PDA

View Full Version : Advantage or Not for Limited Slip Differential



Eric Woodbury
18-Jan-2019, 15:53
Hope this is the correct category...

I drive an '04 FORD E350 van for camping / photography. Standard 2WD. I'm considering a limited slip differential modification. About a thousand bucks. I've never done any 4x4 driving. I understand that a standard diff is really only 1WD and that limited slip will give me more like 2WD. Still, it is twice the traction for practical purposes (I'm told). I don't want to get stuck, nor do I wish to get further from the pavement. However, there have been times on dirt roads and even on nice gravel shoulders, where I've been stuck. In these cases I've been lucky that I either didn't dig-in or somebody was there to help me out. Whew. I carry a tow strap and matts.

Do you have any experience with this conundrum? Will it drive the same except when in sand? What is the improvement and how do I then gauge what terrains are 'safe' and which are not?

I'm not interested in a different vehicle. This one is low miles, works fine, and has Sportsmobile modifications.

Thanks for your help.

-e-

Willie
18-Jan-2019, 16:35
The modification should work well. Will help as it puts traction to the wheel with less slipping. Not a 4WD but better than what you have.
A good option is to carry an electric winch, 2 or 3 metal fence posts and a small sledge hammer to pound them in. You do get stuck and need help pound in a post, hook up the winch and pull yourself out. Works well. With enough cable you go cross a road or lousy spot and don't worry about leaving a post in a roadway - because at times it will be all but impossible to get it back out.
Good luck.

John Kasaian
18-Jan-2019, 16:39
A limited slip will help but IMHO if you start to dig yourself in you're beyond what even a limited slip diff can help you out of.
What size tires are you running? Sometimes letting some air out works magic, and there are small portable cigar lighter operated air compressors that can air you back up when you're on the straight and level.
Small compressors however generally don't like altitude.

Neal Chaves
18-Jan-2019, 19:07
A van (unless heavily loaded, like a pick up truck, is light in the rear end anyway) With posi you can just spin both rear wheels and still be stuck. I had a Chevy van with posi and even with fat tires in the rear it was nowhere as good off the road or on the beach as the VW van with stock tires I replaced it with.

williaty
18-Jan-2019, 19:58
I used to turn Subarus into race cars professionally and diffs are a big part of that.

The "normal" differential in a car is an open diff. That means the differential splits the torque equally to each wheel connected to it without any concern about whether the wheels are going the same speed. When the car has good traction, neither wheel slips and each wheel receives half the torque coming in via the driveshaft (50:50 torque split). The fact that the open diff doesn't care about speed means the outside wheel gets to roll faster than the inside wheel in a turn so the car rolls around the turn without binding or tearing up the tires. The moment one wheel starts to slip, the diff still splits the torque 50-50. What this means is that the torque out of the diff drops to the amount of torque held by the wheel that is spinning. The "other" side that still has grip is limited to the amount of torque the slipping side can hold. The excess power the engine is putting out gets burnt off as *speed* in the slipping wheel. Just keep in mind that an open diff limits the torque you can use to go to whatever the slipperyiest wheel can cold.

A locked diff is the opposite. The diff forces both wheels to turn at the same speed, regardless of torque. Great for getting out of crap because both wheels are always doing as much as they can do. Terrible for driving on bare tarmac because it tears up the driveline and the tires.

A limited slip diff tries to split the difference. It acts like an open diff when the speed difference between the wheels is small (like when going around a corner). If the speed difference between wheels becomes large (like when one wheel is sliding and spinning), the diff "locks up" to try to equalize speed between the wheels by sending more torque to the wheel with more grip.

Yes, LSDs really do help in low-traction conditions. No, they're not magic in really, really bad conditions. Yes, you will get stuck less often and be able to get yourself unstuck easier. No, it won't magically make your van into a swamp truck.

They help, but they can't fix stupid, if you know what I mean.

Two23
18-Jan-2019, 21:30
Some thoughts. The portable winch does work but takes time. A limited slip does help if you just need a small boost in traction. To go along with that considers a pair of traction mats:
https://www.amazon.com/dp/B00AV2HONS/ref=sspa_dk_detail_0?psc=1&pd_rd_i=B00AV2HONS&pd_rd_w=eVgQ7&pf_rd_p=f0dedbe2-13c8-4136-a746-4398ed93cf0f&pd_rd_wg=zyUm1&pf_rd_r=ERCX3E6Q042KRWHXW42J&pd_rd_r=336ec4c4-1ba2-11e9-ad0a-616d18ce5d16

Letting air out of the tires (down to maybe half?) and then airing them back up with a small electric pump can work in softer soil. I'm going to suggest another option. Instead of spending $1,000 on the van you have, would a smaller vehicle work? Are you just going camping by yourself? I'm suggesting a used Subaru Outback. Should be able to sleep one person in the back if you don't use a tent. I have the smaller Subaru Forester and I have to say it's pretty impressive! It's like a mini-Jeep. Here it is parked on Waubay Lake last Saturday. It can handle up to 10 inches of snow and seems to be able to go anywhere.


Kent in SD

rfesk
19-Jan-2019, 06:26
Limited slip differentials have a limited life time before wearing out. (I had a Jeep Cherokee that wore out.) I would look into the Air locker(sp?) type. These act like a open differential until you activate them to lock up both rear wheels with a switch at the dash.

Randy Moe
19-Jan-2019, 06:44
Sand is a problem.

Lot's of good advice so far.

Bald tires work better on sand than snow tires.

I got a electric locker diff on my F150, 2X4, basicly a farm truck as equipped.

I am very careful offroad and sometimes it's better to go faster than slower in sand and not slow down until you find a high clear spot.

I have never bought a 4X4 as they just allow you to get stuck farther out.

4X4 are often sold with plain diffs front and rear, making them basically 2 wheel drive. Lockers front and rear make them far better.

However I found a Splitty VW Bus with low air pressure tires can go almost anywhere. We also made them into dune buggies and drove around stuck Jeeps.

A loaded 2X4 van often has a fragile cargo.