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rein
Regular
Date registered: Sep 2006
Location: Ontario, Canada
Vehicle(s): '83 SWB 280 converted to TD, "86 sold
Posts: 73
| sedan transmission v.s. G transmission
Hi guys,
What are the essential differences between the g transmission and one from a turbo diesel sedan? |
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Cookeville
Member
Date registered: Jan 2012
Location: Cookeville, TN
Vehicle(s): 63' Unimog,84' 300sd,85' 300GD,05' ML500
Posts: 12
| RE: sedan transmission v.s. G transmission
I've got the sedan trans in my rig. I don't like only being able to run 65-70mph max and its got a hard down shift into first gear. That my just be my trans but i've heard of other with the same issues. Other than that its solid and if it goes out I can pop a rebuilt trans in for a couple hundred bucks. I'm sure I've said something wrong but someone will correct. |
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chris505
Date registered: May 2007
Location: San Francisco
Vehicle(s): '79 280E/'80 280GE/'00 G500
| RE: sedan transmission v.s. G transmission
rein - 4/17/2012 6:09 PM
Hi guys,
What are the essential differences between the g transmission and one from a turbo diesel sedan?
One hugely important difference is all of the G auto transmissions stay in first gear when the selector lever is in the lowest gear, very important for low speed off-road driving.
The passenger cars do not stay in first, they will automatically upshift to 2nd when the motor nears redline or when you let your foot off the gas pedal.
I have never heard of a passenger car auto transmission that was modified to hold first gear.
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hipine
Date registered: Jul 2006
Location: US, CO, Bailey
Vehicle(s): 460 1980 280GE w. 617A
| RE: sedan transmission v.s. G transmission
Cookeville - 4/17/2012 7:37 PM
I've got the sedan trans in my rig. I don't like only being able to run 65-70mph max ....
The G trans also is 1:1 top gear and so will have the same top speed as the sedan auto trans. That's the extent of my limited knowledge on this subject! 
-Dave G. |
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sjtymko
G-Class Photo Host
Date registered: Apr 2006
Location: Canada, AB, Sherwood Park (Edmonton)
Vehicle(s): 2002 G500, 2009 B200
Posts: 511
| RE: sedan transmission v.s. G transmission
I forget the exact ratios now, but the G tranny has a first of about 4:1 while the sedan tranny has a first gear ratio of about 3.5:1. Very significant. The above mentioned ability to lock in first is also significant. The G tranny is also stronger. How much? I don't know. However, certain internal components are reported to be stronger. The G tranny is built to be more water resistant. I believe the sedan tranny can be made to be the same with a few minor mods. The 300GD tranny starts in first while the 280GE and sedan trannies start in 2nd - major pain with such a heavy vehicle and wimpy engine. There might be more that I can't think of right now. They both have the same 1:1 4th gear. Some will say, however, that the sedan tranny is the better one to swap in. It is manufactured to go with the TD engine and, therefore, will operate as intended by MB. There is likely some truth to this. I was never happy with my TD engine and G tranny combo. I had corresponded with a guy in Germany years ago who did have success with a G tranny. I don't know what he did to it or if he was just more tolerant than I. Many I know of have reported to be happy with the sedan tranny. Steve
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Inkblotz
Expert
Date registered: Apr 2006
Location: Georgia
Vehicle(s): 90 300GD "Thundering Turtle II", w/ 603A turbo
Posts: 3190
| Re: sedan transmission v.s. G transmission
I believe most if not all of the 300SD s-class diesel sedans transmissions due to the weight of the vehicle start in first.
M |
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Razon
Date registered: Jul 2008
Location: Vancouver, BC
Vehicle(s): 1986 280ge Cabrio, 617A, 5sp manual
| Re: sedan transmission v.s. G transmission
Both gearboxes start in 1'st.
The only time they don't, is when there is a problem with either mechanical adjustments, vacuum system, or the vacuum switchpack on top of the valve cover. Details on this can be found in the manual.
Since you asked about differences, besides the gear ratios, the fact that the sedan doesn't hold 1'st gear, and the torque converter is not sealed:
-they're physically different. The sedan tranny is actually longer (the tranny mount sits futher back). If you want to install it in a G, the A-frame stabilizing bar between the tranny and t-case must be modified. If you want to be able to put the shifter in 1'st gear position (that doesn't mean that it will actually work...I'm only talking to be able to put the shifter in that position), you have to build a custom "blocking plate" that allows teh shifter linkage to colapse, and the shifter to go in 1'st gear position.
