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Discussion Starter #1
I currently have two 1993 300SD w140s. My new one is black and has ASD (hydraulic fluid reservior behind drivers side headlight). My old one is white and does not have ASD (no reservior). Here is what has me confused:
NonASD white car runs at 2700 [email protected] mph, ~2000 [email protected] mph in 2nd
ASD black car runs at 3000 [email protected] mph, ~2300 [email protected] mph in 2nd

The differential gear ratio is supposed to be the same whether with or without ASD. Both cars have stock rims and the correct tire size (225/60R16.) Speed seems to be accurate in both based on my perception (I may have both cars driven simultaneously to verify this.)

Can anyone account for this difference? What rpm does your diesel run? The black ASD car shifts like a dream.
 

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is the 95 a 95.5?

it could be the difference between 722.3 and 722.6 gearing.

What tranny do you have in the 95?
 

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Discussion Starter #4
1993

is the 95 a 95.5?

it could be the difference between 722.3 and 722.6 gearing.

What tranny do you have in the 95?
Both are 1993s. Isn't the newer transmission 5 speed? Wouldn't the shifter look different if that had been dropped in? I'll be checking numbers.
 

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my bad, I thought one is 93 and the other 95.

Yes you're right, the shifter will look different. 722.6 was introduced in late 95/early 96, and it is 5 speed.

722.3 4speed, in all early 400-500-600 and diesels.

722.5 5 speed in all early 300

after ~1995/96

722.6 5speed in all later 300-350-400-500-600
 

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Discussion Starter #6
Yikes

~2750 rpm at 75. Confirmed this morning.

95 S350D with ASD
Thanks much. Not what I wanted to hear. This means my car is different. Does anyone know if gear ratio is on a mercedes sticker somewhere on the w140 cars? I didn't detect anything in EPCNET for trailer towing gearing, just ASD and nonASD. Car shifts great. I don't know if ASD failing could account (I doubt). Maybe ASD differential was put in this car from another merc with different ratio. I am going to confirm with help of another driver that both cars are going the same actual speed in 2nd gear. It seems like they are, but maybe not. I'll check the part number on the differential and transmission. Previous owner claimed to get as high as 28 mpg highway. I am getting more like 23 mpg.
 

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you chould have a slipping torque converter, or one that is not locking at all...

swapped differential is also a possibility... as the 300-320 have much higher ratioed differential...
 

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Thanks much. Not what I wanted to hear. This means my car is different. Does anyone know if gear ratio is on a mercedes sticker somewhere on the w140 cars? I didn't detect anything in EPCNET for trailer towing gearing, just ASD and nonASD. Car shifts great. I don't know if ASD failing could account (I doubt). Maybe ASD differential was put in this car from another merc with different ratio. I am going to confirm with help of another driver that both cars are going the same actual speed in 2nd gear. It seems like they are, but maybe not. I'll check the part number on the differential and transmission. Previous owner claimed to get as high as 28 mpg highway. I am getting more like 23 mpg.
PO may be a liar. :)

I get ~23-5 mpg all the time, nowhere near 28.

I should correct that comment. At 45-55 I could probably get 28+mpg. At 65+mph, I get 25 (and lower) mpg.

As far as RPM: as long as my foot is controlling speed, the RPM is ~3000 at 75 mph. when I engage cruise, it drops to ~2750 rpm.
 

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My 300SEL runs at 120 KPH (75 MPH) at 3250 rpms and it has ASD and 4speed transmission, but my car is not a diesel.
 

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Discussion Starter #10
Cruise

PO may be a liar. :)
As far as RPM: as long as my foot is controlling speed, the RPM is ~3000 at 75 mph. when I engage cruise, it drops to ~2750 rpm.
Great information. I don't understand why this would be the case, but my cruise was out on both cars. I fixed one of the modules and it is now in the new black car. I've not checked the rpms with cruise at highway speed.
 

