wanted: Chev CMP chassis views

[Niels V]

Hi Hanno
Do you need more pictures of C30 and C60 chassis,? I have good access to both (C60L with winch) plus cab 12 CGT in the barn at home.

[Tony Wheeler]

While raving on about optical illusions I completely forgot to post the C15A siderail pic I took today!

TONY8262 - Copy.jpg

[Hanno Spoelstra]

Originally Posted by Tony Wheeler

While raving on about optical illusions I completely forgot to post the C15A siderail pic I took today!

Tony, thanks for the elaborate reply - I see your point and am convinced now!

Hanno

[Hanno Spoelstra]

Now that we have the rail taper question solved, I would like to have some input on my 2nd question please:

Is the only difference between the C60S and C30 in the axles used? 3-ton axles versus 15-cwt axles and heavy versus light steering box?

I am trying to ID a Chevrolet: it is said to be a C60S, but it is on 10.50-16 tyres, which could mean it is a C30. But it does have helper springs on the rear axle and the front axle knuckle has 6 bolts on top. Can anyone help?

Thanks,
Hanno

[cliff]

Hanno I have always thought that the 30cwt trucks had no helper (overload) springs whereas the 3 ton did.

[Hanno Spoelstra]

Originally Posted by cliff

Hanno I have always thought that the 30cwt trucks had no helper (overload) springs whereas the 3 ton did.

Cliff, check!

Hanno

[Hanno Spoelstra]

Originally Posted by Hanno Spoelstra

I am trying to ID a Chevrolet: it is said to be a C60S, but it is on 10.50-16 tyres, which could mean it is a C30. But it does have helper springs on the rear axle and the front axle knuckle has 6 bolts on top.

Not very good quality pics, but they show the 6-bolt steering knuckle ("heavy" or 3-ton axle) and rear axle helper spring. Tell-tale signs of a 3-ton C60S, rather than a 30-cwt C30, right?

Do 16" rims fit on 3-ton axles/drumbrakes?

Chevrolets are not my strong point, sorry

Thanks,
Hanno

DSC_1985-1.jpg DSC_1990-1.jpg

[Hanno Spoelstra]

Originally Posted by Niels V

Hi Hanno
Do you need more pictures of C30 and C60 chassis,? I have good access to both (C60L with winch) plus cab 12 CGT in the barn at home.

Hi Niels,

Yes please: I need confirmation that a difference between the C60S and C30 is in the axles used, as in 3-ton axles on the C60S versus 15-cwt axles on the C30 and heavy versus light steering box?

Possibly Keith O. can confirm the type of axles and steering box used on the C30, too.

Thanks,
Hanno

[Tony Wheeler]

Hanno, I think it's a misnomer to describe CMP axles in terms of load rating. Certainly within the 60L/60S range there's no correlation with componentry such as steering ends or steering box. These appear to be nothing more than design upgrades - early production 60L/60S had small steering ends and steering box, while later production 60L/60S had large steering ends and steering box. I'm not sure exactly when the changeover occurred in Canadian production, but it's not seen in Australian assembly until mid '44, and even later in Indian assembly I believe, perhaps around mid '45. Hence a very large proportion of Australian and Indian assembled 60L/60S/FAT were fitted with small steering ends and steering box.

As we know of course, the 15A retained small steering ends and steering box universally, however I'm not sure that's true of the C30/F30. I've seen at least two F30 ambos in Australia with large steering ends and steering box. As far as I can make out, the only SPECIFIED difference between C60S/F60S and C30/F30 is wheel size. This gets back to our earlier discussion concerning CMP load class rating, which appears to based solely on wheelbase and wheel size.

On the question of auxiliary springs - they're definitely specified in the Ford workshop manual, and while it's not the most dependable source of info, you'd certainly expect auxiliary springs on the C30/F30 Derrick and LAAT. I'm not sure about the various ambos, but it occurs to me they may have been anomalous in many respects.

And yes, 16" and 20" wheels are fully interchangeable, with no difference b/w Chev and Ford.

[Hanno Spoelstra]

Originally Posted by Tony Wheeler

As far as I can make out, the only SPECIFIED difference between C60S/F60S and C30/F30 is wheel size. This gets back to our earlier discussion concerning CMP load class rating, which appears to based solely on wheelbase and wheel size.

Tony,

Agree on the misnomer to describe CMP axles in terms of load rating, that is why I also use the "heavy" and "light" designations, by which I mean the same as your "large" and "small" designations. When I write "3-ton axle" I mean to say "the type of axle fitted to a truck with a 3-ton load rating".

Indeed the factory specifications do not specify a load rating for the axles themselves. But, next to wheel size they also list the differential ratio and number of spring leaves. It is this combination which was required to match the specified load rating for a certain type of truck. The C60S and C60L are thus fitted with 20" wheels, 7.16:1 differential ratio and 18 (12+6 aux.) spring leaves on the rear axle, which enables them to carry a 3-ton load.

