280SL Automatic Transmission has lost third and fourth gear?

[calhippie]

I have searched the forums here extensively, but have not found anything resembling my transmission problem.  Need some thoughts on this: 

As background, my transmission has always been a little "wonky," meaning it lurches a bit when putting into gear or into reverse, shift points too high, little annoyances like that.  About a year ago, I decreased the pressure a bit on the side of the transmission, which made it shift sooner (but didn't cure the "lurch," but that's a separate issue).  A shortage of proper tools (I don't have the correct vacuum gauge fitting to check trans pressure, for example) has made adjustments imprecise, but not impossible.  I have made no other adjustments to the trans, and none since that decreased pressure a year ago. 

Yesterday, while driving up a long incline at about 55mph in 4th gear, I heard a distinct BANG! or POP! from under the car, seemingly within the transmission tunnel.  Pressing the throttle would cause the motor to rev, but power was no longer being sent to the rear wheels.  At the same time, my speedometer dropped to zero, as though the cable had broken.  I put it in neutral and coasted to a stop.  I could hear something under the car flapping around briefly, but that sound stopped when I stopped the car.  Looking under the car did not reveal anything out of the ordinary.  I was not far from home, and so I limped the car back to my garage.  Now, the car starts from a standstill in 2nd gear, as it should, but will not shift to 3rd or 4th gear no matter what I do.  Starting with the shift lever in 2nd, the car starts in 1st and shifts to 2nd as it should,  no problem. 

I jacked the car up on stands to see if I could find anything out of the ordinary.  I undid the vacuum line from the intake to the transmission to make sure it was clean and clear, which it was.  Remembering some old posts on this site, I wondered whether the transmission modulator diaphragm had ruptured.  But transmission fluid levels appear normal (checked with engine running, car at operating temperature as recommended here, and trans fluid/filter are less than 1,000 miles on them), and there is no fouling of the spark plug in cylinder six. 

Thoughts on what to check?  Anybody experienced a similar situation? 

[Pawel66]

I am sorry, I will not help, I do not have enough knowledge, but just to complete the picture - does your speedo work when you drive the car now up to the second gear? Or is the speedo dead? Was your speedo working erratic before?

The 3rd and 4th gear and speedo are related, they are held by the same nut on the output shaft, that is why I am curious - and your answer may help someone more knowledgeable figure out what happened.

Just see that what you are describing may be a match to what you can read in Tech Manual in "Erratic speedo work". But I do not know if this is the issue and I do not know if it is an easy fix of just tightening the nut - I am not sure if any damage might have been done to transmission or what to do to avoid any damage further on.

Keeping my fingers crossed it is an easy fix!

[calhippie]

- does your speedo work when you drive the car now up to the second gear? Or is the speedo dead? Was your speedo working erratic before?

Just see that what you are describing may be a match to what you can read in Tech Manual in "Erratic speedo work". But I do not know if this is the issue and I do not know if it is an easy fix of just tightening the nut - I am not sure if any damage might have been done to transmission or what to do to avoid any damage further on.

Keeping my fingers crossed it is an easy fix!

The speedo is still dead.  For a long time, it had a little "bounce" in the needle, but then would smooth out above about 10mph.  I already have a replacement cable ready to go in. 

I will check the tech manual for the "erratic speedo" symptoms you describe.  I hope it's an easy fix, too! 

[calhippie]

I will check the tech manual for the "erratic speedo" symptoms you describe.  I hope it's an easy fix, too!

Looks like the tech manual describes a different issue, concerning a manual trans:
https://www.sl113.org/wiki/Electrical/Speedo#ErraticSpeedo

 

[Pawel66]

Ok, I guess you are right that the remark on 3rd and 4th gear was about manual... The speedo drive is similar in both. Let's see what others will say.

[ja17]

Sounds like a band or piston might have failed in the transmission. Remove the pan and look for parts. Report back.

[WRe]

Hi,
the workshop manual says: (see attachement):
- speedo working: 1. slide valve 7 stuck; 2. control valve Ü1 stays open, no step pressure
- speedo not working: 1. no pulling of modulator pump; 2. screw drive of modulator damaged
Sorry for not translating this correct but I don't know these special technical expressions but it sounds more for a specialist.
...WRe

[Pawel66]

Good idea!

Same book, same table, just English.

NO shift beyond 2nd gear, speedo does not work:
1. Regulator pump not driven
2. Worm gear drive of regulator defective

[BaronYoungman]

Same thing happened to mine, bam then no 3rd or 4th gear I was on way to drive my then girlfriend, now wife, to the airport.  The pump had failed.   On good side she still married me.
Bob

[calhippie]

Sounds like a band or piston might have failed in the transmission. Remove the pan and look for parts. Report back.

Will do, Joe.  Many thanks. 

[calhippie]

Same thing happened to mine, bam then no 3rd or 4th gear I was on way to drive my then girlfriend, now wife, to the airport.  The pump had failed.   On good side she still married me.
Bob

Bob:  What was the fix?  A "while we're in there" full rebuild?  Would love to hear the details when you have time. 

Glad your wife didn't hold it against you; slow and steady wins the race.  And with no 3rd or 4th gear, we're talking REALLY slow and steady! 

[calhippie]

Sounds like a band or piston might have failed in the transmission. Remove the pan and look for parts. Report back.

Dropped the pan.  No parts, no debris, no residue, nothing.  Trans fluid is crystal clear, looks brand new.  I can't for the life of me get the filter off, though.  Is there some trick?  Screw won't budge. 

[ja17]

Tap on the screw head with a hammer and flat punch (drift). Then try it.

[calhippie]

Tap on the screw head with a hammer and flat punch (drift). Then try it.

A little tapping, and the biggest handle screwdriver I have, worked.  Still no debris, no residue, nothing looks out of the ordinary.  Bolts all snug, nothing loose. 

[drmb]

The drive for the secondary pump and governor inside the rear housing would have failed.

[BaronYoungman]

On mine it was just the pump had failed they looked over all the rest no issues, replaced the pump, that was 4000 miles and 6 years ago, no other incedents.  The pump as I recall was under $400 installed.
Bob

[calhippie]

On mine it was just the pump had failed they looked over all the rest no issues, replaced the pump, that was 4000 miles and 6 years ago, no other incedents.  The pump as I recall was under $400 installed.
Bob

Thanks, everyone. Way beyond my skill set.  Looks like I will have her trucked to the trans shop for a diagnosis and hopefully minor transmission "surgery."     I will update this post with more information soon.