PTO Dump Truck Hydraulic Pump Guide: Choosing, Identifying and Troubleshooting

To choose a PTO-driven dump truck pump, match four things: the mounting (direct to the PTO or remote on a driveshaft), the shaft and flange, the rotation the PTO actually delivers, and the flow you get at the PTO speed your engine will run. To identify one, read the model code or measure the gear width; to troubleshoot one, start with speed, heat and the inlet line, because overspeed, running against the relief and cavitation kill more dump pumps than wear does.

Most dump pumps on the road are gear pump and valve combinations: a cast iron gear pump with a three-position raise, hold and lower valve and a relief valve built into the port end cover. Commercial Intertech (now Parker), Muncie, Permco and others build them, and Parker's Chelsea PTO catalog lists the same Commercial C101/102 and G101/102 pumps. Everything below comes from those makers' own catalogs and training manuals, and where a factory document does not give a number, we say so.

How does a PTO-driven dump pump work?

The power take-off bolts to an opening on the transmission and its input gear meshes with a transmission gear, so engine rotation turns the PTO output shaft. Chelsea's training manual puts it simply: the PTO picks up engine power through rotation and passes it to the driven equipment, either by mounting that equipment directly on the PTO or through a short driveshaft.

The pump is fixed displacement: every turn of the shaft moves the same volume of oil, so flow rises and falls with engine speed. On a Commercial pump and valve, the valve spool has three positions. In raise, the built-in relief protects the pump and the circuit from overload; in hold, the same relief acts as a port relief to protect the hoist cylinder from shock loads on the road. Commercial sets that relief at the factory to 2,000 psi on both its C and G series.

Which dump pump do I have?

Start with the tag. If it is painted over or gone, our Commercial and Parker gear pump identification guide shows how to measure the housing and turn gear width into displacement. These are the dump pump families we have factory data for:

Family	Built on	Sizes (factory)	Drive and mounting	Rotation
Commercial / Parker C101	P30 and P50 frames	2" and 2-1/2" gears, 39 and 48 gpm at 1,800 rpm	Twin drive shafts	Either direction
Commercial / Parker C102	Same pump, different shaft end	Same gear sizes	Single splined shaft in a flanged shaft end cover (per the factory parts drawing)	Check the code before ordering
Commercial / Parker G101	P30 design	3/4", 1-1/2", 2" gears: 9.5, 21, 29 gpm at 1,800 rpm	Twin 1" SAE BB keyed shafts, 2-bolt pad cast into the shaft end cover	CW or CCW without modifying the unit
Commercial / Parker G102	P30 design	Same gear sizes	Direct PTO mount: SAE B 2- or 4-bolt flange, or cloverleaf with 2.75" pilot; single SAE B splined shaft	Specify when ordering
Muncie E and EH series	Cast iron, roller bearings	Five sizes, 22 to 36 gpm; code shows gpm at 1,000 rpm (23 or 27)	Remote mount: 1" round keyed shaft. Direct mount: SAE B, 7/8" 13-tooth spline	Remote: bi-rotational. Direct: R or L
Permco DMD direct mount	Gear sizes 15, 20, 25 in the code	See the Permco sheet for your size	Direct mount	R (right hand) or L (left hand), field convertible

Commercial ratings are 2,500 psi and 2,400 rpm maximum for both the C and G series, though the C series page asks for factory approval to operate above 2,000 psi. The Muncie data is from Muncie's September 2008 hydraulic components list, the most recent Muncie dump pump document we hold, so confirm current sizes before you order.

What is the difference between a 101 and a 102 dump pump?

Mounting and drive, according to the Commercial catalog. The 101 is the pad-mounted, twin-shaft version you drive from the PTO with a driveshaft: the G101 has twin 1" SAE BB keyed shafts on a 2-bolt pad, which Commercial says lets you hook it up clockwise or counterclockwise without changes. The 102 is the direct PTO-mount version: the G102 has a single SAE B splined shaft on an SAE B flange or cloverleaf mount, and Commercial asks you to specify rotation when ordering.

The C series parts list shows the same split. The C102 shaft end parts replace the C101's shaft end cover, seals, bearings and related items, and Commercial lists separate seal kits for each: CM-HC101 and CM-HC102 for the C series, CM-HG101 and CM-HG102 for the G series. Gear sizes, and so flow, are the same within each family. Muncie splits its E series the same way: remote-mount pumps on a 1" keyed shaft are bi-rotational, direct-mount pumps on a 7/8" 13-tooth SAE B spline are built right or left hand.

Direct mount or remote mount: which is better?