So in the case of the subject vehicle, does the fact that it has "heavy"/"large" steering ends (the type with six bolts on top) means nothing to identify it? Or is it the case that an axle with "heavy"/"large" steering ends always has the 7.16:1 differential ratio?

One fact which helps to ID this truck is that it is fitted with 18 (12+6 aux.) spring leaves on the rear axle, which was fitted to the C60S and not the C30 which had only 12 spring leaves on the rear axle. As per factory spec it should thus be fitted with 20" wheels and not the 16" wheels it currently has.

H.

[Tony Wheeler]

Originally Posted by Hanno Spoelstra

So in the case of the subject vehicle, does the fact that it has "heavy"/"large" steering ends (the type with six bolts on top) means nothing to identify it?

In order to answer that question Hanno we'd need to know Chev practice with the C30, which can only be confirmed by checking wartime photographs and surviving examples. If you find the C30 retained small steering ends universally, just like the C15A, then the large steering ends would identify this vehicle as C60S. On the other hand, if the C30 steering ends were upgraded in later production, just like the C60L/S, they would not be definitive.

My own belief is that the C30 would have retained small steering ends, just like the C15A. Certainly this appears to be the case with the F30 chassis in Australian ambulance use. These were very late production chassis, and they differ greatly from late production F60S chassis supplied to Australia. Based on my own observations:

late production F60S: large steering ends, large steering box, auxiliary springs, reinforced chassis.
late production F30: small steering ends, small steering box, absent auxiliary springs, non-reinforced chassis.

Interestingly though I have seen ONE ambulance chassis which is late production F60S in every respect except absent auxiliary springs. For the moment I've dismissed this chassis as anomalous, perhaps reallocated from F60S production, however it may not be the only one.

On the question of diff ratio - normally this correlates with wheel size: 6/39 diff with 16" wheels; 6/43 diff with 20" wheels. On that basis the C30/F30 diff may seem anomalous, however the C30/F30 ran much bigger tyres than the 15A, so it's not a direct comparison. More importantly perhaps, the 2-speed transfer case would call for the more robust 6/43 diff.

Another identifying factor on the C30/F30 is absent brake booster, just like the C15A/F15A. It's worth noting here that the Ford workshop manual associates the booster directly with steering end size:

BRAKES - All Vehicles Having 6" Steering Ends.
Booster..........Yes

BRAKES - All Vehicles Having 4 7/8" Steering Ends.
Booster.........No

This strengthens my belief that the C30/F30 retained small steering ends universally, which also implies 2" front brakes. In other words the C30/F30 chassis was nothing more than a lengthened C15A/F15A chassis fitted with 2-speed transfer case, 6/43 diffs, and big tyres. My only query concerns auxiliary springs specified in the Ford manual - is it an error, or is the ambulance an exception...?

[David Dunlop]

Tony.

One of the standard comments one finds about the CMP production during the war, when compared with other vehicles manufactured, is the very high degree of standardization of parts, not only between the various weight categories, but between the two manufacturers. They kept it as simple as possible and didn't change things unless they really had to do so.

On that basis, your evaluation of the common components between the 15 and 30cwt classes makes a lot of sense. For the 60-cwt, certain things had to be more robust and were implemented accordingly.

Regarding the 60-cwt you ran across that lacked the auxiliary springs, perhaps they were simply removed from that particular vehicle, for whatever reason, but like you noted, one vehicle is interesting, a bunch of them would make a statement.

Cheers,
David

[Hanno Spoelstra]

Interesting discussion guys. Now, concentrating on Chevrolets for the moment as I am trying to ID a C60S or C30 on 16" wheels.
I just looked up some more facts in the Chevrolet MB-C2 maintenance manual and list my findings here:

Front axle:
6” steering ends (”steering arm is a separate part and attached to the lower part of the knuckle by six cap screws”): C60S, C60L, CGT
5” steering ends: C8A, C15A, C30, ”and on some special equipped C60L vehicles”

Brakes, front drum:
15” diameter, 3.5” width lining: C60S, C60L, CGT
14” diameter, 2” width lining: C8A, C15, C15A, C30

Brakes, rear drum:
15” diameter, 3.5” width lining: C15A, C30, C60S, C60L, CGT
14” diameter, 2” width lining: C8A, C15

Brakes, booster actuated:
C60S, C60L and CGT

Wheel sizes:
16” rims: C8A, C15, C15A, C30
20” rims: C60S, C60L, CGT

Differential gear ratio:
5.43 to 1: C8A
6.17 to 1: C15
6.5 to 1: C15A
7.16 to 1: C30, C60S, C60L, CGT

Springs:
As per factory specifications.

Winch:
Standard on CGT, supplied as optional equipment on C30, C60S, C60L.

Steering gear
Ratio is 23.6 to 1, with the exception of C60L with Gun Portee or Petrol Tank which has a ratio 30.6 to 1
C8A, C15 have mounting different from all other types