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I have a Porsche 928s 1980 with an automatic gearbox in with me. I was carrying out a service (plugs and oil etc) and brought the car for a drive afterward. On the motorway, the car was faultless and driving perfect but when I pulled off the motorway and stopped as I went to pulled off again a big bang/thud happened and I couldn't get any drive. I stopped and turned the car off and started it again and cycled through the gears and still nothing. It is making a noise when in drive though as if something has sheared and is now spinning freely but not transferring power to the wheels.
What I have checked:
I have removed the inspection panel at the bottom of the bell housing at the starter motor and nothing is broken at the flex plate.
Both driveshafts are also not moving when in gear so I then removed the rear diff cover and I can see nothing visually broken in there.
I had someone spin the flywheel a bit and could see the torque convertor spin through the inspection hole.
I need recommendations on my next move. Is there a coupling just after the torque convertor that can shear? Should I remove the auto gearbox now to further my search?
Before you condemn the A22.01 Mercedes automatic, check the rest of the driveline. Specifically, check your rear CV axles. A failure in one will cause loss of drive.
Before you condemn the A22.01 Mercedes automatic, check the rest of the driveline. Specifically, check your rear CV axles. A failure in one will cause loss of drive.
Good Luck!
Hi Skpyle,
Is the Mercedes A22.01 auto prone to failure? I was under the impression that there are a robust gearbox. I have check both inner and out cv joints and they are good.
Thanks for the reply
To my knowledge, the A22 is a VERY robust transmission. It takes alot to kill one.
However, they are not infalible.
When you looked in the differential, did you happen to note the condition of the pinion gear?
Your description of a large bang implies something significant broke.
Since you said the torque converter is turning with the driveshaft, the torque converter drive plate is still connected.
Next link in the train is the input lugs on the transmission front pump.
Here is a quick and dirty test for that: Find the plastic reservoir for the transmission fluid on the passenger’s side of the unit. The resevoir should be full with the engine not running. With the engine running, the fluid level should drop in the reservoir.
Verify your reservoir is full with the engine off. Start the engine. If the reservoir level drops, the torque converter is turning the front pump. If not, then not…
I asked about the pinion gear because the pinion shaft is directly connected to the transmission output shaft.
Hopefully Greg Brown sees this thread. He is quite knowledgeable about the early Mercedes automatics.
As well, when I get back to my computer, I can post a couple of manuals for the A22.
Streacy, I had another random thought. Find a way to watch the torque converter with the engine running.
You said you watched it move while someone turned the flywheel. I am grasping at straws here, but the driveshaft between the engine flexplate and the torque converter drive plate could have sheared. Friction could be enough to turn the torque converter slowly when the engine is turned by hand. However, it would fully slip with the engine running.
The CV joints attach to the drive flanges on the gearbox with some hefty bolts that need a lot more torque on them that most want to apply. For grins, make sure the drive axles are still bolted securely to the transmission. Your big clunk and no drive symptom matches the failure mode when one axle comes off. Easy initial diagnosis: can you push the car with the gearbox in park position? A separated axle will let you do that.
^^^ +1. This exact thing happened to me on my 84 a few years ago. The axle studs weren't tightened enough after a gasket replacement and when I was driving a heard a loud "clank" (which was one of the rear axles falling onto the exhaust) and then I couldn't drive.
To my knowledge, the A22 is a VERY robust transmission. It takes alot to kill one.
However, they are not infalible.
When you looked in the differential, did you happen to note the condition of the pinion gear?
Your description of a large bang implies something significant broke.
Since you said the torque converter is turning with the driveshaft, the torque converter drive plate is still connected.Next link in the train is the input lugs on the transmission front pump.
Here is a quick and dirty test for that: Find the plastic reservoir for the transmission fluid on the passenger’s side of the unit. The resevoir should be full with the engine not running. With the engine running, the fluid level should drop in the reservoir.
Verify your reservoir is full with the engine off. Start the engine. If the reservoir level drops, the torque converter is turning the front pump. If not, then not…
I asked about the pinion gear because the pinion shaft is directly connected to the transmission output shaft.
Hopefully Greg Brown sees this thread. He is quite knowledgeable about the early Mercedes automatics.
As well, when I get back to my computer, I can post a couple of manuals for the A22.
Good Luck!
I have tested running the car and noting the transmission fluid level and it dropped after about minute of running. So I'm presuming now the problem could be past the gearbox, maybe the different or cv joints. But I definitely tried the car in gear on the ground and no shaft was spinning. Do the centre diffs break?
Thanks for all the replies so far. Saved me blinding pulling the auto box
Back again, I pulled the automatic box due to customer request and he had the box sent off to be fixed. A week later he got a quote for €3500 to fix the issue and wasn't interested. So I ended up buying the car off him and will be fixing this issue myself. Since the box is now out of the car I would like to carry out a full rebuild. Is there any recommended kits to use for the rebuild?
On doing some research and knowing now the torque tube or torque convertor are not to blame would a broken band cause loss of motion in forward and reverse?
I will have the box home this weekend and begin stripping. I have found a couple members threads who have stripped and rebuilt these boxes and will be leaning heavily on these.
Back again, I pulled the automatic box due to customer request and he had the box sent off to be fixed. A week later he got a quote for €3500 to fix the issue and wasn't interested. So I ended up buying the car off him and will be fixing this issue myself. Since the box is now out of the car I would like to carry out a full rebuild. Is there any recommended kits to use for the rebuild?
On doing some research and knowing now the torque tube or torque convertor are not to blame would a broken band cause loss of motion in forward and reverse?
I will have the box home this weekend and begin stripping. I have found a couple members threads who have stripped and rebuilt these boxes and will be leaning heavily on these.
The only kits there are are gasket sets. The rest you will have to buy from Mercedes and Porsche as individual pieces as far as I'm aware.
You will also need to really read into the supercession of part number to figure out which components work with what, as they did change over the years.
Thanks for the reply, I will definitely be getting a gasket set anyway prior to refitting.
But I may not have to fully rebuild the box anymore, I came across this used good working condition gearbox code R115-271-4201 (see images below). The code on the porsche gearbox is R116-271-0001. Look identical.
My question is can I mount the Porsche bell housing and rear differential to the Mercedes R115 gearbox?
06-15-2021, 12:07 PM
Porsche 928s 1980 Auto Gearbox Issue
