91 300SE Transmission not shifting
 

The car has about 150K mi on it. I doesn't shift to 3 or 4th gear. I can't tell, but I can't go over about 30mph. The shifter has D,3,2 selections. It seems like it's stuck in 2nd gear, but when i move the lever down to 2, it downshifts.
I replaced the filter and fluid. the filter looked clogged, but the fluid was clean and I didn't see any metal shavings. At one time it failed to go in reverse, but that hasn't occurred again.
My questions are, 1)what is the probable cause. Is it repairable, 2) How hard is to take out and 3) I see some low cost Mercedes model around $1000(86-91), Which years/models use the same transmission, that I can swap.
Thanks,
Jerry

there are two very small screen filters that protect the govenor,and if the inlet is blocked the gov will not allow valve body to shift up.you will need to remove the valve body and then the separator plate[with small valve body].on the topside of plate there are four screws holding the small valve body with a strange shaped plate.remove those and small valve body comes off and you now have access to small screen filters.if this doesn't prove to be problem then i would suspect valve body.

David,
Thanks so much for your reply. Where is the plate and valve body. i would like to take a look at the screen as you suggest. Is there a link or a picture of where it is? I have 126 service manual, but it only details changing the filter and fluid, but no further.Can I get access to it with the pan off?
Thanks Again

David,
I'm trying to get at these screens to clean them.
I took off the filter and about 9 10 mm bolts. It doesn't come off. it looks like it's still attached in the front somewhere. there are about 9 long 10mm bolts holding that part on. I'm afraid to take them all off. i wish I had a manual. Please help!
Thanks