-the output flange for the driveshaft is different, but easily interchangable
-the lines that go to the oil cooler have different fittings on the tranny side(smaller)
-G-tranny has much bigger oil capacity (deep oil cooler)
-oil filler/dip-stick different
-throttle position adjustment is different (on the G is with a rod, on the sedan is cable)
- I've heared that teh torque converter is different (different stall speed and torque multiplication factor, but I never checked the numbers)
maybe I'll remember more later...but that's it for now |
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chris505
Date registered: May 2007
Location: San Francisco
Vehicle(s): '79 280E/'80 280GE/'00 G500
| RE: sedan transmission v.s. G transmission
I have installed a turbo OM617 motor into an auto 300GD and the stock 300GD transmission shifts perfectly behind the turbo motor, I was really surprised because I know how much trickery MBZ employed in making the passenger car autos play nice with the turbo motors. |
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hipine
Date registered: Jul 2006
Location: US, CO, Bailey
Vehicle(s): 460 1980 280GE w. 617A
| RE: sedan transmission v.s. G transmission
Thanks for sharing that, Chris. I get a lot of questions like this from people thinking about 617A conversions and since my experience is all with the manuals, I don't know what to tell them. Great inputs here. From what I'm hearing its best to stick with the G trans if one has an auto box.
-Dave G. |
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rein
Regular
Date registered: Sep 2006
Location: Ontario, Canada
Vehicle(s): '83 SWB 280 converted to TD, "86 sold
Posts: 73
| RE: sedan transmission v.s. G transmission
Thanks guys. The reason I posed the question is that when my conversion was done, a lever on the G tranny (kick down?) was wired in a fixed position due to the deletion of a rod mechanism present in the 110 configuration. In the sedan transmission (TD engine) this lever is apparentally activated by vacuum. I thought I might use a sedan tranny for proper interfacing and thus proper function, of the engine to transmission. This is one of a few things that I'm trying to "put right" so I can actively drive this wonderful vehicle on a daily basis. The overheating problem is the next issue. Thanks again. |
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hipine
Date registered: Jul 2006
Location: US, CO, Bailey
Vehicle(s): 460 1980 280GE w. 617A
| RE: sedan transmission v.s. G transmission
I bet it's not necessary to change the whole trans in order to get the G trans to function correctly with the 617A. Maybe Chris can help with what to do with that lever on a 617A conversion. If not (he's busy and maybe not back here often) you might send a PM to the fellow who goes by "WarrenT" on this list. Warren's done a number of auto box 617A conversions and will know what you're talking about.
Do you have a separate thread going for the overheating? I'll search.
Good luck!
-Dave G.
PS Warren is in Montreal
Edited by hipine 4/19/2012 2:37 PM
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dentsmithy
Elite Veteran
Date registered: Sep 2007
Location: NFA
Vehicle(s): 1986 230Ge, , 1979 240gd cabrio, AD-SL
Posts: 912
| RE: sedan transmission v.s. G transmission
chris505 - 4/17/2012 2:46 AM . The passenger cars do not stay in first, they will automatically upshift to 2nd when the motor nears redline or when you let your foot off the gas pedal. I have never heard of a passenger car auto transmission that was modified to hold first gear. Just for completeness ;) I had a 123 series 230TE with an auto box that stayed in first and was also lower than the normal passenger car. It was an MB service vehicle but was made as a short run of 20 cars so not many around but they are there  I did 285,000 miles on it and passed it on to Bill Moss who passed it on to a G wagen owner so may well be alive and kicking still.
Edited by dentsmithy 4/19/2012 5:05 PM
 (123 service.jpg)
Attachments
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 123 service.jpg (10KB - 24 downloads)
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rein
Regular
Date registered: Sep 2006
Location: Ontario, Canada
Vehicle(s): '83 SWB 280 converted to TD, "86 sold
Posts: 73
| Re: sedan transmission v.s. G transmission
I'll start a thread on the overheating as soon as I solve the tranny issue. I have finally realized that multi-tasking is not all that it is cracked up to be! |
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hipine
Date registered: Jul 2006
Location: US, CO, Bailey
Vehicle(s): 460 1980 280GE w. 617A
| Re: sedan transmission v.s. G transmission
rein - 4/19/2012 9:49 PM
I'll start a thread on the overheating as soon as I solve the tranny issue. ...
What's wrong with the trans? Or is it a driveability issue?
-Dave G. |
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Razon
Date registered: Jul 2008
Location: Vancouver, BC
Vehicle(s): 1986 280ge Cabrio, 617A, 5sp manual
| RE: sedan transmission v.s. G transmission
rein - 4/19/2012 10:26 AM
Thanks guys. The reason I posed the question is that when my conversion was done, a lever on the G tranny (kick down?) was wired in a fixed position due to the deletion of a rod mechanism present in the 110 configuration. In the sedan transmission (TD engine) this lever is apparentally activated by vacuum. I thought I might use a sedan tranny for proper interfacing and thus proper function, of the engine to transmission. This is one of a few things that I'm trying to "put right" so I can actively drive this wonderful vehicle on a daily basis. The overheating problem is the next issue. Thanks again.
The sedan and the G auto transmissions function exactly the same with the exception that the G tranny has an extra solenoid to hold 1'st gear.
