This week is the big car week on the Monterey Peninsula. The weekend before the Rolex Monterey Historic Automobile Races at Mazda Raceway Laguna Seca, they have the “Pre-Historics.” A lot of racers are already setup in the paddock and anyone can go in and look around if you pay the $6 parking fee, which is about my speed.

We saw some of the practice for Group 7A, 1964-1971 FIA Mfg. Championship Cars: there were two 1969 Porsche 917Ks, a 1970 Ferrari 512S, 1969 Ford GT-40, a 1968 Alfa Romeo T33/2 and various Porsche 908s.

In Group 7B, 1973-1980 IMSA GT, GTX, AAGT Cars, there was Henry Schmitt’s (whose father started German Motors in San Francisco in the 60’s) 1974 BMW 3.5 CSL. I saw it in the paddock with hood off and took a piture of the engine. There were also a bunch of Porsche 935s, a bunch of 1977 Dekon Monzas and various Porsche 911 RSRs.

There were three Bonhams cars that are going to auction next Friday: a 1975 BMW 3.0 CSL in Taiga, the metallic green that looked ugly to me; a 1929 Bentley 4½-Liter (the Mrs. said, “This must have been where they came up with the term wind screen”) and a 1939 Auto Union 3-liter V12 Grand Prix Racing Single-Seater. When we went back to the parking lot (we drove the Bavaria), there was an E9 parked behind us. As we were leaving, we saw the Auto Union broken down on the track while doing a demo lap – they were attaching a tow rope the a fire truck.

BMW Fuel Sender Repair

BMW fuel sender

The fuel gauge on the Bavaria stopped working.

I was hoping that it was only a bad ground connection on the instrument cluster. On my first repair attempt, I hit the top of the dash above the instrument cluster to jostle the connections and take out some frustration. When only the latter worked, I looked at my BMW repair CD.

To test the fuel gauge, the repair manual said to connect the brown-yellow wire on the fuel level sender to ground and to switch on the ignition momentarily. The gauge deflected to full, so I knew the gauge and grounds were OK. But that meant the sender was broke. lists the price of new sender at $261.40 (USD), so that was a good reason to try to fix it.

BMW fuel sender sensor wire routing

After I moved all the crap in the trunk to one side, I lifted the carpet and unscrewed the floor panel covering the gas tank.

The gas tank was full. When I tried pulling the sender out of the tank, (it’s a bayonet mount) gas poured out into the trunk. I decided to take a drive down Highway 1 a little south of Point Lobos to lower the fuel level.

The fuel sender is basically a variable resistor. The float moves up and down a guide rod and is also connected to a wire of known resistance. The change in resistance (by the position of the float) is translated by the fuel gauge as the range from full to empty.

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One end of the sensor wire had broken off its terminal connection so the wire was now too short to connect to the terminal. I used a piece of 22 gauge solid copper wire (looped and soldered to the connector) to extend the connection so the sensor wire would reach its terminal. Since the sensor wire is a continuous run from one terminal to the other, I had to figure out the routing around the bottom of the sender. It seemed to just wrap around – at least that’s how I did it.

The repair manual says the resistance between the G terminal and minus should measure 3.2 & 73.7 ohms at the extreme positions of the float. I measured 3.4 and 84.7 ohms so at least my repair sorta worked.

Flex-a-lite Fan Failure

Five years ago, when I had our BMW Bavaria‘s radiator re-cored, the radiator shop said a two row core would be enough. I’ve never had any cooling problems.

Instead of replacing the water pump mounted cooling fan, I bought a Flex-a-lite 116 Trimline Fan. It’s a 16″ fan that is 3.5″ deep. The airflow is 2215 CFM (62747.8 LPM) and it draws 11A.

Flex-a-lite says there should be “at very least 1″ from the closest part of the fan to the radiator“. Because I didn’t have that much room, I mounted the fan in front of the radiator, as a pusher.

To switch it on, I mounted a thermostatic switch (61 31 1 364 872 82D) on a bung on the radiator lower hose connection. The other part of the switch was connected to a relay for power.

Because the climate is cool here, the fan rarely switches on. But yesterday when it switched on, I heard a grinding noise. I was hoping a leaf got stuck in it.

I had to pull the radiator to remove the fan. It made a grinding noise when I turned it by hand. I disassembled the motor by removing a couple of Torx screws and a pin retaining the motor shaft to the case. Inside I found a DC motor, not unlike the ones I used in my slot cars, except this one had 4 magnets and 16 poles. I have used Koford quad magnets in my slot cars.

One of the permanent magnets had become unglued from the case. The armature’s poles had distorted slightly from turning against the loose magnet. I used JB Weld to glue the magnet back onto the can and a large screwdriver to straighten out the armature poles.

When I pulled the armature out of the casing, the four brushes and the springs shot out. While wondering how I was going to hold four spring loaded brushes in at once, I noticed two holes at the end of the brush holders. I put a piece of copper wire in each one so I could reseat the armature end bearing and connect the brushes.

After I reassembled and tested the fan, I ordered a new one. I figured $100 USD for a new fan is better insurance for preventing an engine meltdown, even though a 5 year life span for the old motor seems just OK. Maybe when I get the new fan, I’ll put some dielectric grease between the motor covers and the casing to seal it a little better from moisture.

LED Tail Lights

Cree XLamp® XR-E LED (P2 bin)

I had some extra Cree XLamp® XR-E LEDs (P2 bin) when I upgraded some flashlights to Q5 bin LEDs.

When I found a LED circuit board that had an input voltage of 4v-18V, I thought it would work well as a driver for an automotive LED bulb. The circuit board uses a Micro Bridge Technology PT4105 (PDF specs) step down LED driver.

I took an 1156 bulb to use as a base for the circuit board and LED. I broke out the glass and filament and used JB Weld to glue the components together.

BMW Bavaria Tail Light

The LED was brighter than the 1156 bulb, but it had a noticeable hot spot, even though the Cree LED has a 90 degree viewing angle. Heat doesn’t seem to be a problem; the Bavaria’s light socket dissipates the heat well.

Joe Weir, on the Senior Six Mailing List, suggested using a diffuser lens. I’ll have to find something then report back.