Info needed: Building a repro LRDG 1940 Chev.

[Bob Carriere]

Hi Tony

On posting #9 that rim when enlarged shows signs of being a rim with an outside ring........ I have no doubt the rim has been modified and possibly mounted backwards....... if it is mounted on 10 bolts then they have to be mounted to a hub/adapter of unknown size as the actual adapter mounts to the brake drum with only five bolts of different diameter to the 7 1/4 diam 10 bolt pattern............ it is unusual and would not be surprised if it was 18 inches....and here is why I think so

If you look at my mock up posting the brake drum is fully cleared of the CMP rim. The inside diameter of the CMP rim is 15 + inches as it is slopped a few degrees as you get closer to the center....and we measured the stock brake drum which measure a hair over 14 iinches....leaving less than a half inch clearance between rim and drum....The other is that the front picture fo Rick Cove's repro shows clearly the front brake drums outside the front rms and his brake drums are ribbed/fins....... which is a variety of brake drums used on those vehicles by GM.

Another factoid...... just got a hold of two new 1940 Chevrolet and Maple Leaf parts book and in the listings.....although only one size hub/adapter of 4 1/4 inch is listed they have four different offset rims sizes ranging from 4 1/8 to 5 1/4 offsets on the rim center parts....all in 20 inches. My spare rim and spare axle has the inside part of the rim even with the brake plate ...this to me implies that it is the smallest offset......... Philippe in Florida has the opposite on his 1939 Chev and his rim clears the brake drum completely. so GM played with the track width by varying the offset of the wheels and the greater offset seems to be on the larger truck axles....series 15 to 18 had the wide offset....... they were not to concerned with the overloading of the bearings. Honestly I am concerned with the old technology and will search to see if I can find roller bearing that fits that particular hub/adapter....... too much unsprung weight to far outboard for my taste.

Hanno.... I agree they are not split rim as far as I can tell.....but have a closer look at the rim/ring edge........looks to me to be a 2 or 3 part rim of that period with the tire pressure locking the rim bead....

The tight fit of the GM brake drum and the split CMP rim may partly explain the reason for using a two part 18 inch rim......18 inches rim where popular in that period and Ford trucks did use them as well.

It would seem possible that a regular 16 in. CMP rim would fit by reversing the location of my adapter plate and mount the rim backwards.... in any event I will play with the mockup to see if I can have the wheel mounted with less overhang..... yet not quite overlap the brake drum...... might be able to gain an inch or so......

Thanks for the interest and questions in this challenging project.

Now looking at finding mid to late 40s production Chev/Maple Leaf 3 ton front axle...... and Ford also had 3 ton I beam front axles...... but only after this snow cover finally melts.......

Bob C

[Bob Carriere]

Clear view of the brake drums fully exposed with implies a healthy offset....

Second shot shoes the civvy hub/adapter which measures 4 1/4 inch and the only size listed in the civvy book.....

A special one does exist for the C15 at about 2 1/2 inch..... but it is using roller bearing along with a CHEV HD I beam axle........ which must match one of the HD front axle such as the Chev COE...... and why not they already used the 4 spoke steering wheel from the COE for CMPs......

[Bob Carriere]

Which one is Rick's truck.......

One with a small cannon


One with windshield post stubs and machine guns.....


and whose is the last one....same plate different tires smooth brake drums

on the side view of the first......I am correct in saying the spare wheel is not drilled with the 10 bolt holes........

[Bob Carriere]

what I dream of.....

[Shaun Mastin]

I’ve got a spare front beam and pretty sure a couple of those extensions of my truck , if your interested!

[Bob Phillips]

Took a spin out through the snow with my broom for a few photos,
first of the non driving front axle, second of the 41-46 ? maple leaf chassis.
May also have extensions availble will have to check in the spring.. BP

003a.jpg 005a.jpg 006a.jpg 010a.jpg 011a.jpg

[Tony Smith]

Originally Posted by Bob Carriere

Another factoid...... just got a hold of two new 1940 Chevrolet and Maple Leaf parts book and in the listings.....although only one size hub/adapter of 4 1/4 inch is listed they have four different offset rims sizes ranging from 4 1/8 to 5 1/4 offsets on the rim center parts....all in 20 inches.... So GM played with the track width by varying the offset of the wheels and the greater offset seems to be on the larger truck axles....series 15 to 18 had the wide offset....... they were not to concerned with the overloading of the bearings.

Bob C

Ford explained the problem well in their Service Bulletins. Different capacity trucks were fitted with different tire sizes for their weight capacities. This resulted in different tire diameters, but still with the same steering geometry. This would cause tire wear issues on the front tires because the centreline of the kingpin axis should intersect the centreline of the tire contact patch on the road. By using wheels with different offsets with particular tire sizes, this geometry could be corrected and irregular tire wear eliminated.

