Differential Gear Swap?

[JasonA]

Wow. 15.5 seconds isn't bad for the 2.7L Stratus. That's faster than I thought they were. That's just a few ticks behind many Northstar Cadillacs.

I also enjoy the mileage of the LD8 powertrain. I get 20 city and 30 highway. Not many V8 cars do that.

I understand a LSD is harder to implement on a FWD car because of all the addition of the turning function the front wheels have to provide. If you effectively locked the speeds of the front wheels with a LSD, you'd probably have some MAJOR understeer, in a performance situation. I wouldn't mind on in the Caravan. During the one snow situation we had, the van drove great, but there were still times, like accelerating from a stop while turning (like a street corner) produces uncontrolled wheelspin. And that engine is so quiet, without the tachometer it would be hard to detect. Since it doesn't have traction control, and since we don't autocross it, I think a LSD would work good in that case. However, I think Cadillac's route -- all speed traction control -- is a great solution for all season traction, under all situations (performance, cruising, etc).

[tjtjwdad]

jadcock Posted on Jan 14 2005, 06:29 PM

I think Cadillac's route -- all speed traction control -- is a great solution for all season traction, under all situations (performance, cruising, etc).

Saturday morning was pretty slick here in the Portland area. I decided to really try the Caddy out in the ice so I drove it to work. Gotta admit, other vehicles were doing doughnuts and stress testing the curbs, while my car went right where I pointed. I was quite impressed.

Jim

[danbuc]

A LSD in a FWD car is no problem as long as you are not flooring the gas when turning. If you did this, then yes the diff could lock up and you would have major understeer. How often do people floor the gas when turning though. That is bad for an open diff as well. The LSD is an advantage when flooring the gas from a dead stop in a straight line. Other than that, it will not interfere, as it is designed to slip when turning as an open diff would. They wouldn't make them, if they posed such a problem. Just look at all the FWD Autocross racing cars (Acura RSX, Honda's,...ect). They all used a LSD in the front. They do this to imprive traction, and keep the inside wheel from spinning on turns.

[JasonA]

A LSD in a FWD car is no problem as long as you are not flooring the gas when turning. If you did this, then yes the diff could lock up and you would have major understeer. How often do people floor the gas when turning though.

Uh....more often in the Cadillac than in the minivan....and I'll leave it at that.

I believe a good T/C system is a more-than-adequate solution in a FWD car. Better than a LSD? I don't know. Cheap FWD cars have LSDs, expensive FWD cars have T/C systems. I don't know if that says anything or not.

[danbuc]

The only real reason I WOULD put in a limited slip differential, would be in addition to a high stall torque converter. Becaus eof the increased force being applied to the wheels, it would be nice to have to prevent wheel slippage. Now before you go off saying, "Why would you ever put in a high stall torque converter?", call up Yank Converters and ask them how many people have done it. There are actually quite alot out there. I make a habbit, not to floor the gas around a turn, simply because it's bad and there is no reason for it. The traction control system in the caddy is great, but it's not as good as a limited slip diff. I don't think it will be able to handle teh increased power transfer from a high stall torque converter as well as a limited slip diff could either. I'm sure it would handle it would work, but it probably would work as well. Since it is limited slip, and not locking, you would not have the draw back of a clunk, or understeer. This is because it functions as an open diff when not under heavy load. I am planning on getting a highstall torque converter in the future, and I will probably get the limityed slip diff also. I would not have suggested it, unless it was in conjunction with something that would warrant it. A high stall torque converter will cause more slippage than the OEM one will, this will make the T/C system have to work even harder, not to mention that torque steer will probably become more noticable. The LSD is only there to reduce the amount of work the T/C system must do, and reduce torque steer as well. That's about it. It is true that cheaper cars that do not have a sofisticated T/C system like a Cadillac, have a limited slip diff, but there engine are also not producing 300hp. Our T/C system has to do alot of work, and the limited slip diff, would help alleviate some of that, by more evenly distributing the load across both wheels.

Sorry for the long post, just had to explain myself I guess.

[danbuc]

Guru, thanks for the info. I do have a question however. The limited slip diff I'm looking at, is not a locking diff. It's designed to operate like an open diff, under normal to moderate acceleration. The main reason I was interested in it, was because I'm looking into the high stall torque converter. Even when I floor it now, the traction control seems like it working really hard to modulate wheel spin. Quite often, this ends up slowing down the car quite a bit. I never spin the wheels if I can help it when turning, simply because it's not safe to begin with. Even with an open diff. If I get the high stall torque converter, I don't want to have to deal with T/C cutting the power, and breaking the car, every time I want to have a little fun. This is the link to it. It is built by Engineered Performance. They specialize in FWD GM vehicles-

http://www.domesticperformance.com/product...products_id=282

Thanks for the info Guru

[JasonA]

Yes, thanks for that good info Guru. I probably wasn't making my case clear to Danbuc either...I was really coming from the angle of, a Cadillac isn't a race car, so I didn't see the advantage of having a full LSD vs. a good T/C system...in the Cadillac. But I certainly understand the benefits of LSD...and I've had them before. Great tools for RWD cars with no T/C, that's for sure. "Good T/C system" is the operative word above, because I've driven a few cars which had pretty lousy T/C systems. The Cadillac's is definitely top-notch.

[danbuc]

I see what you mean. The reason I think it would be fine, is that in most cases (snow), I want both wheels to spin. It's snowing here today, and I notice that with T/C on, both wheels would spin, but the PCM would cut engine power. I turned off traction control all the way to school, so that I would start in second gear, and could have wheel spin. I've noticed that both wheels spin with/or without T/C. When this happens, I just let off the gas, and cost a bit. Then I ease onto the gas, and pull away normally. There are certain times, when both wheels spinning together is a good thing. Like when I pulled into the parking lot. It's a pretty steep hill, anbd without both wheels spinning straight ahead, I probably would not have made it up the hill. The LSD probably won't make any difference, since I don't drive fast in the snow. With or without it, I've still got both wheels spinning. I only want it for more traction in dry weather. That where I feel it will make the most difference. I don't have to worry about locking up the diff around turn either, because I never floor the gas unless I'm pointed straight down the road. Like I said, I will probably get the torque converter first, and see how that reacts with the T/C. If I still get traction control trying to brake the front tires to limit spinning, them maybe I'll get it. I'll have to see what happens. Thanks Guru.

[DustyS]

Dan-I think you may REALLY like a LSD! I agree, with the cadillac TCS engaged, I've generally noticed two front tires spinning. A good example of open diffs making a fool out of two vehicles is this: A visitor stopped by my home this fall, on a warm sunny day. The end of the driveway, nearly where it meets the road, has a small ditch on both sides. I have reflectors and some markers for guides, but people still back down in it, and such did a poor, kind visitor. Being a good SUV, it should just drive out, huh? NO. It stayed in place, spinning the right hind tire and the left front tire, about as helpless and stupid looking as could be! It was simply the angle, or axis, that was carrying the weight of the vehicle, causing only those two tires to freely spin with the stupid open diffs! The SUV was rendered completely useless, none-the-less making the high price paid for it a waste. OK, OK. At any rate, with even one good locking diff or LSD, it would have propelled forward and been on its way. Instead, a tow strap was attached between it and the Stratus (as a quick, last resort). The Stratus, pulling in reverse, was mostly just straining (its 41TE trans, Jason-lol), but with the accelerator pushed nearly to the floor the right front tire broke loose and enough progress was obtained that the SUV was able to complete driving out of the ditch, while its right hind and left front tires dug up the yard a bit. At any rate, had there even been ONE good LSD on ONE axle of ONE vehicle, the situation would have been outstandingly better. To force the Stratus into spinning both front tires to aid the tow, I had to mash the brake really hard, thus causing the brake pressure to generate equal resistance between the front tires, yet the added brake pressure required more throttle-which was nearly at the floor, to make the vehicles move. Even if the SUV had TCS, it should have moved, and likewise if the car had TCS it wouldn't have been stressed as much. Events like this have nearly caused me to form open differential hate groups LOL!

On the other hand, I have experienced LSD, and even TCS, equipped vehicles simply slide sideways, with the potential of striking objects. And yes, the typical soccer mom with a van full of distracting children would be better off with an open diff (yuck) needing additional assistance, rather than sidewinding the vehicle into a worsened situation. Personally, I would rather learn how to control the thing knowing all drive tires will spin.

On and on.....I went Ford Escape shopping, to replace the Stratus. After some test driving and extensive questioning, I was told a LSD was not possible. Some sales people literally became nasty with me, saying I was foolish for allowing that feature to be a deciding factor...you're being rediculous...nobody needs that....thats only for a HD towing vehicle....what are you going to do with this, plow snow...etc. etc. Anything to make a sale.

Good traction, especially in wintery conditions, is vital for not only safety, but being able to have mobility! I think using open diffs, which always distribute nearly all engine power to the worst possible wheel(s) with the smallest ability to move the vehicle (the whole purpose of a vehicle) is like designing a steller sports car that cuts fuel to half the cylinders during WOT.

Devin-sorry for going off topic on your question. I think your deville will be great with the 3.33 gears. As your car has high amounts of torque, a LSD may be a good idea, as you will gain even more torque multiplication with 3.33! Good luck! I wonder if TCS was standard on 4.9 cadillacs with the 3.33 gears- 92 STS ETC?

[danbuc]

Thanks for the reply DustyS. You make a good point about the LSD. . I think as long as you can properly control the vehicle, then it should be okay. I'm gonna start savin' up.