A few days ago I started up my 300sd and the transmission whined in park. Didn't do it before. It did sometimes in first under load while driving but this time it was whining in P and N stationary in my garage.

Then I put it in reverse to back out and it got louder. Then in drive it quieted down. As I drove down the street it got quieter. Stopped at a light and popped it into N and P and it whines again. Sounded like low fluid.

So I check my level after getting it warm and it is ok. I check my log and realize I have 35000 miles on the fluid and filter. I get some Mobil 1 synthetic and a filter kit and change 6qts with torque converter drain. It still whines in P, N, R and slightly in D while underway. I painstakingly check the level and top off. It is spot on between min and max when hot.

The fluid looked ok for 35000 fluid. It had some fine metal sparkles in it at the bottom of the pan. Probably aluminum because they didn't collect on my pan magnets. Nothing on the magnets. The filter was pretty dirty. I was hoping the fluid/filter service would help but no, it still whines.

So I start searching. There was somebody here with a similar problem in a w126 SD awhile back but he never posted his solution. Also a lot of 928 folks have whines in their 722 trannies. Whining trannie wow that sounds bad

Another interesting thing is I can quiet it down by putting my mityvac on the modulator and pumping it down to 18mm HG. Not fully gone but it goes away. I then put my pressure gauge on the modulator banjo and read 33 psi and started spinning the modulator T. If I turn it higher it gets louder. If I turn the T lower to like 10 or even 0 psi the whine gets quieter. The car shifts like a champ. I run 12 mm HG at the modulator. If I disconnect the vacuum it gets louder in P.

So am I looking at a rebuilt? It's funny, I bought this car in 2010 from a guy who said its 3rd gear flare (or 2nd?) was so bad it needed a rebuilt. I tuned the flare out and compromised with a stiff 1-2 using a K(1?2? Cannot recall) spring upgrade.

So Ive been getting off easy for a years. Luckily I am in SoCal near Sun Valley Transmission. I think I may drop the car off with them and hand over the credit card.

Any thoughts guys? I think I've tried the easy stuff.

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79 300TD “Old Smokey” AKA “The Mistake” (SOLD)
82 240D stick shift 335k miles (SOLD)
82 300SD 300k miles
85 300D Turbodiesel 170k miles

I found this thread here.

300SDL: loud grinding transmission 722.321, noise in P and N position

Apparently this member had a bad key switch that put his starter solenoid in the on position and made his starter motor whine on the ring gear after the engine was started.

I checked it out on my car. No luck. I measured the voltage at the starter solenoid. 0v when off. I hit the key and boom up to 12v then as the engine fires I release the key and the voltage goes back to 0v again. Key switch works. Assuming the solenoid doesn't stick I'm probably good.

This is t consistent with the whine sound in D on my car. The thread said on P and N which makes sense since the neutral safety switch would cut off the starter signal in D. I get whine in P, N, R and D. More or less in each.

Wish it was something easy like this.

It is looking like an internal problem. Switching the gears is going to change pressures inside. It is probably something like my pump or governor is bad. In that case pulling the tranny might as well be to drop in a reman.

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79 300TD “Old Smokey” AKA “The Mistake” (SOLD)
82 240D stick shift 335k miles (SOLD)
82 300SD 300k miles
85 300D Turbodiesel 170k miles

I'm starting to wonder if rebuilding the valve body would help. Eaton99 posted a great video on how to do this. At this point I'm looking at a rebuilt for thousands or a crap shoot like Trans X or valve body work. I read up on the governor and it looks like I have a strong reverse and drive so my pressure must be okay. There may just be a clog in there someplace.

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79 300TD “Old Smokey” AKA “The Mistake” (SOLD)
82 240D stick shift 335k miles (SOLD)
82 300SD 300k miles
85 300D Turbodiesel 170k miles

New data
I notice the worst whining is in reverse. Also when in reverse it takes a lot of brake to hold it back.

If I'm stationary in reverse besides whining the speedo needle jumps. Why? Something to do with the sender? Maybe I should take it out or look into taking it out. Not sure what is going on in there. Seems like a hydraulic pressure problem but I really don't know.

