Cadillac engine swap in GMC motorhome

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

 

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

 

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

 

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

 

Thanks for the information!

 

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.

Gary Kosier

 

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

 

Here's the poop on the serpentine. Since there's no reverse rotation water pump for the big Cad, you need to
use two belts, just like the factory. 81-89 Ford Galaxy with a 302 motor has the pulleys. The water pump
pulley uses the small bolt pattern, while the Cad uses the big pattern. Since they both have a 5/8" shaft, just
bolt them together with a 5/8" bolt, use a 5/16" transfer punch to mark the holes and drill them. On the crank pulley, I didn't like the way it lined up, so we cut the front pulley off, turned it around and put it on the back,
with .090" spaceing between the pulleys. This lined the back pulley up with the PS pump and the front pulley
with the water pump. This is with a 1/2" aluminum spacer behind the crank pulley. For the alternator, I
picked up a CS130D alternator off a 3100 Chevy(105 amps output) To mount the alternator, I took the
bracket off a smog pump motor and cut all the extraneous material off, and inverted it to move the alternator
in closer. a .600" long tube put the alternator in line with the WP pulley. I mounted the alternator and PS
pump so they could swivel freely as I built spring loaded tensioners for the belts. I have a detailed writeup
if any one is really interested. Yes, I even have some pictures somewhere.

Gary Kosier

 

Gary thats cool stuff!! You must have allot of patience for that. Just trying to get the alt. to line up had me confused until i realized i was trying to use the pontiac bracket. Yeah stupid bone head mistake. I got in a hurry and tossed the brackets into the same milk create that had other pulleys and brackets. Most were easy to find because of the caddy blue.
PJ

 

Bruce. The 3.21 planetary final drives have 8 bolt covers. Rest of your posted information is right on. Just trying to avoid problems.

John Biwersi

 

Well that was my dumb typo, I even knew that. Thanks for the correction. Bruce

 

Well, here is a pic of the serpentine conversion. The final version has the original front brace to the alternator reworked to fit.
I can't seem to find that pic. I've been using this set up for several years with zero problems. So naturally I'm planning to
change it to better suit the Motorhome.

Gary Kosier

 

Could someone please explain the 'planetary drive' ? Is this as opposed to a ring and pinion ?

 

Nick,

Instead of a normal bevel geared differential, it has a spur geared planetary geared differential. It was supposedly done because of lack of space,
but since they managed to fit a normal diff in the same space in 1968, I believe it was just the engineers showing off their abilities. Supposedly,
it gives a mild limited slip effect, which would mean it has a little more internal friction IMHO. I've got a couple, but I doubt I'll ever get one
installed, unfortunately.

Gary Kosier

 

Thanks, do you have any pics ?

 

Nick,
I do have a 1977 Eldo Shop Manual. I'll have to see if I can get my wife to copy a pic to my computer.

Gary Kosier

 

Okay, back on March 30, I posted a pic of my "Thrifty Guy" Serpentine Belt Conversion for the 500. Since nobody showed any interest, I'll go ahead
and mention that I also built one for the 455 Olds. Probably no interest in that either, but you never know.

Gary Kosier

 

Howdy Gary,

I read your posting in March which showed your serpentine setup. You've done a nice job. In fact, it was a much earlier posting of that picture here on the forum that caused my to consider your approach for my project but for me the issue became one of space. While you do use serpentine belts, there are two of them and that pushes those drives further forward. My sole reason for going serpentine was to have a single belt, one that could be tucked in as close to the block as possible. Space is just that tight in the '50 Studebaker.

As was said above, you have a nice, clean, straightforward setup, one that will likely answer the needs for some builders; but for me, space was the deciding element.

Best,

bro. d