source for trans for 85 300SD? - PeachParts Mercedes-Benz Forum

dankephoto · #1 01-24-2009, 01:49 PM

Hi folks, my first post here and hoping the collective wisdom will help get me back on the road ...

I think I'm going to need a tranny and I'm wondering which car models could provide the correct 722.303 gearbox I need. I'm pretty sure the '82 to '85 W126s use the same box, but do the W123 300 turboD cars as well?

Here's the story ...

My 280K miles '85 300SD lost forward motion last week while driving. Still had reverse but forward gears (1st/2nd at least) produce no motion. Reverse still works, so my first thought was the dreaded B2 piston failure had struck.

I pulled the B2 cover off to find the piston perfectly intact. Pulled the pan and replaced the filter, but cleaning out the pan I discovered a whole lotta golden flakes (well, bronzey anyhow) down there. That can't be good.

I've yet to install the replacement ($150!) piston as I can't get the blasted seal out. I just bought a hook-shaped seal puller but weather is so dang cold I haven't taken a crack at it yet. I'm going to at least try the replacement piston and bushing once the (now wrecked) seal comes out, but I have little hope that'll be a cure.

So, what I'm foreseeing is the need to replace the trans. I'm pretty sure the '82 to '85 SDs use the same gearbox (722.303), but so far locally I'm having no luck locating one. I seem to be reading the W123 300 turboD cars use the same 'box, but I need to know for sure. Can anyone confirm? If so, that'd make it alot easier to find as junkyard W123 cars are plentiful around here.

Also, I don't have an available garage or tranny lift, is this a job for one man (experienced with clutch replacements and the like) alone in the driveway, or will I really need to hire this one out?

TIA for any words of advice and/or encouragement,

Dan K (in central NJ)

dankephoto · #2 06-12-2009, 06:36 PM

. . . . car has set for months as I couldn't get out the flippin' seal and bushing . . . .

None of the B2-failure sites had all the part numbers I needed to do this fix, so here's what I bought.
For a 722.303 transmission (non-California MY81-85 300SD):

B2 Piston 107 270 04 32 - $120
B2 Piston cover o-ring 005 997 70 48 - $2
B2 Piston seal 006 997 73 47 - $4
B2 Piston bushing 126 277 08 50 - $7
. (prices approx.)

Sadly, replacing the piston, seals and bushing didn't fix the problem. I suspect the failure is a worn brake band, there was a lot of bronzey-looking flakes in the bottom of the pan. A replacement band costs >$325, so just fixing this would add up to more than a complete used gearbox.

I ran a bunch of VINs (culled through eBay) through the http://old.mbclub.ru/mb/vin/?lng=eng VIN decoder, W123 turbo chassis (mostly) use a different transmission, usually 722.315. I did find one MY82 300TD with a 722.303 trans. I dunno what the difference is between the .303 and the .315 but I can't take a chance on the latter bolting straight into my 126 (though I bet it would.)

I'm buying a used tranny from a MY81 car and figure to do the swap myself. When I get it I'll swap in the new piston and new seals and bushing before I install the tranny. No sense leaving that $120 piston in a scrap gearbox . . .

Hope this info helps someone,

Dan

PS: searching VINs on eBay I came across WDBCB20A0CB026990, a MY82 with what must be euro delivery:

Dealer United States - tourists (707)
with
option 663 - 60 liters of fuel

How big is the standard fuel tank?

JimFreeh · #3 06-12-2009, 09:32 PM

The 85 has a different torque converter than the 81-84 SD trannys. Keep your 85 torque converter if you change to another year.

W123 82-85 300D trannys will work, if you change the tailhousing.
Same for the W123 300TD trannys, but 81-85 will interchange.

Need to change the tailshaft since the SD has an electric speedo, the W123 has a mechanical drive.

If you can jack up all four corners of the car, you can swap the tranny.
I can R & R one in a day, not too bad if you prepare and have all the tools ready.

Jim

dankephoto · #4 07-01-2009, 01:14 PM

I picked up the used tranny, out of a MY84 chassis turns out, US$450 + NJ tx, and swapped it over a couple of days work. I figure it took me about 15 hours total, which seemed respectable for a firsttimer considering the US$600 labor figure quoted by a local mechanic.

All in all, I'm very pleased with how it went. I had expected a monster-sized gearbox, the reality is very compact and light, under 100lbs. Up in the air on four ramps (plus some extra jacking at the front) and using the cheapo tranny lift from Harbor Freight all went very smoothly. Handling the mufflers, I did break an exhaust hanger tho . . . so add an hour or so of welding time in there.

Thanks Jim for the converter tip, I wouldn't have known about that. Your post came just in time too, just days before I did the swap.

The replacement shifts a bit hard through all the gears, but I've some other vacuum-related issues so hopefully sorting those out will also smooth the shift. The only other issue was the shiftpoints were initially waay high, but a quick adjustment to the kickdown cable cured that.

Dan K

tbomachines · #5 07-01-2009, 01:18 PM

Glad to hear it! Just curious - had the B2 been replaced with the updated version on your replacement tranny? It is a pretty common failure item.

dankephoto · #6 07-01-2009, 01:28 PM

Nutz, I don't remember absolutely, but . . . I'm _pretty_ sure the replacement box's piston was the original type. I know for sure the bushing was the metal version. I stuck the 84 box's piston in the broken tranny when I pulled the new piston back out (to use in the replacement 84 box), so without opening the old box again I'm not positive.

The source chassis was allegedly relatively low miles (~120K), I didn't see the car though as the yard is kind of snippy about allowing in snoopy customers like me.

Dan K