Hi all,

I've searched the Brickboard forums hoping to find someone with a similar issue, but haven't found one...so here goes:

I've got a 1985 Swiss-market 245 GLT, B230E, M46 with 240,000 KMs (150k miles). Excellent mechanical condition overall, but I've got an issue with the overdrive unit. When I'm decelerating from 120km/h (75mph) down to 100km/h (62mph) the unit starts to grumble (slight vibrations, audible groan) as though it's going to slip out of OD. If I accelerate, it will take 2-5 seconds to work itself out. Revs do not jump during this so I'm pretty sure it's staying in OD. If I let the car continue to decelerate under 100km/h it will drop out of OD. It also seems to complain if I'm driving down hill, drop throttle. It's as though the load on the unit is stressing it. In my part of Switzerland we have a lot of hills and long incline/declines on the highway, so the conditions vary when trying to diagnose the problem. Furthermore, it doesn't seem to matter whether the car is cold or hot...but I can do more extensive testing to see if there are any significant differences. Also, decelerating from 140km/h (87mph) to 120km/h doesn't have the same effect. The OD seems happy between these speeds.

Other background info. I've just had the car in for service. Oil change, etc. and asked the garage to check the functions and replace the oil in the OD. Apparently it's fine although I have not asked the garage to fully road test and diagnose the issue - yet. All the electrics function (gear switch, wiring, solenoid). The previous owner included another OD unit in the sale. He's a mechanic so I think he wasn't pleased with the OD operation either - just didn't get around to swapping the units.

I'm looking for your expertise on the existing OD issue but also what to do with the replacement. Since it's already separate from the car I could have it looked at with the intention of simply replacing the current one. Honestly though, I'd rather keep the original OD unit that came with the car. At this point either one would probably need to be opened up, overhauled, etc. It doesn't seem worth having the garage replace the units without doing any inspection or service first.

I look forward to your insight and opinions.