W126 Auto Transmission swap, 3 speed to 4 speed? - PeachParts Mercedes-Benz Forum

James L · #1 09-03-2008, 09:09 PM

Will a 4 speed automatic transmission from a newer W126 work and fit in my 1984 300SD that has a 3 speed automatic transmission? (Bolt patterns, vacuumn stuff, ect..)

Hatterasguy · #2 09-03-2008, 09:11 PM

What did you lose 4th gear on the 84?

If you can get one from an SDL it might work, but your best bet would be to stay with 85 and older, or 300SD's.

bustedbenz · #3 09-03-2008, 09:13 PM

Quote:

Originally Posted by James L

Will a 4 speed automatic transmission from a newer W126 work and fit in my 1984 300SD that has a 3 speed automatic transmission? (Bolt patterns, vacuumn stuff, ect..)

I've never even HEARD of a 3 speed automatic in a w126, is that a polite way of describing a failure or have you got something we all need to be educated on?

pawoSD · #4 09-03-2008, 09:13 PM

Quote:

Originally Posted by Hatterasguy

What did you lose 4th gear on the 84?

If you can get one from an SDL it might work, but your best bet would be to stay with 85 and older, or 300SD's.

The starter is on the wrong side in an SDL, its on the passenger side for the 617.

All MB auto trannys of that era were a 4 speed, if you don't have 4 gears than yours is simply malfunctioning, or you might think its revving too high.

How fast can your car go? what RPMS is it running at 55mph? 75mph? If its about 2400 at 55 and 3400ish at 75 then its going through all 4 gears just fine.

Hatterasguy · #5 09-03-2008, 09:16 PM

Yeah thats true I forgot about the starter switch. So you need to find another 300SD if you want the auto box out of it.

James L · #6 09-03-2008, 09:37 PM

I feel dumb....Is there a 5 speed auto transmission? Does my 1993 300D 2.5 have a 5 speed or 4 speed AT? ( it revs alot lower at speed).

My 1984 300sd has started acting up, the last gear does not engage at different times. It just revs. If i cut it off and let it cool down it works fine for a while. Can this be fixed w/o pulling trans?

I have a trans in my 1983 300sd parts car that sits in my driveway.

pawoSD · #7 09-03-2008, 10:30 PM

Quote:

Originally Posted by James L

I feel dumb....Is there a 5 speed auto transmission? Does my 1993 300D 2.5 have a 5 speed or 4 speed AT? ( it revs alot lower at speed).

My 1984 300sd has started acting up, the last gear does not engage at different times. It just revs. If i cut it off and let it cool down it works fine for a while. Can this be fixed w/o pulling trans?

I have a trans in my 1983 300sd parts car that sits in my driveway.

Nope, 5 speeds didn't come around until like 2000-2002 or something....maybe a little earlier, no idea.

I don't drive that new.

Your 1993 300D 2.5 has a totally different motor/trans/differential ratio, thats why it rev's lower. The rear end ratio on a 300SD is 3.07 on almost all of them and 2.88 for the 1985 model year. Your 300D has either a 2.88 or lower ratio, thus less rpms at speed.

Have you checked the fluid level on your 300SD? Changed the filter and fluid lately? Vacuum and bowden cable adjustments?

James L · #8 09-04-2008, 02:40 PM

I changed the fluid and filter on 6/02/2006, about 17,000 miles ago. The dipstick seems to be a little over the full mark when cold and more brownish-redish color than the bright red color of new transmission fluid.

I have adjusted the bowden cable and modulator.

pawoSD · #9 09-04-2008, 04:22 PM

Quote:

Originally Posted by James L

I changed the fluid and filter on 6/02/2006, about 17,000 miles ago. The dipstick seems to be a little over the full mark when cold and more brownish-redish color than the bright red color of new transmission fluid.

I have adjusted the bowden cable and modulator.

That brownish color could be from burned fluid, does it smell burnt? If it "revved" in 4th gear without engaging you could have easily been roasting the fluid and 4th gear clutch pack.....never good to rev if it doesn't engage, always let off the throttle.

2.5Turbo · #10 09-04-2008, 10:31 PM

Quote:

Originally Posted by pawoSD

Nope, 5 speeds didn't come around until like 2000-2002 or something....maybe a little earlier, no idea.

I don't drive that new.

Your 1993 300D 2.5 has a totally different motor/trans/differential ratio, thats why it rev's lower. The rear end ratio on a 300SD is 3.07 on almost all of them and 2.88 for the 1985 model year. Your 300D has either a 2.88 or lower ratio, thus less rpms at speed.

Have you checked the fluid level on your 300SD? Changed the filter and fluid lately? Vacuum and bowden cable adjustments?

How low can you go...2.65 on the 124.128. Turning straight up 3k at 75mph is nice

...although I've always wondered how much fuel mileage I'd gain if I had an overdrive...

5 speed didn't come along until the electronic 722.6 of the mid/late 90's

Oracle12345 · #11 09-04-2008, 10:34 PM

Quote:

Originally Posted by pawoSD

That brownish color could be from burned fluid, does it smell burnt? If it "revved" in 4th gear without engaging you could have easily been roasting the fluid and 4th gear clutch pack.....never good to rev if it doesn't engage, always let off the throttle.

Yeah brown is burnt atf