There is no trick, or anything special for that matter to make the G tranny shift perfectly behind the om617a. You just have to make sure that the vacuum source is good, the throttle position linkage is adjusted properly and that the kickdown and hold 1'st gear switches are wired and work properly.
The rod you're talking about cannot be in a fixed position, and it's function cannot be replaced by vacuum.
You simply have to modify one of the "levers" on top of the valve cover on the 617a so that the lever that comes from the tranny clips on the little ball at the end of the lever. Then you have to adjust it in such a way that when the gas pedal is at idle , the lever that goes to the tranny is all the way towards the back of the car. This means you have to make sure that the lever in the tranny is at it's full travel, towards the back of the car.
As you press the gas pedal, the rod, and the lever on the tranny must move towards the front of the car, without much backlash.
This is the only critical thing you need to do to have a smooth shifting tranny... You'll find that it even downshifts by itself when pressing harder on the gas and hold if there for a little while, before you even hit the ( you will see this on steeper hills)
The kickdown shifts it into a lower gear without delay, even if the rpm are allready rather high. It also holds the lowest possible gear until the "redline" (for the lack of a better choice of words)
The vacuum mainly adjusts how hard the shifts are, and it makes the tranny start in first ( when starting from standstill...without pressing the kickdown).
The hold 1'st gear, it does exactly that. The tranny will never shift out of 1'st.
As far as a car tranny holding 1'st gear...as in NEVER shifting into 2'nd (regardless what model the car is)...unless the car has a 1'st gear selection on the gear shifter, I don't really belive it. The auto tranny that cand behind the 617 and 617a engines didn't have a 1'st gear selection.
I can take pics of the rod, and hiow it's connected to the engine tomorrow. |
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rein
Regular
Date registered: Sep 2006
Location: Ontario, Canada
Vehicle(s): '83 SWB 280 converted to TD, "86 sold
Posts: 73
| RE: sedan transmission v.s. G transmission
Thank you. That would help greatly. |
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hipine
Date registered: Jul 2006
Location: US, CO, Bailey
Vehicle(s): 460 1980 280GE w. 617A
| RE: sedan transmission v.s. G transmission
Razon - 4/20/2012 2:07 AM
...This means you have to make sure that the lever in the tranny is at it's full travel, towards the back of the car.
As you press the gas pedal, the rod, and the lever on the tranny must move towards the front of the car, without much backlash....
Intersting. What is that rod-operated lever on the G-style trans controlling? Another way of stating it would be, what's happenning if it's disconnected and fastened in a single position? Just "idle" curiosity... DOH!
-Dave G. |
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chris505
Date registered: May 2007
Location: San Francisco
Vehicle(s): '79 280E/'80 280GE/'00 G500
| RE: sedan transmission v.s. G transmission
Dave,
That rod/lever dictates when the transmission shifts into the next gear. When the pedal is to the floor that lever is also all the way forward, making the upshift occur near redline. The lever is attached to a valve inside the valve body that controls fluid pressure.
Strangely enough the 1985 300GD I mentioned above came from the Graz factory with no lever/rod on the passenger side of the transmission, the only way it senses when and how hard to shift is through the one vacuum line hooked to the brake booster/vac pump line.
Im not sure when the 300GDs were first fitted with this style of transmission but I know the earlier 300GD autos did have the lever/rod, just like all of the 280GE autos.
Making a 280GE auto work behind the diesel motor will be difficult, it will drive and shift, but it will want to up-shift near 6000RPM when driven at wide open throttle. The only way I know of making a 280GE transmission shift like a 300GD transmission is by installing a 300GD specific valve body. |
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kmaser
Extreme Veteran
Date registered: Oct 2008
Location: Alberta canada / UAE
Vehicle(s): 1988 280GE SWB 617A with IP mods and HX30
Posts: 301
| Re: sedan transmission v.s. G transmission
I have the 280ge auto behind my OM617A and it shifts great. It took some patience in adjusting that rod to work properly and shift when you want it to. I took the cable from the sedan tranny and played with the length and position of where it is attached to the lever to get the right ratio of travel between the valve cover mounted arm and the lever. I will have to revisit the manual though because my tranny does not start in 1st gear unless I hit the kick down switch. |
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hipine
Date registered: Jul 2006
Location: US, CO, Bailey
Vehicle(s): 460 1980 280GE w. 617A
| RE: sedan transmission v.s. G transmission
That's fantastic information, Chris. Thanks so much for taking the time to share it here. I know it will help a lot of people going forward.
It's interesting that they changed the transmission later in the model cycle. I wonder if they figured out a different way to sense load, other than throttle position (vacuum in the booster line won't do it, it's constant on the diesel of course). Or maybe they figured with the small rev range and torque characteristics of the diesel, it just didn't matter enough to justify the added complexity and they found a way to "set it and forget it" like Ron Popiel.
Thanks again for your recent posts. Always great to hear from you.
-Dave G. |
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