Unhappy 1985 low mileage 300D

Greetings...this seems to be an active forum so I have high hope of getting some good info. My nearest Mercedes Benz dealer is over 60 miles away, and if my car goes there, it will be on the flat bed of a tow truck! I suspect it is going, but I want to be prepared when I get there.

Don't know if you can give me a clue about what is going on, but I seem to be having two problems - unrelated I think, but I don't know.

I have driven a diesel mercedes since 1987, I sold my first 1976 300D with well over 200,000 miles, and my current 85 300D is a youngster with just 66,000 miles. I took it to the dealer in Charlottesville for the 65K service, and they said everything looked great. But on the drive home, up and over the Blue Ridge, I thought the engine sounded "different." They told me that was because of the adjustments that they had just made and that was normal. So I didn't think much about it. This was in the fall.

This winter, I noticed that at times, the engine sounded odd, and right before Christmas, I was driving along at about 30 mph, when the RPMs suddenly shot up to 4000. I rode my breaks a block or two, parked the car, went to work, came out later and everything was fine.

This happened a couple of more times in December and January and it started to worry me, but I thought I would wait to see what would happen. I really don't think I used my brakes enough to damage them, but I could be wrong.

Last Friday, I had driven about 3 miles when the car started to stutter. No matter how much I tried to accelerate, it was really hard going. I immediately pulled over into a parking lot. My rear brakes were hot and smoking and seemed to be locked up.

I had the car towed to my local mechanic. By then the brakes had released, but on the test drive, they locked again. He inspected the rear calipers and said all was well, so the "only" thing that could be wrong was the hoses. So, they replaced the two rear hoses and the break pads and sent me on my way. (This was 6:00 on a Friday night.)

On the drive home (less than 10 miles) I had the distinct feeling that something wasn't right. When I got home both the front and rear brakes were hot but not smoking. I called the mechanic and he said he didn't understand why the front brakes were hot unless my master cylinder had gone bad, but it was normal for the rear brakes to smell hot since the pads were new. ???

Since then I have been hestitant to drive the car, so last night I took it out and drove it through the neighborhood up and down hills trying to brake as much as possible to make sure that everything was ok.

As I was coming down a steep hill, the engine rpms went way up and I could hardly control the car. What the heck does that have to do with brakes? It was almost like the cruise control was stuck on 60 mph. I couldn't slow down and therefore braked as I went down the hill. I went about 1/4 of a mile and was home, by the time I got home, my brakes had failed, the engine was racing, and the only way I could stop was to turn off the car. YIKES! Glad that didn't happen on the way to work!

So I got out of the car. The rear brakes were red hot, the front brakes were smoking, and apparently a hose or something failed, because behind the passenger front wheel, my car was squirting brake fluid.

So I seem to have two problems, the acceleration issue and the brake issue. I don't think the acceleration issue caused my initial brake lock up since it wasn't accelerating when my brakes locked up the first time. I do think the acceleration issue caused my front brakes to fail, because I could hardly control the car with the brakes fully applied. I just had a rear brake job and am sure I will be having a front brake job, but what is causing the acceleration?

My 76 300D went through a period of wild acceleration until one day I was driving along and a large pulley fell off. I was able to limp to my old MBZ mechanic (boy I miss him) and he fixed it whatever it was. The current symptoms are similar to that, wish I could remember what the fix was last time.

Thanks for taking the time to read this and if you have any thoughts about what is causing this strange behavior, I would really appreciate your $0.02.

I expect that you will be able to cure the engine run away problem by examining the cruise control and the throttle cable from the dash board as they attach to the throttle lever. You will have to just look at it and open and close the throttle lever until you see what is hanging up.

Your brake problem is a strange one. I had the rear brakes hang up like that one time on my 240D. I released the pressure by cracking open the fluid line at the master cylinder. Once the pressure was released everything was hunky dory. I expect that yours is something to do with the master cylinder or the H block that proportions the front/rear wheel braking.

Best of luck,

When was the last time you lubracated the throttle shaft on the injection pump? My 500k car is regularily serviced, but the throttle was sticking for a while and one I realized no one had lubricated it! If you look at the pump, the shaft goes through and you can spray a lube on both sides, it might help?
Greg

Glad to hear no one saying the "transmission" word...My 76 300D went through 3 transmissions in 216 thousand miles.

I'll check the cable when I get home.

Cheers,
J