Cadillac engine swap in GMC motorhome

Cadillac engine swap in GMC motorhome

Postby shiftless » Wed Nov 25, 2015 1:54 am

OK, so who has actually done this? I found a PDF file which is some GMC driver's written out instructions on how to do it. This was apparently written back in 2004. As you all know, there is always more than one way to do something like this. So I'm just wondering who has done the swap and how accurate these instructions are. One thing I'm not sure about is the need to move the alternator over to the driver's side. Is this really necessary, and if so, exactly what combination of brackets/pulleys need to be used? Anyone got pictures?

http://www.gmcws.org/Tech/Caddy_Swap.pdf
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Cadillac engine swap in GMC motorhome

Postby Bruce Roe » Thu Nov 26, 2015 7:29 pm

If you go to the GMC lists, you will find this is quite common. i would start by noting all the
parts that are different between a Toro and an Eldo, such as the cross over shaft & attachment
bracket, final drive support bracket, etc. An Eldo parts car should cover this stuff. Bruce Roe
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Re: Cadillac engine swap in GMC motorhome

Postby cadillackeeper » Wed Dec 02, 2015 8:27 am

Somehow the motorhome guys are all a little different.Fuel injection and turbos and ... They all have different opinions.Most stay stock olds and carb,some have piped the shaft Through other engine oil pans.
As far as I know the 66/7 Eldo /Toro is different than 68-78.Spline count and size of shafts and hangers and placement.Most desired for the motorhome is the sp/3.21 out of the early cars.
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Cadillac engine swap in GMC motorhome

Postby Bruce Roe » Wed Dec 02, 2015 11:01 am

cadillackeeper wrote:Somehow the motorhome guys are all a little different.Fuel injection and turbos and ... They all have different opinions.Most stay stock olds and carb,some have piped the shaft Through other engine oil pans.
As far as I know the 66/7 Eldo /Toro is different than 68-78.Spline count and size of shafts and hangers and placement.Most desired for the motorhome is the sp/3.21 out of the early cars.


The 66-67 final drive was 3.21:1, recognized by the 10 bolt cover. It had a smaller cross over
shaft, different support brackets on both ends (and the Cad was different from the Olds), and
a different bolt through the support. Those happen to be SWitch Pitch transmission years, a lot
of GMCs got converted to SWP. There is a lot of support for GMCs.

One opinion is, the ideal gearing is an Olds 455, SWP TH425 with a CASPRO POWER DRIVE
chain of 65:57 ratio (instead of 1:1), and a 3.21:1 final drive, for a 3.66:1 overall. I have
seen this move quite well. The last ones had a 403 with standard TH425 and 3.07:1 final dr.

There are all kinds of engine variations out there. 500, 454, diesel, turbo, headers, aluminum
heads. Some have put a huge effort into fuel injection conversion, some good results, some bad.
For the limited mileage usually involved, I wonder if its worth it? Bruce Roe
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Re: Cadillac engine swap in GMC motorhome

Postby gary kosier » Fri Jan 29, 2016 7:02 pm

Nathan,

The Cad is an easy swap into the GMC. There is a lot of misinformation out there. First, you need a 68-72 Eldo
front motor mount and brackets. Sorry, I sold all my spares to Kanomata. Then you must get the motor mount
remanufactured because it was poorly designed and it caught all the oil that invariably leaked out of the front of
the motor. Steele Rubber in Denver, North Carolina does that. About $90.(Ouch) Alternatively, Ken Henderson
has a design on the Photosite for a set of brackets to use the Olds mount. With the Cad mount you have to drill
two new holes in the front crossmember 3/4" forward and a bit to the right. I forgot how much. Measure the
difference from the center of the crank. I cut a section out of the gas line that goes across the front cross
member and coupled it back with a compression coupling. Oh yes, don't forget to get the final drive support
with the front motormount. Personally, I like the 76 Eldo engine with no smog pump. Use all the stock brackets
and the big alternator. I just pulled all the wires out of the loom and laid them in front of the pass seat till I was
done and then made them fit. I had the bigger exhaust before, so I kept a short piece of the original pipe and
made a new piece to slip over them and transition down to the muffler location
The Cad is a little taller, so you have to raise the floor above the carb. I've got big feet, so I didn't want to give
up much. I went to Jeg's and bought a bonnet and some fittings and hose made by Spectre and made a small
raised section which the wastebasket sits on. Hardly noticeable and the carpet still fits. There's a bunch of
other little things, but I just had a mess of pizza and can't think. Too sleepy.

Gary Kosier
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Re: Cadillac engine swap in GMC motorhome

Postby shiftless » Mon Feb 22, 2016 5:35 pm

Thanks for the information! :thumbup:
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Re: Cadillac engine swap in GMC motorhome

Postby gary kosier » Thu Feb 23, 2017 6:11 pm

II just want to add that all the bracketry on the front of the motor is stock. I just reworked the original wiring to match.
I had to rework the bracket for the throttle cable to get it right. I reworked it again when I switched to the GM stepper
motor cruise control. Later I made my "thrifty guy" serpentine belt conversion. There's no opening in the water pump
on the Cad for the return heater Hose. The CARQUEST store has a tee to go in the lower heater hose. Careful fitting and
a couple of Gates shrink band hose clamps make it very inconspiculous. I also made up an upper hose that goes across
above the fan shroud to keep it out of the way. Transfer the oil cooler adapter to the Cad and buy the stainless braided
hoses from J.R. Slaten to hook up to the original cooler in the radiator. While you've got the motor out is a good time to
change the vent fitting at the top of the trans chain case and extend it out to the side. There's probably more that I can't
remember.

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Re: Cadillac engine swap in GMC motorhome

Postby shiftless » Fri Feb 24, 2017 8:21 pm

What parts and pulleys did you use for the serpentine conversion?
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