Differential Upgrades

[l008com]

I've got lots of questions about my differentials. First, the basics:

From what I read here, the SS has a 9.5" rear, the EXT & 5.3 have an 8.6" rear, and the i6's have a 8" rear. Is all of that correct? Do they all share the same front end? If so, what size is that? Also, for comparison, anyone know what a 1500 and 2500 pickup has for front and rear diffs? Are there any other specs i'd need (like bolt count or spline count) to pick out one that works with my truck?

All my old ZR2 Blazers had G80s in the rear, and it was very nice. I had 4 wheel drive but I rarely used it. With my trailblazer (open front and rear), I'm constantly using 4 wheel drive in the winter. I originally wanted a G80 in this truck, but my mechanic has suggested a Truetrac would be a better fit for me. While I never had any problems with any of my G80s, even when they were old.... a 5.3 is putting a lot more torque into it than a 4.3 can. So I have some Truetrac specific questions...

First, do they make them for our fronts, whatever those are? Front and rear traction differentials would make my truck a traction beast, that would be nice. Mostly for the snow, but sometimes I launch my boat on a beach, or I could potentially have to get into some mud to rescue the boat if things ever got sketchy. Or a million other unforeseen reasons* why more traction would be good. Upgrading rear only is my basic plan, and if I can do both without breaking the bank, I'd like to.

Leading to another important question, it sounds like a truetrac shouldn't affect steering at all in the front? I was originally told it might understeer a bit, but from how I understand they work, it seems like it shouldn't? Other than when I'm sliding in the snow and have all four wheels slipping, but when that happens, a little under or oversteer is not important.

I'm also not 100% clear on when a truetrac will lock. I read that if one wheel is in the air, it might not engage causing that wheel to spin. But if you tap the brake, that will get it to 'engage'. This will rarely if ever be an issue for me. But if it were, wouldn't the traction control automatically his the bakes of the free spinning wheel causing this to engage? I know stability control turns off in 4 LO, does traction turn off in 4 HI? And if I was in 2 HI, shouldn't it definitely do this?

Also, related to this. I'd be concerned about one tire spinning on ice preventing the system from engaging. This is the real world situation I'm in regularly in the Winter. Is it sensitive enough that ice/snow slip will prevent it engaging? Or is that a case where I may have to tap the brake (or let traction control tap the brake) to get going?

Are there any other good options I should consider for rear end traction enhancement? Like a Torsen? I have no interest in a full locker. I'd prefer something fully automatic for the rear, though I'd consider an electric locker in the front if that were the only option. Although how would a TB handle in the snow with the front axle fully locked, and the rear running a truetrac? While writing this thread, I googled up the Torsen diff and watched a 'how it works' video, it actually sounds like it's better than a Truetrac?

*Here's another unforeseen reason. One night at like 3am, I was driving home the long way from my GF's house and I went by what looked like a night work crew doing work on a side road in Arlington. They threw down a lot of sand on the road like they had just paved a section. Well turns out it wasn't paving, something must have dumped some kind of oil or fluid on the road. When I got to the next traffic light, I hit the brakes and kept on going! Even further down the road, I get to a rotary and fish tail my truck like it's the middle of February. The roads were bone dry when this craziness happened! A few miles later everything had gone back to normal.

 

[HARDTRAILZ]

I've got lots of questions about my differentials. First, the basics:

From what I read here, the SS has a 9.5" rear, the EXT & 5.3 have an 8.6" rear, and the i6's have a 8" rear. Is all of that correct? Do they all share the same front end? If so, what size is that? Also, for comparison, anyone know what a 1500 and 2500 pickup has for front and rear diffs? Are there any other specs i'd need (like bolt count or spline count) to pick out one that works with my truck?.

Front diffs are all the same except for gear ratio. It is a 7.2 I think, but it is same all across platform and all open diff.
The full size stuff does not interchange front or rear and they have multiple sizes, so best to google if you really care all the sizes.
Bolt or spline is of no matter. You will need a different Ujoint to swap in a 9.5 and most have needed to shorten the driveshaft slightly.

