Questions and Answers

Mercedes Benz 300 SEL Transmission Q. Dear Vince, My car is a 1986 Mercedes Benz 300 SEL fuel injected 4 speed automatic transmission with 64,000 miles on the odometer, all accumulated in Hong Kong. It is equipped with ABS brakes, P/S, and A/C.

It has recently arrived in my country Australia. I have traveled about 150 miles in it since it arrived. The only previous mileage in Australia was for delivery to and collection from service and government certification points. As you can see from the mileage traveled, the car has not had significant usage over its life. The body is consistent with the mileage and is rust free. You may not be aware that in Hong Kong traffic conditions it is relatively rare for a car to get the chance to move into top gear.

My query is whether the fact that on one occasion it has slipped out of drive to neutral for no apparent reason is indicative of any and if so what defect. The shift occurred when I was traveling at about 80 kilometres per hour in fourth gear. It went back into gear while I was still traveling, with very little loss of speed, after I moved the shift lever into neutral and then back into drive.

My concern is that if I ignore the miss I may be causing damage by continuing to drive. On another isolated occasion the car seemed reluctant to change up to fourth gear and unusually went up to 3,000 rpm before changing even though I was not applying any serious throttle.

Other than what I have noted, the gears have changed flawlessly and noiselessly, both up and down. Around 2,000 RPM on the tachometer represents around 68 mph in fourth gear. Engagement of REVERSE gear takes about one or two seconds after the lever is moved to that position whereas engagement of DRIVE is immediate. Reverse engagement comes with something of a jolt whereas drive is accompanied by a much less marked take up.

Before the car came into my possession but after it had arrived in Australia, and was being checked by the importer before sale to me, the importer's service record supplied to me with it showed the transmission was serviced "to evaluate shift pattern and normal operation," and the transmission oil was drained and refilled. There is no transmission oil leak.

The extra query is whether it is reasonably possible to retrofit a cruise control to my December 1986 300 SEL from standard parts. The chassis number of the car is WDB126025-2A-288059. It is fitted with the a 3.0 liter, injected petrol motor and 4 speed auto transmission, ABS brakes, P/S, and A/C. I know many of the later production run of this series was equipped with CC.

Regards,
John

A. Something like this will be very hard to find the cause. Since it only did it once I would not be overly concerned about it. Mercedes do tend to have a one time hiccup now and again.

The delay into REVERSE is normal and always a little harder than DRIVE

I would still monitor the performance of the transmission for any abnormalities, but unless the problem becomes more consistent, there is really not much we can do to troubleshoot it.

If you can find a 1986 Mercedes Benz 420SEL, 126 chassis in a junk yard, you can transplant the whole cruise control system into your car. Ask them if they will let you take it out, then grab everything, cruise control switch, actuator, control unit, cruise control relay and wiring harness.