Direct mount to the PTO

Muncie calls direct coupling a common practice because it gets rid of a driveline that needs regular service. The PTO output shaft and flange have to match the pump, and the weight has to be supported:

• Bracket rules. Muncie requires a rear support bracket whenever the pump, fittings and hoses together weigh more than 40 lb or the pump is longer than 14 inches, tied to two points on the pump and two on the transmission. Chelsea voids its PTO warranty without a bracket when the combined weight passes 40 lb or the PTO and pump measure 18 inches or more from the PTO centerline to the end of the pump. Use whichever rule is stricter for your hardware.
• Cracked PTO cases. Chelsea lists an unsupported direct-mount pump as one cause of a cracked PTO case, which can drain the transmission.
• Spline fretting. Muncie reports spline wear from fretting on direct-coupled pumps, which it ties to engine vibration, and leaves a brownish residue on dry splines. Its countermeasures are a greaseable spline PTO, pre-greased splines, and moving from the 7/8" 13-tooth SAE B shaft to the 1" 15-tooth SAE B-B shaft on the same pilot and bolt circle. Commercial's failure guide adds: clean the coupling regularly and put on a light coat of synthetic grease.

Remote mount on a driveshaft

• Use a balanced tubular shaft. Muncie does not recommend solid shafting: it cannot be balanced, can vibrate and damage PTO and pump shaft seals, and long solid shafts can have a critical speed below PTO operating rpm. Chelsea aims bar-stock shafts at low-torque jobs under 1,200 rpm.
• Watch the joint angle. Muncie computes the true joint angle from the side and top view angles as TJA = √(A² + B²), and the allowable angle drops as shaft speed goes up.
• No side load. Commercial warns that any pump with an integral drive shaft can rifle its gears and thrust plates if an external push or pull is applied to the shaft, for example from an interference fit on the drive coupling.

Solid shaft length	7/8" shaft	1" shaft	1-1/4" shaft
24"	5,425 rpm	6,200 rpm	7,750 rpm
36"	2,400 rpm	2,750 rpm	3,450 rpm
48"	1,350 rpm	1,550 rpm	1,925 rpm
60"	850 rpm	1,000 rpm	1,250 rpm
72"	600 rpm	675 rpm	850 rpm

Those are Muncie's critical speeds for solid shafting. A hanger bearing in the middle turns one long shaft into two short ones for this purpose.

How do I match pump rotation to the PTO?

PTO makers state output rotation against the engine, not clockwise or counterclockwise. Muncie explains that every engine crankshaft turns clockwise viewed from the front, so a PTO is listed as turning the same as the engine (CRNK) or opposite (OPP). In most cases a PTO on a manual transmission turns OPP and one on an automatic turns CRNK. Chelsea gives a rule of thumb for Allison highway transmissions: the PTO turns opposite to the same type of PTO on a manual box, because the Allison has no countershaft.

Two things change it. Muncie says an adapter gear always reverses PTO output rotation, and its application catalog shows rotation with the adapter when one is listed in the adapter column. Chelsea uses adapter gears for the same purpose.

Pump rotation, on the other hand, is always judged looking at the pump's own shaft end. Parker's rule for Commercial-family gear pumps: shaft toward you, idler gear below, and a clockwise pump moves oil left to right. Permco's version: shaft end toward you, belly down, inlet on the left is clockwise. Because a direct-mount pump faces the PTO, the pump's shaft end looks back at the PTO, so the pump sees the opposite hand to what you see looking at the PTO output shaft from the pump's side. That mirror step is where most wrong dump pump orders come from.

1. Get the PTO model and its listed rotation (CRNK or OPP) from the PTO tag and the maker's application catalog, and note any adapter gear.
2. Work out which way the output shaft turns looking at its end from where the pump will sit. If you mark the shaft and bump the engine to check, keep hands clear and the PTO disengaged until you are clear.
3. Flip it: the pump, viewed from its own shaft end, must turn the opposite way to what you just saw.
4. Check the pump's code (rotation letter or shaft end cover code) or its inlet and outlet sizes against that.

A remote-mount, twin-shaft or bi-rotational pump takes most of this pain away, which is why the 101-style pumps exist. More on reading rotation for every brand is in our hydraulic pump rotation guide.

Can I change the rotation of a dump pump?

Sometimes, and the method is pump specific:

• Permco direct-mount dump pumps: Permco publishes a field procedure. With the shaft end cover in a vise, remove the bolts and the valve body, move the plug behind the idler gear to the other bore, turn the gear housing 180 degrees on the shaft end cover, refit the valve body 180 degrees from where it was (plug still behind the idler gear), then torque the bolts to 200 lb-ft, or 160 lb-ft on the DMD300, DMR300, DMD400 and DMR400.
• Commercial P30 and P50 based pumps: rotation inside these frames is set by a plug and check valve position in the shaft end cover, but the Commercial catalogs do not publish a field conversion procedure for the C or G dump pumps. Treat it as a parts question and send us the code.
• Muncie direct-mount E series: ordered R or L. We did not find a Muncie field conversion procedure in the literature we hold.

