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Peterbilt 379 & CAT C15
About this creation
Since I was a child I has been a fan of big trucks, and specially of American style trucks(in Spain is strange to see trucks with long noise).

For this MOC I have chosen one of the most charismatic and representative models of these trucks: a Peterbilt 379.

Also I have endeavored to put a version of CAT C15 engine (I'm also a fan of the brand CAT).

This MOC is made in a 1/10.2 scale, giving a final size of 31 studs width, 99 length and 40 high.

Here you can see some pictures taken in Skaerbaek where you can appreciate the size, there are: this Pete, the Crow's Vampire GT(scale 1:10 too...), the Nathaniel's Supercar and my Veyron.

The total weight is 5.5kg, and has been one of the main problems I've had. Front axles deforms and look like the wheels has huge camber angle. This is a esthetic defect which I hate, but it has not solution if I want to keep all functions and therefore the weight of the truck. I will try to fix it comming soon.

The electric system is huge, and it has:

- 2 AA PF battery boxes
- 4 PF IR recievers
- 5 PF XL motors
- 5 PF M motors
- 1 PF switch
- 3 PF large extension wires (50cm)

Probably, the most “wanted” picture for Lego Technic followers:


When did the truck I always wanted to do it complete, including the sleeper, but later I had to discard it because the cost would have been huge.

The hood can be raised, and remove if you want removing only 2 axles.

Also if the hood is open, you can remove the steering wheel and before remove the cabin in one piece just pulling up on it. Under the cabin you can find both AA battery boxes and the 4 IR receivers.

The two huge fuel tanks are used to cover part of the mechanisms of the truck: on the left the mechanism of the gearbox and on the right part of the pneumatic system.

As curious data, only the bodywork weight is more than 1 kg...

CAT C15 Engine

Under the hood you can find a replica of the CAT C15 engine, with its 6-cylinder in line.

The engine doesn't have the sides covered to appreciate that the cylinders are located in the same order as the real engine, with 120 ° intervals between them. Getting those 120 º between cylinders was very complicated but I thought it was necessary to be more faithful to the original.

The engine also has a motor M to rotate it, which is connected directly to a battery. Between the engine and the M motor there are a differential, which is also connected to the drive motors, so that the engine is always at idling, but when you starts the drive motors the C15 accelerate adding both speeds. The rotation speeds grow up from 250 rpm up to 700 rpm aprox.

Pneumatic system

After almost 10 years without using pneumatics in any of my MOCs, I decided this was the perfect model to use it.

The pneumatic system the truck runs along the complete truck, mainly controlling the suspension and brakes on all axles.

The pneumatic system is composed mainly:

- 2 Small pumps (6L)
- 1 Large pump (for emergencies).
- 2 Air tanks
- 7 Small cylinders
- 8 Large cylinders
- 7 Valves
- 1 Manometer (LEGO part n.64065)
- 22 T connectors
- And about 5 meters of pneumatic tube in 3 colors: blue, black and light gray.

The pneumatic tube color code is this:
- Blue: general system and suspension
- White: Brakes on
- Black: Brakes off

All pneumatic control is located on the right side of the truck inside the fuel tank.

The pneumatic system starts in the air pumps. A M motor is responsible for operating them asynchronously.
The compressor has auto-stop system, it stops approximately at 2 bars pressure, and restart in 1 bar. This compressor control uses a small cylinder, a PF switch and a small spring to counteract the cylinder. To have enough air to the suspension and brakes the truck has two air tanks, they are located inside the chassis and just above the gearbox.

Also in the cab, between the seats, there is a manometer to measure the system pressure, it is very useful to know how much air have you at any moment.


As the real truck it has live axles. Both rear axles are driven without differential between them.
In each axle between the differential and the wheel the axls has gear ratio 12/20 to reduce necessary torque in the differential and protect bevel gears.

The front axles uses the same steering system as the real Pete, of course the steering wheel turns too, also it turns 4 laps, again as the real Pete

- Suspension

The suspension is fully pneumatic in all axes, and it doesn't use any spring to help.
The front axle has 4 big cylinder and each rear axle 2.

