the leak originates at that point or is further up the line. The reservoir emptied quickly, though.

[PrimeMvr]

Without running out to the garage, my visualization of the front suspension leads me to believe your brake fluid to the steel hard line was the only path to ground. Everything else is rubber.

Strut tower bolt > strut > caliper > brake fluid > hard line > body

Seems plausible.

[timmy2]

Originally Posted by PrimeMvr

Without running out to the garage, my visualization of the front suspension leads me to believe your brake fluid to the steel hard line was the only path to ground. Everything else is rubber.

Strut tower bolt > strut > caliper > brake fluid > hard line > body

Seems plausible.

My thoughts exactly. Rubber isolator at top of shock tower won't conduct so your described path is logical. Maybe he has/had braided brake hoses....

[darrin]

very interesting! tangential question -- is there a reason it's BETTER to connect the negative cable to ground rather than simply attaching it to the negative battery terminal?

[javadog]

The idea behind connecting the last cable to someplace other than the battery terminal is that the spark that generally occurs when connecting the cable will be away from the battery. Batteries can give off hydrogen gas when they are charged and it's very explosive. Also, a battery that is low on fluid can sometimes spark internally. A battery explosion will ruin your day and maybe your life.

You do need to find a suitable ground. Something that is unpainted and in direct contact with the chassis of the car. The ground you chose was not a good one.

JR

[darrin]

JR -- thanks so much for the clarification -- makes perfect sense

[E Sully]

As Steve and Dennis noted, the top of the shock makes a very poor connection to ground. Most of the suspension components are isolated from the true chassis ground by rubber bushings, leaving the fluids to transfer the current. The current would have to pass through the shock internals as well as the brake components, as the control arms and sway bars are all normally isolated from the chassis by rubber bushings.

[jac1976]

Thanks for the input.
Where would the collective suggest to ground?
Other than the obvious (brake line), any additional damage suspected due to my error?

[Joe Bob]

In hind sight, jumping the 911 isn't the best thing to do. Too easy to FUBAR the operation, especially if at home.

Once you've sorted the issues of the lost smoke, get a Battery Tender. My ride can sit for 3 weeks on occasion and I always hook it up. My yellow top Optima is going on 11 years now.

Every vintage 911 owner should have a Tender and an analog style Battery charger. The digital ones suck.

BTW, when I saw the thread title I was a expecting, "Smoke, Fire......Freaking Lucas"......