[DSouth]

I'm going to try to be as specific and detailed as I can about this, because it has me a bit concerned.

On Monday I took drove my 73 911 from North Orange County to San Diego for work. All total it was about 90 miles one way. I left at 7:15 AM and arrived by 9 AM. I had the windows up for most of the trip with the ventilation lever open. A completely uneventful drive.

Last night I drove home after spending one night in SD. I left around 7PM and arrived around 9 PM. This time I had the windows up and the ventilation lever closed. An uneventful drive up until I got to Carlsbad CA(about 20 miles into the trip). That is when I noticed a burnt rubber smell. The smell came and went, and I just let it go thinking perhaps it was just another car.

Then it came back. Again very briefly, and went away. This happened 2 - 3 more times, and I decided to pull over to investigate. Stopping in Oceanside I inspected the car with eyes, ears, and nose at a gas station. No rubbery smells around any of the 4 tires, nor did had any of the rubber oil lines come in contact with anything hot or spinning. I then checked under the hood, near the back of the guages. No smells or evidence of melting of fire. Both battery cables looked fine and were not loose. I went back inside the car and sniffed around under the dash and glove box. But nothing stood out.

So I threw a few gallons of gas in the car and hit the road. No rubber smell again for 10-15 miles, until I got to San Clemente, where after climbing the first hill on I5 after El Camino exit the smell returned. Again very briefly, but strong enough to notice. I moved into the slow lane and dropped speed to 65mph(previously I was going 70mph).

After driving @65mph for a few more miles all through San Clemente and all the ups and downs of I5 I thought "load" on the engine from going up hills was not a factor, but all the previous times I had smelled the burning rubber smell coincided with loading the engine as I went up a hill in the road.

I cautiously proceeded to the 133 toll road which I like to take to cut my journey short on my way back to Yorba Linda. I figured the sustained hills off the toll road would be another good test of whether or not "loading" the engine played any roll in causing the burning rubber smell. I made it all the way up to the 91 freeway, without incident. No more burning rubber smell. Until......

I exited the freeway at Weir Canyon/Yorba Linda Blvd. After exiting and stopping for the light, I turned right onto another street and accelerated, after I got up to speed the smell came back again just for a moment. This made me very nervous, so I shut off the headlights. Recalling threads on this forum outlining how the stock headlight setup can be an electrical fire hazard. I made the last few miles of the journey without the headlights on, and the smell did not return, but I also did not do any heavy accelerating either.

When I got home I immediately disconnected both batteries. Just to be safe. But the question remains. What could be causing this seemingly random burning rubber smell? It may be worth noting that this was the first trip I had made with some extra weight in the back seat. I took some luggage, and my tool box. It was also the longest drive I've made at night with the headlights on.

I do not feel comfortable driving the car until I can get this sorted out. I'm hoping that it was maybe just the tire rubbing, but I did not hear anything that would coincide with that occurring. Any thoughts on how to proceed to root cause this?

Thanks!