High Performance Big Block Cadillacs
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Author Topic: 1980 cadillac eldorado 368ci swap for 425  (Read 6807 times)
dave brode
C5
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Posts: 1074


Best of 11.66, 113.96, 1.59 sixty


« Reply #15 on: September 25, 2009, 01:50:30 PM »




I know people get tired of seeing these pics, but here they arte again. This was my car: The Cadinator:img]

Cody G. Carson


Not me. Best looking 79-84 Eldo I've seen.

Dave
« Last Edit: September 25, 2009, 06:36:49 PM by dave brode » Logged

3960 lb '71 C-10. 11.7-1 CR 514". PEP I beam rods floating MTS 18cc dish Probes, Elgin solid cam, home ported heads, MTS 2.19/1.84", Potter/Probe shaft rockers, edel 2115, 4781 850. Switch-pitch TH400, 12" 1800/3200 Tri-Shield convertor, 4.30 gears. Best so far of 11.66, 114.8 mph and 1.59 sixty
CadVetteStang
Eldorado Autocross Racer
C2
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Posts: 52


"BattleCar Cadillactica" at home in the pylons


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« Reply #16 on: September 26, 2009, 06:58:49 AM »




I know people get tired of seeing these pics, but here they are again. This was my car: The Cadinator:

Cody G. Carson


Not me. Best looking 79-84 Eldo I've seen.

Dave

Thanks, Dave.

Oh and Nick, and I remembered more info that I wanted to share: Before you begin the swap, pay attention to things like trans shift lever bracket, Exhaust manifold studs for accessory bracket mounts, location of wiring harness grounds that attach to the engine and look for ways to duplicate them on the 425 before you start the swap. If the trans shift linkage is going to be a problem because of how it bolts to the back of the 368 head (not sure it does bolt to the head of a 368, but it was bolted to the head of my 4100), then you can use a Toronado column, trans shift cable, and either install the cable shift trans linkage (difficult when the trans is in the car and you have to go under it). Or you can swap transmissions with the Toro. I went with the cable shift because I installed a floor shifter and console from a 90 Eldorado (which required me to reverse the direction of the linkage throw on the trans). 

You will not have to change torsion bars because your engine is in the same weight class. And if you convert to a carb with your pre- overdrive setup, you don’t have to worry about your torque converter lockup feature. Another nice thing about your swap is that your 368 already has the distributor you need to run your fuel injection & it has the longer wire to reach the front of the engine.

If you do decide to go with the TH425 tranny, and if your tranny is vacuum shifted, it might be possible for your car’s computer to run the TBI even with that transmission (I’m not sure of that). But if you want to run the TH425 tranny in that car, you will need to cut and weld (or use a hammer) to make clearance at the lower part of the firewall to clear the chain drive and you will need to fabricate front and rear tranny mounts. That will also add 100 lbs. to the car and you may want to consider using 80-81 touring coupe torsion bars or installing 71-78 Eldo/Toro torsion bars (and using drop keys with them) to firm up the suspension again.)

If you run the TBI and computer, a stock or mild cam like the MTS #5 series would work better than a more radical cam. Since the 425 (tuned for 200 HP at the wheels) is not too overboard on power for a non-overdrive 325, it was me, I’d keep it for the simplicity of the swap, lighter weight up front, and since it requires 40 less HP to turn it, it will be like a 40 HP bump in performance and it will give you better MPGs.

One last thing I just remembered. The 500 Eldorado manifolds I used, required a small amount of hammer shaping on the passenger frame rails. I think my problem with the frame and the air box was that I may have used a RWD manifold on that side.

I have not measured, but is possible that 71-78 Eldorado headers could be used. Again, I would have to measure and it may require firewall massaging with a 4 lb. sledge to get the down pipes located in the right place. But again, for 200 HP at the wheels in a 425, the 500 exhaust manifold should be enough.

Remember that the Edelbrock  manifold will not fit under the hood, and if you use a cast 472/500 intake, then you will be 50 pound heaver than the 368 with its aluminum intake.

