Central Pneumatic
       Model 40400 Air Compressors

The Central Pneumatic Model 44400 air compressor is one model of the Central Pneumatic house brand sold by Harbor Freight air compressors.

The 40400 is a small, DIY type air compressor, and appears to be manufactured off-shore for Harbor Freight with a 2 HP motor positioned on the top of an 8 gallon tank, with pull handle and wheels under the tank for easier movement.

The 40400 is oil lubricated, and must be filled with compressor lubricating oil before being run for the first time. Check the oil level in the sump by looking at the sight glass located under the oil fill plug on one side of the pump. If filled to the correct level, oil will be visible in the sight glass, and level with the center of the dot in the middle of the sight glass. Do not overfill. If you do, use the drain plub below the sight glass to drain off excess oil.

Central Pneumatic 40400 air compressor

With so many questions submitted about the operation of the model 40400, it has earned its own forum page here on www.about-air-compressors.com. If you are looking for help with your 40400 you will find it below.

Please do read the existing posts to see if your compressir issues has already been addressed. It's also a good idea to review the troubleshooting pages too to see if your question has already been answered there as there, are many common compressor problems have already been addressed on those pages.

If you can offer advice on another vistor's posting about their Central Pneumatic model 40400 air compressor, please do so by adding a comment on the existing question.

Download a copy of the manual for the Central Pneumatic #40400 air compressor, by clicking here.

As the numbers of comments added to this page grows, it may get harder for you to find the specific answer you are seeking so I've added a search box here for your use to help you find the information you need.


Central Pneumatic Compressor 40440 Questions

Having an issue with your Central Pneumatic Model 40400 air compressor? Here is the place to ask about it.

I work on responses to information and technical requests daily. Please allow up to 24 hours for a response. Thanks. Bill

Other visitor's issues with Model 40400

Please see below. You may find a solution to your problem already posted.

40400 Safety Pressure Valve Replacement 
Central Pneumatic Air Compressor 2 HP - 8 Gallon Model 40400. I need to replace the Safety Pressure Valve. Harbor Freight does not have them. Where …

40400 central air compressor runs but no pressure buildup  
Problem: No pressure buildup. Tank and tool tap- off gages both read zero while compressor is running. While the unit was on: 1.Oil level-OK. …

Power supply for 40400? 
Does the 40400 run on electricity and gasoline, or just electricity?

Need replacement 40440 petcock. 
Somehow or another I seem to have lost the petcock on my 40400 compressor tank. Do I need to use an OEM part, or can I replace with a ball valve of some …

Thread size on air intake 40400? 
What thread size on air intake filter for Central Pneumatic 40400 compressor ?

Can't find a check valve for 40400 
i have a central pneumatic 40400 and cant find a check valve, i have ordered two an both come back with the correct 7/16 size but with 1.25mm thread instead …

Help with fitting for 40440 
Broken fitting on tube (part no 42in manual) for 40490 mode lCentral Pneumatic. Tried to replace with 3/8 tubing and fittings but must be metric. Is …

Pressure switch for compressor 40400  
Can not fine a pressure switch rubber diaphragm , mine is round with 4 holes.

air intake filter 
I need a new air intake filter. I have the plastic "donut" housing, but no filter.

Oil is spitting out of the oil plug 
The air compressor turns on and starts spitting oil out of the oil plug right away. Massive amount spills out, turn off to avoid mess and damage. What …

Pressure switch fell apart on 40400  
small spring fell out under black box with four wires. cant figure out how it goes back in . central pneu 40400 inside pressure switch box. can you help …

Need to replace the fill tube on my 40400 
A metal bar fell and broke the check valve and tank fill hose on my 40400 compressor. I was able to find the check valve on EBay and installed it. Only …

Buying Parts for 40400 
I over tightened the cylinder head bolt and cracked the head. I cannot find one anywhere. I am almost ready to buy another brand. Do you know where I can …

Intermittent start issues with 40400 air compressor 
My 40400 hums when turned on. I opened the shroud looking for the reset switch and could not find it. However, the fan blades will difficult to rotate. …

Air hose needs replaced 
Air hose leaks

Unit will not pump air or show air pressure on gauges 
Needing to know how to repair, unit will not pump air or show air pressure on gauges. The unit will turn on, but the tanks will not fill with air.

Stripped threads on oil fill plug - get a new one? 
This issue is with the plastic oil fill plug on my Central Pneumatic air compressor model 40400. Where can I purchase a new one ?

I'm trying to find the sizes of metric fittings to connect to check valve 
To make a long story short, the two compression nuts that connect the copper tube that runs to the check valve on the model 40400 are cracked. I need …

Air Pressure  
I have a Model 40400 air compressor it runs but won't build air pressure. Central pneumatic harbor freight.

Need to replace pressure switch? 
I have model 40400 with a leaking valve inside the switch. Two outlet on the bottom of the switch with a pull/push, on/off switch I need to replace …

40400 has big leak - all air leaks out 
my compressor suddenly all air leaks out. model 40400 will not build pressure, big leak

40400 fills well but releases air when it reaches the set pressure limit . 
My CP 40400 fills well but releases air when it reaches the set pressure limit . Do I need to replace the pressure switch? And where can I find …

Replace electric starter 
Will not start, would like to replace starter

Unloader valve hose / tube for air compressor 
Need to know what the part number is and where to buy it. Approx cost? This is the hose that goes from the tank to the regulator dials. The end connector …

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Parts for a Central Pneumatic 40400 compressor 
I can't find connector to fit the compressor. I have tried a 3/8 inch and it is too big and a 1/4 inch is too small.

My compressor just won't turn on.  
I've read a few people say hit the reset button. I can't find a reset button on my unit anywhere. Can you point it out? I was a small engine mechanic …

Motor does not run on Central Pneumatic 40400 air compressor 
while filling tires, the compressor started...s l o w l y...and then quit. Since then I have been unable to elicit any response whatsoever out of the unit? …

Central Pneumatic air compressor will not stay running 
my compressor all of the sudden started to run for a few seconds then shut off then after a few seconds i hear a click and it starts back up and will do …

40400 runs in bursts then trips overload 
I bought a Central Pneumatic #40400 two years ago, used it for a little while, then put it away and just began using it again. When I run it, the …

40400 check valve shattered? 
Check Valve for Model 40400 - had a crack in it. When I went to remove it, it shattered into a half dozen pieces of Chinese pot metal (its not brass).. …

Check valve blew on 40400 compressor 
I have a Central Pneumatic 2HP 8 Gal compressor (40400) about 2 or 3 years old. I use it only about once a month for a few minutes at most. It just …

Central Pneumatic compressor overload protection has to be reset frequently 
I have a model 40400, and the diaphram in the air pressure switch has a hole in it. Harbor Freight said it will take 3 months to get a replacement switch. …

What is causing oil leaking on model 40400 
Central Pneumatic #40400 oil leaking at cylinder head and regulator valve? Also starts on its own, came on and it was running about an hour..room full …

Central Pneumatic model 40400 will not start  
CENTRAL PNEUMATIC AIR COMPRESSOR 2 HP-8 GALLON 40400 I need to know what to do when the compressor doesn't start? ___________ Hello Don. Nice to hear …

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