Info needed: Streetable CMP truck

[Hanno Spoelstra]

Mike O'Sullivan has set a benchmark for this with his C15A, I reckon. Mike drove it from Turkey to Normandy in 2009, which is where I met him.

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Mike has since moved to the USA with his business and the C15A. In 2022 he did a Dallas Texas to Fairbanks Alaska round trip covering 10,000 miles and he does 55 on the way to a convoy and 35-40 miles an hour on the convoy.

His C15A is fitted with a 235 c.i. engine, different seats, CB radio and some more mods. I hope Mike can do a write up of the modifications he did.

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[Grant Bowker]

For boosted brakes, have you considered fitting a CMP booster from a 3 ton truck to your 15cwt?
I see more modern (Michelin) tires under Mike's truck. I've never driven a truck with them but I've been told they make an extreme improvement to ride.

[Hanno Spoelstra]

Originally Posted by Grant Bowker

For boosted brakes, have you considered fitting a CMP booster from a 3 ton truck to your 15cwt?

Yes, but I understand spares for the CMP booster are hard to find so I am also looking at aftermarket power boosters like shown here: https://www.prinstruckshop.nl/c-5242...ster-complete/

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[Grant Bowker]

Understood that original CMP boosters are about as common as NOS Chevrolet master cylinders...
For the style shown, you will need to check for available space in line with the brake pedal (easier to find this space on a C15 without the transfer case to get in the way...). Another option is a remotely mounted booster, mounted to the outside of the frame - sometimes fitted between the supports for the step (at least partly hidden by the battery box).

[Harry Moon]

1. The original transmission gives me no grief at all, you get used to it.
2. Taller tires! I run the 1050 X 16 .
3. Fenton exhaust manifolds, wakes up the motor and no more exhaust gasket leaks.
4. Check wheels for straightness with a dial indicator, use the best you have. Put a couple hundred miles on before balancing at a truck shop.
5. Pertronix ignition for reliability with matching coil.
6. Line the doghouse, the frame channels and the engine compartment with insulator/sound deadener. wouldn't hurt to do that to the underside of the floor to.
7. Spring seat cushions and don't use just a foam block. I use the original seatsas I need all the legroom I can get and a set of van seats that were in it when i got it pushed me to far forward.
8. Single wire alternator with 12 volts, led bulbs in the signal lights.
9. Brakes have never been a problem for me but if you want power install a remote hydro vac if you can't procure an original set off of a C60L

[Hanno Spoelstra]

Originally Posted by Grant Bowker

Understood that original CMP boosters are about as common as NOS Chevrolet master cylinders...
For the style shown, you will need to check for available space in line with the brake pedal (easier to find this space on a C15 without the transfer case to get in the way...). Another option is a remotely mounted booster, mounted to the outside of the frame - sometimes fitted between the supports for the step (at least partly hidden by the battery box).

The first modern brake booster I saw fitted on a CMP was on John Hotson’s C30. He modified his trucks to make them suitable for modern traffic. Look where he managed to fit it:

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[Bob Carriere]

A top speed of 55 mph with standard C15a axle gear ratio.......

My 261 stock rebuilt gives me 44 mph with the 10:50 Chevron tyres and that is pushing near 2990 RPM........

Now my speedometer has not been calibrated using a GPS reading and I think my rpm meter is reasonably close to a testing separate rpm meter gauge.

Planning to calibrate the NOS GMC speedo with a telephone app this Spring.''I do have a mounted set of NOS 9:00 x16 Michelin that have not tried yet.. I believe from all account thats the radial are far smoother b ut not sure they would increase the top speed unless the rolling diameter is greater than the 10:50.......

How do I get more top speed without pushing the 261 much over 3000 rpm????

44 mph is a handful not sure I would feel comfortable at 55.......

Note that non of my tires have ever been balanced yet....... one truck tire shop would not tackle the 10:50 on my CMP rims ..... have yet to check with Benson truck shop....

Properly adjusted new brake linings on radius linings matched to turned drums seems quite adequate.

Comments/suggestions welcome before I paint RED racing stripes on my CMP.......

[Bob Phillips]

I think Bob C. has preempted my question about roadspeeds on stock 15cwt drivelines. I have had severaal roadworthy CMPs over the years and could never achieve speeds any where near 50mph without fear of engine destruction or vehicle instability resulting in catastrophe.
I have 20 inch wheels and tires on my current 15cwt chev it it wont do 50mph
without fear of imminent disaster.
So what experience do others have on this question?