How do I size a PTO pump for a dump truck?

Size it at the PTO speed the truck will actually run in the dump, then check it at the highest engine speed it could ever see.

1. PTO speed. Muncie and Chelsea list PTO output as a percentage of engine speed. PTO rpm = engine rpm × PTO % (as a decimal).
2. Pump flow. Permco's formula: gpm = engine rpm × PTO % × displacement (cu in/rev) × efficiency ÷ 231.
3. Overspeed check. Divide the pump's maximum speed by the PTO ratio to get the highest safe engine speed. Chelsea prints exactly this on its Ford PTO page: maximum engine speed = maximum pump speed ÷ 1.54 for a PTO turning 154% of engine speed.
4. Shaft check. Muncie's Shaft Torque Limit (STL) is displacement times operating pressure, summed across sections on a tandem. Pick a shaft whose limit is above it, and Muncie's advice is to choose the largest shaft available.
5. Duty check. If maximum torque runs 5 minutes or more out of every 15, Muncie and Chelsea both treat it as continuous duty and derate the PTO by 0.70. Muncie also treats any PTO output speed above 2,000 rpm as continuous duty and rates all Muncie PTOs to 2,500 rpm maximum.

Dump pump displacement and flow

Pump (Chelsea code)	Gear width	Displacement	Flow at 1,000 rpm	Avg. flow at 1,800 rpm (Commercial)	Max pressure / speed
C101/102-20	2.000"	5.10 cu in	22.0 gpm	39 gpm	2,500 psi / 2,400 rpm
C101/102-25	2.500"	6.38 cu in	27.6 gpm	48 gpm	2,500 psi / 2,400 rpm
G101/102-1-0.7	0.750"	1.48 cu in	6.4 gpm	9.5 gpm	2,500 psi / 2,400 rpm
G101/102-1-1.5	1.500"	2.96 cu in	12.8 gpm	21 gpm	2,500 psi / 2,400 rpm
G101/102-1-2.0	2.000"	3.94 cu in	17.0 gpm	29 gpm	2,500 psi / 2,400 rpm

The 1,000 rpm column is Chelsea's and works out to displacement × 1,000 ÷ 231, the theoretical flow. The 1,800 rpm column is Commercial's average tested output at 2,000 psi, which runs below theoretical, more so on the narrow gears. Size from tested output when you have it.

Worked example

Say the truck dumps at 1,200 engine rpm on a PTO rated 80% of engine speed (pick your own numbers from the PTO catalog). PTO and pump speed is 1,200 × 0.80 = 960 rpm. A C101/102-25 at 6.38 cu in gives 6.38 × 960 ÷ 231 = 26.5 gpm theoretical, a little less in practice. Now the overspeed check: 2,400 rpm ÷ 0.80 = 3,000 engine rpm, so this pairing cannot overspeed the pump on most diesels. Swap to a PTO at 154% and the limit drops to about 1,558 engine rpm, which a driver can exceed easily. Shaft check: 6.38 × 2,500 psi = 15,950, just under Muncie's 16,500 limit for a 7/8" 13-tooth shaft; at the 2,000 psi factory relief it is 12,760.

For the flow you need, work back from the hoist: cylinder oil volume in cubic inches ÷ 231 = gallons, and gallons ÷ the raise time you want in minutes = gpm. Get the cylinder volume from the hoist maker. Parker's dump cylinder catalog puts minimum reservoir capacity anywhere from 1 to 3 times pump output, and the reservoir must hold all the oil that comes back when the cylinders retract, with room left for expansion and foam. Our hydraulic pump sizing guide covers the flow, torque and horsepower math in full, and the hydraulic calculator does it for you.

Should I use a 2-line or 3-line hookup?

Commercial is clear: in a 3-line hookup the oil passing over the relief valve is vented to tank, which allows continuous or intermittent use. A 2-line hookup is for intermittent use only. In a 2-line system the relief oil stays in the pump and valve circuit instead of going back to the tank to cool, so a 2-line pump left working against the relief, or a truck plumbed 2-line that sees long cycles, runs hot.

The 3-line versions carry a sleeve in the valve: Muncie's 3-line E series pumps include an AA1257 or AA1257-2 sleeve, Permco codes its 3-line pumps "Z, 3 line with sleeve" against "X, 2 line", and Commercial lists the sleeve as an optional part. If you are converting, get the sleeve and the third line, not just the hose.

