wanted: Chev CMP chassis views

[Hanno Spoelstra]

Who can help with some good views of the C60S and/or C30 chassis?

I found this plan view in the thread CMP chassis:

1. Does anyone have a side view of the chassis? I am asking because I want to know if the chassis side rails taper towards the end (as on Ford chassis).
   
2. 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?

Thanks!
Hanno

[Phil Waterman]

Hi Hanno

Here are some photos of the frame on my Pat 13 1942, C60S from its restoration in 1990.



If you need a view of a particular section of the frame can probably blow it up and re-post.

This was back when I didn't have a shop big enough for a C60S.

Cheers Phil

[Keith Orpin]

Hi Hanno,
Give me a couple of days, and I'll take some pictures ( or scan some of the rebuild) of my C30 chassis and post them for you.
Best regards
Keith

[Hanno Spoelstra]

Thanks Phil,

Your pictures confirm the C60 chassis rails are tapering, albeit not as much on Ford chassis.

Next question: is this tapering also apparent on the CGT chassis? The picture below is well known and (to me) it seems to show straight frame rails, at least on the rear section. I recall seeing pictures of a Cab 13 CGT in Norway with straight frame rails too.

Was the CGT frame a shortened C60S or C60L frame, chopped just before the tapering started?

Or am I drawing conclusions based on wrong sightings?

Hanno

[Tony Wheeler]

Originally Posted by Hanno Spoelstra

Next question: is this tapering also apparent on the CGT chassis? The picture below is well known and (to me) it seems to show straight frame rails, at least on the rear section. I recall seeing pictures of a Cab 13 CGT in Norway with straight frame rails too.

haha, it's an optical illusion Hanno! I've fallen for it myself in the past with Chevs. It only happens in photographs, because they're two dimensional, so we lose our distance perception. When photographed from rearward, the Chev siderail taper is cancelled by parallax, so the brain interprets the image as straight channel, based on a lifetime of conditioning by common straight channel. In other words we see what we expect to see. Conversely, when photographed from the side, there's no parallax effect, so the brain perceives the taper quite readily. It's easily perceived in Phil's sideview, but in the 3/4 rear view you'd almost swear it was straight channel. It's even more difficult to perceive in partial view, even if photographed only slightly rearward. I think you'll agree the taper is virtually undetectable in the pic below, and yet my tape measure shows almost 40mm difference end to end. The camera doesn't lie, nor does the tape measure - it's our brain that lies!



Of course, when we view the actual chassis, the brain is receiving distance input, which enables it to factor in parallax when processing visual information, and come up with the right answer! Try it next time you're near a Chev chassis, you'll find the taper quite obvious from any angle. The brain can't be fooled in three dimensions!

Getting back to your question Hanno - the CGT frame is nothing more than a C15A frame. Unlike the FGT frame, which is a modified F15A frame, there's no difference between the CGT and C15A frame. Likewise throughout the whole CMP 4x4 range, because unlike Ford frames, all Chev frames were built with a winch crossmember. It's sometimes suggested the CGT frame is different by virtue of double skinned midsection, but that's standard on the C15A frame.

I find the best way to think about CMP frames in general, be they Ford or Chev, is to consider the siderail as 3 separate sections: front section, rear section, midsection - the latter being straight channel. All front sections are identical, and all rear sections are identical - it's only the midsection that varies, and only in length, according to wheelbase. No doubt this greatly simplified production, and may have been standard industry practice in truck manufacture. Of course, it also means you can cut and shut a 60L or 60S chassis to SWB.

[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!

[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 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

[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

[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

H.

[Hanno Spoelstra]

Translating the above to identifying technical specs per vehicle type (limited to C30 and C60S as this the object of our discussion):

C30:

• Front axle with 5” steering ends
• Brakes, front drum: 14” diameter, 2” width lining
• Brakes, rear drum: 15” diameter, 3.5” width lining
• Wheel size: 16” rims
• Differential gear ratio: 7.16 to 1
• Rear spring leaves: 12

C60S:

• Front axle with 6” steering ends
• Brakes, front drum: 15” diameter, 3.5” width lining
• Brakes, rear drum: 15” diameter, 3.5” width lining
• Booster actuated brakes
• Wheel size: 20” rims
• Differential gear ratio: 7.16 to 1
• Number of rear spring leaves: 12 + 6 Aux.

So the Chevrolet I am trying to ID is a C60S, by virtue of having:

• 6” steering ends - see the picture with six cap screws
• 12 + 6 Aux. rear spring leaves - see the picture showing the auxiliary springs
• True, it is fitted with 16" rims, but it is possible to fit these on 15" diameter brake drums (C15, C30 have 16" rims on 15" diameter rear drum brakes)

Now, if I check if the subject vehicle has (had) a brake booster, I am sure this is a C60S rather than a C30.

Riddle solved!
H.

[Tony Wheeler]

Originally Posted by Hanno Spoelstra

Translating the above to identifying technical specs per vehicle type

Excellent work Hanno. It occurs to me we've never seen the 15/30/60cwt differences specified like this before. They're always buried within tables containing other information. It's very useful to see them presented separately as you've done here.

It would appear the exact same differences apply to both Ford and Chev, although I wasn't aware of 14" & 15" brake drums. Evidently the Chev manual provides a lot more specs than the Ford manual.

All in all a very instructive discussion - I now have a much better understanding of the 30cwt CMP.

[Hanno Spoelstra]

Originally Posted by Tony Wheeler

Getting back to your question Hanno - the CGT frame is nothing more than a C15A frame. Unlike the FGT frame, which is a modified F15A frame, there's no difference between the CGT and C15A frame. Likewise throughout the whole CMP 4x4 range, because unlike Ford frames, all Chev frames were built with a winch crossmember. It's sometimes suggested the CGT frame is different by virtue of double skinned midsection, but that's standard on the C15A frame.

