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:
c30.jpg

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.

W C60S Restortation -5.jpg W C60S Restortation -7.jpg W C60S Restortation -10.jpg W C60S Restortation -11.jpg W C60S Restortation -12.jpg

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!

IMGP1627 - Copy (2).jpg

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!

TONY8262 - Copy.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

[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):

c15a.jpg c30.jpg

[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.

[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".

Chevrolet CMP Frame dimensions_redlined.jpg

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:
IMG_3515.jpg IMG_3517.jpg

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:

IMG_3519.jpg IMG_3520.jpg

H.

[Eduard Sorokin]

Originally Posted by Hanno Spoelstra

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.

Well, one more enigma is here.
I always thought, all images in technical manuals, handbooks and spare parts catalogues have the factory blueprints as their base. And looking on CMP frame drawing in Manual, I was glad, because of this drawing could to be very useful (for example, in scale modelling of any CMP truck).

Now dear Hanno and Niels provided us with exact dimensions of frame side member heights.
Having those dimensions, I tried to measure those heights on that image from Manual to compare them. Using rear spring length (49 1/2 in.) as basic dimension, I have found the scale of Manual drawing and measured and calculated the remaining dimensions.

My results are below:
C: 15,03 cm,
D: 14,4 cm,
E: 13,28 cm,
F: 10,28 cm.

Thus, the results are very different from the actual dimensions. And my conclusions are:

1) The Manual's authors used some random "drawing" (based of factory plans of frame), which is similar to all frames of all CMP models (for the purpose not to give different drawing each time, in each Manual on each other model). The author's intention was to give general view (overall arrangement) of CMP frame, without too many particular detailing.

2) Possibly, the authors used frame drawing from lighter models - from C15 or even from C8. Only measuring of frames of those exact models could to confirm or to refute this assumption.

3) Finally, the Manual authors could made simple sketch drawing of frame - "by eye", and without use of any factory drawing, to show only general shape of frame.

This is big, big enigma...

[Hanno Spoelstra]

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

Datum point "D" (left) and datum point "E" (right) - distance is 150 cm:
IMG_3527.jpg IMG_3528.jpg

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:
IMG_3502.jpg

For reference, the C30 has one extra cross member between "D" and "E". The C60L has two (see right hand drawing):
IMG_3523.jpg C60L winch.jpg

H.

[Harry Moon]

!6 inch CMP wheels don't fit on the big front axle with the large brakes. tried, don't fit?

[Hanno Spoelstra]

Originally Posted by Harry Moon

16 inch CMP wheels don't fit on the big front axle with the large brakes. tried, don't fit?

Thank for the input, Harry. Have not tried to fit them myself, but others told me the 16" rims fit on 15" diameter brake drums.
Also, C15A, C30 have 16" rims on 15" diameter rear drum brakes, right?