View Full Version : 472 will a th700r4 swap directly or...?

04-23-10, 08:03 PM
I have a stock 472 in my 73 fleetwood hearse but the 3 speed is killing gas. Could I drop in a 700r4? or is there a better option?

04-23-10, 10:26 PM
You can't just drop it in. The 700R4 was built for the Chevy bolt pattern only, likely because the SB Chevy became the "corporate" engine. There are adapters though, and I believe the Cad Company has them, and maybe MTS does too.
The word is, that the 700R4 wont live long behind a big Caddy engine, if pushed very hard. Don't know that myself.

The 4L80 is the heavy duty over-drive transmission, and developed from the venerable TH400. Not cheap, but some may be around at salvage yards that have late model stuff.

Oh yeah, the drive shaft yoke is the small TH350 size on the 700R4, so a drive shaft mod will be required.

04-23-10, 10:42 PM
will the 4L80 swap in directly?

04-23-10, 11:54 PM
also doesn't that require a computer? This is a 73 carbed car

04-24-10, 02:18 AM
You would need an adapter to bolt to the engine, same as the 700R4, plus you would need a stand alone trans controller as the 4l80 is an electronically shifted trans....

In the early 80's there were some 700R4's with the proper bell housing to bolt to the Caddy.. There was also the 2004R OD trans that came with the proper bell.. Now days however those particular trannies with the right bell are scarce..

Neither of these transmissions would live long in stock form either.. Keep in mind these transmissions blew apart behind anemic mid 80's 305 Chevys.. You could have one built up to handle the load, but you'd be looking at some significant expense.. Probably till you found the right trans and had it build to last you'd be nearing the cost of a 4l80E, controller, and adapter..

There are also the options of an add on overdrive unit such as the one's offered by Lokar, Gear Vendors, and US gear.. None of which are still real inexpensive options.. And all woudl involve some drivehsaft mods...

04-24-10, 10:25 AM
Your main fuel use is the power needed to get all that weight rolling. Also, I think the hearses used a lower gear set than the other production models of those years. The hearses and the limos were built on commercial chassis that helped add weight to the vehicle.
Check all vacuum lines and replace as needed. These engines with vacuum operated options, run more efficiently when there are no vacuum losses. Don't forget the hoses in the passenger compartment. These lines don't dry out as much as the ones around the engine, but sometimes they will. Do some resaerch here on the CO. This subject has been covered several times
If you have and understand how to use a multigauge, check the resistance and condition of your plug wires. Longer wires will have more resistance. You have to use a scale of distance = x amount of resistance. This is usually covered in any repair manual. I use a sliding scale for this, as the readings you will get aren't going to be dead nuts on what the manuals recommend. Check resistance at the distributor cap. Replace if needed.
If your distributor is original, it has points. Check the condition of the point set. Do you have a timing light and dwell meter and do you know how to use them? Check the condition and gap of you spark plugs. If the engine is set up properly, your gas mileage should improve.
If your distributor has been replaced with an HEI unit, check wires, cap, rotor and plugs as well. Plug gap still is important for proper and efficient engine operation.

04-24-10, 10:41 AM
on the "CO"? I was told the engine and trans is the same out of any other fleetwood? Maybe they would change the rear diff but I might even doubt that as well. I know the spark plugs are 5ish years old. The plug wires are only a few weeks old and the engine seems to run fine... just the car could use an overdrive. I am not sure what the resistance "should" be on the rotor and the vacuum lines I see seem good. I don't know the correct gap setting on this. Also I think this is still a distributor and not an hei system but I am not sure.

04-24-10, 04:59 PM
Driving land yachts for years, I agree that it's the take off that kills the mileage more than cruising.. The 700R4 has a lower 1rst and 2nd gear than the 3 speeds which is where I think alot of the gain is seen.. I had a '77 Continental that consistantly got 12 city and 18 highway.. I change the rear end gears from 2.47:1 to 3.00:1 and saw my city milage jump to 15.. Highway stayed the same..

What kind of mileage are you getting exactly for curiousity sake??

As deVille spoke of, plain old maintenance goes along way.. You driving habits, the gas you are using, etc will also make some huge differences....

AN HEI unit is still a distributor, it's just GM's electronic ignition.. THe coil is bolted to the top of the dist cap..

04-24-10, 05:25 PM
I have only had it a week but I would estimate 8 city and 12 or 15 highway but I can't be sure as some of it has been working on it.

It is also 8,000 lbs but I speed up very slow on this and get passed like crazy HAHAHA

04-24-10, 08:57 PM
Sadly even an OD trans is probably not going to give you huge gains.. Keep in mind you're about as heavy as a 4x4 pickup...

Have you done a lot to the car yet, such as tune up, or carb work? A good state of tune, some good flowing exhaust (duals! :highfive:) and if you don;t have it already electronic ignition (Either HEI or even something aftermarket) will be the biggest help..

Since that sounds like a commercial chassis I'm going to guess it has a slightly lower rear end gear than most.. Not that that's a bad thing.. As I mentioned earlier, I've found the slightly lower gears actually help with the mileage..

Unfortunately this ethanol "enriched" gas they're pushing on us really hurts too..

04-25-10, 12:58 PM
CO = CadillacOwners forums

04-29-10, 09:00 PM
I was trying to fix an exhauste leak BUT the bolts just break off inside the head :( for the manifolds.

04-29-10, 11:23 PM
Those engines are terrible for cracked exhaust manifolds & broken off bolts. I have had to take the heads on more than one engine to a machine shop, to get the broken studs out. Use a #8 bolt replacement, I believe the originals are only #5. Bruce Roe CLC # 14630

04-29-10, 11:50 PM
2 are broken off inside the head and I don't know what to do for fixing it or trying to get the rest loose.

04-30-10, 09:57 AM
In the early 80's there were some 700R4's with the proper bell housing to bolt to the Caddy..

These trans were found in the trucks with the Olds based diesel engine. You have to change out the torque converter.

05-04-10, 07:32 AM

and you are hoping for more than 15 mpg...?

05-20-10, 12:31 AM
What's 8000lbs? More like 5500 or so.(Egads, I missed the Hearse part. Yeah, that might just weigh a full 4 tons).

Re-gearing into the mid 3's and a well built 700 will get you into the low 20's on the highway(assuming well tuned ignition and free-breathing air intake and exhaust). The factory gears were the compromise to gain highway fuel economy. They kill in town performance though. A gear switch alone is great if you don't plan on much highway use. The car peps right up and so does the fuel economy, but it's usually tough on highway MPG.

Better is a 4l80E with a controller. It's essentially a Turbo400 with an OD and computer controlled valve body and will take anything the 472 will dish out, bone stock. With an adapter and controller a good used one won't cost you as much as buying and building the 700.

05-20-10, 07:43 AM
haha the 4l80e by itself would be over a grand then on top of that the stand alone computer would be 1500+ I don't think I would ever get the gas mpg to make that amount up unless I DD the car

05-20-10, 10:20 AM
Gas is getting close to $3.00 again, and 92 is over that. Recalculate. :)

05-21-10, 12:18 AM
Used 4l80E: $600 or less. Rebuilt if you carry it in: $800 or less. Controller, las time I looked(was going to put one behind my 500 intended for the M715): $500. Do a mild shift kit yourself. Stall converter...I forget...$275? All told maybe five or 600 more than building a 700 the right way. And you still don't have something as bulletproof as a built 80.

Drawback to the 80 is carried over from it's TH400 daddy: Parasitic loss. It just takes more to get that mass wound up than it does for the lighter TH350, 700 or especially the 200.

If making it pay for itself is your goal, give up now. Do you think the guy that trades off his 20mpg paid for sedan for a 35MPG econobox ever makes his money back in fuel savings? If he's lucky he breaks even in the life of the car. Might as well keep the old one and avoid the pymts. :)

05-21-10, 09:49 AM
I thought Mr Paradox overestimated those prices a little. Since I have never killed a th400 in my life I wouldn't even rebuild any used 4l80e that I bought. I have that much confidence in GM's ability to build a super dependable transmission for the heavy duty applications. I think either swap has it's advantages so I would take the path of least resistance. Whatever deal comes your way first will probably be the easiest.