Replace all tires for a flat one?

So 4 RPM on one tire results in 2 RPM increase on the driveshaft for that end of the car. Is Control Trac so sensitive that it would trigger on a 2 rpm difference? Especially a difference that was present for a sustained amount of time. It would seem Ford would have to allow for long term differences in RPM from front to back. Engine computer does something similar with long term fuel trim doesn't it?

Hmmm... I wonder what those differentials are there for? Tirerack, in case eyou missed it, sells tires. You don't think thety may have an ulterior motive, do you? Nah, couldn't be.

Differentials are there for just such a purpose. We hardly ever drrive in a straight line, even on straight stretches of road. Check your own steereing wheel as you drive; it's constantly moving, making small adjustments, which makes the car turn. This makes the tires take different tracks, making them turn at different rates. That's why the differentials are there.

4X4 should not be used when the tires can't slip. Even lockers (which, BTW, lock not when power is applied, but when there's slippage betweent the tires on the same end).

Your tires slip with 1/4 throttle?

Why would the diff need to lock at such low power? Do you oil your tires?

"Big Bill" wrote in message news: snipped-for-privacy@4ax.com...

Don't be a blockhead, they do not LOCK from slippage, they lock from Torque.... Duh!

Stop by I'll demonstrate it to you...

Here I'll repost this since you seam incapable of following the thread.

The most common limited slip differentials found in performance cars and trucks are of the cone or clutch type. Many cone or clutch type differentials use preload springs to help keep some tension on the unit at all times. There is torque applied to both axels, not just when there is slippage.

Limited Slips: (LSD's) come in a variety of designs. Most use friction plates, cones and/or gears to reduce slippage between each of the tires. these units have a dual power path from the differential case to the axle shafts. some power is transmitted through the spider gears to the side gears in the conventional manner. The remainder is transmitted by friction between the differential case and the clutch plates and the side gears. A certain amount of "clutch preload" is built into the unit in a static condition. Then, as load is applied to the differential, the separation forces between the spider gears and the side gears increases this clutch loading. This increase in friction provides for a good positive power flow from the case directly to the side gears. When traction is available to both wheels, the power going to the differential causes the plates to bind tightly together, giving even power to both wheels. However, in a situation where there is little or no traction available to either one wheel or the other, the amount of power that can be transmitted to the other wheel which has traction is dependent on the friction or "preload" in the clutch plates. High levels of "clutch preload" will result in good torque transfer but some chattering of the clutches during cornering may occur. Lower levels of preload results in minimal chatter but reduced levels of torque transfer to the wheel with traction. Because LSD's restrict true differential action, tire wear is accelerated. Changes in vehicle handling may also occur, particularly in short wheelbase vehicles. Wear rates on limited slip differentials are generally higher than on other types due to the reliance on friction to reduce wheel slippage. Also, special lubricants may be required to minimize rough and noisy operation.

I realize your being stuck in this funk may be genetic, pun intended, but please do try to follow along.

But you didn't answer the question. Why would a 1/4 throttle accelleration cause your tires to slip? I know I understand how diffs work; I'm just not sure why *your* diffs lock under 1/4 throttle accelleration on pavement.

performance

conventional

accelerated.

Just because you have a reading comprehension problem DOES Not mean I don't know what I am talking about or how to explain it...

Generally every time you take off with more than 1/4 throttle... That for many drivers is every time the start from a stand still.

The key here is "more than 1/4 throttle". Duh...

I understand exactly how the different types of differentials work. You have not explained in anyway why a locking diff would "lock" under conditions that do not cause one of the wheels to slip relative to the other. If you can't answer that just say so. Your saying "..it locks.." is not an explanation of why you think it locks. There is zero reason for it to lock (or for the clutch pack in a LSD to "engage") under the conditions being discussed, whether at 1/5 throttle or 2/3rds throttle) so I'd like to know what makes you think it would lock. I've taken off many times in Chevy's with Eaton lockers on pavement at full throttle without the diff locking. Conversely, the same truck on loose gravel might lock at less then quarter throttle if started on loose gravel while turning.

-- Elbridge Gerry, of Massachusetts:

"What, sir, is the use of militia? It is to prevent the establishment of a standing army, the bane of liberty. . . Whenever Government means to invade the rights and liberties of the people, they always attempt to destroy the militia, in order to raise a standing army upon its ruins." -- Debate, U.S. House of Representatives, August 17, 1789

What the hell makes you think it is not locked??? Unless you are spinning one tire on pavement and not the other, at full throttle without the differential locking, in which case you are describing that your limited slip differential is not functioning properly. Just because you are not losing traction (spinning your tire(s)) ABSOLUTELY DOES NOT INDICATE THAT THE LOCKING MECHANISM IS NOT LOCKED or that you are not applying power to both axels!!! On the other hand it may simply be that you don't have enough power to spin either of your tires on dry pavement, let alone both of them...

