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  #1  
Old 04-17-2007, 12:22 AM
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W116 300SD 3-speed transmission?

Hey guys,

My car doesn't appear to shift into 4th gear. I have to limit my speed to around 60 mph (speed limit is 75 mph here) because I don't want to risk over revving it.

It was around 4000 rpm at 80 mph and that seems WAY too high for a diesel. My Lotus does that but 4000 rpm isn't even half of it's redline.

Any ideas? Other then that the transmission is the best I've felt on a older diesel Mercedes. It's super smooth and operates great besides the fact it won't shift out of 3rd gear.

Any ideas? I don't think the 300SD is normally a high revving car on the freeway... my 83 wasn't this way.

Thanks!

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Old 04-17-2007, 09:35 AM
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Its going into 4th. If it makes you feel any better mine revs almost that high as well... its just normal for these diesels...

If you put it in L you'll find that there is a first gear you never knew you had. Also, I imagine your kickdown functionality doesn't work. There is a box that is supposed to kickdown the tranny into first whenever you take your foot off the brake from a complete stop (otherwise it starts in second, to prevent brake creep at lights and such).

The kickdown has never worked on either of my W116s... I even replaced the solenoid on the current one.
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  #3  
Old 04-17-2007, 02:50 PM
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Quote:
Originally Posted by Tymbrymi View Post
Its going into 4th. If it makes you feel any better mine revs almost that high as well... its just normal for these diesels...

If you put it in L you'll find that there is a first gear you never knew you had. Also, I imagine your kickdown functionality doesn't work. There is a box that is supposed to kickdown the tranny into first whenever you take your foot off the brake from a complete stop (otherwise it starts in second, to prevent brake creep at lights and such).

The kickdown has never worked on either of my W116s... I even replaced the solenoid on the current one.
Thanks

Is it safe to run these things at 80 mph? It didn't feel/sound like it was struggling... the RPM just looked way too high to be safe for a 28 year old diesel.

I put it in L gear and it didn't seem to make any difference. It accelerates GREAT from a dead stop (never thought I'd say that about an old diesel) so maybe the kickdown switch is working? I need to find another W116 to compare against.

Finally my last question is... can we swap the ratio in the rear differential to bring the RPM down a bit on the freeway? I wouldn't mind sacrificing a bit of acceleration for lower rpm on the freeway.
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  #4  
Old 04-17-2007, 03:02 PM
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Quote:
Originally Posted by gtmotor View Post
Is it safe to run these things at 80 mph? It didn't feel/sound like it was struggling... the RPM just looked way too high to be safe for a 28 year old diesel.
I would... if it can't do 80mph, how long will it last at 65mph? IMO, if I'm not comfortable with its reliability at 80, I'm not comfortable with it at 45 either... so I wouldn't worry about it

Quote:
Originally Posted by gtmotor View Post
I put it in L gear and it didn't seem to make any difference. It accelerates GREAT from a dead stop (never thought I'd say that about an old diesel) so maybe the kickdown switch is working? I need to find another W116 to compare against.
If you put it in L it should not shift into 2nd until near red-line in first. Maybe try to shift yours like a manual to verify that you are in fact shifting through all 4 gears. A second failure mode of the kickdown switch is stuck on, which will prevent you shifting into 4th until redline in third (~60mph, IIRC).

Quote:
Originally Posted by gtmotor View Post
Finally my last question is... can we swap the ratio in the rear differential to bring the RPM down a bit on the freeway? I wouldn't mind sacrificing a bit of acceleration for lower rpm on the freeway.
Yep. Search for "i've found the MB easter egg" or some such... there is a thread about doing just that. Keep in mind it will make your speedo inaccurate. Personally, I want that acceleration
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Old 04-17-2007, 03:10 PM
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Thanks again

I did a search right after posting and found a lot of info but it's all on the W123 cars... do you know if the W116 has the same differential? I also need to jack it up and check the flex discs before I take it on a longer trip.

