I didn't see a forum for transmissions, so I thought I would toss this question in here. I have been assigned to fix a 1978 Cadillac Coupe deVille, with what I would assume is a 425 engine. The transmission went for crap, and I am going to replace it. My question is does this have a special transmission in it, or would something out of a similar vintage chev / pontiac fit it? Also I was considering going a little more modern, maybe something with the fourth (Overdrive) gear. Amongst my junk is a 1993 Fleetwood brougham. Would that transmission fit the 425, either directly or with some small modifications to the bell housing?

Thanks for your assistance, and mods please move this if I am in the wrong forum again.

First off, you have a TH 400. The bellhousing is the BOP design (looks like it has two cat ears.) A TH400 from a Buick Electra/Park Ave, LeSabre and Olds 98/Delta 88, Pontiac (full size) from this vintage will work. The transmission in your 93 will be a TH700 with over drive, this is sometimes referred to has a TH 700-4R or 4L60 (maybe a 4L60E, don't recall when they went to this, someone can chime in).

For the swap of the current transmission in your possession(assuming it is not the "E" version) would require at a minimum, a bellhousing adapter, brackets (or modifications) for the kickdown, the transmount may need modified and the driveshaft length may need to be adjusted. In addition, the transmission internals may need some beefing up to handle the torque of the big block Caddy.
The bottom line is the Caddy did not have an "exclusive" on the TH400 transmission that is currently in the 78 Caddillac and is a very sturdy transmssion. With that said, what was done to destroy the TH400?

I believe they ran it low. The car was leaking something when running at one point, but I did not get a chance to see it. The son came to me a week later and said it 'didn't want to go into gear right away'. On the test drive it didn't make it more than a mile before losing forward gears. It worked backwards for a bit but that gave up after a 1/4 mile or so too. Adding more fluid didn't help. but what I saw on the stick looked fairly clean and did not smell burnt. When the car is cold, it will go into reverse right away, and will go into first fairly easy if you drop it down there (instead of drive). However after about the length of a parking lot you lose both. I also heard what sounded like a pump low on fluid a couple of times when it was sitting there idling.

They just got this thing about 2 weeks before and barely drove it. It looks nice and came safetied, but I have a feeling it was a hot safety because things like the power seats don't work and the windows are fickle. I never got a chance to drive it when they first got it, and neither of them know enough to have been able to tell if it was not right from the start.

Either way, if my Caddy transmission is not economically feasable, then the next suggestion is to get a rebuild kit for this tranny. Someone told me that they run for about $300-$400 around here at one place. OR.... Would there be a more modern car that would have the overdrive that would mount the same and not need modification? Late 80's wagon maybe? Truck? I like the 4 speed idea just because I might end up with this. My boss is strange that way. He basically said to someone that offered to buy the car today that he 'gave me the car' and may purchase back if I fix it.

I was also considering servicing this tranny (filter & fluids, check and clear the lines) in case it is some sort of fluid flow problem. As I said, I saw no signs of burning, and adding fluid did not help it's performance, only cooling down did. Think there is any point in trying that?

Thanks for the help.

Found a picture of the pimpin beast to toss up here for the heck of it...

EDIT - Oh, and I started it up today just to run it and what was leaking (and still is) turns out to be gas at the fuel pump, so it most likely did not leak all the tranny fluid out.

200r4 came in mid 80's Olds Ninety Eights andBuick Park avenues and some other cars. It's pretty hard to kill a th400 but yours does sound dead.

Well I came across this on Ebay, so I think I might be sending $200 out their way.

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=8005426676&ssPageName=MERC_VI_RSCC_Pr4_PcY_BIN_Stores_IT&refitem=180255056646&itemcount=4&refwidgetloc=active_view_item&usedrule1=StoreCatToStoreCat&refwidgettype=cross_promot_widget&_trksid=p284.m184&_trkparms=algo%3DDR%26its%3DS%252BI%252BSS%26itu%3 DISS%252BUCI%252BSI%26otn%3D4

Sounds like a good deal to me. I hope that pimpin beast lives a long life.

Similar situation here, started losing gears.

I found a 472 w/ trans from an unknown donor (it was put in a Jeep). What are the chances that it's a long shaft (havn't looked at it yet) that can swap into my 78 CDV?

thanks

I doubt anyone would use a long shaft in a Jeep. My 78 CDV has a short shaft; I thought it was original.

I doubt anyone would use a long shaft in a Jeep. My 78 CDV has a short shaft; I thought it was original.

I should have been more clear, it is an old Jeep Grand Cherokee, the big wood sided ones.

Honestly, I'm learning as I go, I always thought 78s had long shafts

Have you dropped the pan and checked the filter element? If the fluid is clear and not deep dark in color your trans may need no more that that. If you can hear the torque converter at low speeds, like it has metal pieces rolling around in it, your converter may have given it up. The TH400 is pretty formidable and can take a conciderable beating. If one of your clutch packs gave up you will have a lot of broken down clutch material in the bottom of the pan. If you let the trans sit the material will drop to the bottom of the pan and you can drive the car for a short distance until the filter gets clogged up. Then the pump will cavitate and you'll hear the whine.