I bought new to me Excursion a month ago. Before that I had a 95 Suburban.

I noticed tonight when I put the Excursion in 4wd low to go over a curb.....That it acts different than my Suburban did. It seemed more jerky and klunky.

So since I have never had a 4wd that was not a CV style type of axle.

What are the main differences between the 2 styles other than the mechanical parts?


What are the do not's of the 4wd setup in the Excursion?

 

Do no use 4wd on pavement. At least not with locked hubs.

 

The front U-joints (any single u-joint) spins at the same speed when input and output shafts are on the same plane (lined up) but when at an angle the output shaft speeds up and slows down with every revolution. This is because the trunnion (crosspiece) doesn't maintain the same plane (it wiggles) and this causes the distances at it's ends to change constantly (in relation to its linear axis) and it is constantly playing catch up. (For the lack of a better term). The Ford type front U-joint was invented in the seventeen hundreds by Mr. Cardan , which is where the double Cardan joint got it's name. That is 2 joints together that cancel each other's speeding up and slowing down action and is also still used today. The double Cardan was invented a hundred years later but named after Mr. Cardan................so there you have it.

 

Don't the hubs lock automatically when I flip the switch?

 

darn lagging isp!!!! Double posted me!

 

Yes they do, with two caveats:

1: The hub dials have to be in the "automatic" position for the switch on the dash to turn them on.

2: The system must be in good repair. Many people have systems that have not been serviced or repaired properly. The automatic hubs depend on vacuum to operate them. When you throw the switch on the dash to 4WD, two things occur:
A. The transfer case is engaged electrically and this engages the front driveshaft and axles to turn.
B. An electrically driven vacuum valve opens and allows vacuum to the front hub/knuckle assembly to activate the hubs which locks the front axle shafts to the wheels.

Most of the issues with the system not working are related to seals and hoses. The hose that delivers vacuum to each hub could be dryrotted and leaking. Seals, such as the "O" ring at the base of the hub, the "O"ring between the unit bearing and the knuckle, or the vacuum seal that allows the axle shaft through at the back of the knuckle could be compromised and leaking.
These hoses and seals need to be inspected regularly and replaced when needed.

Other items that go wrong but are less common are the electric motor that operates the trasfer case shifting, the electrical vacuum switch, or the dash switch.

Regular inspection of the system is important as the vacuum leaks could cause issues with other things that depend on vacuum, such as heater and A/C controls, or braking (gassers). Fuel mileage may also suffer with a vacuum leak.

To verify that the seals in the hub are working properly, disconnect the vacuum hose at the hub and attach a Miti-Vac to the hub. Pull a vacuum on it, and the hub should attempt to lock within 45 seconds and no leaking. Attaching the same Miti vac to the vacuum hose and engaging 4WD (with engine on and in Park) will tell you if you are drawing enough vacuum in the system to operate the hubs. If not, then inspect the system above the hub for leaks.

 

4HI is great when traveling along on snow covered roads. Then when it senses a slip it locks in the hubs. Living in UT and CO we used 4HI several times a year even driving down the interstate.

 

From the Ford 4WD suppllement: provided with every Excursion and Superduty 1999 - 2005:

"Do not use 4WD on dry, hard surfaced roads (except models equipped

with Auto 4WD or AWD). This may damage the drivelines and axles."


Excursions do NOT have Auto 4WD or AWD, which is the circuit that would "kick in" 4WD when needed.

 

Yeah, lol, you are right. I guess I should have waited till I was spun off the side of the interstate before engaging the 4wd like some of the guys I drove past. I removed the "anytime" statement that I had on that post. Some common sense has to be applied when using 4wd.

 

Hi Scott,

I think that Bion was only trying to point out that this system is fundamentally different from AWD systems that operate similar to what you described. When our hubs are set to auto and shifted into 4wd lock immediately and stay that way regardless of driving conditions. The PCM doesn't detect slip and lock the driveline in, the system is much more primitive than that. If the hubs are working correctly they are locked 100% of the time that you are in 4WD.

Still loving the shocks by the way!

 

Thanks Tom. I understood what he was saying and was not trying to be contradictory to his comment. I just didn't think about the perception of my original statement as I had stated that everyone should "use 4wd anytime". I shouldn't have stated it that way.

I have driven hundreds of miles in 4wd going straight down the interstate at say 15-50 mph and never lost control of my vehicle unlike some of the "less fortunate" that ended up into the side of a Semi or the side of the road. I sometimes forget that not everyone pays attention or "feels", listens, and/or monitors there vehicle while driving. I like the assurance of having all 4 wheels capable of keeping me going straight down the road under adverse weather conditions. I also changed my axle and transfer case fluids more often then most, but again.... assurance.

Glad the Bilstein's are working out.

 

Completely agree here. As long as the tires are the same circumference you should be able to go indefinitely on dry pavement in 4WD without any binding as long as the road is perfectly straight. Of course the sharper the turn the greater stress on the system, but with common sense I've never heard of anyone getting into trouble like this.

 

I should clarify, not to do it on dry pavement.

 

Perfect post, but you spelled with wrong...lol.............Perfect

 

I don't think they ever roll along in 4WD anywhere without binding and then adjusting itself which probably isn't harmful and not even felt in the cab but I see no reason to be in 4wd on a snow covered road (or any road) unless there is a slipping problem or need for a quick recovery. Everything has to be perfect for the front and rear to maintain synchronization which is impossible but probably not a problem. A 4WD truck will slip off the road just as easily as a 2WD.