300SD lost fourth, now third gear - any ideas? Searched forum for an hour! Need help

[85MB300D]

Hi Guys,

It's been a while since I've been here. I am looking at a 300SD, but current owner states he stopped driving it because it lost fourth gear, now third.

I've been searching the forum for at least 1 hour, and I've found tons of stuff on needing proper vacuum, B2 piston failure (when the car flares or doesn't shift into first gear), but I have not been able to find the exact problem this car seems to be having - the complete loss of fourth, now third gear.

What specifically could cause this? Any ideas?

Also, are all 5cyl. diesel transmissions interchangable? In other words, would a trans from a W123 300D fit this W126 300SD?

Thank you for your time.

[rrgrassi]

The tranny is the same, for the most part, but the SD (w126) uses an electrical pick up for the speedometer, while the 300D (w123) uses a speedometer cable.

I would recommend that the tranny come from the same year w123 as the w126, so that you do not get bit be some small modification for the model year.

No idea on what can cause loss of gears 3 and 4. What condition is the fluid in?

[rs899]

Could be a valve body issue (?)

[Hatterasguy]

Rebuild time; I second the valve body.

[82300sd]

When was the last time the transmission oil and filter was changed? I encountered losing fourth gear (never shifted to 4th) and a transmission oil and filter change corrected the problem.

[rs899]

This is one of the few cases where changing fluid and filter MIGHT help matters. A valve body can be swapped in fairly easily without pulling the tranny and may fix it.

[85MB300D]

Originally Posted by rs899

This is one of the few cases where changing fluid and filter MIGHT help matters. A valve body can be swapped in fairly easily without pulling the tranny and may fix it.

I am liking the sounds of this...

I believe the trans in the 300SD is a 722.3, correct? What is the difference between 722.3 and 722.4 transmissions?
Are the transmissions (internals) used on the gas motors the same as the diesels, or do I need to look for a valve body from a diesel trans? In other words, what are my options?

Would you guys suggest new or used and where would you find a specialized/specfic part such as a Valve Body?

Thanks a million

[Narcoleptic]

This wouldn't happen to be in Texas, would it? Specifically Weatherford? Sounds a lot like one I've seen for sale and the owner said it ran low on fluid.

[rs899]

Got a u-pull-it in your area? They are also a great source of non-lethal training.

[compress ignite]

722.3 and 722.4 are not the same transmission!

You want a diesel tranny as close to the type that's in the car(so the Valve Body shift points MATCH)

[85MB300D]

Originally Posted by compress ignite

722.3 and 722.4 are not the same transmission!

You want a diesel tranny as close to the type that's in the car(so the Valve Body shift points MATCH)

Thanks for the tip.

So what trans is in the 1982 300SD?

Thanks!

[85MB300D]

Anyone have any other comments/suggestions on what will make an '82 300SD not shift into/lose third and fourth?

Thanks!

[jim16671836]

The tailshafts are different because the speedometer is mechanical in the 123 transmission and the 126 uses electrical.. You can't change the Instrument cluster from mechanical to electric. I think you can change the tailshafts but not such an easy fix.. jim16671836