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1985 300D
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130 Posts
Discussion Starter #1
At the risk of jacking another member's thread here, I decided to start another thread. Someone mentioned that the 722.3 was a stronger transmission than the 722.4, and that the .4 was also smaller.

First thing I would like to know, what are the differences between the two transmissions? overall length, shift points, reliability, anything I missed?

Second, what are the advantages of one transmission versus the other?

Third, why did MB change from the .3 to the .4?

I had other questions in mind when I started this thread, but I can't recall them at the moment.
 

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'95 E300 DIESEL, '91 600SEL, '92 600SEL
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17,535 Posts
Use the search feature.

IIRC, our moderator Zeitgeist upgraded his OM602 powered turbodiesel from a 722.4 to a 722.3 trans. I think the 722.3 has a higher torque rating, thus making it a stronger box. Do keep in mind that longevity is determined by driving patterns, driving behavior, service upkeep and a bit of common sense. If you believe in the "filled for life" marketing ploys, then even a 722.3 will disappoint at some point.

While not for a novice, it is definitely doable. I intend to do the same in a few years when the 722.4 in my OM606 powered diesel is at the end of its useful lifespan. This could take a while though, since the diesel is a low miler at just over 90K original miles.
 

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'04 W211 E240, MY10 W204 C300, MY11 W212 S350
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843 Posts
Are you thinking of putting a 722.3 in your 190e?

Don't bother. There is a little bit of gear ratio differences between the 722.4 and 722.3 which make the smaller engines struggle with the larger. The diff ratio is compensated for the difference in 2 and 3 rd gears.

Besides that.

The 722.3 is longer, heavier and uses a different sized yoke to connect to the drives shaft.
Then there is the NSS electrical connector on the side. They're different. You can screw around changing this if you like.
You will need to take the car to an auto specialist to get the vacuum modulator adjusted to spec.
The cooling pipes to the radiator are different. The Banjo bolt sizes at the transmission end is different. You need to get the original 722.3 pipes and replace the 722.4 ones - a P.I.T.A. job while the engine is in the car.
The transmission dipstick on a 722.3 may not fit correctly on a M102 motor.

The torque converter is different. You need to take the T.Q. from the 722.4 and use that on the 722.3.

How do I know these things?
I changed out the 722.4 for a 722.3 on my 300e 2.6.
I had the 722.3 in four around six weeks before I changed it back to a 722.4 again.
The performance in 2nd and 3rd gears was less than satisfactory.
I wasn't happy with it.

The extra length and bulk of a 722.3 may not fit under a 190e. It may fit if your car was a 190e 2.6 but I wouldn't count on it.
 

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1985 300D
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130 Posts
Discussion Starter #4
Ivanerrol, this isn't for my 190, that is a 5spd getrag and I'm keeping that till it's end. I'm actually looking more for my 2.5 swap into my project truck. Being a truck, when I saw the stronger gearbox commented in the other thread the 722.3 looked pretty appealing. I may still stick with the 722.4 for simplicity in my swap (IE not needing more parts.) I'll try to search for Zeitgeist thread, I didn't look for a swap originally which might be how I missed his thread.
 

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1985 300D
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130 Posts
Discussion Starter #6
Thanks for the link, nice detail about the driveshafts and everything. Answered all but last question (why MB changed, who knows?)

Zeitgeist, if I may pick your brain for an opinion, would you rather use the .3 or the .4 for a small truck application, occasionally tow but not often? Vehicle weight factory is about 2300 for my short bed model. Rear end from factory is 3.909.
 

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'87 300TD/'90 300D/'94 Quattro/'89 Vanagon TDI/'01 EV Weekender VR6
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I can't tell you why MB changed, but the internal gearing is different for each model. The .3 was a huge improvement for my 602, but that engine is slightly tweaked so that it performs better than stock. I think a .3 is the better trans for durability, so it should be more appropriate for towing.

I think your rear diff ratio is going to be an issue with either trans. The diff ratio in your current car is only 2.65. I believe 3.9 is considerably lower than the ratio used in any 602 passenger car with an auto.
 

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1985 300D
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130 Posts
Discussion Starter #8
hmm, that is going to be a fun issue. The highest rear end used on ANY of the Jap Mazda trucks was a 3.23, and that diff wasn't known for it's reliability. I'm trying to avoid needing to swap over the rear suspension from the 300 if at all possible, I don't want to have to worry about doing the front as well (I'm the type that wants all the wheels to be the same on the vehicle.) However, Mercedes wheels would look good on my truck, hmm.....

I'll do a search for the gear ratios of both the .3 and the .4 transmissions, see exactly what I'm working with. I'm also trying to figure out exactly how the speedometer gets it's signal. I just wish it'd stop raining and freezing on my days off so I can actually dive into the 300.
 

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'04 W211 E240, MY10 W204 C300, MY11 W212 S350
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843 Posts
Speedo feed for early transmission whether 772.3 or 722.4 is mechanical. For the later 722.4 post ,93 is electrical.
If you are going to try and utilise the drive shaft out of the Benz in your truck I would take the appropriate one from whatever transmission you use.