If you choose to run a carb, aluminum 368 Carb intakes that will fit under the hood are out there, but again, it would need to be port matched to let the heads breath. I have also heard that there are aluminum 425 intakes also, but am not familiar with what cars they come on.

You are also invited to join my yahoo group that is specific to the 79 – 85 Eldorado & Toronado. That group is not meant to compete with group in any way – it’s more of a data collection place for performance mods of this car. I still want to share the information learned with this (and other) foums, but I am trying to make a focal point specifically for this car and support for its performance upgrades.

http://autos.groups.yahoo.com/group/79thru85Eldorado_Toronado/

Cody G. Carson
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“Battlecar Cadillactica” 70 Eldo that raced SCCA autocross in 1985 & 1986

“The Cadinator” 82 Eldo w/ TBI injected 472 and autocross handling pkg.

“CadVetteStang” 72 Fastback Mustang w/ Caddy 500; awaiting a cage & C4 Vette front suspension when the guy storing it- sold it w/o permission
Bruce Roe
C1.5
C2
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Posts: 25


« Reply #17 on: September 26, 2009, 06:33:54 PM »

If you want to change your push rod shift linkage to a Toro/Riv cable (I did), you can make a simple adapter bolted to the trans shift arm.  No need to take the trans apart, it is so much more complex than a THM425 shifter, I gave up trying on a junker.  I still have the adapter around (I think), it could go to a good cause.  I used it on the 3 speed Cad THM325.  Bruce Roe CLC # 14630
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~JM~
Shop Keeper
C5
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Posts: 1849


« Reply #18 on: September 27, 2009, 11:02:26 AM »

...I still have the adapter around (I think), it could go to a good cause.  I used it on the 3 speed Cad THM325.  Bruce Roe CLC # 14630 

Bruce,  Is there any chance of posting a few pictures of this adapter? If you are not familiar with how to post the pics. I could take care of it, as long as you could e-mail them to me.

Thank you
~JM~
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PS. You don't have enough cam. Grin

...Summit has a kit for $99.... Shocked
Nick Campagna
C3
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Posts: 180



« Reply #19 on: September 27, 2009, 02:32:03 PM »

That would be great, as I want to use a Hurst Dual Gate with my THM425 '76 Eldo.
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Is the defect in what I see, or in what I'm seeing with ?
Bruce Roe
C1.5
C2
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Posts: 25


« Reply #20 on: September 27, 2009, 08:29:27 PM »

    
I found the THM325 pushrod to cable shifter adapter in my
box of shift linkages.  ALSO the actual shaft with arm from
the now deceased 325.  I haven't learned how to transfer
pictures from my brand new digital camera yet, but I'll
describe it now.  A 4 speed could vary a bit. 

The 325 arm is about 2  3/4" long with a big hole in the end. 
It's about .95" wide with an offset out of .36".  I welded 3
pieces of steel to form a channel .95" wide, just slips over
it for its whole length.  The channel is deep enough to
contain all including the offset.  A bolt + washer goes
through the big hole to secure it, the channel prevents it
from rotating around.  Part of a CABLE shift arm is welded
on at around 135 degrees CCW from the original arm, it
should be at 90 degrees to the cable half way through the
shift pattern.  The stock pin in the end of the cable arm is
faced toward the trans due to clearance issues.  Radius
to the pin was about 1.85" for my 3 speed. 

I changed my column first, drove the car till I could take on
the THM425 transplant.  I did some welding on the 425 shaft
for a cable shifter.  I don't need this adapter any more. 
Bruce Roe CLC # 14630
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Bruce Roe
C1.5
C2
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Posts: 25


« Reply #21 on: September 27, 2009, 08:35:11 PM »

Did you fix the yellow EMISSIONS tag?  Bruce Roe
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Bruce Roe
C1.5
C2
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Posts: 25


« Reply #22 on: September 28, 2009, 09:06:41 AM »

