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I'm stumped on this one, no 5th gear

16399 Views 31 Replies 9 Participants Last post by  jtdavis1312
After doing some maintenance work on my car and doing the K1 upgrade it seems iv lost 5th gear, iv done the following diagnostics but nothing :confused:

1) I have checked the 3 prong connector

2) Removed HGS controller in the effort that the car is supposed to go from 3rd to 5th but still no go

3) Replaced the valve body, flushed out tranny fluid and put in new fluid and filter

It seems to be not willing to shift into 5th at all and if i remove my foot from the pedal, the RPM will drop to idle (as if the car is in neutral)

R129 SL300-24 No 5th Gear - YouTube

I surrender and ask for your help! :surrender::bowdown:
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Good day, Have '96 SL320 and last year I performed the K1 spring change out.At that time the shifting was rough and after the change was a little better. Did you have the 5 th gear engaging before the K1 spring changeout. If all worked before change, I would replace the old spring assembly to see if working with that spring.
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5th gear was working before K1 change however as the valve body was changed yesterday, the K1 is not in the new valve body but the old one
Hey its me Noblesse Oblige Zero on YouTube. Continuing our previous conversation, I have looked it up as well and done all of the things that you state, still having the same problem. I'm still looking into it, but did you look at the micro switch in the shifter? I looked at mine it was fine had no problems,Also does your cruise control work?? Mine has never worked.. I hear it might have an effect on the electronics if its not working. One thing I haven't done is look at the codes, it can be checked on the diagnostic ports near the computer electronics side, Quoting from ArcticDweller on a different thread

On your 1993 300SL, with 5-speed Electronic automatic Transmission Control (ETC), your model has the 16-pin diagnostic connector.

The ETC diagnostics are read from PIN # 13.

If the ETC is functioning properly, you should be getting "1 FLASH".

Just to be sure you are using the proper chart it is:

Electronic Transmission Control 5-speed (722.5)
Models 129, 140
Model Years 1990-1996

Fault Code Table

DTC.... Possible Cause of Failure

1...... No fault found
2.......Engine control module (N3/4) does not match TCM
3.......Transmission overload protection switch 4th/5th gear defective
4.......CAN data line from EA/CC/ISC control module (N4/1) signal distorted
5...... CAN data line from DI control module (N1/3) or HFM control module signal distorted
6...... CAN data line signal distorted, Short or open circuit
7...... Control valve block (Y3/1y2), open circuit or TCM (N15/1) defective
8...... Automatic Transmission Control Module (TCM) (N15/1) defective
9...... Control valve block (Y3/1y2)
10.... Control valve block (Y3/1y2), short circuit

Please re-test, using PIN # 13, and determine the CODE(s). Then get back to us, and the Forum members will go from there.
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did you look at the micro switch in the shifter?
I was told by my mechanic then even if the micro switch in the shifter was bad, if the tranny control module was removed, the car would skip 4th gear and go from 3rd to 5th but that didnt happen.

Im using my E38 right now so ill report back later
Im actually starting to think it might be the Transmission overload protection switch... because it started to happen after I did some undercarriage work near the transmission. maybe I knocked it loose? I'll report back with an update when I take a look tomorrow.
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in same boat...

I think I triggered no 5th gear on mine this weekend....another thing to look at..
Bill SD, are you having the same situation as i posted on youtube?
Check and repair vacuum line between intake manifold and
ignition control unit.

I found this on an different forum

Your theory on the vacuum line may have merit!

Hey Bill can you post a picture of this vacuum line or explain exactly where this is?

Here's the original text doc
in the zip folder


Where would the line go into the intake manifold?
Bill SD, are you having the same situation as i posted on youtube?
when I let of gas, my rpm does not drop like your video....5th gear in mph engages at 50mph, revs drop from 2500 to when I accelerate to 55-60 and let off gas, the rev's walk back down at corresponding rate..5th gear does not engage
I think you might be having a more electronic issue with the 5th gear, I think ours is more mechanical... our transmissions go into neutral... when we let go of the gas... then shifting back to 4th when we resume accelerating, it may be trying to shift into 5th gear, by going into neutral and awaiting 5th to engage. This is my theory based on driving it... This happened for no reason, one day it happened... That's what confuses me, and makes me believe that it might be something else... Edit: one more thing that confuses me is that if I shift in to neutral after letting go of the gas. It shifts... then when I shift back. it shifts back to the same gear running at low revs...
5th gear started again

think the switch in console for 5th gear may have been sticking, I moved it back and forth from several times (hard) and now it goes to 5th on schedule at 50mph revs drop to 1800 rpm...whew!!!
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I opened it up and checked it and it seemed to work fine, I did what bayhas once stated on another thread. He said to put a cable and bypass the switch and see if it goes into 5th. I did and it did nothing, I think it might be a electronically operated valve that switches it to 5th. it use to not have 4th gear... Shifting into it for a split second then onto 5th... the 4th-5th switch never did anything.. I remember since I bought it. I would switch it and it wouldn't do anything. I think my theory may be correct, ill post back after I do some work with the valve use to not have 4th gear... Shifting into it for a split second then onto 5th...
so you rpm at 50mph are ??? if you are approx 2500 you are still in 4th...mine reads 1800 at 50mph....
Currently its stuck on fourth... Revving at 2500-3000 at 50-60 mph before it never did this, this whole thing started happening recently. Before I barely had fourth gear. now I completely have it...
Sorry guys, i forgot to update this thread but i partially solved my problem. I was messing about in the engine bay and replaced the TCM and Ignition module from a 300 i parted out not to long ago. Now i hold 4th gear. Hope that helps
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does it have a down shift switch under gas pedal?
Yes, photos and/or description would be GREAT : ) I too am very much wanting to check this vacuum line on my '90 300sl.
Yes, photos and/or description would be GREAT : ) I too am very much wanting to check this vacuum line on my '90 300sl.
Ill post some when i get off work but basically look to the car head on. On the driver side, there should be a plastic cover with 2 screws. Unscrew them and you should see the EZL or ignition module, there is a nipple in the center of it that goes down to the main harness and comes out at the tranny side. Like i said, try changing the module and see that never know, you might get lucky like me
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