Hi folks,

I recently bought a 1975 300D (W115) automatic and am working my way through the long list of problems that it has because it's been so neglected.

I'm now on the transmission part. Currently, the box takes ages to shift from 1-2 and is slightly better from 2-3, 3-4. It doesn't crunch but it's just a bit harsh. Any recommendations for how to remedy this? I've tried unplugging the kickdown switch to see if that makes any difference and it doesn't appear to.

When the car is cold (recently imported California car now in the UK) the car is very sluggish pulling away, although it's a heck of a lot better when it's warmed up a bit.

Probably gear oil change time - and potentially some transmission treatment additive too? What sort of oil is recommended? I've seen a number of suggestions when searching online. Also, what is the capacity of the transmission?

Thanks!

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1975 W115 300D

For the transmission I'd use Valvoline MaxLife in the red bottle and a tube of Lubegard ATF additive. IIRC the capacity with a converter drain is around 8 quarts.

For the rear diff, 85-90 if it is a cold climate. If it is warm or a high mileage car I'd use 75-140.

For the late shifting, have you tried loosening the detent cable 1-2 turns. How late is it shifting? 1-2 is a slightly prolonged shift on those transmission.

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

Thanks for this. I'll look these up.

Re: detente cable. I haven't touched anything at this point aside from the kickdown switch. It doesn't want to change until it's screaming pretty bad. Not ideal - it's definitely far from normal (at least not compared to my old '74 240D automatic)

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1975 W115 300D

Additives should never be used in oils.


Use straight synthetic ATF thats listed as DEX-III compatible.

I would not put additives in it.

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Jim

j:

1) Identify the model of the transmission. It is a 722.1xx. The identifying numbers are found stamped into the right side pan rail, just above the pan gasket. The "xx" numbers are important.

2) Since it is a 722.1 there is no control pressure cable. Some versions of 722.1s do not have any mechanical linkage to control pressure; vacuum only. And some do not have vacuum, mechanical only.

Advice can be offered only after the transmission model is identified.

Here's what I can see where you described:

115 270 1701006178

That is what is stamped into the metal above the pan gasket

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1975 W115 300D

Good. The highlighted number is the part number; it corresponds to 722.109
Attached is a scan of a manual page which details the linkage adjustment process.
Suggest that you ensure that the engine valves are correctly adjusted before doing the linkage adjustment.
If the scan is not clear enough to read when enlarged, send me an email from my screen name; I'll reply with an attachment.

Attached Thumbnails

 

Brilliant, thanks Frank. I've printed this off and will take it with me when I head over to work on the car later. Fingers crossed!

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1975 W115 300D

Hi Frank, apologies for bothering you again. I'm trying to figure out the actual capacity of the 722.1 transmission and I keep getting a huge array of answers. I think (repeat: think) it's 7 quarts but I've seen so many other answers I'm really not sure. Any ideas?

Thanks

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1975 W115 300D

Per the Service Manual for the 722.109 (yours):

In-car drain and refill, including removal of the pan, change of filter, and drain of torque converter: 4.8 liters.

Note: Even if the trans had been removed, disassembled/reassembled, and hence was dry, the capacity would be 6.1L.

I rarely use additives but Lubegard was recommended by a long time transmission shop. It slowly stopped a hard banging shift.

Fo years GM recommend Shudder Fix to stop torque converter shudder, it worked well.

What about additives for limited slip diffs sold by an specified by GM?

IMO some additives work, some don't. I respectfully disagree with additives should never be used in oils.

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer