94 Caprice Wagon fuel economy project, stock LT1--46 MPG so far

This is pretty awesome!  Been waiting for someone to do an eco mod on one of these whales for years.  I've gotten descent mileage when I really try hard and the weather and traffic permits.(2:56)  It sure takes allota patience.  Man, I wish you lived closer to me so I could come over and see/obsess over your mods in person  I've been wanting to put a manual tranny in forever.  Could you post some more pictures?  I did order a set of fender skirts for my highway cruiser, so I'm slowly on my way to a more efficient whale!  Anyways, nice work-I'll be following

I know it's been a while, but I thought you all might be interested in what I've been doing with this car for the last 3+ years.

In short, my best tank is now 50.55 MPG, and the car is basically sitting on the drivetrain and suspension of a 3/4-ton truck.

Instead of posting everything twice, I'll just include a link to the detailed update that I put on Ecomodder:

https://ecomodder.com/forum/showthread.php/94-caprice-wagon-5-7l-project-46-mpg-33961-8.html#post614665

I know that's a lot to read through, but if you have the time to do it I welcome any questions or feedback that you may have.

-Funkhoss

funkhoss wrote:

phantom 309 wrote:

I had/have no idea the fleetwood rear end is a 14 bolt with car axles,.??
Would you please take a picture of this, and explain what years it came in etc,.?

MalibuSSwagon wrote:

the 14 bolt came in the Commercial chassis, hearses, limos and such. It's just a 9.5 semi floater with the car lug pattern. GM did the same thing with the 454SS. Also, fun fact, I'm told the alloy wheels that came on those cars that looked like the base Fleetwood wheels were heavy duty and marked "Limo only" on the inside.

That is correct.  The Cadillac 14-bolt axle came only in 1991-1996 commercial chassis vehicles--hearses, limos, and also armored vehicles.  1991-1993 had either 3.08 or 3.73 gears, and 1994-1996 had 2.93 or 3.42 gears (just like regular production Fleetwoods).  In my experience from trying to find one, the 2.93 and 3.08 axles are more common than the 3.42 and 3.73 axles.  I also know that some had the G80 option and some didn't; I don't know whether it was a "Gov-Lock" like a truck or a clutch-style Posi.  Mine is an open 3.73 from a 1993 hearse.

Mechanically, the Cadillac 14 bolt is just like the truck 14 bolt 9.5" semi floaters--same housing, carrier, gears, axles, axle tubes, bearings and brakes (brakes are 11x2.75 vs. the 11x2 on our wagons).  The only differences are that (1) they are built to the same width as a standard B/D sedan axle, (2) they are five lug instead of 6 or 8, and (3) they have all of the  mounting brackets needed for a B/D sedan.

I'm not at home right now, but here's an eBay auction for one where you can see some pictures: http://www.ebay.com/itm/14-Bolt-9-5-5-lug-car-rear-end-axle-Dana-60-size-and-stronger-than-12-Bolt-car-/161860233016?fits=Make%3ACadillac&hash=item25af9f2738:g:AfcAAOSwl9BWIUmZ&vxp=mtr

The commercial chassis Cadillacs also came with, in addition to the 14 bolt rear, the J55 front brakes/suspension.  In comparison with the standard B/D front end, the J55 had heavier duty knuckles/spindles, larger inner bearings (outer are the same), thicker rotors (diameter is the same), larger calipers to match the thicker rotors, 5/8" lower ball joints, different outer tie rods, and no ABS.  Dimensionally, these parts are the same and will interchange into a standard B/D body.

The 14 bolt rear and J55 front gave the Cadillac commercial chassis a GVWR of 7200 lbs.--3500 lbs. front and 3700 lbs. rear.

phantom 309 wrote:

There is a write up you may be interested in for increased front braking power, is reasonably cheap too,.
It involves cutting down the b-body front rotor into a hub, and using astro van rotors,.
cheap bigger brakes

Thanks.  I've seen that write up--the J55 rotors are very similar to the rotors in that write up, in terms of thickness.  If you use the J55 knuckles, lower control arms, and outer tie rods with them, they bolt in with no modifications AND have heavier duty bearings and ball joints than stock.  I've got all these parts ready to go in my storage shed.  

phantom 309 wrote:

To help my friend/neighbour i pulled hay wagons in from the field last year with my orange wagon,. 16 bales at 1000lbs a piece or so plus the wagon,.our wagons have a 1/2 ton truck rear end in them,.my son drove our old 3/4 ton 4x4 pulling 2 at a time,.

16,000 lbs. plus is impressive.    Being hay wagons, though, there was no tongue weight involved.  Towing 16,000 lbs. is something else entirely.

phantom 309 wrote:

the limiting factor with the wagon was traction to get rolling,.

Even with the little bit of towing I've done with the car so far (3000-3500 lbs on a few occasions) I've found traction off road to be challenging too.  I plan to move the 29" LRR tires to the front and put 29" A/T tires on the rear when I set up the wagon in "towing mode."

phantom 309 wrote:

perhaps a 12v cummins and a 10 spd roadranger might be perfect for you?

Conversion to diesel would be awesome!  I'd want to wait for the LT1 to die first, though, which might take a while...

Cool project and cool results - I've done the hypermiling bit before in my 03 Jetta TDI, done over 1200 miles on a single tank (over 70MPG) so have some idea what it takes. I had 2.14's in an 83 Regal with a 5.7 Diesel that I swapped a 700r4 into - first time it shifted into overdrive I thought the engine shut off! That did ~35 MPG with big wheels/tires, lifted up, driving 60-70 MPH, etc



Regarding the 9.5" commercial chassis rear end, you are correct that it's the same dimensions as the sedans, however your wagon is not the same dimension as the sedan. The Wagon frame is 2-3 inches wider and therefore the axle mounting locations on a wagon are 2-3" farther apart as well. The flange to flange dimensions are also wider. You can "bend" the rear control arms in to make the 9.5" fit in the wagon (control arm bushings have a lot of give in them), but you'll still have issues with the wheel mounting locations being too narrow and the wheels will hit on the frame.

I'm hoping to get well into the 30's with my current project (6.6L Duramax/6L90E in a 96 Roadmaster Wagon). Should know this summer!

Great work with the Jetta TDI! That Regal sounds neat, too. I'm interested to hear more about the Duramax RMW once you get it completed.

Did you read the (long) update that I posted on Ecomodder? I've actually had the 14-bolt J55 rear (now with 4.10 gears and an Eaton E-locker differential from a Hummer H2) in the wagon for over 15,000 miles. I used the "factory upgrade" LCAs with an Impala SS rear sway bar, and UMI adjustable UCAs with roto-joints. I had to use adjustable UCAs to correct the pinion angle after I put in the NV4500 transmission, but the UMIs with roto-joints also serve to increase rear-end stability. The entire setup works great--there's NO binding, and it feels very solid and stable, even towing heavy loads (up to 8000-9000 lbs. at this point).

As you suggest, I did also end up using some 1.25" wheel spacers to clear the frame and increase the rear track, but otherwise everything else went in without issue.

-Funkhoss

Thanks - I won't clog up your thread with stuff about my adventures.

I did not read the Ecomodder thread - Glad that you were able to make the J55 14 bolt work for you. I considered putting one in my Duramax wagon, but decided against it. We'll see how the 8.5" wagon rear end holds up - they're pretty tough .