I'll look in the trans info to see how the electronic speed sensor works in a 722.3.

So I've been looking at flow diagrams of auto transmissions for a day and it appears that reverse is somehow related to pressure regulation in he valve body. That is, one of the reverse circuits is on a spool valve that is connected to the regulator. Why? I haven't been able to figure it out. Maybe so you don't get a Big Bang in R? Perhaps this valve is sticking.

I felt like tearing the valve body out of the car and disassembling it on my bench but I think I'm at the limit of my bravery. I'm going to call it a day and have a rebuilt installed. I've been saving up for one a few years.

__________________
79 300TD “Old Smokey” AKA “The Mistake” (SOLD)
82 240D stick shift 335k miles (SOLD)
82 300SD 300k miles
85 300D Turbodiesel 170k miles

About to get a remanufactured transmission. I guess I'll never really know what failed internally in mine. So I did a few last tests. I noticed when I pulled the line off the vacuum modulator the whining sound in park got a lot worse. When I connected it the sound got quieter. If I put a mityvac on the modulator line a pumped it to -15mmHg the sound would totally go away.

I think it is all related to the fact that I can no longer get banging shifts when I disconnect the vacuum line. The modulated pressure is all over the place too. Must be some kind of internal leak.

Lastly I got to see the speedometer read 30mph while I was in Reverse with the car sitting stationary in the garage. In D it all comes back to normal and reads the correct speed. I cannot imagine why it does this since the electronic speed pickup is on the output shaft and shouldn't be moving a lick if the car is standing still. Maybe there's magnetic material swirly around in the tail cone?

Well, I guess I'll never know. This is where part of me wishes I dropped the tranny and tried to rebuild it myself. I'd have the pride of tackling an auto trans and I'd know what failed. But alas I'm at my limit stop. I need to call it a day.

I look forward to my car after it has a reman tranny. It was always a little wonky from day one. I bought it from an older gentleman who bought it new but let his teenage grandson drive it a year. Only 159k miles back then. A teenager can really wreak havoc on a car.

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79 300TD “Old Smokey” AKA “The Mistake” (SOLD)
82 240D stick shift 335k miles (SOLD)
82 300SD 300k miles
85 300D Turbodiesel 170k miles

for the past 9 years I have only had 722.4 transmissions in my diesels and none of them whined like this.

This year, I have owned 2 with the 722.3. BOTH of them have this same whining. It made me really nervous at first, but they shift fine.

Why would you get a new trans if it was shifting fine? Were there other reasons as well?

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From what you describe, the front pump and or pump bushing is coming apart. Reverse generally needs higher clamping force to prevent slippage, this places a higher load on the pump. Pulling the vac modulator also increases line pressure.

I don't have an explanation for the harder to hold the car in reverse other than the turbine of the converter hitting the pump side ( not oil pump, this is internal to the converter. ). I can't recall having a trans do this.

Does this car have an electronic speedo? If so, metal can stick to the sensor tip increasing sensitivity and any vibration will trigger a signal and move the needle.

Hey thanks for the replies. Yes the trans shifts fine most of the time. Kind of. It has a harsh 1-2 and a soft. 3-4. I've compromised between the two by adjusting the VCV. Twice, while,driving in hot LA traffic the trans will whine and freewheel while in Drive. I don't know why but I suspect one of the clutches doesn't behave when hot. I'm hoping the reman will solve this. It is disconcerting to have the car just freewheel in the middle of LA traffic while everyone honks at me.

Right now the car shifts fine but it never whined while staying stationary before.

I thought pulling a vac decreased line pressure...but hey I never checked. Front pump sounds like a likely culprit. So your explanation makes sense that pulling a vacuum on the modulator would increase the clamping pressure in reverse and thus kill some slippage.

The car has an electronic speedo. I may pull the sender for kicks and see if there is crud on the end of it.

Thanks. Well, soon to be a bad memory I hope. I am really looking forward to getting my new trans.

__________________
79 300TD “Old Smokey” AKA “The Mistake” (SOLD)
82 240D stick shift 335k miles (SOLD)
82 300SD 300k miles
85 300D Turbodiesel 170k miles