What ever transmission you use you will need to bodge up some switches for the Neutral safety switch and foot brake lockout - unless you transpose the gearshift mechanism from the Benz.

You will need to play with the vacuum modulater if you change to a 722.3

You will need to work out your diff ratios carefully.

Even though most documentation doesn't list the differing 2nd and 3rd gear ratios between transmissions you will need the last two digits of the transmission number to accurately find this e.g 722.358 or 722.320 or 722.409 etc etc
 

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1985 300D
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130 Posts
Discussion Starter #10
I was actually planning on using the shift console and setup from the Benz in my truck, fabbing a brake switch would be pretty easy I would imagine. If all else fails I have a parts car to adapt :)

Guess I have an even more epic build on my hands now, lol :(
 

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1985 300D
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130 Posts
Discussion Starter #11
Ok, now that I have more questions, I was wondering if there were ANY Mercedes cars that utilized a solid axle. While an IRS setup in the truck would be pretty slick, it would be a really big task that I'd rather not undertake.
 

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'95 E300 DIESEL, '91 600SEL, '92 600SEL
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If you consider the G class or Unimog to be cars, then yes MB does do solid axles (a.k.a. recycled lamp poles).

Didn't Mazda sell a diesel powered pickup somewhere around the late 70s/early 80s??? That might be a viable and much easier option for you.

Alternatively, import one of the Mazda BT50 pickups which are sold globally except North America and only comes in diesel power.
 

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'87 300TD/'90 300D/'94 Quattro/'89 Vanagon TDI/'01 EV Weekender VR6
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I'm not sure of the diff ratio, but the closest thing to a live axle would be the funky swing axles used in the Heckflosse and a few other models. That would be really weird in a truck
 

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1985 300D
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Discussion Starter #14 (Edited)
rats, I was hoping for an easier way out, hoping that something from the 70s or early 80s used a solid axle.

Guys, thank you very much for all of the answers, you all are making this easier for me with your previous knowledge.

To answer your questions, the Mazda diesel rear end used a 3.23 diff, same as the gas versions 82-84. The older ones are hard to find by themselves, let alone one of the diesel variants. I've never seen one in person. I've only seen about half a dozen of the first gen B pickups at the parts yards as well, and the axles are usually missing as they are very popular for lowered applications (they are narrower than the 2nd gen axles, popular for people who like to 'tuck frame'.) I'm checking around to see if any of the older 626s or RX7s used higher gearing, but they also are harder to find in the yards.

I'm also looking at IRS converted pickups, seeing how they have been done before. For what I am seeing, it isn't as hard as I was originally thinking. I have seen 2 swaps performed, one using an RX7 and one using a Skyline component.

This might be a hidden blessing for me, done right I might be able to use the 300D driveshaft unmodified.

Another question, is it possible to remove the IRS in the 300 as a rolling assembly like this

(pic borrowed from iizuka over at MazdaBScene)
 

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'87 300TD/'90 300D/'94 Quattro/'89 Vanagon TDI/'01 EV Weekender VR6
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52,233 Posts
Yes, the rear subframe comes out as a modular unit very similar to your pic
 

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1985 300D
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130 Posts
Discussion Starter #16
awesome! Thank you for the information. This will make things a LOT easier :) Seems that the hardest part will be to take the front brake setup from the 300 and incorporate it into my truck.
 

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1985 300D
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Discussion Starter #17
Ok guys, I do have another question. What are the OD gear ratios and the 1st gear ratios for the two transmissions? I know that the 2-3 gear ratios differ from trans to trans.
 

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1985 300D
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130 Posts
Discussion Starter #18 (Edited)
I found a thread here that covers some of the answers that I asked.

PDF, I know that the ratios may vary from trans to trans, but it is a good baseline.
http://www.w-124.info/w124/mercedes tranny_ratios_722.3_722.4_722.5.pdf

722.4 ATX
1st gear 4.25:1
2nd gear 2.4:1
3rd gear 1.48:1
4th gear 1:1
Reverse 5.14

M519 Mazda stock 5spd
1st 3.622:1
2nd 2.186:1
3rd 1.419:1
4th 1:1
5th .858:1
http://www.mazdatrucking.com/B2200/TrannyInfo.html

So for what I am seeing, the ratios are pretty close to each other for what was stock on the truck versus what is in the automatic, minus the lack of an overdrive on the 722.4. Zeitgeist, do these numbers look right to you for the .4 trans in a diesel, or did I find something that really pertains to the gas models only?

What I am seeing here is that I might be better off using the IRS if I plan to use it more for fuel efficient trips and such, and keeping the solid axle if I were to decide to use it more as a truck.
 

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1985 300D
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130 Posts
Discussion Starter #19
Ok last transmission related question for a while. What about the 722.5? I noticed that it has an overdrive on it.
#1 is it as solid a transmission as the .3 and .4?
#2 will it bolt to the OM602?
 

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'87 300TD/'90 300D/'94 Quattro/'89 Vanagon TDI/'01 EV Weekender VR6
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The .5 has an even weaker reputation than the .4
 
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