: Just what are people talking about...One wheel drive??!!



Rob Benham
12-19-08, 04:23 PM
More than one person had tried to tell me that for the most part, the power on my FWB is put onto the road by the rear RIGHT wheel. The diff takes over under this or that kind of circumstances.

Can this be true?

I thought the whole point of a diff was to impart the power onto the road evenly between the two rear wheels. The diff being needed to accommodate cornering.

The last person to tell me this had just pulled the diff gear cluster from another car, and was standing there with it in his hand as he spoke...so he knows a thing or two, but the theory? What do you think?

Submariner409
12-19-08, 05:46 PM
Depending on the rotation of the engine, and the resulting torque transfer, a non-locking differential will supply the most driving power to the most unloaded wheel. That's why the wheel in the slipperiest ice, snow, or mud always spins first. Absent some sort of positraction arrangement, straight line rear wheelspin can be evened out with spring and shock experimentation as well as air shocks or spring bags used in order to load both wheels to the same power requirement. Several companies make variations of a positraction differential, in which the spider gears are loaded by a spring and clutch pack, thus tying the axles together, or nearly so, under slip conditions. The clutch pack still allows some slippage in order to accomodate tight turns.

Aron9000
12-19-08, 11:58 PM
I don't think any of the fleetwoods came with a posi-track rear.

When you get a chance, find an open parking lot or vacant, wide, straight street. Turn off the traction control, hold the brakes and mash the throttle. Let up on the brakes a little bit until the car starts to lurch forward, then hold the car still with the brakes while you're spinning the tires. You'll notice only one wheel is spinning. Let off the brakes and hold the gas, it'll take off and start laying rubber with that one wheel, and you'll only have one black mark.

Rob Benham
12-20-08, 01:16 AM
I know that it's most likely that one wheel will 'lift' and become light...and therefore spin, but surely, the diff is trying to impart drive through both wheels is it not?

96Fleetwood
12-20-08, 08:05 AM
All Fleetwoods came with an open diff, with either 2.56 2.93 3.42 or 3.73 (93 only) gearing.


I put a Eaton Posi with 3.73 gears in mine to wake it up a bit and get both rear tires to lay rubber :thumbsup:

ShadowLvr400
12-20-08, 09:31 AM
Wait, even the V4p tow package in the 94-96, a 3.42 gearing wasn't posi? And I sprung for 3.42 posi on my build. Excellent decision.

As for your question on the open differential, if both tires have equal resistance, they both will get power. However, since an open differential does not have the counters, if one tire has more resistance than the other, the power will just take the path of least resistance.

Rob Benham
12-20-08, 05:30 PM
yep, that's much as I thought. In other words, it's just a diff. Rather glad about that!


I think that my pal was overthinking it. Probably some left-over idea from mec school. I'll talk to him again if he ever stands still long enough to listen.



Having said all this, he proved me wrong this week. Or did he?

There are times when I would have bet my last dollar on thinking I was right. My pal was pulled over by young woman...she tells him the R rear wheel on his muscle car ($30,000 restoration) looked buckled. He checks the nuts then creeps home.

Sure enough, there is serious run out. The engineer, his son in law, swaps the wheels, no change. Pulls that shaft and changes the bearing, and even tries a "new" axle that he happened to have. No change.

Maybe it was me that was overthinking now, because my best guess was that the second (loan) axle was also bent a similar amount, but the engineer launched into changing the inner bearings. It seemed to cure the fault.

How the heck could a 1" movement on the radius of say 10"...then amplified along a shaft that was at least 2' long, be contained in the distance a warn baring would wobble. It makes no sense at all, but there it was.

N0DIH
12-21-08, 08:37 AM
All FW's with Traction Control I know had open, there are people who have found the FW rear (77-84) with a posi, but it is RARE and they are coveted. The Deville rear works in a FW, and those are easily upgraded to posi (I recommend an Eaton clutch type, not the Auburn Cone type, but that is my personal pref).

What I strongly believe from info I have dug up....
The FW's from 71-84 actually got the Pontiac "P" axle, which from 71-76 is a 8 7/8" ring gear and from 77-84, an 8 3/4" ring gear. You should be able to install 71-76 guts in a 77-84 axle. I detailed a lot on these axles a long time ago, with all RPO codes and all. The 71-76 cars got better gearing, 2.41's-2.73's were common, 3.23's at best, 77-84 2.18's were common and anything else was rare.

