Replace reverse valve ir 2135

see this link... should fix the problem
02 03 Reverse OR

YOU NEED TO COMPLETELY DISASSEMBLE THE WHOLE TOOL.
START BY REMOVING THE 4 MOTOR HOUSING SCREWS, SLIDE THE HAMMER CASE, HAMMER ASSEMBLY AND MOTOR ASSEMBLY FROM THE MOTOR HOUSING.
THE REVERSE VALVE WILL BE VISIBLE NOTE THE ORIENTATION ON THE AIR OPENING IT LOOKS LIKE A HALF MOON, THE VALVE WITH EITHER BUTTON PRESSED IN SHOULD AT A 45 DEGREE ANGLE.
NEXT YOU WILL NEED TO REMOVE THE INLET BUSHING ASSEMBLY THAT IS HELD IN BY A CLIP THE IS VISIBLE THROUGH 2 SLOTS LOCATED ON THE LOWER SIDES OF THE GRIP, THEY NEED TO BE PRESSED IN TO SLIDE THE INLET BUSHING OUT THE BOTTOM OF THE TOOL. THERE IS A SPECIAL TOOL THAT SIMULTANEOUSLY PRESSES BOTH SIDES OF THE CLIP BUT CAN BE SUBSTITUTED WITH 2 SMALL FLAT HEAD SCREWDRIVERS.
ONCE THE INLET IS REMOVED, THE TRIGGER CAN SLIDE OUT THE FRONT OF THE TOOL
NEXT USE A SMALL FLAT HEAD SCREW DRIVER TO PRY THE REVERSE BUTTON OUT OF THE HOUSING, INSERT THE SCREW DRIVER INSIDE THE INNER EDGE TO PRY OUT,
ROTATE THE VALVE 45 DEGREES IN THE OTHER DIRECTION TO REMOVE THE SECOND BUTTON.
NEXT PUSH DOWN ON THE REVERSE VALVE IT WILL COME OUT THE BOTTOM.
FOLLOW THIS LINK TO VIEW THE PARTS SCHEMATIC.
http://manualarchive.ingersollrandproducts.com/ir_pdfs/Tools/IR%20Industrial%20Tools/Impact%20Tools/04584033_ed2.pdf

I would check my reversal valve and make sure the knob is on the number 5 on both sides first and check my air inlet for trash. Other then that I would tear it down and inspect the tool for any broken parts or grooved front and rear plates in the air motor. If it all looks good I would order a tune up kit with bearings and replace everything that they give you in the kit.
IR 231-TK3

Follow this link to view your parts diagram.
http://manualarchive.ingersollrandproducts.com/ir_pdfs/Tools/IR%20Industrial%20Tools/Impact%20Tools/04584033_ed2.pdf

The IR 2135-k303 air inlet repair kit along with a IR 2131-322 inlet removal tool should fix your problem.

The I.R. 2100G shares parts with the 2135 series impact, the throttle valve seal on these models have a tendency to wear out or deteriorate casing the throttle valve to by pass air. On the model 2100G the parts in question is only sold as an assembly (item# 22).
But you can disassemble the inlet bushing and install an inlet parts kit p/n 2135-K303, it includes all the necessary parts.
I will provide to links for you to look at
2100G: http://manualarchive.ingersollrandproducts.com/ir_pdfs/Tools/Vehicle%20Service%20Tools/Air%20Impact%20Tools/45667599_ed2.pdf

2135Ti : http://manualarchive.ingersollrandproducts.com/ir_pdfs/Tools/Vehicle%20Service%20Tools/Air%20Impact%20Tools/45534070_ed3.pdf
The I.R. parts list shows the inlet bushing in detail.

If the unit will start and run and mower deck can be engaged but will not drive forward/reverse your hydro relief valve has failed.

never use a hone on a air tool cylinder! use 00004 steel wool! make sure the compression rings are concave facing up! then if the vanes have the cut out on one side put that to the bottom of air motor.

There is only a few areas that could cause this. Did you rebuild the valve assembly? If you go to (irtechpubs.com/ir_pdfs/Tools/IR%20Industrial%20Tools/Impact%20Tools/04584033_ed2.pdf) you will see an exploded view of the whole assembly. Note part 28, and then part 28c, this is the valve that controls the inlet air, possibly you have the pin broken off, or the trigger not actuating the valve. Check up the handle for blockage in the exhaust (unlikely). Also check the parts of assembly 29 to make sure nothing is broken, if they are you could have the direction stuck between forward and reverse, thus not allowing air to pass through to the motor (items 10, 11)

Readjust the band, I have ran into this same problem with another C-4.Found the reverse spool valve was sticking in the valve body. Hopes this helps.