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Discussion Starter #11
LWB

My 300SEL runs at 120 KPH (75 MPH) at 3250 rpms and it has ASD and 4speed transmission, but my car is not a diesel.
Wow. I didn't know 1993 300 came in long wheel base. I'll be checking out differential part numbers in the next week and see if it gets me anywhere. I'm a little slow checking things out because I've got the car accross town in a two car garage where I can have the two vehicles side by side. Not over there every day.
 

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Great information. I don't understand why this would be the case, but my cruise was out on both cars. I fixed one of the modules and it is now in the new black car. I've not checked the rpms with cruise at highway speed.
No Problem. I had the chance to run it to and from work last night, I figured it was an interesting piece of information, at the least. Good luck, let us know what you find out!
 

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Wow. I didn't know 1993 300 came in long wheel base. I'll be checking out differential part numbers in the next week and see if it gets me anywhere. I'm a little slow checking things out because I've got the car accross town in a two car garage where I can have the two vehicles side by side. Not over there every day.
Yeah LWB 300/320 was available for the EU market, US didn't get 300/320 in LWB but you guys have other good features like standard soft close and standard bose sound system which my car doesn't have.
 

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Yeah LWB 300/320 was available for the EU market, US didn't get 300/320 in LWB but you guys have other good features like standard soft close and standard bose sound system which my car doesn't have.
We did get LWB 300/320, there are lots of post face lift S320 LWBs running around. Although I haven't seen production numbers based on what I've observed I think more were LWB than SWB although I could be wrong.

As for trans in 300SD / S350D all were 722.367. As for difference in rpm at road speed in one car vs the other I can't say because I don't know enough about the signal generator on these and where it comes from. They should have same rear differential.

One other thing to check is tire circumference. If the tires are different mfgr there may be a difference in circumference. Just because they're both 225/60r16 doesn't mean they're identical. If the tires are new enough you can find circ info online perhaps. It may not explain it all but it could account for some of it.

Good luck and post back, I'm curious about this. I will have the 300SD out today so I'll see what rpm it's doing at 65. As for mpg I got 28.5 this past summer with AC on driving 65.
 

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Discussion Starter #15
One other thing to check is tire circumference. If the tires are different mfgr there may be a difference in circumference. Just because they're both 225/60r16 doesn't mean they're identical. If the tires are new enough you can find circ info online perhaps. It may not explain it all but it could account for some of it.

Good luck and post back, I'm curious about this. I will have the 300SD out today so I'll see what rpm it's doing at 65. As for mpg I got 28.5 this past summer with AC on driving 65.
I'll be switching out the tires late next week so I'll see if difference. My mpg comments were for 75-80 mph. The old car got 26-27 mph at 75 mph. I am hoping the cruise difference noted above is a feature of the ASD. I've got the car at another garage so won't try until tomorrow at the earliest.
 

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I currently have two 1993 300SD w140s. My new one is black and has ASD (hydraulic fluid reservior behind drivers side headlight). My old one is white and does not have ASD (no reservior). Here is what has me confused:
NonASD white car runs at 2700 [email protected] mph, ~2000 [email protected] mph in 2nd
ASD black car runs at 3000 [email protected] mph, ~2300 [email protected] mph in 2nd

The differential gear ratio is supposed to be the same whether with or without ASD. Both cars have stock rims and the correct tire size (225/60R16.) Speed seems to be accurate in both based on my perception (I may have both cars driven simultaneously to verify this.)

Can anyone account for this difference? What rpm does your diesel run? The black ASD car shifts like a dream.
Well, I have 300SEL, which has 722.3 transmission (4 speed) just as both yours should have. All 722.3 have same gear ratio (1:1) in 4th speed, but vehicles may have different final drives.

My 300SEL has 1:3.46 final gear ratio giving me 61 mph @ 2700 rpm, which corresponds exactly with the 75 mph @ 3000 rpm as for your 300SD with 1:2.82 final gear ratio as standard for your model (white one).

For W140 it should not matter whether ASD, ASR or any other configuration. However, the 300SE/SEL model came with an optional 1:3.65 final gear ratio but it appears as if 300SD came only in the standard version.

