74 Dodge block numbers

[mbmcmahan]

I have read and confirmed several 318 block numbers found under the driver side exhaust manifold being 318-3 in raised letters from the casting, where the -3 specifies the "premium" 318 block having heavy duty cooling etc.

I am being told that a certain engine from an alleged 74 D27, that I have purchased, is a 318 however, the number on the block in the same location is five numbers 306xx (xx being some numbers with no dash, which I cannot exactly recall while writing this post).  I can confirm and update since I already bought the engine and transmission with the intent of swapping out a 318-3 in my 69 D24 M300 since it has developed a "dead" cylinder and runs and sounds like a lemon:\

Anyone know what the engine may actually be having that number scheme?  If it truly was a 74 D27 then all the brochures indicate that it would be a 440 on a RM400 chassis.  The scale of the under carriage equipment would be significantly larger and would likely NOT fit an M300 chassis.

For instance I would like to upgrade to disk brakes in addition to swapping the engine.  The front axel assembly is available.  The rear end is also available but all of it seems to be a larger scale (so to speak).  One thing is confirmed is the tire size being 8R17.5 eight lug flat.  My tires are 16x6 widow makers having 7.50 bias ply tires.  I do have measurements and pictures of the possible upgrade parts but need to bounce all this against my under carriage components to confirm they match (or not).

[DaveVA78Chieftain]

16" 8 lug split rims were only used on the 69-73 M300 chassis (front & rear drum brakes).
17" 5 lug split rims were only used on the 69-73 M375 chassis (front & rear drum brakes).
The 17.5" 8 lug tubeless rims were introduced on the 74 & later RM300 chassis (front disk [single piston caliper]/ rear drum)
The 17.5" 8 lug tubeless rims were also used on the 74 & later RM350 (M400) chassis (front disk [dual piston caliper]/ rear drum)
19.5" 5 lug tubeless rims were only used on the 74 & later RM400 (M500) and M600 chassis (front disk [dual piston caliper]/ rear drum)

69-73 M300 had either a 318-3 or optional 413-1
69-73 M375 had a 413-1
74-78 RM300 had either a 318-3 or optional 440-3
74-78 RM350 (M400) had either a 318-3 or optional 440-3
74-78 RM400 (M500) had a 440-3

[mbmcmahan]

I have taken certain key measurements with my phone camera of the leaf spring mount brackets for both front and rear assemblies.  I'm hoping to use these to determine if they will fit my M300 chassis.  I have one rear drum that is in bad shape and unturnable but I am most interested in upgrading to front disk brakes.

Is there a tell tale way of determining whether the components are RM350 or 400 therefore too big for my M300?

I am assuming that my M300 can only accept RM300 under carriage assemblies, not 350 or 400.

At this time I do not have access to the mfr chassis plate

[DaveVA78Chieftain]

RM300 (M300) has a single piston caliper


RM350 (M400) has a dual piston caliper


Dave's Disk Brake Info

[mbmcmahan]

Thanks very much.  I have studied the drawings in order to recognize what to look for.  I will have to try a get the seller to send me a picture or else drive down to look them over once more.  In spite of the popular literature of the time (1974) it seems a small block 318 could be fitted in a RM400 by the factory rather than what the 440 big block, if requested by the original buyer.  I am going with the RM400 theory for now until proved otherwise since the owner claims the unit was a 27 footer (the coach was demo'd due to severe dry rot and unrecoverable DMV issues).

I remained confused by the engine number not being what I expect (ie 318-3).  Did Chrysler quit casting this type of number scheme in 74?  I need to go to storage and take a picture of the raised numbers and try to find any other clues that would absolutely confirm that the engine is indeed a 318-3.

[DaveVA78Chieftain]

The 74/75 Dodge motorhome chassis supplement manual states:
RM300 (M300) had 318 with a 440-3 option
RM350 (M400) had 318 with a 440-3 option
RM400 (M500) had 440-3

318 engine ID (e.g. 5M 318 R 4805 0000) - Front face of block directly below driver side cylinder head.
440-3 engine ID (e.g. 5 T 440 T) - Top of block adjacent to water pump housing on Drivers side.

[mbmcmahan]

Thank you... I check this out.  Am I correct the to think that M400 under carriage parts will not fit on an M300 chassis?  I am trying to get confirmation from seller of front disk brakes if single or dual piston.

[DaveVA78Chieftain]

I do not know.  I have never measured them to see if they would interchange