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450 transmission swap Question

Started by JHead, 06 August 2022, 01:06 PM

JHead

I have recently bought a 1973 450SE with a bad auto transmission. After doing some research I bought a 1980 450SLC auto transmission for the swap. After the mechanic took the original transmission out and compared it to the 1980 one, he thinks it won't fit. He has been light on the details but has sent pictures of the P/N of both - they are the same number with one exception:

1973 450SE   transmission P/N R 115 271 43 01
1980 450SLC transmission P/N R 115 271 42 01

I can't find anything on the internet to decode the P/N or what the '3' or '2' represent.
Does anyone know what this number represents or have any advice on making this swap?

Thanks in advance!
1973 450SE

UTn_boy

Those part numbers are only casting numbers for the case itself, and will be of very little use, if any at all. 

The difference between your original transmission and the one out of the 450SLC is all internal.  The outside physical dimensions are the same, and they're both the same transmission.....a 722.004.  Between 1973 and 1980 there were internal improvements made, but they are interchangeable.  If your mechanic says they won't fit, then we have to assume that he doesn't want to do the job, has bad eye sight, or is ignorant (literal meaning, not the offensive demeanor) on the whole subject matter.  Possibly any combination of all of the above.  Either have him take a leap pf faith and see that they're interchangeable, or find another mechanic. 

Bear in mind that whoever does this swap for you will not be able to warranty or guarantee the used transmission.  So if the transmission out of the 450SLC lasts only three days or starts leaking, then that'll be your tough luck, and nothing to do with whoever installed the transmission.  Installing a used transmission without at least re-sealing it while it is out is very risky.   
1966 250se coupe`,black/dark green leather
1970 600 midnight blue/parchment leather
1971 300sel 6.3,papyrus white/dark red leather
1975 450se, pine green metallic/green leather
1973 300sel 4.5,silver blue metallic/blue leather
1979 450sel 516 red/bamboo

s class

I'm in agreement with Aaron, the transmission will fit, but whichever one you use,you should consider resealing it.  If budget is a constraint,at the very least you should replace the front radial seal where the torque converter neck goes into the primary pump,plus the o ring around the primary pump.  Those are two notorious leak sources.

If either of the cars is a euro spec, the transmission will be a 722.001 iirc,but even so it will be a bolt in interchange


[color=blue]'76 6.9 Euro[/color], [color=red]'78 6.9 AMG[/color], '80 280SE, [color=brown]'74 350SE[/color], [color=black]'82 500SEL euro full hydro, '83 500SEL euro full hydro [/color], '81 500SL

JHead

Thank you both so much for the replies, greatly appreciated, I thought I was losing my mind. You are right about the mechanics not having any knowledge of the subject matter. I will speak to them this week and hope they will give it a go. I have also ordered a number of seals and gaskets so thank you for that advice as well. I have scoured this website for a transmission manual / diagrammatic breakdown but it doesn't seem to exist. I want to ensure I have all the right seals. If it does exist somewhere here can you point me to the right place?

I think next time I will take it to a specialist shop - I've done some snooping and I see your shop is in the state UTn_boy.
1973 450SE

JHead

New transmission is finally in but we have concerns with the part in the image. It appears to move fluid from one part of the tranny to another, the new one is being held in the photo looks like it might have had an electronic component? We have installed the old one and removed the newer as it didn't fit on the old fluid line. Will this cause issues? Is this just a sensor that was added in the later models?

Cheers.
1973 450SE

daantjie

That is the vacuum modulator.  It controls the firmness of the shift. 
It gets vacuum from the intake, so you need a tight seal on the cap and rubber line.
Make sure you have the pin that goes into the transmission.  It is loose in the bore of the modulator so it can easily fall out if you are not paying attention.
Clockwise turns on the key gives firmer shifts and vice versa.
Daniel
1977 450 SEL 6.9 - Astralsilber

JHead

Thanks Daniel, that's very helpful.
I've done some quick digging and looks like the all metal modulators where made for the 450's from 73-76. This replacement transmission is from 1980. Using the 73' vacuum line we had to keep the 73' modulator. Do you think this will be an issue, are the modulators/lines interchangeable for these 722.004 transmissions? Or should we buy a 1980 vacuum line instead and get the newer modulator back on?
1973 450SE

daantjie

Quote from: JHead on 24 August 2022, 01:10 PMThanks Daniel, that's very helpful.
I've done some quick digging and looks like the all metal modulators where made for the 450's from 73-76. This replacement transmission is from 1980. Using the 73' vacuum line we had to keep the 73' modulator. Do you think this will be an issue, are the modulators/lines interchangeable for these 722.004 transmissions? Or should we buy a 1980 vacuum line instead and get the newer modulator back on?

Hmmm not sure really to be honest.

If the new transmission is a later one then likely you will need the plastic version with updated vacuum line feed.  It all depends on the valve body as well.  I'm by no means a transmission expert so I can only speak from my own experience.

The pin I spoke of pushes in on a valve in the valve body and this in turn modulates the fluid pressure so it gives you softer and harder shifting under varying vacuum/throttle positions. At hard/full throttle it needs to have a tight and very firm shift with no flaring or slipping.  This is by design and a function of these older Benz transmissions, they must shift quick and firm under load.

What is the current setup of the old modulator?   I am not familiar with these all steel ones to be honest.   Does it also have a pin going into the transmission?
Daniel
1977 450 SEL 6.9 - Astralsilber

daantjie

To further perhaps muddy the waters...also confirm your setup for control pressure.  Is it the cable or rod configuration?
Daniel
1977 450 SEL 6.9 - Astralsilber

JHead

I'm not sure. Haven't got a hold of the mechanic in a few days - the car is off the rack for a moment. But I have found a low res diagram of both modulators in question (335 is the all metal modulator). It looks like they are both similar in construction - is this the rod or pin you were referring? I hope the old one will work fine if so. We haven't started it up yet, there are still a few things to connect up. 
1973 450SE

daantjie

Yup might be best to button it all up as is then go for a test drive.  You will have to fine tune the shift points anyway.
Daniel
1977 450 SEL 6.9 - Astralsilber

JHead

Thanks again Daniel. I'll tell you how it goes.
1973 450SE

s class

You can use the early version metal bodied modulator valve on the late transmission, as long as it's internal diaphragm is in tact.   You will moat likely need to adjust to suit though.

That transmission will have rod type control for kick down, the cable arrangement was only from 722.3 onwards


[color=blue]'76 6.9 Euro[/color], [color=red]'78 6.9 AMG[/color], '80 280SE, [color=brown]'74 350SE[/color], [color=black]'82 500SEL euro full hydro, '83 500SEL euro full hydro [/color], '81 500SL

JHead

Thanks everyone. Got the car back yesterday from the shop and it shifts great. I will definitely take it to a specialist shop next time. I'm a new owner so there's still a bit of work to do on it but its running well now. Once I give it a good wash I'll make a new member post.
Cheers.
1973 450SE