It should be noted that tires would scrub out and become unserviceable much quicker than wheel bearings would fail from being overloaded or not in line with the tire centre.

This geometry will be a more critical issue in determining your wheel offset than exposing some brake drum.

[Bob Carriere]

Thanks for the diagram Tony..... explains a lot...... also shows the roller bearing...... the ribs on the brake drum which I have seen in books only and the picture of the LRDG I posted yesterday.

Could you tell me from what book/manual it was taken from so I can see if Grant has such a copy.....

On the brake drum..... if you look at the last pictures from Bob Phillips you will see the exposed brake drum has a very flat face to which a 4 1/4 inch adapter/hub/spacer is attached by 5 bolts.

Thanks Bob...... that tubular axle is just the ticket and a match to the picture I posted. Your 41 46 Maple Leaf axle is identical to the one that Philippe J.has in Florida with the front brake drum fully exposed.....on my truck the 20 in. rim totally overlaps the brake drum and the backing brake plate is even with the rim's edge..... which means my track is narrower than his truck...both trucks are 1940 1 1/2 ton pick up with the long cargo box and duals on the rear wheel..... a WA model.

Bob the brake drum and adapter that allows a CMP rim to be bolted is very similar to the adapter used on C15...... no measurements just visual... but nonetheless interesting.

When will this snow ever melt....?

Again thank you guys.....

[Tony Smith]

Originally Posted by Tony Smith

Ford explained the problem well in their Service Bulletins.

It is in the "FORD Canada Service Bulletins", the brake drum pictured is from the Ford Truck. I used the diagram because it illustrated quite well how tire diameter relates to kingpin geometry.

Ford don't use a spacer, they use a one piece cast hub/drum with proper roller bearings. Instead of different offset wheels, they use a different dimension on the hub/drum. The brake backing pate and brake shoes remain the same, as do the spindle and wheel bearings. Ford also used the same axle, spindle and bearings with a different hub/drum for the F8 and C11ADF.

[Bob Carriere]

Will consult the resident librarian Grant..... I am sure he has that book and I may have seen that axle in the two volumes of Ford Assemblies that he owns....

So much to learn so little time....

Philippe in Florida was asking about a small spring at the back of his rear brake plate..... we found it Brake cover spring rear axle....... 24 hours later we found a pair listed on Ebay........ some days it works!!!!!!

Cheers

[Tony Smith]

Some interesting points from Cletrac (From this thread, posts #40 and #103):

Originally Posted by cletrac (RIP)

Today I took the rear end carrier assembly out of my Maple Leaf 2 ton parts truck to compare it to the C15 and F15A rear ends. It's the same as the C15 (same ratio too) but the Chev rear ends in the F15A are about two or three inches more in diameter. They must come from the civvy three tons. It makes me wonder which civvy models they sourced the C60 units from.

Originally Posted by cletrac (RIP)

Well, I came up with another bit of insight today. On my C15 the outside of the frame rails are 36" and on the F15A they're 34". I also measured the distance between the axle flanges and it's 65" on the C15 and 72" on the F15A.

A C15 is looking more and more like a good parts donor.

[Bob Carriere]

thanks Tony.......

Ideally the front and rear axle from a C15 would be perfect...after all that is what they used on the 1942 LRDG GM made LRDG......

BUT I cannot find one in Canada........ shipping from Europe is ridiculous.

Trying hard to do like the early 1938/39/40 conversion done in Egypt with cowl/frame that were converted from civilian model....... I may have to use a HD Maple Leaf front axle with roller bearings for better endurance.

Currently playing with using an adapter plate to allow the use of CMP rims with the 10 bolt GM bolt pattern.... made a mock up using wood and it is feasible to machine a 3/8 plate to fit........... big issue is the rear axle is narrower to accommodate the previous dual wheels and may require fabricating a spacer or just plain using a C15a rear end which I have but then it is wider and the frame width had not been standardized yet as discovered by Dave Pope...... so the spring plate on the CMP axle would need torching off and replacing to fit the 1940 frame width I plan on using...

The worst part is the 1940 truck is currently enclosed in ice/snow and can't be access yet for measurements.

Blah!!!!!!!!

Thanks for your help.

[Ganmain Tony]

Now I know GM/Chev is not my forte' Bob.

But the axle used on a GMC 6x4 is the axle you are looking for.....

(famous last words....I think)

Have a look at the "Its infectious" thread in the softskin forum.