300D Auto transmission interchangeability

[3DB]

Hi all,

I have a 1976 model 300D with a manual kick-down transmission and have been offered one of two spares (I assume both are vacuum kick-down):

• One from a 1982 model 300D; and

• Another from a 1984 model 300D.

Does anyone know off the top of their head whether either of these would make more sense in terms of easy interchangeability with my car?

[Tony From West Oz]

Both of these use a vacuum modulator. The '84 also uses an throttle position cable.
Your IP does not have a vacuum control valve (to supply vacuum to the transmission modulator.
These will make the installation of either of these transmissions problematic.

[3DB]

Thanks, Tony.

I did wonder about the vacuum modulator, but didn't realise the IP was different.

I also have a spare IP.....it is off a later car and looks slightly different. I recall that one is an 'M' pump and the other is an 'MW'.....not sure which is which and if it is even relevant. Also not sure if the spare IP is serviceable.

In theory, if I was to put a new trans in my car with the old IP, is it only kick-down that would be affected if no vacuum was applied, or all gear changes? Reason I ask is I find I manually shift a lot anyway (especially up and down between to 2nd & 3rd) as the shift points are sub-ideal and finicky when cold.

[Tony From West Oz]

Without the vacuum supply to the modulator the engine would rev out very high before up shifting and shifts would be harsh.
You could apply full vacuum to the modulator, but then shifts would be soon and very soft. In fact, if you were trying to accelerate a 300D in traffic the tranny would most likely slip significantly during shifting and your acceleration would be even slower than was before. I suppose you could use a vacuum restriction and a valve set to leak vacuum off, so you could adjust the vacuum for a compromise between transmission acceleration and shift points.
If that sounds OK they I would recommend the '80 - '83 transmission rather then the '84 one.
How much are they asking for the transmissions:?

[tsharkey]

Hi Ethan,
Everything Tony said plus ,,,,,

You can fit the vacuum modulator onto the side of the IP and you will have to get the throttle linkages for the top of the valve cover. All quite doable but there is a bit of fine tuning.

If you fitted the late IP, you will need the Injector lines as well as the later IP is smaller and closer to the engine. You will also need to block off the oil return between the block and IP as the later doesn't use it. Once again, all doable but with some complexity.

Interestingly, the Factory Turbo diesels use the early style IP through out.

I am not 100% sure if the transmissions themselves are the same length - so a tailshaft revision might be required. It may also trigger a different rear cross member that the gear box bolts onto and different NeutralStart / Reverse Light wiring requirements and speedo cable length ....

If you had access to the donor car with all the minor bits - Then you would be OK. Without, inevitably you will get into the I need to source / adapt incremental upgrade game as you are doing the job .....

The later transmissions are oK but are notorious for developing very weak reverse. You tighten the band till there is no more and then still loose reverse when the trans is cold. That plus flaring over time and leaking rear seal. This developed on the family wagon, so I had the trans fully reco'ed by a workshop that only does transmissions and when I rang them, they could immediately tell me the various flavours of auto's the W123 had (as Tony listed above) and their common problems (demonstrating they had the right knowledge beyond transmissions themselves).

It cost about $1,500 turn key (I drove in and they did the job - Got the car back a week later).

[mathuisella]

:) the transmissions are mine, i'm moving house and my car is manual transmission, so i offered one to 3DB. I don't want much, just make me an offer that's fair :) otherwise they'll sit in the garage wrapped up at the new place.

location brisbane :)

1984 transmission

26855009_10213100679284416_942508506_o.jpg

1982 transmission

26942131_10213100679364418_1825528988_o.jpg

all covered in the corner of the garage protected from the elements

26942002_10213100696324842_738458128_o.jpg

[tsharkey]

:) the transmissions are mine, i'm moving house and my car is manual transmission, so i offered one to 3DB.

I think 3DB would want an upgrade kit that includes

1. Vacuum regulator that connects to the side of the IP
2. The Vacuum valves and hoses that connect to the accelerator lingages, the IP Vacuum regulator and transmission

Are they different lengths ? Get 3DB to measure his as well.

The 84 would be the best as I suspect it is common to the M110 version as well and is the strongest (her has a turbo so the upgrade is worth it). Stamped on the side of the 84 will be a number 1232711901722xxx - What is the XXX ? that will spell out which series transmission it actually is, I couldn't get it off Google but the 123 271 19 01 was fitted to Turbo Diesels in the US.

[3DB]

Crikey, nothing is ever simple is it?

Thanks for all the good knowledge there.

Tim - my ears pricked up a bit when you said the factory turbodiesels use the old IP......off the topic here, but is the ALDA unit on those a modular part that bolts on? Or do you need a completely different IP with factory ALDA?

(another way that I can increase power and break the trans faster)

[GrampiansMerc]

Hey there 3DB

for your information I put a trans from a 280 (petrol) in my 300TD (diesel) it changed better and perked it up a bit!

[Tony From West Oz]

Crikey, nothing is ever simple is it?

Thanks for all the good knowledge there.

Tim - my ears pricked up a bit when you said the factory turbodiesels use the old IP......off the topic here, but is the ALDA unit on those a modular part that bolts on? Or do you need a completely different IP with factory ALDA?

(another way that I can increase power and break the trans faster)

3DB, While the IPs are from the same series, they are different inside the housing. The ALDA acts on the Max Fuel adjustment to increase fuel on boost (or reduce fuel on a NA engine at altitude). The old style IPs I have seen in Australia (other than ones for a turbodiesel) did not have an ALDA fitted (probably because MB didn't believe we had any significant traffic at high altitudes.

I can provide you with photos explaining how to increase the Max Fuel adjustment, if you want to increase the power of your engine. You should easily get 10%, maybe 20% increase at the expense of fuel economy and increased black smoke.

[mathuisella]

viewtopic.php?f=20&t=24690

put the two transmissions up for sale, $100 each :) come grab a bargain for in 10 years time you'll be kicking yourself when the tranny blows and the cheapest replacement is north of $1000

[3DB]

I can provide you with photos explaining how to increase the Max Fuel adjustment, if you want to increase the power of your engine. You should easily get 10%, maybe 20% increase at the expense of fuel economy and increased black smoke.

Thanks, Tony - I'd be grateful to receive that information.

[Tony From West Oz]

3DB,
I posted in the relevant section - The Mod Squad (not sure if this is accurate for a NA 300D LOL)
viewtopic.php?f=30&t=24706