Personally, got a 77-96 car, get a std 8.5" axle, and toss in a posi and some improved gearing and enjoy it. I have 3.08 posi in mine now, and LOVE it, will get back to 3.42's when it gets warm with an Eaton posi. But Posi and no Traction Control is FAR better in the snow than the car with 3.42's and open diff. And I still like my FW in the snow over my Buick....

csbuckn
12-21-08, 09:02 AM
So a rookie question. When it comes to rear diff, the higher the number-the faster the wheel turns...correct? So a 3.42/1 means the drive axle turns once and the wheels turn 3.42 times right? Also, some people say these are harder to do and should be left to a professional but when I look into getting one, the pic of one looks very easy to install. How hard are these to put in if I where to get one that was a direct fit?

ShadowLvr400
12-21-08, 09:23 AM
Doing a gear swap is simple in concept, but the detail and accuracy needed relegates it to something a professional should do. If you're off by a hair on the build, the vibrations will make for an unpleasant day.
On gear ratios, I'm not sure if you have it dead on, or backwards. I know that the higher the gear ratio the better your torque amplification. So a 4.11 gears will magnify the torque more than a 3.42 or 2.56... Most drag racers go for something like a 4.11, the average street vehicle runs about a 3.08. I researched the best overall gear for my car, and found the 3.42 wouldn't comprimise my top speed, or highway driveability, but would gain me a lot in launches. For a daily driver fleetwood, I certainly would not go any shorter a gear than 3.73, and even that's if you don't do a lot of highway driving.

My_favorite_Brougham
12-24-08, 01:06 AM
So how do these numbers affect fuel economy?

N0DIH
12-24-08, 01:24 AM
My 94 FW with factory 3.42's NEVER got better than 22 highway. But mine with 3.08's doesn't seem any different either.....

But 3.42's are fun!

deVille33
12-24-08, 08:21 AM
Esencially, gear ratio = 1:1 = 1 turn of the drive shaft = 1 turn of your drive wheel and gas mileage or performance from that point is determined by diameter of your tires.
Gear Ratio = 2:1 = 2 turns of your drive shaft = 1 turns of your drive wheel, etc.
Gear Ratio = 3.02:1 = 3.02 turns of the drive shaft = 1 turn of your drive wheel, etc.
In drag race application, a 4.11:1 application is generally applied, but an additional factor is the diameter of the wheel/tire. Slicks, if used, are larger in diameter than stock tires and rims, plus they have a added plus in that they grow as the rotational forces increase. All this should be factored into the build into your race engine and drive train.
Fuel Mileage = The closest ratio you can get to 1:1 plus the largest diameter tire you can use, but you also have to factor in your engine's torque range. With the earlier Cadillac engine, no problem, they produced gobs of low end torque.

jlini0014
12-24-08, 01:56 PM
All Fleetwoods came with an open diff, with either 2.56 2.93 3.42 or 3.73 (93 only) gearing.


I put a Eaton Posi with 3.73 gears in mine to wake it up a bit and get both rear tires to lay rubber :thumbsup:

I have an 85 RWD. Any suggestions for the rear end for more torque w/ the stock small block? I know the horsepower is terrible but I can't help but think it may be more responsive with a different rear end. If not any suggestions for mods.? I think that's why you have a 96 for it's power lol

Thanks Joe

N0DIH
12-24-08, 02:10 PM
85 FW, HT4100? They came stock with 3.42's. You can get the "high alt" gearing, 3.73's. You have OD, so even 4.10's are not a real problem. Remember, cars of yesteryear without OD, had 3.08's, 3.42's, 3.73's, and cruised for hours at 75 mph, so don't worry about. You could use 4.56's and it would be fine. Might not be great on mpg, but it would not hurt it.

With a THM200-4R, overall ratios
4.56's in OD = 3.06
4.10's in OD = 2.75
3.73's in OD = 2.5

So really, going with a short gear isn't a BAD thing...

96Fleetwood
12-24-08, 04:44 PM
I have an 85 RWD. Any suggestions for the rear end for more torque w/ the stock small block? I know the horsepower is terrible but I can't help but think it may be more responsive with a different rear end. If not any suggestions for mods.? I think that's why you have a 96 for it's power lol

Thanks Joe

Does it have the 4.1? If so, you really need to ditch it for a higher displacement SBC motor like a 350 and pair it up with a 700r4. Then you can put some 3.73 gears with posi ;)

N0DIH
12-24-08, 10:45 PM
I second that!

If it was me, totally honestly, I would drop in a 5.3L GM engine. I know I know, not a Cadillac, sorry, not a purist, I am into the technology. GM is GM anymore, I want the efficiency and power from the new engine. You can't do it with a similar sized Cadillac engine without a lot a work.

5.3L, DOD/AFM, you will get killer mpg out of it, reliability like no other.

It is just plain worth it. And 5.3L engines are cheap and easy to find WELL under $800 all day long.


Does it have the 4.1? If so, you really need to ditch it for a higher displacement SBC motor like a 350 and pair it up with a 700r4. Then you can put some 3.73 gears with posi ;)