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"NEW OWNER" of a 1991 SL 500 weekend toy. Hope I don't go broke maintaining it!
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Discussion Starter #1
Happy Holidays everyone - I'm home this week doing some odd and end work on the house and cars.

I have one remaining bug on my SL I want to post to see if anyone else has info or suggestions --

The auto trans shifts fine in most conditions except for one:
  1. When going up a 10-15% grade
  2. And I floor the gas
  3. It gets "confused" shifting out of 3rd into 4th and instead returns to 3rd
  4. It does this abrubtly about once per second jerking the car
  5. until I let off the accelerator
  6. Once the rpm's drop (and I don't have it pressed against the floor board)
  7. It stays in 3rd until I reach the freeway an shifts back into 4th when cruising
It only does this under a) full acceleration (pedal to the medal) b) during an include (hi-torque)

THere's a freeway entrance ramp by me which is about 150 yards long and mid-way up the ramp it jerks back and forth between 3rd and 4th. Apparently it "Thinks" that 4th won't give me enough power, so it drops in to 3rd, then realizes the rpms' are too high in 3rd, so it shifts back into 4th, only to repeat (about two shifts per second or so until I let up.)

This is the only time I have an issue with the otherwise smooth transmission.

Might there be a simple component or adjustment needed?
Any thoughts?

THANKS to everyone and Happy Holidays
 

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Greek God of the R129
SL500-500SEL-190E
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8,391 Posts
Maybe adjust/replace the modulator and boden tranny cable.

Regards,
aam.
 

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"NEW OWNER" of a 1991 SL 500 weekend toy. Hope I don't go broke maintaining it!
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Discussion Starter #4
Thanks but according to the threads I read on K1 - that resolves issues between 2nd and 3rd only.

Mine is specifically between 3rd and the final cruising gear which is 4th gear.

Again - only under hi accelration and strain.
 

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2000 Obsidian Black Metallic Mercedes SL 320 V6
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iresfrank just a thought: when was the last time the tranny was serviced (fluids and filters)? Sometimes too old fluids and filters tend to give issues and also if the fluid level is too low under hard acceleration the gearbox might go out of gear.

As I said tho just a thought.

Hope it helps.

Cheers.
 

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Premium Member
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9,274 Posts
Happy Holidays everyone - I'm home this week doing some odd and end work on the house and cars.

I have one remaining bug on my SL I want to post to see if anyone else has info or suggestions --

The auto trans shifts fine in most conditions except for one:
  1. When going up a 10-15% grade
  2. And I floor the gas
  3. It gets "confused" shifting out of 3rd into 4th and instead returns to 3rd
  4. It does this abrubtly about once per second jerking the car
  5. until I let off the accelerator
  6. Once the rpm's drop (and I don't have it pressed against the floor board)
  7. It stays in 3rd until I reach the freeway an shifts back into 4th when cruising
It only does this under a) full acceleration (pedal to the medal) b) during an include (hi-torque)

THere's a freeway entrance ramp by me which is about 150 yards long and mid-way up the ramp it jerks back and forth between 3rd and 4th. Apparently it "Thinks" that 4th won't give me enough power, so it drops in to 3rd, then realizes the rpms' are too high in 3rd, so it shifts back into 4th, only to repeat (about two shifts per second or so until I let up.)

This is the only time I have an issue with the otherwise smooth transmission.

Might there be a simple component or adjustment needed?
Any thoughts?

THANKS to everyone and Happy Holidays
I agree with msbarsi that I would change the fluid and filter just because it's easy and its a good thing to do if you haven't and might fix it. I will also add that I would unplug and reconnect all terminals on the trans to make sure they are getting good contact and to look for leaks at the various gadgets or ATF in vac lines or other possible problems around the gadgets. Those are also easy things to do that could be relevent to your problem. I know I'm just confirming things you have probably already thought of. I just can't help putting in my two cents in for trans issues because I've felt the pain myself :thumbsup:
Beyond that, hopefully an expert will come along or someone who has had the same problem.
 

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You could also check the vacuum lines for leaking but I dont know if that would cause your problem or not. It shifts awful and hard without proper vacuum to the modulator on my 95 but I dont know about going up hill.
 

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Outstanding Contributor
1997 SL600 Brilliant Silver Sport with grey/dark metal interior, 234K miles
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Mine is specifically between 3rd and the final cruising gear which is 4th gear.

Fine, then replace the K2 spring.

If you've been driving this car for long and have never had the tranny serviced, it may be time. Fluid, filter, pan gasket and whatever else your Benz technician recommends upon service.