The cylinder are controlled by a valve connected to the same axes. So that the truck can maintain the height to the floor regardless of the weight above it. If the weight increases the suspension is compressed and the valve opens getting more air into the cylinders, then the suspension turns to stretch and returns to its normal height and the valve closes.
If the weight is reduced same thing happens, the valve opens and lets out some air until the pistons down to the normal position.

- Brakes

The brakes as the real truck are drum brakes, there are a drum on each side of each axle, all of them controlled by a small pneumatic cylinder.
The control of these pistons are made through two valves, one for the front axle and one for the rear axles.

For normal braking the brakes operate all at the same time, but only while you are keeping push the brakes botton.

But you have also parking brake mode, if you push the brakes botton in the opposite direction only rear brakes works, and they will not disabled if you stop pressing botton. To remove the parking brake you only need use the normal brakes.

- Auxiliar output

Behind the cabin there is an auxiliar pneumatic output(blue connector), where you can connect anything you want. The valve to activate it is located before the rear-right wheel


The transmission is the biggest mechanism of the truck, and it has an approximate size of 25x7x45 studs.
It uses 4 XL motors for drive.

The transmission has 18+2R speeds(this is true, is not a joke...).

The transmission is divided in two parts: the main gearbox with 9+R speeds with automatic clutch(this gearbox is based on the LR Defender), and a transfer case with 2 speed (H and L)

The main gearbox uses a XL motor to shift gears, it has a speed indicator behind the cabin, and speeds ratio are the next:

1 - 1:0.36
2 - 1:0.48
3 - 1:0.6
4 - 1:0.8
5 - 1:1
6 - 1:1.33
7 - 1:1.67
8 - 1:2.22
9 - 1:2.78

The transfer case uses a M motor, and the speeds ratio:

Low (L)- 1:0.9
High (H)- 1:1

Joint both gearboxes the result is this:

1L (1) - 1:0.324
1H (2) - 1:0.36
2L (3) - 1:0.432
2H (4) - 1:0.48
3L (5) - 1:0.54
3H (6) - 1:0.6
4L (7) - 1:0.72
4H (8) - 1:0.8
5L (9) - 1:0.9
5H (10) - 1:1
6L (11) - 1:1.2
6H (12) - 1:1.33
7L (13) - 1: 1.5
7H (14) - 1:1.67
8L (15) - 1:2
8H (16) - 1:2.22
9L (17) - 1:2.5
9H (18) - 1:2.78

Auxiliar electric output

As I said before, the truck has an auxiliar pneumatic output, but also it has an auxiliar electric output too.
There you can connect anything you want, and control it with the remote controller.

To avoid leaving this connetor without any use I have added a fifth wheel(trailer connector).

- Fifth wheel

Note: right now I don't have intention to do a complete trailer.

It is very simple and effective. The kingpin diameter is 1 stud.

The fifth wheel is on the chassis, but it is not part of it. You can remove it removing only 4 pins.

Finally as always, you can see a complete video with all features showed:

And see all pictures here:

I hope you like it!!


