Rear End Diff

[madmaysey]

on an 88 xlt lsd or posi?

 

[madmaysey]

Well I guess what im asking is it the rear end an open diff or is it limited slip?

Im also curious about the front diff too

 

[Broncobill78]

Chances are that it's a standard open differential but it's possible you have a traction-lock (just as a bit of general info, "posi" is an, uh, ahem, Chevy term. GM called their limited slip diffs "positraction" & street guys shortened it to "posi". Ford's are Track-loc)

You almost certainly have an open front diff, but again it's possible the original owner ordered it with track-loc's front & rear but Ford didn't make too many that weren't specifically ordered. Pretty much every truck that was built without a customer order was equiped with open diffs.

To ck and see what you have jack up the back of the truck so both wheels are off the ground. With the transmission in neutral spin one of the tires. If the other tire spins in the same direction you have a limited slip differential and if it spins in the opposite direction you have an open.

 

[madmaysey]

and the rear end doesn't lock up like the front does it?

so you could be in mud something and have to rely on 3 tires to get you out while one is diggin you into a hole?

 

[Justshootme84]

mad, look at the axle code on the safety sticker on the driver's side door jamb. Axle code "I9" is open 3.55 gears, while "H9" is factory limited slip (L/S or lsd). Very few have the front L/S, which would be a "2" in the code as in "H92". With open rear and front axles (no L/S in either), you're basically in 2 wheel drive when in 4Hi or 4Lo. One rear tire and one front tire will each spin while the opposite tire will not. One way to combat this in the rear axle is to lightly apply the e-brake. Doesn't always work, though. JSM84

 

[bidibronco]

I thought that with a limited slip they spin the same way and with an open they go oposite? I've seen the inside of my diff and it's a confermed open diff and they spin oposite? Wait, I'm confused?

 

[jsomedaysoon]

mad, look at the axle code on the safety sticker on the driver's side door jamb. Axle code "I9" is open 3.55 gears, while "H9" is factory limited slip (L/S or lsd). Very few have the front L/S, which would be a "2" in the code as in "H92". With open rear and front axles (no L/S in either), you're basically in 2 wheel drive when in 4Hi or 4Lo. One rear tire and one front tire will each spin while the opposite tire will not. One way to combat this in the rear axle is to lightly apply the e-brake. Doesn't always work, though. JSM84

i dont mean to butt in on this guys thread but this is something i've been interested in for a while. i looked and my truck has the H9 so as you said i should have the factory l/s right? so i shouldnt worry about installing an aftermarket one right?

 

[madmaysey]

I thought that with a limited slip they spin the same way and with an open they go oposite? I've seen the inside of my diff and it's a confermed open diff and they spin oposite? Wait, I'm confused?

i have heard that they spin the opposite way before too....

 

[madmaysey]

mad, look at the axle code on the safety sticker on the driver's side door jamb. Axle code "I9" is open 3.55 gears, while "H9" is factory limited slip (L/S or lsd). Very few have the front L/S, which would be a "2" in the code as in "H92". With open rear and front axles (no L/S in either), you're basically in 2 wheel drive when in 4Hi or 4Lo. One rear tire and one front tire will each spin while the opposite tire will not. One way to combat this in the rear axle is to lightly apply the e-brake. Doesn't always work, though. JSM84

if the front hubs are locked the 2 front tires will turn at the same time right but the rear end if you lose traction is basically useless without l/s right?

 

[Broncobill78]

if the front hubs are locked the 2 front tires will turn at the same time right but the rear end if you lose traction is basically useless without l/s right?

Whoa, whoa, whoa here guys. Everybody hold up here for a minute because there seems to be a LOT of confusion about this. Let's all start from scratch and take it one step at a time.

To begin with. Once again, to determine what you have in the axle you can follow JSM's advise and ck the axle code on the door sticker or maybe the axle tag if you still have either. If not then take the practical route and jack up the truck so the axle you want to ck is off the ground (both tires). Spin one tire and if the other tire spins in THE SAME DIRECTION then you have a *limited slip differential*. If the other tire spins in the OPPOSITE DIRECTION then you have an *open differential*. Don't ask me the specifics, I'm not a drivetrain engineer, that's just the way it is.

Now with an OPEN differential both wheels will recieve equal power as long as they both have *equal traction* such as a dry, paved road. Once one wheel starts to lose traction the differential transfers power to that wheel. Sounds stupid but there it is. If one tire is on ice & the other is on dry pavement the wheel on the ice will get all the power (same thing if one wheel is off the ground). That's an open diff for you.

Now a limited slip differential is very similar but most of the factory units have a clutch pack in them. The clutches *limit* the speed differential between the two wheels so that when one wheel starts spinning faster than the other (like when it's on ice or up in the air) the clutches kick in and transfer power to the other wheel which DOES have traction. Thus we have both wheels recieving power. Clutches are not the only way to do this, just the cheapest which is why the factories use them. After some years the clutch packs wear out, especially if they do not get regular doses of friction modifier added to the gear oil in the differential housing. Some limited slips use dog gears or helical gears to mechanically achieve the *limited slip* function.

