High Performance Big Block Cadillacs
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Author Topic: 425 bb transmissions  (Read 5976 times)
fx4matt
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« on: December 17, 2009, 06:17:13 PM »

hey guys new on this forum, i have a 425 caddy with plans on putting it in my 91 tracker. sounds ridiculous but its gonna be custom frame and 3/4 ton axles. i have a turbo 350 behind it with a np203, im wondering if there are any stick shift transmissions that bolt behind the 425 or is the th350 or 400 my only options? thanks for your help
matt
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OldSub
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« Reply #1 on: December 17, 2009, 08:18:38 PM »

You need a BOP bellhousing, which isn't real hard to come by, and you need an expensive aftermarket flywheel.

The Cadillac was never offered with a manual transmission, but uses the same bellhousing pattern as Buick, Olds and Pontiac (BOP) so that is why the bellhousing is easy.

You also need to provide a pilot bushing in the crank.
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~JM~
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« Reply #2 on: December 18, 2009, 10:41:21 AM »

hey guys new on this forum, i have a 425 caddy with plans on putting it in my 91 tracker. sounds ridiculous but its gonna be custom frame and 3/4 ton axles. i have a turbo 350 behind it with a np203, im wondering if there are any stick shift transmissions that bolt behind the 425 or is the th350 or 400 my only options? thanks for your help
matt

Hey Matt,

Welcome to the forum. You are going to have to try much harder than that to come up with a combination that most of the members of this board will think is "ridiculous" or crazy. Grin  Sounds to me like a good combo except for your possible tranny candidates. When I began to mentally design my Cadillac/Jeep swap, I was a dyed in the wool manual tranny guy, especially in an off-road vehicle. I was seriously considering the 455 Buick over the Caddy due to ease of installing a NV4500 behind the Buick vs. the Cadillac. The Cadillac won simply due to 500 cubic inches. In retrospect... The Buick may have been a better choice, but then we wouldn't be having this conversation. Until fairly recently, the Buick had much more support in the aftermarket as far as aluminum heads, intake manifolds, etc. Fortunately there have been several serious advances in the Cadillac aftermarket that has begun to even out the playing field.

The Cadillac 425 engine is commonly believed to weigh about 100lbs. less than its big brothers the 472/500. That is a nice weight reduction off the nose of your rig. As has already been posted, the Cadillac engine was never intended to have a manual tranny behind it. It has been done & it is not that difficult to accomplish, but it is not cheap. The 2 key difficulties (in my opinion anyway) are the Flywheel & the Pilot Bearing. Obtaining a flywheel is simply a matter of digging deep into your pocket & ordering one. The pilot bearing will require that the tail end of your Cadillac crankshaft be drilled to accept a suitable bearing. This is a procedure that I always assumed must be performed by a machine shop with the crankshaft removed from the engine. There was an old web-page that was produced by one of the members of this forum that detailed how to accomplish this job without disassembling the engine. Unfortunately that web-page is long gone & the member has been away for a while. From what I recall… He machined a bushing that fit into the end of the crank & then he carefully drilled the hole into the crank with a hand drill. This provided the clearance required & the bushing that he made held the pilot bearing in place.

You will also need a Bell-Housing of course. Supposedly a standard manual tranny bell-housing from a Buick with the BOP bolt pattern will fit. I seem to recall some discussion on starter motor location being on the opposite sides of the block & the BOP bell housing may need to be cut to clear the Cadillac starter. As you can see… The automatic tranny requires a whole lot less work & $$$’s. Many folks believe that the TH350 is not capable of reliably handling the torque production of the Cadillac engine & that the TH400 is the only way to go. I would think that a “Properly Prepped” TH350 should hold up. It might require enough upgrades & expense that it doesn’t make sense to use it though, if the same money could be put into an overdrive tranny, or simply use a TH400 & put the $$$’s saved into suspension, etc.

Well hopefully this will give you something to think about. Please let us know what you decide. It would be nice to follow along on another Cadillac powered 4x4 build.

Good luck
~JM~
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PS. You don't have enough cam. Grin

...Summit has a kit for $99.... Shocked
gary kosier
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« Reply #3 on: December 18, 2009, 04:14:53 PM »

There are some Pontiac bellhousings that are set-up for starter on either side.
Look on Evil-Bay for Pontiac bellhousing.

Gary Kosier
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dave brode
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Best of 11.66, 113.96, 1.59 sixty


« Reply #4 on: December 18, 2009, 09:26:34 PM »

There are some Pontiac bellhousings that are set-up for starter on either side.
Look on Evil-Bay for Pontiac bellhousing.

Gary Kosier

olds too, iirc.

I would spend the money for a aftermarket steel bell. Spendy, but so is the $350 ish aftermarket flywheel.

Matt,

Have you considered a A TH400? Would be cheaper.
Dave


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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
fx4matt
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« Reply #5 on: December 20, 2009, 01:34:38 PM »

thanks for all your info guys, i think to get my project rolling im gonna run the 350 till she blows then look into the manual swap, if the funds are there ill probably dish out the cash for the parts, im probably only gonna run some 35 in tires on the thing for now because of the chevy d44 front, but i guess i gotta build a frame first. hopefully i can get my project rolling mid january with welding the frame up and setting the body on it. im gonna defiantly post pics when its under way!
matt
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OldSub
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« Reply #6 on: December 20, 2009, 05:00:26 PM »

chevy d44 front
Better start looking now for a replacement for that!
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