I got some fuzzy pictures of the THM325 rod to cable, shifter shaft adapter (I'll have to redo them later with my film camera).  Go to

     http://s93.photobucket.com/albums/l71/bcroe/

(that is a lower case "L"71, not an upper case "i"71)

  click on Album "Switch Pitch Transmissions", first 2 pics

Bruce Roe CLC # 14630
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CadVetteStang
Eldorado Autocross Racer
C2
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Posts: 52


"BattleCar Cadillactica" at home in the pylons


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« Reply #23 on: September 28, 2009, 10:48:07 AM »

I got some fuzzy pictures of the THM325 rod to cable, shifter shaft adapter
Bruce Roe CLC # 14630
That was a nice piece of work, Bruce! I wanted to do the same thing, but I can’t weld. That’s why I did the nightmare job of switching linkages in mine from a Toro shift rod. I spent two hours on my back under the car and chewed up my knuckles doing it. If I thought my next build was going to be a re-do of a 79-85 Eldo, I’d sure try to pickup that adaptor from you.

Idea: Keep the one you have to use as a guide and offer this thing as a for sale item. There are enough people out there interested in doing this swap that you could develop and market a swap kit for the car. I know I would market it in my Caddy performance yahoo groups for you, and a kit like that could be put in the classified section of the Caddy forums. One of the Caddy performance vendors might even use you as the manufacturer and stock (or special order) your kit.

Not many of us have done this swap, but plenty of people think about it. I think more would attempt it if these “hang-up” issues didn’t have to be so much of a DIY process.  I had planned to swap in a 325-4L from a Toro next time to avoid the shift lever swap.

Something I had worked out in planning, but had not yet done with my 82 Eldo, was to use the Toro column as the means of reversing the direction of my floor shifter throw and adjusting for the slight difference in throw length. I had planned to disengage the column shift selector lock so that the column was “dead stick” loose. Then, I was going to hook the floor shift cable to the Toro column inboard of the Colum to trans cable (or in another DIY adjustment slot if needed). This way, my floor shifter would move the column and lock it into the respective gears. The column would actually do the shifting and would retain the neutral safety switch and could continue to let the computer know when the car was in drive.

As it was in my car, I connected the floor shifter cable of the 90 Eldo donor car to the trans shift cable of the Toro on a homemade bracket. That bracket (which was made from bending a piece of metal that was too thin) flexed enough to magnify the difference in the throw lengths between the shifters. P,R,N & D matched up okay, but 3& 2 required extra effort to shift into, and I was as yet unable to get it into 1st. (But that was only a temp fix until I could do the modification I described above. If you look close at the pictures, you can see how the two cables looped together over the fender brace and join close to the power booster. It wasn’t pretty but it was a step toward the intended end result.        

Cody
Logged

“Battlecar Cadillactica” 70 Eldo that raced SCCA autocross in 1985 & 1986

“The Cadinator” 82 Eldo w/ TBI injected 472 and autocross handling pkg.

“CadVetteStang” 72 Fastback Mustang w/ Caddy 500; awaiting a cage & C4 Vette front suspension when the guy storing it- sold it w/o permission
Bruce Roe
C1.5
C2
*
Posts: 25


« Reply #24 on: September 28, 2009, 01:25:41 PM »

Cody,

I can't really weld either, but with a MIG anyone can pretend to be a welder.  The adapter is pretty crude, I wasn't planning to use it long.  1/8" steel, it was pretty solid.  Copies would mean sawing off more cable shift arms with that drilled pin.  I actually asked someone about 425 conversion kits, but the up front cost is so high, and the market so small, it just didn't fly.  So I just show one way it could be done.  Maybe just the half shaft adapter plates would be a starting point, they take some precision.  I made left + right shaft versions, but now I think it might be better to eliminate the slack by using 2 left side half shafts. 

The linkage trick, is to get joints at right angles in the middle, and adjust arm length so both ends cover the right range.  And not get it reversed.  My 79 W30 floor shifter worked as you describe, drove the column with its switches.  The column had no shift lever, but had everything else.  Maybe its still in the shed. 

Bruce Roe CLC # 14630
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