With 75 mph @ 3000 rpm you would have a final gear ratio of around 1:1.13 which to my knowledge does not exist (1:2.07 and 1:2.27 exist for W126).

Could it simply be your RPM meter out of calibration?

Or a slipping torque converter as pointed out by someone else?
 

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Discussion Starter #19
Swap instrument clusters?

...Could it simply be your RPM meter out of calibration?

Or a slipping torque converter as pointed out by someone else?
Wow. First I'll say that engaging the cruise did not help. Runs the same rpm. At 65 mph I am 2500 rpm (not far from Mr. Lloyd), at 75 mph 3000 rpm. Also remember that in 2nd gear it is running 250 rpm faster than my white one at 15 mph. Does that not rule out lockup torque converting failing to lock?

I'll be getting tires sorted out later this week. If the rpm meter is out of calibration would swapping instrument clusters work? (Will car mess up if I do that?)

I will say this that the car runs and shifts differently from old white 300sd. It just gets off the line much better and seems like it trully had a different ratio in the differential. I think its this or tire size since I can't think of anything that would make the car feel different and have higher rpms in 2nd hear and top gear.
 

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Wow. First I'll say that engaging the cruise did not help. Runs the same rpm. At 65 mph I am 2500 rpm (not far from Mr. Lloyd), at 75 mph 3000 rpm. Also remember that in 2nd gear it is running 250 rpm faster than my white one at 15 mph. Does that not rule out lockup torque converting failing to lock?

I'll be getting tires sorted out later this week. If the rpm meter is out of calibration would swapping instrument clusters work? (Will car mess up if I do that?)

I will say this that the car runs and shifts differently from old white 300sd. It just gets off the line much better and seems like it trully had a different ratio in the differential. I think its this or tire size since I can't think of anything that would make the car feel different and have higher rpms in 2nd hear and top gear.
First of all, that transmission does not have lockup torque converter (it came with the 722.5 version, and you are supposed to have 722.3 with the SD).

The torque converter works by having the engine shaft driving a hydraulic pump, which in turn drives a turbine on the transmission shaft. The more difference in speed between the two shafts, the more pressure is provided by the pump and the more torque is provided by the turbine to the transmission.

If the pump is worn, it takes more difference in speed to provide the same pressure, and if the turbine is worn, it take more pressure/flow to provide the same torque. In other words if the torque converter as a whole (pump and turbine) is worn, it takes more engine speed to run the vehicle at a certain speed at a certain load.

This is just the background to understand what happens.

Next, the fact that the torque converter does not have lockup makes it difficult to exactly compare rpm's because it depends on the vehicle load. That also explains the guy, who experienced different RPM with an without cruise control (it shows that cruise control is better to go easy with the accellerator pedal).

With a final gear ratio of 1:2.82 (as you are supposed to have) and nominal wheel circumsphere, you should run 2646 rpm @ 75 mph and 2293 rpm @ 65 mph - that is if torque converter is locking, which it is not - then add some 50 -100 rpm for the torque required to keep the vehicle running at that speed, and you end up with some 2700 rpm @ 75 mph and 2350 @ 65 mph.

This is also what you have in your white one, right?

Now, if final gear ratio was 1:3,13 (which does not exist), that would transform to 3000 rpm @ 75 mph and 2600 @ 65 mph. You don't have that much at 65 mph, right? So, numbers do not match well with that theory.

Your figures are 3000/2500, and assuming a original final gear ratio of 1:2.82, that would give a "slip" (rpm difference required to provide enough torque) of some 350 rpm @ 75 mph and 200 @ 65 mph. These numbers match well with a worn torque converter.

My other theory mentioned earlier was that an offset of the rpm meter of say 250 rpm could explain the 3000 rpm @ 75 mph, but that should then show 2600 rpm @ 65 mph. So, numbers do not match with that theory. Anyway, verify that idle shows around 600 rpm.

I hope this will guide you a bit further (but I don't hope for you, that the conclusion is rigth, i.e. worn out torque converter).

Good luck.
 
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