I've only got 299,000 miles on my 83 300CD transmission. It shifts solid from 1st to 2nd, slips a tad on the shift from 2nd to 3rd under medium/light load, slips on the shift from 3rd to 4th with light load. I let up on the accelorator when it is ready to upshift to the next gear to try to eliminate the slip during those shifts.

I'd like to get another 300,000 miles out of this tranny but I doubt that will happen. I've have the bowden wire adjusted about how I like it and will probably have my indie adjust the modulator when I have the tranny serviced to see if he can firm up the 2-3 and 3-4 shifts.
I put a quart of trans-x about 40 miles ago to clean out any varnish before I have the tranny serviced. Yes, I drained some fluid out first so as to keep the level exactly correct.

1) My first question is, how long should I let the trans-x work before I have the transmission serviced?
2) Any other suggestions on what to do to help with the weak shifts?
3) Any suggestions on how to extend the life of this transmission, I'd like to get my moneys worth out of it before a rebuild
I'm mostly kidding on getting much more out of this tranny and I know at some point I'll have it rebuilt or replaced. I'm not sure if I'll rebuild it the next few thousand miles or wait until it gets worse.
I guess when it is time to rebuild, I'll see if my indy can recommend a trans. shop that he would trust if he won't do the job himself. This car has been taken car of by the same mechanic since new and I don't trust just anyone to tinker with it.
Sorry for the long message here. Just trying to get some input from other owners who know and love these cars.
Thanks, Tom

If I remember correctly trans X says to drain the fluid after 100 miles. It says right on the bottle. Just use cheap regular atf and change it every 20k-30k. I wouldn't waste money on Mobil 1 for a 300k trans. When you rebuild it then use Mobil 1.

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1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200

Your trans sounds a lot like mine.

If your 2/3 valves are working well and shunting high vac at closed throttle, you can up the line pressure and adjust the vac valce to firm up shifts withouth haveing neck snaping downshifts(important for not driving one crazy). Otherwise, it's just worn out, probibly the seals dried up in the clutch drum, not holding fluid pressure. Your description sounds almost exactly like mine, and it's been just this way for 50K miles or so. It'll last, adjust your settings and driving style, and start looking for a replacement.

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One more Radar Lover gone...
1982 VW Caddy diesel 406K 1.9L AAZ
1994 E320 195K

What does it cost to have a trans. rebuilt ?? or is better to buy a remanufactored one?? Dennis

Considering the age and mileage on the car, I'd say buy a used one that was working before it was pulled -- much cheaper than buying a rebuilt one or even rebuilding yours by yourself. That's what I did on my 500SEL which has even much fewer miles.

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1999 Mercedes-Benz S600, 103K miles - garage queen
1988 Mercedes-Benz 560SEL, 89K miles - daily driver
2007 Hyundai Sonata Limited, 31K - daily driver

Before I bought my 300TD I asked a fellow I know at a local shop what a replacement (rebuilt) trans would cost, installed. He quoted $1,800.00.
I was concerned about what I thought was slipping. (No power, early shifts)After buying it I found a problem with the Bowden cable and now it shifts crisply at higher rpm.
Good Luck,
Ron

Could you guys shed some lights on that ? I think I have the same problem. Thanks.

Not sure if this will help on a 300K mile transmission, but mbz.org has a nice article on installing a K1 spring kit in the valve body to firm up the 2-3 shift:
http://transmission.articles.mbz.org/k1/

I've got the kit in hand, waiting for my next trans fluid change. As I recall, my local stealer wanted something like $15 for it.

Russ M

Thanks for the input. Okay then, after the trans-x has about a 100 miles on it, I'll have the transmission serviced, verify the modulator vacuum is correct and adjusted for a firmer shift. If I can't get any improvement on the slip during shift issue, I'll decide when I want to have the tranny rebuilt or replaced. I won't go with someone elses used tranny, I'll get it done right. Even though this coupe has 300,000 miles on it, the engine was replaced with a factory new engine at 90,000 and runs great. The car has had only 2 owners and the same mechanic it's whole life, it's always had all maintenace and any repairs when needed. The previous owner is an aquaintence of mine that took great care of the car and used the same mechanic that I use. It's rust free, runs great and look even better. This is my 4th 123 diesel and I finally found a great coupe. I'll spend the money to do the tranny right because I think the car will still go for several years. Now I have to sell my 240d, I'm having a bit of trouble putting it up for sale. I loved the 240D and it's simplicity. It has manual windows, manual dual heat controls, runs and shifts perfectly. I just wanted a couple.
Thanks again for the advise.