Questions about Caddilac Rearends

[muddwhumper]

Does anyone know what kind of rearend is in a 1975 Coupe De Ville with the 500 engine and 400 tranny? I have the entire car and would love to put the drivetrain into a 1986 Chevy K-5 Blazer. It currently has 454 w/a 700r4 tranny and the 208 transfer case. I don't like the combo and would like to put the 500, 400, and a 205 into the Blazer. While I was at it go ahead and ditch the rear 10 bolt rear and put the caddy rear if it was a 12 bolt or something and if I could get gears to match the front gears of the blazer. Any and all suggestions are welcome--even if you think this idea sucks.

Thanks

[mepr]

well i know my 77 Sedan Deville came whith an 8.1" 10bolt. In which case you would be better off whith your trucks stock rear(8.5" 10bolt whith ALOT thicker ring gear).

[DOC]

mudwhumper,

It's been our experience with that combo (Cad, 400, 205) that the Blazer axles will last about 5 minutes. Lots of torque and big tires is death on smaller axles. I suggest that you look for a matching set of 73-82 one ton axles. If you cannot find them (I see them on ebay all the time), the next best set is 73-79 3/4 ton axles. They are a 44 up front and a 10.5 in 14 bolt corporate rear. The Cad rear axle could be made to fit, but they are limited on gear ratio, and it would suffer the same fate as the factory Blazer axles.

With a name like mudwhumper, I doubt this rig will be babied much. Build it tuff and have a ball!

DOC

[KadillacKid]

My 75 CDV has a 12 bolt, but from what I have read on the Cad posts is this version does not have many options on ratios, as mentioned by Doc...... :!:

[muddwhumper]

Thanks for the info and suggestions. I looked underneath the caddy and thought that the rear looked beefier than my 10 bolt (probably cause the caddy has more bolts--haha) Thats why I was thinking of the swap into the k5. I love the idea of getting one ton or 3/4 ton front and rear, the only problem seems to be that shipping one ton running gear gets to be cost prohibitive and all the local junkers I have contacted-- say they don't have this stuff. So I am at a little bit of a quandry. How can I find the model/ ratio for this caddy rear I already have or do I just try to beef the 10 bolt?
Better yet, do you all have any one ton stuff lying around?

I really want to thank you guys for your help.

Muddwhumper

[dave_brode]

muddwhumper,

The Caddy rears are oddballs, with no aftermarket support. Gear ratio selection for the caddy rears is very limited, and it might be tough to find a front diff gear to match.

The Factory 8.5" rear in your truck is actually pretty tough. I'm pretty sure that 33 splined posi units are available for it. 33 spline aftermarket axles for sure. Another easy option for the rear would be a 12 bolt chev rear from another 1/2 ton chev. If axle strength is an issue, 33 spline aftermarket axles are available for sure, as is a 33 spline posi from Eaton, afaik. The c-clips can be eliminated by ordering the axles with ends set up for Ford wheel bearings. You can buy special weld on ends that mate to the ford bearings and allow chevy backing plates to be used, or Ford back plates, and brakes can be run. Ford drums can be re-drilled for the chevy bolt pattern.


For a bit tougher rear, a Dana 60, Sterling Ford, or a chevy 9.5" / 10.5 rear could also be used in the rear, and fitted with 5x5 axles. The same 5x5 brake options as above can be used on such 3/4 ton rears.

I'm no 4x4 guru, so I can't comment on the front diff options.
Dave


"]Does anyone know what kind of rearend is in a 1975 Coupe De Ville with the 500 engine and 400 tranny? I have the entire car and would love to put the drivetrain into a 1986 Chevy K-5 Blazer. It currently has 454 w/a 700r4 tranny and the 208 transfer case. I don't like the combo and would like to put the 500, 400, and a 205 into the Blazer. While I was at it go ahead and ditch the rear 10 bolt rear and put the caddy rear if it was a 12 bolt or something and if I could get gears to match the front gears of the blazer. Any and all suggestions are welcome--even if you think this idea sucks.

Thanks[/quote]

[muddwhumper]

I'm not sure but I think my rear is the 7.5 one. I looked at a link on another thread that pictured the different axles and if memory serves on my 86 blazer it isn't the totally round housing but kind of oblong. Here is the link

http://truckparts-specialists.com/catalog/differentials/axle-and-differential-picture-guide.htm


I have heard these are notorious for weakness; hence the scramble to find anything else that could work.

Thanks again for the help guys.

[dave_brode]

muddwhumper,

Afaik, the 7.5" was never used on K, or C trucks, only S series.

Fyi, The 7.5s were 26 spline until a change to 28 in '88 or so. The 8.5s were 28 spline until mid 90s, iirc, when they went to 30.
Dave


"]I'm not sure but I think my rear is the 7.5 one. I looked at a link on another thread that pictured the different axles and if memory serves on my 86 blazer it isn't the totally round housing but kind of oblong. Here is the link

http://truckparts-specialists.com/catalog/differentials/axle-and-differential-picture-guide.htm


I have heard these are notorious for weakness; hence the scramble to find anything else that could work.

Thanks again for the help guys.[/quote]

[STDog]

Since the 75 and 74 are so similar, I would expect it had the 2.73:1 that the 74s had. There was a controlled diff option in '75 but I'm not sure how to identify it externally.

[CadillacPat]

Dave,
I was looking to get an early '90's GMC/Chevy 4X4 6' box and extended cab to install a 472/500 in (one with a bad Diesel to keep costs down). I would probably use one of my '74 500's with a 8.5:1 CR for towing to keep detonation in check). However, the '99-up trucks have the newer "hydroformed" frame (technology from the C6 'vette) that makes the trucks handle more like cars. Should I be looking for a 3/4 ton (HD2500), and if so, with what front/rear axles? Dana 60's? Also, would using a 4L80E be best? A friend has a '00 3/4 ton with the Diesel, and the 4L80E trans lost reverse after only 100,000 miles (and, only six years old). I thought this trans was very similar, in both sharing some parts and strenght as a TH400.

[CadillacPat]

Dave,
Or would a TH400 be a better option? If so, would I have to use the 4L80E output shaft with the transfer case? Finally, would the NP203 transfer case bolt in? I have one, but it is from a TH350. It is usually cheaper to find one from a TH400 (different input/output shaft sizes) than to convert one.