 I like it 
  May 23, 2014
hello, this is a very beautiful model. Can it Benefit eventeull buy a building plan. mfg uwe hallo, das ist ein sehr schönes modell. kann man davon eventeull ein bauplan kaufen. mfg uwe
Sheepo's Garage
 I like it 
Charlie A
  October 13, 2013
Ok thanks
Sheepo's Garage
 I like it 
Charlie A
  October 13, 2013
Another question. I saw the brake instructions but don't understand them. Im trying to add realistic brakes to my sets. If you could explain that would be helpful. Thanks
Sheepo's Garage
 I like it 
Charlie A
  October 11, 2013
How does the self leveling work? Thanks
 I made it 
  October 11, 2013
Quoting Charlie A How does the self leveling work? Thanks
It is very simple, just pneumatic cylinders controlled by a valve, and the valve is controlled by the suspension position.
Sheepo's Garage
 I like it 
Luis Eduardo López V.
  May 20, 2013
Just amazing!!!
 I like it 
  March 17, 2013
im amazed, it looks so cool and i love that it has a real 18 speed like the real ones. can it pull alot in bulldog [1-3 gear]?
 I like it 
  February 17, 2013
This must be the best made Technic Truck ever. Love it.
 I like it 
  February 14, 2013
maybere the best i've seen on MOC pages or anywhere!! love the pneumatics for the brakes (don't know how you did it), keep it up!!XD
 I made it 
  January 17, 2013
Quoting jon greenland I gotta ask How fast does it goes? And brilliant design with 4 xl motors it looks like its very fast.
It has 4XL motors, but 5.5kg and a lot of gears too... so the top speed is not highm it is only around 1.5kph
 I like it 
  January 14, 2013
I gotta ask How fast does it goes? And brilliant design with 4 xl motors it looks like its very fast.
 I like it 
  November 29, 2012
ravishingly beautiful!
 I like it 
  November 16, 2012
Technic at its best. 5/5
 I like it 
  November 14, 2012
Incredible engineering. Bravo!
 I like it 
  November 14, 2012
Oh, my! So many wonderful functions that I don't even know how you managed to make them all work like that! A huge WOW to you and your monster!
 I made it 
  November 13, 2012
Quoting Jetro de Ch�teau Love it! I'm glad to see you have finally accepted Pneumatics can be very useful :)
The pneumatics are useful only on a few occasions, but in this occasions, they are incredible xD
 I like it 
  November 13, 2012
I think my favorite part is the fake engine but everything else is amazing too!
  November 13, 2012
Love it! I'm glad to see you have finally accepted Pneumatics can be very useful :)
 I like it 
  November 12, 2012
Impressive build! Huge truck and nice CAT engine :D Lots of functions too
 I like it 
  November 12, 2012
I had the same idea as you, to build a Peterbilt 379 using the unimog wheels but mine was going to be black and run on a LPEpower I3 engine but it would only be forward and reverse gearbox and no brakes and much less fantastic. But I had to stop because of the price and other reasons. but I am going to try again soon. now onto your model... HOLY %#@* THAT IS AWESOME!!!!! BETTER THAN MINE WOULD HAVE BEEN. I didn't really think mine would be good so I stopped and started something more my style... 1976 John Deere 300. but I am very glad to see yours and how good it looks and I would love to see it as a set, maybe you could put it on cuusoo. INFINITY/INFINITY/INFINITY/INFINITY/INFINITY/INFINITY/INFINITY/INFINITY/INFINITY/1
 I like it 
  November 12, 2012
Fantastic truck!
 I like it 
  November 12, 2012
outstanding this is probably your best moc ever well done so much detail it is brilliant
 I like it 
  November 12, 2012
 I like it 
  November 12, 2012
This is not from this planet....if Lego would bring this to market nobody couls pay for it....But I would want it for sure.....amazing...please never stop this level design.....I will look at this many times to get understand it all...
 I like it 
  November 12, 2012
I have no words for this, it's just too amazing !!!
 I like it 
  November 12, 2012
WOW! What an amazing truck! Incredible stuff!
 I like it 
  November 12, 2012
Holy.... How do you do it Sheepo?! Some of the tech I understand (I couldn't replicate it, but at least I can fathom the mechanics), but that self leveling air suspension.... just... how...? An incredible, astonishing, awesome piece of LEGO-engineering. 10/10 - probably the most technically brilliant model on this site
 I like it 
  November 12, 2012
Impressive level of detail and engineering skill. Awesome rig!
 I like it 
  November 12, 2012
Amazing! the size is enormous! great work, also on the cabin and the wheel arches.
 I like it 
  November 12, 2012
Wonderful use for those Unimog tires. All those functions are just stellar, especially the pneumatic goodies. BTW your on The Lego Car Blog again! Congratz.
 I like it 
  November 12, 2012
Wow, amazing!
 I like it 
  November 12, 2012
Wow, it's amazing, a real Technic masterpiece. There are so many functions and the bodywork is awesome! My favourite detail is the brake system. Great job, maravilloso!
 I like it 
  November 12, 2012
Epic! So much detail and info that it took me awhile to read it all! How heavy is this rig? Lego should make this set and give you royalties. 5+/5. Hats off to your MOC!
By Sheepo's Garage
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LEGO models my own creation MOCpages toys shop Peterbilt 379 & CAT C15

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