Seriously, all the stuff mentioned by the responders so far need to be evaluated, especially if the car's tranny has never been maintained by you. These trannys put up with a sick amount of abuse and neglect and (for the most part) keep on chugging away. Winter always seems to bring on a spate of tranny complaints.
 

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'93 SL500 (sold), '88 GMC Sierra 360,000 miles, '86 Yamaha FJ1200 (criminally fast)
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770 Posts
You could also check the vacuum lines for leaking but I dont know if that would cause your problem or not. It shifts awful and hard without proper vacuum to the modulator on my 95 but I dont know about going up hill.
I have to "help" my tranny shift, by backing off the gas a tad, then it shifts when I think it should..... It should be glitching due to my not have replacing one of my computer modules yet? ($)

Sometimes, it shifts well, when the throttle/speed agrees.

I can't get underneath my SL yet, but I'd sure like a couple photos of what & where these tranny components / vacuum fittings are.
 

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Greek God of the R129
SL500-500SEL-190E
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I agree with the above.
Start with the fluid, filter, if it wasn't done.
My first thought was that you did all that.

I also sometimes had a downshift clunk when going up on steep hills.
Changing the oil & filter took care of that.....

As preventive medicine.
I replace the oil & filter every two years and sometimes if car is up on jacks I empty the pan.
Dexron III is cheap, tranny is not. ;)
Guys don't bite. Haha.
I am talking first generation that uses Dexron III.

Regards,
aam.
 

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"NEW OWNER" of a 1991 SL 500 weekend toy. Hope I don't go broke maintaining it!
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Discussion Starter #11
I appreciate the tips. I will ask my MB Mech to replace fluid/filter on tranny during next service. I'm having PS pump done anyway and he's reasonable with things like that.

I'll start there. If that doesn't do it - I'll get under and look at K2
 

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I appreciate the tips. I will ask my MB Mech to replace fluid/filter on tranny during next service. I'm having PS pump done anyway and he's reasonable with things like that.

I'll start there. If that doesn't do it - I'll get under and look at K2
Have him visually check in general and check for loose connections or leaky vac lines too while he's under there.
 

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1991 500SL V8 NEOKEN modified T/B. 2000 F350 4x4 V10. 1995 SL500
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I agree with alchemy. It sounds like a vaccum leak to me to. The K-1 spring issue is dealing with shifting slippage from one gear to another. You can adjust the shift point yourself if you want to by turning the knob with the red indicator on it.Turn the knob not the red indicator. Turning it counter clockwise makes it shift long from one gear to the next (RACIER). clockwise will shift abit quicker. It's located behind the engine on the driver side just by your throttle cable. I suggest turning it clockwise about 1/2 turn if it's not a vaccum leak.
 

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'93 SL500 (sold), '88 GMC Sierra 360,000 miles, '86 Yamaha FJ1200 (criminally fast)
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I agree with alchemy. It sounds like a vaccum leak to me to. The K-1 spring issue is dealing with shifting slippage from one gear to another. You can adjust the shift point yourself if you want to by turning the knob with the red indicator on it.Turn the knob not the red indicator. Turning it counter clockwise makes it shift long from one gear to the next (RACIER). clockwise will shift abit quicker. It's located behind the engine on the driver side just by your throttle cable. I suggest turning it clockwise about 1/2 turn if it's not a vaccum leak.
The what knob??? A manual knob? Where is it?? Is there one on a '93 500?
 

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1991 500SL V8 NEOKEN modified T/B. 2000 F350 4x4 V10. 1995 SL500
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The what knob??? A manual knob? Where is it?? Is there one on a '93 500?
If your year model has one it will be where I descibe above. It's a shaft like thing sticking up from behind the engine coming from the transmission on the drivers side. It reminds you of a dip stick except it has a knob with a red indicator on top of it. Hope this helps my friend. And yes you have to turn it with your hand.
 

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Discussion Starter #16
Crash - maybe next time we meet you can point these things out to me. Hope you are there in March. I'm not racing - but will be there.
 

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1991 500SL V8 NEOKEN modified T/B. 2000 F350 4x4 V10. 1995 SL500
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I'll be glad to show you. You can change your shift points to change as quick as you want or you can red line it.
 

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Discussion Starter #18
I realize this is last year's thread but I thought I'd update. I had the tranny filter replaced and did a "COMPLETE FLUSH" of the system. my mechanic - twin transmissions of Charlotte - said he would not even do a flush unless the fluid was clean as gunky fluid can lead to failure when the "flush" pushes gunk into the wrong places. but he sid the fluid was sparkling clean. I still have the glitch of no shift under high RPMS

I will try bowden cable but I think MB will have to look at this. Its either vaccuum or eletrical and if I had to bet money - M money is on electrical as that has been the root cause of everything so far on my car.
 
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