What kills PTO dump pumps?

Failure	How it happens	What you see
Overspeed	Driving with the PTO or pump engaged, or a PTO ratio too high for the engine speed. Parker's dump cylinder manual says not to drive the unit while the PTO or hydraulic pump is engaged. Commercial lists excessive engine speed as a cavitation cause.	Muncie lists burnt PTO clutch packs, twisted driveshafts, overheated hydraulics, failed hoses and damaged cylinders. Muncie and Chelsea both offer overspeed controls that disengage the PTO at a set engine speed.
Running against the relief, or long idle cycles	Oil dumping from high to low pressure without doing work turns into heat, as Commercial puts it. Worst on a 2-line system.	Hot oil, varnish and sludge, blackened or cracked thrust plates, blued gear teeth. Parker gives 120-140°F as the optimum oil temperature for dump systems.
Cavitation	Commercial's list: clogged strainer or breather, strainer too small, inlet line too long or too small, collapsed inlet hose, too much suction head, excessive engine speed, oil too thick in cold weather.	Noise, heat, pitted thrust plates on the pressure side, erratic hoist action.
Aeration	Low oil, a whirlpool above the strainer, loose inlet fittings, a worn pump shaft seal or cylinder rod seal, foam from sloshing.	Same damage pattern as cavitation, plus foamy oil.
Pressure and shock	Relief set too high, slow or failed, or missing; undersized fittings after the valve.	Cracked housings at the ports and bolt holes, broken drive shafts, worn bearings, excessive housing cut-out.
Contamination	Poor filtration, open breather, dirty fill practices.	Scored thrust plates and worn shaft journals. Commercial suggests a 25 micron return filter on systems rated 2,500 psi or less.
Spline fretting	Vibration and dry or gritty splines on a direct-mount pump.	Worn splines, brownish residue, eventually a coupling that spins.

If the body raises slowly or not at all, the pump may be worn, but check the relief and the hookup first; our guide to a hydraulic pump not building pressure walks through the order. Running hot? Read why is my hydraulic pump overheating.

Which seal kit fits my dump pump?

Pump	Factory seal kit (Commercial catalog)	RestoPower part
C101	CM-HC101	C101 dump pump seal kit
C102	CM-HC102	C102 dump pump seal kit
G101	CM-HG101	G101 dump pump seal kit
G102	CM-HG102	G102 dump pump seal kit
C101 / C102 air shift	314-9414-017	Air shift kit 314-9414-017
G101 / G102 air shift	308-9414-049	Air shift kit 308-9414-049
Muncie, Permco, Chelsea and others	By model code	Send us the tag

Before you fit a shaft seal, look at the shaft. Commercial's failure guide notes that dirt wears grooves under the ring seals on roller bearing pumps until high-pressure oil reaches the shaft seal, and its rule is that if you can feel the wear with a fingernail, the shaft should be replaced. Commercial also rates typical pump shaft seals at only 15 to 20 psi. A new seal on a grooved shaft leaks again; see hydraulic pump leaking from the shaft.

After a reseal or a replacement pump, Commercial's start-up steps apply: clean system, relief backed off, ports filled with clean oil, run at zero pressure and low speed for at least two minutes, then bring speed and pressure up over about five minutes and reset the relief with an accurate gauge. Commercial adds that its pump and valve units should be started with the valve shifted to raise, to make sure the pump primes and to prevent heat damage, so have the body empty and the area clear. The full procedure is in our pump start-up guide.

What should I send to get the right dump pump or parts?

• The full code off the pump tag, plus the PTO model and the transmission make and model.
• Mounting: direct to the PTO or remote, flange type (SAE B 2-bolt, 4-bolt or cloverleaf) and shaft (keyed or splined, tooth count).
• 2-line or 3-line hookup, lever or air shift.
• Rotation viewed from the pump shaft end, or the PTO's listed rotation.
• For an untagged Commercial: overall width at the port end and the gear housing width, as shown in our identification guide. Not sure of the brand? Start with identifying a pump with no tag.

For Muncie PTO parts and pumps, see our Muncie parts page, the Muncie products we list, and where to buy Muncie PTO and pump parts.

Frequently asked questions

Related reading

• Parker Commercial dump pump seal kits and air shift kits
• Commercial and Parker gear pump identification
• Hydraulic pump rotation: how to tell it and change it
• Hydraulic pump sizing: gpm, displacement, rpm and horsepower
• Muncie PTO and pump parts
• Where to buy Muncie PTO and pump parts
• Parker PGP and PGM gear pumps
• Hydraulic pump start-up procedure
• Hydraulic oil viscosity guide by pump type
• Hydraulic calculator
• Parker seal kits
• All hydraulic guides and resources