"there's no difference between the CGT and C15A frame".....

...... but for the rear end of the frame where the winch fairleads were fitted - compare with the C15A (left) and C30/C60S frame with winch (right):

[Hanno Spoelstra]

Originally Posted by Tony Wheeler

Getting back to your question Hanno - the CGT frame is nothing more than a C15A frame. Unlike the FGT frame, which is a modified F15A frame, there's no difference between the CGT and C15A frame. Likewise throughout the whole CMP 4x4 range, because unlike Ford frames, all Chev frames were built with a winch crossmember. It's sometimes suggested the CGT frame is different by virtue of double skinned midsection, but that's standard on the C15A frame.

"It's sometimes suggested the CGT frame is different by virtue of double skinned midsection, but that's standard on the C15A frame"....

.... but according to the information in Is the FAT a 60cwt or 15cwt truck?, none of the frame side rails listed in the CGT parts manual match the parts listed in the C15A parts manual.

The CGT parts list lists 4 types of frame rails, without and with reinforcements, while the C15A one lists 2 types of frame rails, without and with reinforcements.

H.

[Tony Wheeler]

Originally Posted by Hanno Spoelstra

The CGT parts list lists 4 types of frame rails, without and with reinforcements, while the C15A one lists 2 types of frame rails, without and with reinforcements.

Very interesting Hanno, I wonder where the variation occurs. The parts list description "MEMBER AND REINFORCEMENT ASSY" suggests to me it's related to riveted crossmember fishplates, rather than welded double skin midsection, which may have been present universally. In other words the siderail part may have been supplied with fishplates already riveted in place. I notice they're listed as 1st type, 2nd type, etc., which normally indicates design changes over the years. This occurred with F60S/L frames too, with late production frames featuring additional rear crossmember fishplates. I guess the only way to know is to inspect surviving vehicles. We need C15A and CGT owners to submit chassis photos for comparison.

As you point out, the rear crossmember fishplate differs on winch equipped chassis, to accommodate the rear fairlead assembly. This applies to both Ford and Chev frames.

[Keith Orpin]

Hi Hanno,

Apologies for the late response, been a bit busy recently. Having read the conclusions on the differences between C30 and C60S chassis, I have to add that certain C30 chassis were actually fitted with brake booster systems, although it's NOT shown in MBC1 or 2, nor is it mentioned in the parts catalogue!

My C30 LAAT (20/08/1942) has the following :

• Small 5" knuckles
• 11 leaves in the front springs
• 12 leaves in the rear springs, + 4 helper springs
• Brake booster and additional riveted brackets on the chassis.

I have to say that the brakes work really well on stopping 4.5 Tons of Chevy.
I'm sure Rob Fast in Canada has a C30 of a similar year, so maybe he can verify the above info.

Best regards
Keith

[Hanno Spoelstra]

Originally Posted by Keith Orpin

Having read the conclusions on the differences between C30 and C60S chassis, I have to add that certain C30 chassis were actually fitted with brake booster systems, although it's NOT shown in MBC1 or 2, nor is it mentioned in the parts catalogue !

Keith,

Thanks for letting us kwow about your C30, the brake booster is definitely a variation on a theme.

Thanks,
Hanno

[Hanno Spoelstra]

Originally Posted by Tony Wheeler

I find the best way to think about CMP frames in general, be they Ford or Chev, is to consider the siderail as 3 separate sections: front section, rear section, midsection - the latter being straight channel. All front sections are identical, and all rear sections are identical - it's only the midsection that varies, and only in length, according to wheelbase. No doubt this greatly simplified production, and may have been standard industry practice in truck manufacture.

Niels was so kind to measure up the chassis of his CGT and C30 trucks - please refer to the attached drawing from the Chevrolet manual to which I added red lines at datum points "C", "D", "E" and "F".



He reported the following frame height dimensions on the outside of the C30 frame rail:
C: 20 cm
D: 20,5 cm
E: 18 cm
F: 14,5 cm
On the CGT it was bit hard to get the measurements, but from what Niels could tell they where the same as on the C30.

As the distance between "C" and "D" is the same on all chassis (transfer case is fitted to cross member "D"), this means the difference in chassis length is in the mid-section "D"-"E" as follows:
C30: 150 cm
CGT: 73 cm

The difference between the two is 77 cm. I would expect it to be equal to the difference between the wheelbases: 134" - 101" = 33" = 83,8 cm, so there may be some more measuring up needed.

Tomorrow I will post some of the pictures Niels made.

Hanno

[Hanno Spoelstra]

Pictures of chassis at datum points "C" and "D", plus dimensions:

Datum point "C" (at tip of pen), right hand external view (left) and right hand internal view (right).
Frame height is 20 cm at this point:


Datum point "D" - the transfer case cross member - left hand external view (left) and left hand internal view (right).
Frame height is 20,5 cm at this point:



H.

[Hanno Spoelstra]

Pictures of chassis at datum points "E" and "F", plus dimensions:

Datum point "E" left hand internal views; view from the front of frame member (left) and view from the rear of the frame member (right).
Frame height is 18 cm at this point. Note the frame reinforcement (inner frame rail) in the left hand picture:


Datum point "F" at the rear frame cross member.
Frame height is 14,5 cm at this point.


H.

[Hanno Spoelstra]

Distance between datum points "D" and "E":

Datum point "D" (left) and datum point "E" (right) - distance is 150 cm:


H.

[Hanno Spoelstra]

PS: don't be confused by what you see sitting on the chassis in some of the pictures - the cab is removed from the chassis and sits much further back:


For reference, the C30 has one extra cross member between "D" and "E". The C60L has two (see right hand drawing):


H.