1975 fleetwood towing capacity Help me out fleet!!

lesinfamous · #1 (**permalink**) 09-16-07, 05:30 PM

Ok so iam looking for a receiver hitch for my '75 fleetwood 9 passenger sedan. Any clues to how much it can tow with its 3.15 standard gear set? I do know that full size caddies of this year could tow between 2000-6000 lbs. It probably has an almost 6,000 pound curb weight so iam unsure how much it could tow....
also any mods recommended to set it up for towing...? (fleet, how much can you tow and where can i get that same receiver hitch thats on your '76 limo???????)

lesinfamous · #2 (**permalink**) 09-16-07, 05:36 PM

Alsooo what do people think about installing 3.73 gear set and a limited slip differential??? Is it difficult to do or nearly impossible on this specific model??? Or should i leave the stock gear set??

N0DIH · #3 (**permalink**) 09-18-07, 12:02 PM

With the HD Cooling, Y72, and the shortest gear you can get from these axles, which is 3.23, 500 CID, and THM400, 7000 lbs was max. Without the 3.23's you are probably limited to 5000 lbs. And being a 9 pass, probably take off 1000 lbs. The limiting factor is really the gears more than anything. The problem with really the pinion tries to climb the ring gear, which leads to breakage.

So no 3.73's ever available, just rare 3.23's. I priced them many years ago at the dealer, $600, but that was back in the 80's and GM still had inventory, but I doubt it now.

NO aftermarket support of the 8 7/8" and 8 3/4" "P" type axle which you have. You CAN however, look at swapping in a 77-96 axle, I suspect highly they WILL bolt in, but you need to some measuring. I have a 95 axle out and measure too if you need help. Then you can get anything from 2.41 to 4.56.....

Lots of posi's and such for the 77-96 8.5" axle. But for the "P" axle, posi's were rare, and few between. If you find one, hang on to it. And I think they were Auburns, so once they were worn out, they are shot, no rebuilding. Although I have heard of people taking the case, take apart and milling 0.050 or so off and reassemble to compensate for wear of the case.

Look at my details on the 94-96 Fleetwood Brougham RPO V4P, which is the return of the 7000 lb tow package, which I have.

Mods? 7 blade clutch fan. External engine oil cooler, external trans oil cooler, HD cooling (limo probably has), Shift kit for the THM400, tires that are rated to carry that much weight. Fatter front sway bar, add the rear sway bar. Make sure springs up up to the task. Add 94-96 Caprice police package (9C1) front and rear shocks.

lesinfamous · #4 (**permalink**) 09-18-07, 07:20 PM

wow....thanksss sooo much for the info. i did manage to find the 3.23 gear set for the 8 7/8 axle on ebay http://cgi.ebay.com/ebaymotors/GM-8-...spagenameZWD1V
however you said i have a 8 3/4 p axle? i have not found any leads...any ideas as to where i would have luck??? Also, my most important question....do you think that if my 500 was to put out around 550-575 lb ft torque that i would be able to tow 7000 lbs provided that i have the 3.23 gears and the other equipment?? I need to find out how wide my frame is to start finding receiver hitches. thanks for the suggestions in mods too!!!! anyone else have more info???

N0DIH · #5 (**permalink**) 09-18-07, 10:27 PM

If m LT1 powered Fleetwood (260 hp and 335 lb/ft torque) can tow 7000 lbs with 3.42's you surely can do it with 200+ lb ft more!

A lot of people mistakenly think the 8 7/8 (8.875") axle is a 12 bolt. It is NOT. It is a 10 bolt Pontiac designed axle. 2 axles were available in the 71-76 B/C/D cars, the 8.5" and the 8.875". The 8.5" is the Buffalo axle (Chevy design, basically an upgraded 8.2"). The 8.875" aka 8 7/8". In 77 is was redesigned with a slightly smaller 8.75" ring gear. This axle died in 1984 and was most commonly, if not exclusively on the Fleetwoods.

Look for a hitch at some of the hitch sites on the net, there is plenty out there. You might be able to use a truck hitch with some mods. But I wouldn't think it should be too hard to find. A 77-96 hitch might be best to work with.

lesinfamous · #6 (**permalink**) 09-19-07, 12:17 AM

thanks so much again, just to flush out the me guessing which rear end it is, im including a pic of the rear end. My guess is that its a 8.875 am i wrong?

N0DIH · #7 (**permalink**) 09-19-07, 12:59 AM

Pretty sure that is incorrect. Not sure if that is a truck Chevy 12 bolt or ?
.

This is a 1970 Olds "Type O" axle

And this is a Chevy 12 bolt:

N0DIH · #8 (**permalink**) 09-19-07, 01:21 AM

Here is a list of GM axles: http://www.ringpinion.com/DiffList.a...peID=5&Type=GM But I don't see that one...

At car-part.com it lists the Commerical chassis having a different axle than the rest of the cars (Deville, Fleetwood, Fleetwood Brougham and Calais). A real odd ball???

Fleetwood, exc. Brougham--Different axle than the rest
Commercial Chassis--Special axle, different
Calais and DeVille--Same as FleetwoodBrougham (not listed above)
Fleetwood, Brougham--Same as Calais and Deville

Ape? Got any clues?

lesinfamous · #9 (**permalink**) 09-19-07, 02:42 AM

Can it possibly be a GM12T??? It is the only one that resembles it.

N0DIH · #10 (**permalink**) 09-19-07, 02:45 AM

And the 77-84 Fleetwood 8 3/4" axle

lesinfamous · #11 (**permalink**) 09-19-07, 06:22 PM

N0DIH, i do not know if it helps but the brochure says that i have a hypoid type axle and i do know that it has a 3.15 gear set....

The Ape Man · #12 (**permalink**) 09-20-07, 08:21 PM

The axle in question bears no resemblance to later Cadillac axles. 3.15 was the highest gear you could get. That is plenty with a long stroke engine like yours. You don't need to scream down the road and lose economy with a real Cadillac engine. I'd stick with a weight below 5000 lbs trailered weight due to sway and brake capacities.

lesinfamous · #13 (**permalink**) 09-20-07, 10:37 PM

For once i think i just might drop my ambitions of making my caddy a real deal towing sedan...and take your advice ape. i guess id still want to buy the extra equipment just to be safe and get a modified modern class 3 hitch....any more suggestions anyone??

N0DIH · #14 (**permalink**) 09-20-07, 11:44 PM

Many people over the years have towed upwards of 7000#s, probably more often than not, campers and trailers. But I am sure things like cars and stuff too. The longer the wheelbase the better, which controls sway naturally.

I like the idea of using a truck to trailer more than my Cad, but I would do it if I needed to, but I have a 99 K2500 454 Suburban to tow with, and it tows like a dream. I have a wimpy Class II hitch on my Cad, I have put a 1500 lb trailer back there to save gas bringing it back to the rental place and it doesn't tow great due to the poor hitch. It shook the car a lot on bumps. The truck is just plain built to abuse....

For long term towing, I would get a truck, for the occasional tow, even heavy, the Cad is fine.

Can you take any other pictures of the axle? I posted it on FullSizeChevy.com and it has got a lot of people wondering what it is.

lesinfamous · #15 (**permalink**) 09-21-07, 12:16 AM

that's hilarious that people cant id it....for now i cant take any pics but i will probably be able to in 2 weeks. Iam just going to talk plans over with a shop but one other major concern is getting a radiator built for the extra stress...the radiator for my year is a 3 row, im trying to see if i can get a it modified by a shop to include an extra row....wish i had an older suburban to tow with though, thats for sure...whats your opinion on the towing capabilities between an older suburban and say a 2007 one???