C120 weak trans

[Mwh0428 0]

I am new to this forum and my dad has a c120 automatic and a while ago we got a filter and changed the filter and refilled it with 10w-30 motor oil. now it has no forward power it moves but not how it should, and you can spin the wheels in reverse what is wrong with it and what will be the cost.

[can whlvr 993]

if it was ok before the filter change i hope you didnt get any dirt in it,but maybe you have an air lock,or the wrong filter,did you use a wheelhorse filter,someone else may have more insight on this

[squonk 41,345]

I think you got some air in it still if it worked ok before the oil change.

[JackC 617]

If it goes strong in one direction but not the other, it could be linkage or a check valve.

I have a C-160 that is fine going forward but very weak in reverse.

The service manual for the transmission points to a check valve.

There is one for forward and another one for reverse.

If the rubber O ring in the check valve is worn the check valve will not work properly to change fluid direction in the transmission.

I have not had a chance to work on my C-160 but I did read the service manual.

You will need the Sundstrand transmission manual or have someone do it.

You will need a 3/8 drag link (looks like a big screw driver blade) to get the check valve out to inspect it.

If it is the check valve, and you can service it then the cost to fix it is minimal.

I also picked up a few Sundstrand pumps cheap on eBay just in case (less than $50 each including shipping).

Swapping the pump is a lot more work than fixing a check valve which you should be able to get to by removing some sheet metal.

[JackC 617]

If it worked OK before the filter change, then it is likely not a check valve.

Perhaps it is the wrong type of filter or there is an air lock such that the fluid has not saturated all internal locations allowing all of the components to work properly.

[Mwh0428 0]

How do get the trans to not be airlocked any more

[can whlvr 993]

that im not sure of,when i had my sundstrand rebuilt it primed up perfectly,on fork lifts we took off a hose to the lift cylinder and ran her through a while