The whole idea is for the locking differential to drive both axels and avoid one or the other of them from having to slip...

The limited slip information I posted in my other posts was not what I said it was on a web page I have nothing to do with...

the Limited Slip section, I included the link so you can read ityourself...

It is real easy for you to check yourself provided you have access to a working limited slip differential. If you jack both wheels off the ground and spin one axel one way the other axel will spin that way too! As matter of fact, if you ask a friend to hold one axel while you spin the other they will not move separately. this is the no-load no-slippage PRELOAD that is always being applied. This connection between the two axels never gets any less than in that neutral state, unless enough torque is applied to break the grip of the clutch. When torque is applied the clutch grips harder yet.

FYI: If you don't know it, a standard OPEN differential if jacked up and one axel is spun, the other axel will spin the opposite direction.

If you still can't understand it take a class.

OK, put on your thinking cap here... If the diff is locked, how does the diff allow differential speeds betweent he wheels on turns under power? Answer: they aren't locked. So then, how do these things actually work? Answer: they sense the slippage beyond a preset amount,and then lock. This doesn't happen under normal accelleration.

I have to admit that what you're saying defys my knowledge of how diffs work, and the nortmal physics of vehicle accelleration. Why does accelleration of *more than* 1/4 throttle lock the diff? What's slipping? Do your vehicles all spin tires at 1/2 throttle accelleration?

I think I see the problem here. You're assuming the the diff is locked becasue you don't experience tire spin. Not true. That's not the way they work. They lock when they sense the different rates of spin on the different axle shafts. Otherwise, the diff would remain locked even around turns, which is not a good thing.

Yes, my slouchiest is a 3/4 ton 4x4 with a 460 5 speed, and it spins the tires at far under 1/2 throttle. All of my Ford cars with Traction Loc's can spin the tires in all gears, and easily in 1st at well under 1/2 throttle. Even the wife's Toyota Camry 3.0L 5 speed spins its tires if you don't try not to...

That's rather amazing. I think I now undertstand where you're coming from. I always tried to keep decent tires on my vehicles so that didn't happen. I do think tho that you might want to reconside your thoughts on diff locks; they lock on a speed differential between the wheels, not on power. The fact that *your* vehicles spin their tires so easily is not characteristic of other vehicles.

Please explain the mechanism that would cause this. On pavement, 1/4 throttle won't cause any difference in tire slip between the two tires. No differential (between sides) slip = no lockup in any "Locking axle" I've driven. So how do you figure they lock up??

-- Elbridge Gerry, of Massachusetts:

"What, sir, is the use of militia? It is to prevent the establishment of a standing army, the bane of liberty. . . Whenever Government means to invade the rights and liberties of the people, they always attempt to destroy the militia, in order to raise a standing army upon its ruins." -- Debate, U.S. House of Representatives, August 17, 1789

Because I know how they work. They don't lock when there is no differential wheel rotation because there is no need to lock.

-- Elbridge Gerry, of Massachusetts:

"What, sir, is the use of militia? It is to prevent the establishment of a standing army, the bane of liberty. . . Whenever Government means to invade the rights and liberties of the people, they always attempt to destroy the militia, in order to raise a standing army upon its ruins." -- Debate, U.S. House of Representatives, August 17, 1789

You are being lied to and taken advantage of. There is another solution to your problem.

The ONLY reason I could see what the "dealer" is saying is if the other tires were worn and needed to be replaced anyway..but that is because it would make since to buy 4 new tires instead of buying one new and having 3 badly worn others.

Is this the ford dealership or a tire dealer? What town are you in? If you have the spare still on shop around Monday..find a friend you trust to help you make your decision.

Thanks,

Sam in Raleigh.

All vehicles with computer controlled AWD must have all tires replaced at the same time. As discussed before, the newer tire will have a greater diameter and circumference and will in turn spin at a lesser rate than the other three tires. Greater diameter means less revs per mile. This will be interpreted as wheel spin by the computer and will engage the differentials. This will burn out the clutches in the diffs.

There have been a lot of vehicles coming in for service that requires the replacement of the differentials. This is due to the computer keeping them engaged all the time and burning them out. This is why they are telling you to replace all four tires. He will note this in your maintenance log in the computer. If the vehicle comes in at a later date with burned out clutches in the diffs then they can and will deny you warranty coverage because it was not caused by normal wear and tear. You were advised and then failed to take the advice of the service technician.

I have read all these horror stories on the Audi and VW forums. The Quattro AWD system has a service note in the manual informing the owner of this.