I don't mind the slow acceleration... I have another car for going fast

I asked about the reliability at high RPM because the force inside the engine increases exponentially as the RPMs rise... I haven't heard any horror stories about the cars flying apart at moderate to high RPM but you never know...
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  #6  
Old 04-17-2007, 03:17 PM
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W116 + Speed

If your car is well maintained and has speed rated tires you can enjoy 80mph. If fact the W116 is one of the best at a high rate of speed. I use mine only for Highway and have found of all the cars I have enjoyed over the years my 79SD is the best at covering the miles at 75-80.
I have also pondered how or what rear-end ratio would work.
For now enjoy your car as she can be a great alternative to Airlines .
Happy Motoring
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Last edited by 2dieseljohn; 04-17-2007 at 04:00 PM. Reason: spelling
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  #7  
Old 04-17-2007, 03:21 PM
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Quote:
Originally Posted by gtmotor View Post
I did a search right after posting and found a lot of info but it's all on the W123 cars... do you know if the W116 has the same differential? I also need to jack it up and check the flex discs before I take it on a longer trip.
I have no idea on the W123, but I'm pretty sure MB used a lot of similar sized differentials. I also think that the W126 uses the same diff since a lot of the suspension is shared between the W116 and W126. I'm almost positive that they use the same differential mount...


Quote:
Originally Posted by gtmotor View Post
I asked about the reliability at high RPM because the force inside the engine increases exponentially as the RPMs rise... I haven't heard any horror stories about the cars flying apart at moderate to high RPM but you never know...
No doubt, but I haven't heard of anything unless the engine was on its way out to begin with (bad rod bearing or such). I've also seen lots of other people concerned about high RPMs, and there always seems to be lots of re-assurances that its okay. YMMV of course

All that said... I wouldn't mind an overdrive to keep the noise down a bit
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Old 04-17-2007, 06:50 PM
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Quote:
Originally Posted by gtmotor View Post
Thanks again

I did a search right after posting and found a lot of info but it's all on the W123 cars... do you know if the W116 has the same differential? I also need to jack it up and check the flex discs before I take it on a longer trip.

I don't mind the slow acceleration... I have another car for going fast

I asked about the reliability at high RPM because the force inside the engine increases exponentially as the RPMs rise... I haven't heard any horror stories about the cars flying apart at moderate to high RPM but you never know...
Hey, how's your Elise handle compared to the 300SD
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Old 04-17-2007, 07:22 PM
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It's like a driving a go kart compared to piloting an ocean liner.

I love them both the same though. The 300SD is WAY more comfortable on the freeway (at lower speeds ). It's nice not having the aluminum tub resonating exhaust/road noise from a high-strung gasoline engine in my ears the whole time.

I would sure love to keep the Benz as the freeway cruise by lowering it's RPMs on the freeway though. Then it would be perfect.
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  #10  
Old 04-17-2007, 07:29 PM
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I have cruised at around 100mph for over 10 miles before in my SD....and it was around 4600-4700rpm at those speeds. Handled it fine. Most of the time I go between 75-80. On my recent trip to Florida I went almost the whole way both there and back at 85-90, just to keep up with traffic. It did fine with that too.
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  #11  
Old 04-17-2007, 07:34 PM
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Quote:
Originally Posted by gtmotor View Post
It's like a driving a go kart compared to piloting an ocean liner.

I love them both the same though. The 300SD is WAY more comfortable on the freeway (at lower speeds ). It's nice not having the aluminum tub resonating exhaust/road noise from a high-strung gasoline engine in my ears the whole time.

I would sure love to keep the Benz as the freeway cruise by lowering it's RPMs on the freeway though. Then it would be perfect.
Hmm.. yeah I wouldn't like 4000 RPM at 80 mph either. My car has a 2.88 I think gear ratio so I get 4000 RPM at 90. It cruises very well at 80-85. I would love to drive an Elise. I've driven Mazda Miatas before but an Elise is like 500 lbs lighter and way more horsepower. Must be nuts.

What color is yours.
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Old 04-17-2007, 09:22 PM
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Quote:
Originally Posted by pawoSD View Post
I have cruised at around 100mph for over 10 miles before in my SD....and it was around 4600-4700rpm at those speeds. Handled it fine. Most of the time I go between 75-80. On my recent trip to Florida I went almost the whole way both there and back at 85-90, just to keep up with traffic. It did fine with that too.


Excellent! Thanks for the good news guys. I took it home at 70 mph again today because I'm a wuss

Ara: My Elise is starlight black. Yes she's quick... an Elise won at the SCCA nationals in 2006 against the Z06 Corvettes and the Porsche GT3s... hugely outgunned horsepower wise but they handle beautifully

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