At the top of the heap you have lockers which will physically "lock" the axle shafts together (not quite like a spool because they DO unlock when they "sense" the tension caused by the speed differential of the wheels when turning. Unless of course you have an Air locker but that's really getting beyond the scope of this thread and I'm already getting a headache)

Now as far as the FRONT AXLE goes. Just because you've locked the hubs *does not mean* that the wheels are somehow locked together. All you've done by locking the hubs is to effectively "attach" them to the ends of the axle shafts. A front axle with locked hubs will act JUST THE SAME as a rear axle, no differently. If you have an open differential up front and one tire is on ice or up in the air then it will spin & the differential will transfer most of the available power to it. A truck in the mud with front & rear open diffs will spin TWO tires (one front & one rear), not three. Once again, locking the hubs mearly attach the wheels to the axles they do not in any way lock the axle. You still have an open differential or a limited slip differential (depending on what was installed) and it will act accordingly.

Whew, now I need a beer. I hope that explained it a little better for everyone and if there are STILL any questions go ahead and ask away. I'm going to toss back a few quick ones and once my headache is gone I'll be happy to amplify on anything that seems confusing (at least until I get a migrane)

 

[madmaysey]

yea i got all that, i was just hoping thats not the way it was?

but if thats the case why would you ever bother unlocking your front hubs?

just to prevent unnessary wear or what?

 

[madmax]

Chances are that it's a standard open differential but it's possible you have a traction-lock (just as a bit of general info, "posi" is an, uh, ahem, Chevy term. GM called their limited slip diffs "positraction" & street guys shortened it to "posi". Ford's are Track-loc)
You almost certainly have an open front diff, but again it's possible the original owner ordered it with track-loc's front & rear but Ford didn't make too many that weren't specifically ordered. Pretty much every truck that was built without a customer order was equiped with open diffs.

To ck and see what you have jack up the back of the truck so both wheels are off the ground. With the transmission in neutral spin one of the tires. If the other tire spins in the same direction you have an open differential and if it spins in the opposite direction you have a limited slip.

also when in 4X4 if it's really hard to turn on pavement, thats usually trac loc (hard chugging as both front wheels try and turn the same speed), most people find it annoying, but if you've got the track-loc front you'll usually have the trac loc rear, so you won't need 4X4 as much, both my bronco and my old explorer had track-loc front and back, the explorer had little trouble in a foot of wet heavy snow w/o 4X4, the bronco hasn't found any winter road conditions that 4X4 was absolutley needed, though it does help with turning in snow as well.

 

[Broncobill78]

yea i got all that, i was just hoping thats not the way it was?
but if thats the case why would you ever bother unlocking your front hubs?

just to prevent unnessary wear or what?

You unlock the front hubs because when they're locked it wears the **** out of them to be driven on dry pavement *in 4wheel-drive*. The front axle isn't like the rear since the tires turn. This creates a LOT of stress and the tires want to slip & scrub which they CAN do just fine on dirt or mud but pavement will cause the stresses to build until something breaks (usually a U-joint or axle shaft). You can feel this if you drive with them locked *and in 4WD* and turn in a circle. The tighter the radius becomes the more & more you'll feel a See-saw motion in the nose of the truck. Eventually you'll hear the tires starting to scrub & then shortly afterwards something will break. Off-road or in slippery conditions (sleet, ice, snow) it's no problem but again, on dry pavement you'll break something. Full-time 4x4's like the Blazer have this problem & owners learn to either make large diameter turns or install locking hubs so they can disconnect the wheels from the axles.

A lot of us will go for 5-6 months at a time an not unlock the hubs. The wear & breakage problem is only there when the axle is powered. If you have the hubs locked and the truck is in 2WD there's no problem because the axle isn't getting any power from the transfer case. when I lived in New England I would routinely lock the hubs in October and leave them locked until March. When I needed 4WD I'd shift the transfer case lever into 4Hi and I'd have 4WD, when I didn't need it I'd shift back to 2-Hi and leave the hubs locked.

 

[madmaysey]

also when in 4X4 if it's really hard to turn on pavement, thats usually trac loc (hard chugging as both front wheels try and turn the same speed), most people find it annoying, but if you've got the track-loc front you'll usually have the trac loc rear, so you won't need 4X4 as much, both my bronco and my old explorer had track-loc front and back, the explorer had little trouble in a foot of wet heavy snow w/o 4X4, the bronco hasn't found any winter road conditions that 4X4 was absolutley needed, though it does help with turning in snow as well.

i don't understand this part

if you have limited slip on the front you wouldn't ever be using it with out 4 wheel drive right? or am i missing something

i don't understand if the front is limited slip why wouldn't you need 4x4 as much?

