Muncie PTO troubleshooting
Most PTO trouble shows up as a noise, a leak or a shift that will not finish. This page condenses the troubleshooting tables in Muncie's owner's manual and TG Series guide, and points to the parts each fix needs.
Start with the application
A PTO that keeps failing early is often doing a job it was never specified for. Muncie's owner's manual is blunt about it: the unit has to be matched to both the transmission and the equipment it drives, or the transmission, the PTO and the driveline can all be damaged. Before replacing the same gear a second time, confirm the series, the speed ratio and the torque rating against what the pump or blower really needs.
The published ratings assume intermittent work, meaning on and off under load. Muncie's manual treats anything that runs at full torque or horsepower for five minutes or more as continuous service and says to multiply the intermittent horsepower rating by 0.70. A PTO sized on the intermittent number and then run all day is a common cause of early failure.
Noise: whine, clatter or clicking
Gear noise almost always comes back to backlash, the small amount of free play between the transmission's PTO drive gear and the PTO input gear. Muncie calls for 0.006 to 0.012 inch on a standard installation, set with the mounting gaskets (shims) between the PTO and the transmission.
| What you hear | Likely cause | What to do |
|---|---|---|
| A steady whine | Backlash too tight, gears mounted too close | Remove the PTO and add a mounting gasket to open the backlash |
| Clatter or rattle | Backlash too loose | Remove the PTO and take out a mounting gasket |
| Clicking | A nicked or damaged gear tooth | Replace the damaged gear, then reset the backlash |
Two warnings from the manual are worth repeating. Never set backlash by sound alone; check it with your fingers through the inspection opening or, better, with a dial indicator. And a PTO mounted too tight undercuts the gear teeth and can end in a broken gear or a cracked housing, so a whine is not something to live with.
On Allison 1000 and 2000 Series automatics, Muncie notes that some PTOs make noise while disengaged that goes away once engaged, and treats that as normal for that transmission. Those installations use a spacer and a wider backlash range of 0.010 to 0.024 inch.
Leaks
| Where it leaks | Likely cause | What to do |
|---|---|---|
| Output shaft seal | Dirt under the seal lip, a damaged seal or bearing cover, or a seal that was not fitted squarely | Replace the seal and check the shaft surface for scoring |
| Mounting surface | A torn mounting gasket, or a cracked mounting pad | Replace the gasket, with no silicone sealant; a cracked pad means a new housing and a fresh backlash check |
| Bearing cover or shift cover | A torn gasket, or cap screws that are loose or tightened unevenly | Replace the gasket and tighten the cap screws evenly to the torque in your series manual |
| A crack in the PTO housing | Too little backlash, an unsupported direct mount pump, overload, or something caught between the gears | Replace the housing, reset the backlash, add a pump support bracket and review the application |
Silicone on the mounting face is a mistake that shows up twice: it can hide a torn gasket for a while, and it makes correct backlash impossible to set. Muncie's TG guide lists 18 lb ft for hex head and 9 lb ft for button head shift cover cap screws on that series; check the book for your own series before you torque anything.
The PTO will not engage or will not let go
Cable shift. A frozen inner cable, a bend tighter than the cable's minimum radius or a worn control head will all stop a cable PTO from shifting fully. Keep the cable away from road spray, seal its end, and never hook lever rods to a cable shifter. If the shift fork has come out of the gear collar, the PTO has to come apart.
Air shift. Muncie air systems feed through a pressure protection valve that holds air back from the PTO until the truck's system passes about 65 psi, so a PTO that will not engage right after start-up may simply be waiting for air. Electric over air systems need about 80 psi. Water and dirt in the lines, a sticking air valve or a piston that will not move are the other usual causes, and the fix is to bleed the air system more often and clean or replace the parts.
Lectra Shift (TG Series). Check the wiring harness and the solenoid ground first, then the 5 amp and 40 amp fuses. The Lectra Shift solenoid has two coils. Muncie's guide gives about 0.3 to 0.5 ohm for the engage coil (white wire to ground) and about 4.7 to 5.9 ohms for the hold coil (red wire to ground); a reading far outside those means a new solenoid.
Clutch shift (CS, A and similar series). Look for a poor ground, a blown fuse, a solenoid valve that does not click open with the key on, or hydraulic lines on the wrong transmission port. Muncie's pressure test puts a gauge at the PTO piston port and another at the solenoid valve: under about 90 psi, or more than 50 psi of difference between the two, points to a blocked hose or screen. If the output shaft keeps turning with the PTO switched off, check the lines first, then the adjustable drag brake on series that have one, such as the CS6 and CS8. Engaging a clutch shift PTO under heavy load or above about 1,200 engine RPM wears out the clutch pack.
What to look at on the bench
- Gears: pitting, galling, cracks or deformed teeth or splines mean the gear, and often the PTO, needs rebuilding. Remove the shift cover or inspection cover to see them.
- Shafts and splines: rust-red wear on the PTO and pump shaft splines is fretting corrosion. Grease on the splines slows it down but does not stop it, which is why direct mount pump joints need regular regreasing on severe duty trucks.
- Housing: look for cracks around the mounting pad and the pump flange, especially where a heavy pump hung without a bracket.
- Shift parts: a worn shift fork, collar or detent, or a damaged shift cover, causes partial engagement and jumping out of gear.
Parts that usually fix it
Gasket packs and mounting shims, output shaft seals, shift cover gaskets, shift covers, air shift cylinders, cables, solenoids and complete rebuild kits are all listed by series on our store. Find your series on the Muncie PTO parts page to see its parts breakdown, or send us the model number from the tag and we will pick the parts for you.
The tables above follow Muncie's PTO owner's manual (IN84-03) and TG Series troubleshooting guide; both are on our manuals page. Your series manual always has the final word on torque values and backlash for that unit.
Still stuck? Ask a Muncie PTO expert
Send the model number off the PTO tag, a part or item number, or simply what the PTO is bolted to. A parts specialist answers during business hours.