97 5-sp manual

rpm's jump up but no corresponding acceleration...
seems to be happening only in 4th but not 100% sure about that yet
is it possible i broke something loose in my tranny?

 

4th is direct, so you are slipping the clutch. When I was "breaking in" my new clutch it only slipped in 4th as well.

 

huh that's weird. i tried to get it to slip in 2nd and 3rd by accelerating pretty hard up hill but no slippage that i could sense

why only in 4th?

this clutch is well broken in. would it be slipping due to oil contamination?
how to diagnose/repair?

 

If the clutch is slipping, 5th should cause it as well. Lower gears generally don't provide enough load to slip unless its really bad. If you broke something in 4th, you should have zero forward acceleration or be able to maintain speed. You should be able to put it in 4th at a dead stop and let out the clutch and the engine shouldn't notice. It would be possible to lose only 4th, as its the only gear that doesn't use the countershaft. But generally, that is the strongest gear as well.

 

ok, that makes sense.
what are the potential causes and repairs for a slipping clutch?

 

A slipping clutch can be due to worn/broken pressure plate springs or worn throw out bearing on the shaft causing it to hang up and not engage fully. Either way, the only fix is a clutch replacement as those items aren't serviceable. Clutch prices have come down in recent years and the job can be done by yourself if you have a good tranny jack.

My only suggestion is South Bend Clutch. Peter has been doing the Dodge Diesel clutches as long as I have been on these forums (1998) and has the customer service to prove it. FWIW.