I locked my hubs this morning, and noticed quite a bit more drag, driving to work on the freeway. There are some hills that I normally don't have any problems holding 60mph in 4th, where I could barley hold 45-50mph with the hubs locked. I also noticed more vibration that usual. I just changed my front diff fluid. Does this sound normal, or should I be looking for problems?

 

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The cv axle spindles could be low on grease, causing some drag.

 

Several things:

- You can't judge one tank against one tank, there are too many variables. You need to run several tanks with the hubs locked, and several with them unlocked. Post up the results and I will run the statistics to show if there is a difference or not, at what confidence level, and what the difference is.

- Winter gas

- Cold weather lowers your tire pressure - make sure they are still inflated where you have them in the summer. These days, tires are cheaper than gas. Better to suffer a LITTLE premature wear in the center of the tire than pay for the extra gas every week IMHO

 

So in a non ADD front end, the diff is always spinning? I know the CV's aren't spinning when un-locked, but the front diff always spins? What causes it to spin if the CV's aren't spinning and pushing it?

Does the front driveshaft always spin, even when not in 4WD?

 

Without ADD, the front diff and driveshaft is spinning if the hubs are locked. It doesn't spin when the hubs are in FREE (or 4x2 for the Warn guys).

With ADD (stock setup with drive flanges) the CV's always spin. The spider gears inside the diff always spin, but the ring gear and the driveshaft do not.

 

One way to check drag forces at a certain speed it to see how long it takes to slow down a certain amount. For instance, if you're interested in the forces your engine is working against at 70mph, get up to 75, have a friend start a stopwatch just as you let off the pedal (and push in the clutch, maybe) and stop as soon as the needle passes 65. Some back-of-the-envelope kinetic energy change calculations (KE = 1/2*m*v^2) will give us an idea of the rate of change of energy (KE/time) which is the power necessary to maintain the speed.

In other words, if you consistently find that you slow down quicker with your hubs locked you can be assured that you're using more gas. If you want to do a calculation you may be able to quantify it pretty well.

 

This is pretty clever. Just to make sure, 'm' = mass, right?

 

that vibration could be caused by a slightly worn lower ball joint a wheel bearing in need of grease, worn tie rod end [would cause more shimmy then rumble but worth looking at], or underinflated tires...

FWIW I checked my tires the other day and I'd lost a lot of psi since I checked them on sept. {IK I should look at that more often no lectures pls}
normally I run 50psi rear and 40psi up front [higher then most need and higher then the door sticker recommends but I carry a LOT of wt. around and the truck needs the extra] FWIW since I brought the psi back to where I need it it drives much better then at the 32psi I found them at...

 

Right, m would be mass.

I may try this soon. If I do I'll report back with findings

 

x2 There will always be some extra drag with the hubs locked, but it shouldn't be a "Huge" decrease in mileage.

Try lubing the spindle bushings/bearings - here's a creative technique:
http://www.toyotanation.com/forum/sh...d.php?t=283617

 

interesting idea walker... too bad the OP did'nt post any pics of the actual operation...

 

do a search on here for Spindle Lubricator tool or something along those lines...

i did a PVC version of the spindle lubricator last night and lubed my pass. side spindle...now i have no ROAR with the hubs locked..but i do notice a decrease in performance, takes longer to get up to speed and such.

i'm going to do my driverside spindle today as soon as i get some more grease lol i'm sure it's completely dry just like the pass. side was

 

I have a CV rebuild kit lying around somewhere, it might be a good idea to use it.

I have a new motor in the truck, i may resume my research when I get the exhaust welded up.

 

I went from 13.5 mpg to 14.8 mpg after unlocking my hubs.

 

that's about the average difference I used to see with my 87. locked/unlocked is not that big a hit mileage speaking. It is noticeable over the course of a full tank though. lol

 

One tank numbers are meaningless. Post up several tanks both ways and get back to us.

 

i dont notice any diff when the front hubs are locked or not.

 

I agree. Too many variable from one tank to another. Was your driving style exactly the same? The ambient temperature? Road and traffic identical?

If there is a difference, it's slight.

 

actually, i think y'all have it backwards. If you drive a short trip, say 50 miles, and then drive that same trip, you've got less variation than if you drive 200 miles with different trips.

Driving a thousand miles before calculating mpg will give you a better average of mileage over a greater range of driving styles and conditions. Is that more 'real' than figuring your mileage for a particular driving trip?

Since this truck is my daily driver, and I drive pretty consistently, I have some short trips that are very comparable in driving style and driving conditions. So much so that using these same short trips I was getting 13.5 mpg--consistently. First short trip after disengaging the hub? 14.8.

Edited:
I should also add that on a hill near my home, before disengaging the hub I can't gain as much speed coasting down the hill as I can now, after the disengagement.

 

This may very well be the correct state of our trucks. It makes me wonder what may be causing the difference. Perhaps there is some trouble in the front diff in my truck?