Info needed: Building a repro LRDG 1940 Chev.

[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.

[Bob Carriere]

....during a lull a t the barn today....... we no longer have to keep moving to keep from freezing...... Grant urged me to check out part numbers in the C15A book and the C60 L parts book....... now I realize that the C15a rear axle and the C60 rear axle are identical....except for the gear ratio and from what Dave Pope observed the rear axle are also the same for the civilian 2 ton axle...although I still have to see the proof in the parts book.....

Quite common here in Canada for CMP owners to replace the single wheel CMP drum and rim with a dual civilian drum and rim and they fitted...... so bearings and brakes worked......

The things you learn when you can read.....

We took apart a 47 to 51 Chev front axle/hub today just to learn about the bicycle bearings...... now to see if the HD roller bearings will fit in the same hub carrier.... or need machining.....more to follow.