 

[madmaysey]

You unlock the front hubs because when they're locked it wears the **** out of them to be driven on dry pavement *in 4wheel-drive*. The front axle isn't like the rear since the tires turn. This creates a LOT of stress and the tires want to slip & scrub which they CAN do just fine on dirt or mud but pavement will cause the stresses to build until something breaks (usually a U-joint or axle shaft). You can feel this if you drive with them locked *and in 4WD* and turn in a circle. The tighter the radius becomes the more & more you'll feel a See-saw motion in the nose of the truck. Eventually you'll hear the tires starting to scrub & then shortly afterwards something will break. Off-road or in slippery conditions (sleet, ice, snow) it's no problem but again, on dry pavement you'll break something. Full-time 4x4's like the Blazer have this problem & owners learn to either make large diameter turns or install locking hubs so they can disconnect the wheels from the axles.
A lot of us will go for 5-6 months at a time an not unlock the hubs. The wear & breakage problem is only there when the axle is powered. If you have the hubs locked and the truck is in 2WD there's no problem because the axle isn't getting any power from the transfer case. when I lived in New England I would routinely lock the hubs in October and leave them locked until March. When I needed 4WD I'd shift the transfer case lever into 4Hi and I'd have 4WD, when I didn't need it I'd shift back to 2-Hi and leave the hubs locked.

and another thing is if the front diff is open why would you worry about the front end jumping if the tired arent actually locked together?

i guess part of my confusion is if the tires aren't locked and the diff is open then why are you see sawing and jumping around doesn't that mean the tires aren't slipping?

 

[Broncobill78]

and another thing is if the front diff is open why would you worry about the front end jumping if the tired arent actually locked together?
i guess part of my confusion is if the tires aren't locked and the diff is open then why are you see sawing and jumping around doesn't that mean the tires aren't slipping?

/emoticons/[email protected] 2x" width="20" height="20" /> Ok, I can see you're still confused. I think the problem here is that you're dealing with two seperate things and not understanding it. First off there are the wheel hubs. Part-time 4WD trucks have hubs that lock & unlock (now don't confuse this with auto locking & manual locking hubs, they BOTH do the same thing, they just do it differently). What the hubs do is to essentially "disconnect" the wheels from the axle. When the hubs are unlocked the tires freewheel and even if the axle is recieving power fron the transfer case it is NOT being delivered to the wheels because they are physically disconnected from the axle. Once the hubs are locked the wheels are now parts of the drivetrain and can accept power from the axle and deliver it to the road. When the hubs are unlocked it doesn't matter WHAT type of differential is in the axle because the wheels are disconnected and recieve no power. If the hubs are NOT locked then the truck behaves just like a car or any other 2WD vehicle because it IS a 2WD vehicle when the hubs are unlocked

The front end will only see-saw when 2 conditions are met. 1) it must be in 4wheel-drive. This means the hubs must be locked and the transfer case engaged in either 4-hi or 4-lo, and 2) you must be making a tight diameter turn. If both conditions are present then you will feel the nose of the truck see-sawing.

Now as far as whether the front has a limited slip or not, it's really a moot point. All the L/S is going to do is increase your traction beyond what you already have. Here's where you may be getting stuck. With standard open differentials only one wheel of any given axle will recieve power in poor traction conditions (ice, snow, mud, etc) because that's they way they work. The wheel with the least ammount of traction gets all the power from the axle. SO, when you have 2 axles (a front and a rear) on a "4-wheel-drive" truck when you get into mud, snow, ice, etc you're ONLY GOING TO HAVE TWO WHEELS RECIEVING POWER. Detroit has chosen to market these as "4 wheel drive" because on dry pavement and good traction surfaces they ARE 4-wheel drive but not in poor traction conditions. A Limited slip differential or a locking differential eliminate that problem and actually deliver equal power to all four wheels. That's why people upgrade to these differentials or order them as optional equipment.

Hopefully that makes things a little more clear. I'm going to get a beer /emoticons/[email protected] 2x" width="20" height="20" />

 

[Justshootme84]

BB78, when you jack up the axle and do the test to tell if it's open or L/S. The wheels on the OPEN axle will turn OPPOSITE of each other. The wheels on the L/S axle will turn in the SAME direction. When on the ground, with both wheels getting traction like on pavement, both wheels get power and move the vehicle. But when one tire loses traction, it gets more power. That's why you can get stuck on wet grass with an open rear axle. One tire spins out, and the other does not move. Same applies on an incline or level ground. Locking the front hubs doesn't change this aspect. It just engages the front axleshafts to the transfer case, which splits power to both axles in 4WD instead of only the rear axle in 2WD. And yes, H9 is the factory L/S rear with 3.55:1 gear ratio. While that will allow some power to go to both wheels rather than just the one that loses traction, it often doesn't work if the L/S is worn out or the clutches don't engage anymore. I've seen several rigs get stuck, knowing they have the factory L/S rear axle. JSM84

 

[madmaysey]

while not totally useless 4x4 with out atleast one limited slip diff is kinda pointless isn't it?

and i have heard from multiple sources that confirm that on LSD's you spin one tire and the other spins the OPPOSITE way...open diff they spin the SAME way....sounds kinda backwards but i have seen it first hand

 

[madmaysey]

and back to the other problem i am having trouble understanding is what is the point of unlocking your front hubs?

why wouldn't you just always have them, ready standing by waiting for the 4 wheel drive?