'74 Argosy rear axle ratio

[bkahler]

Well I can confirm that my 74 20' Argosy motorhome has a 4:10 rear axle ratio.

It wasn't easy determining the ratio because the motorhome has been sitting so long the drum brakes had locked up. Had to use a long pry bar to get the drum to turn and the brake shoes never did loosen up to where I could turn the wheel by hand.

Also a word of advice when working under a vehicle...keep our mouth shut

[Jjona5]

Trying to find an easy way to get the gear ratio on my rv without having to jack up the rear tires(they are no longer on pavement and I no longer have a forward gear). Are they all 4.10/.11? I have a 77 28" argosy. I'm about to send out the engine and transmission computer soon and they will need my rear axle ratio and the tire size for my engine swap.

[bkahler]

Originally Posted by Jjona5

Trying to find an easy way to get the gear ratio on my rv without having to jack up the rear tires(they are no longer on pavement and I no longer have a forward gear). Are they all 4.10/.11? I have a 77 28" argosy. I'm about to send out the engine and transmission computer soon and they will need my rear axle ratio and the tire size for my engine swap.

I don't believe your 28' has a 4.10 differential. I've been told more than once that the ratio is marked on the differential housing but I never did find the markings on mine.

I don't remember for sure but I thought the longer Classic coaches had something like a 5.46 ratio. Other than rotating the rear wheels I'm not sure what else you could do to figure out the ratio.


Brad

[shepherd57]

Brad I think you mean 4.56 don't you

[bkahler]

Originally Posted by shepherd57

Brad I think you mean 4.56 don't you

John, you might right. I was going to put down 4.56 first and got to thinking about it at which point I thought about the large wheels that are on the Classics and decided 5.46 might be right.

I'll have to do some digging around to see if I can find that info. At one point while I was dismantling the 345 I knew what the number was but I've slept since then

[bkahler]

Ok, everything I found points to the diff on 28' and larger is 4.56.

Thanks for the info John!

Brad

[Jjona5]

I'll get under there and see if it's tagged. I halfway looked while rebuilding the brake system in the back.

[martin300662]

Could it just be original 16.5" wheels used 4.10, and 19.5" wheels 4.56 rather than based on length?

[Jjona5]

Well I have 19.5 wheels and disk rear brakes

[Boom Sounds]

Mine can be determined from the RPO VIN code read out. I can't recall whether you have that, but I though GM vin code reports are available from 1972.

[Boom Sounds]

1991 250 VIN readout shows = GT5
AXLE,REAR,4.10 RATIO 4.10R(GT5)
1,709
G50
SPRING,HEAVY DUTY REAR HVY DUTY RR SPR(G50)

[martin300662]

The GM truck VIN were still the old 13 digit style (that has very little data) at least until 1978 (based on Peanut (1977) and the old parts donor (1978)), so there is little value in decoding (unless you want to confirm year or original engine configuration).

The newer 17 number VIN did not start until 1980 for GM (with the A code) and wasn't mandatory under NHTSA until 1981

Based on the fast you have the smaller wheels Nick, do you have the 4.10 ratio from your VIN code? Yours may be different because in came with the overdrive from the factory.

[Boom Sounds]

Yes, the RPO codes come direct from the VIN code. The RPO code denotes the axel ratio. You can't see it purely from the VIN. Think of it as set of sub-codes. You can see my full list or RPO codes in the serial number thread. In terms of the 1991 250, it was 16 inch wheels with factory overdrive with 4.10 ratio.

I would have thought you still have RPO codes either from the 13 digit VIN or written in the coach (they may be long gone). Several Chevy sites will provide mapping description from the RPO code. I appreciate you might not get them for the older coaches, but worth the effort if you can find them because they provide things like the axel ratio and brake set up etc etc.

[bkahler]

Originally Posted by Boom Sounds

I would have thought you still have RPO codes either from the 13 digit VIN or written in the coach (they may be long gone). Several Chevy sites will provide mapping description from the RPO code. I appreciate you might not get them for the older coaches, but worth the effort if you can find them because they provide things like the axel ratio and brake set up etc etc.

I believe on the older vehicles RPO codes were on a piece of paper supplied with the vehicle when new. Personally I've never seen one of those papers.

On mine I've basically just figured out what the RPO numbers were for things like the brakes and the diff and the only way I could do that was visual comparison to the descriptions for RPO codes found in the service manual.

Brad

[Boom Sounds]

I reckon that is correct, they were on a sticker in the glove box