All my old ZR2 Blazers had G80s in the rear, and it was very nice. I had 4 wheel drive but I rarely used it. With my trailblazer (open front and rear), I'm constantly using 4 wheel drive in the winter. I originally wanted a G80 in this truck, but my mechanic has suggested a Truetrac would be a better fit for me. While I never had any problems with any of my G80s, even when they were old.... a 5.3 is putting a lot more torque into it than a 4.3 can. So I have some Truetrac specific questions...

First, do they make them for our fronts, whatever those are? Front and rear traction differentials would make my truck a traction beast, that would be nice. Mostly for the snow, but sometimes I launch my boat on a beach, or I could potentially have to get into some mud to rescue the boat if things ever got sketchy. Or a million other unforeseen reasons* why more traction would be good. Upgrading rear only is my basic plan, and if I can do both without breaking the bank, I'd like to..

No on the front truetrac. Was a locker available years ago, but they are gone now. There is one guy doing a limited slip but it runs near a 1000 bucks. The front in the snow creates steering issue, hence I never wanted the front locked.

Leading to another important question, it sounds like a truetrac shouldn't affect steering at all in the front? I was originally told it might understeer a bit, but from how I understand they work, it seems like it shouldn't? Other than when I'm sliding in the snow and have all four wheels slipping, but when that happens, a little under or oversteer is not important..

False. In loss of traction situations the truetrac would affect steering big time. Normally, it would do nothing, but you start spinning and loose any control pretty quick esp if off chamber at all, but even on pavement since you have nothing dragging and trying to grip.

I'm also not 100% clear on when a truetrac will lock. I read that if one wheel is in the air, it might not engage causing that wheel to spin. But if you tap the brake, that will get it to 'engage'. This will rarely if ever be an issue for me. But if it were, wouldn't the traction control automatically his the bakes of the free spinning wheel causing this to engage? I know stability control turns off in 4 LO, does traction turn off in 4 HI? And if I was in 2 HI, shouldn't it definitely do this?
.

I run a lockright in my 9.5. It ratchets when turning, but fully locks in the air or whatnot. The truetrac I believe works like you say, but the traction control wont hit the brakes to engage it. Only 4-lo turns off traction control. Tractin control does not hit the brakes so you would need to manually do so.

Also, related to this. I'd be concerned about one tire spinning on ice preventing the system from engaging. This is the real world situation I'm in regularly in the Winter. Is it sensitive enough that ice/snow slip will prevent it engaging? Or is that a case where I may have to tap the brake (or let traction control tap the brake) to get going?

Are there any other good options I should consider for rear end traction enhancement? Like a Torsen? I have no interest in a full locker. I'd prefer something fully automatic for the rear, though I'd consider an electric locker in the front if that were the only option. Although how would a TB handle in the snow with the front axle fully locked, and the rear running a truetrac? While writing this thread, I googled up the Torsen diff and watched a 'how it works' video, it actually sounds like it's better than a Truetrac?.

I am not a fan of much but a full lock exactly cause of the one tire on ice BS. I like my ratchet, noisy but solid engagement and no worries about not engaging or needing to drive differently. Isn't torsen just a basic limited slip like the G86 in the SS and some of the AWD models?

*Here's another unforeseen reason. One night at like 3am, I was driving home the long way from my GF's house and I went by what looked like a night work crew doing work on a side road in Arlington. They threw down a lot of sand on the road like they had just paved a section. Well turns out it wasn't paving, something must have dumped some kind of oil or fluid on the road. When I got to the next traffic light, I hit the brakes and kept on going! Even further down the road, I get to a rotary and fish tail my truck like it's the middle of February. The roads were bone dry when this craziness happened! A few miles later everything had gone back to normal.

Locker or whatever diff won't help you in that kinda situation...if anything its worse when you start spinning if you are not used to being locked. Stuff like that on the road I would take an open diff, but that is about the only time I would ever say that.[/QUOTE]

 

[l008com]

Front diffs are all the same except for gear ratio. It is a 7.2 I think, but it is same all across platform and all open diff.
The full size stuff does not interchange front or rear and they have multiple sizes, so best to google if you really care all the sizes.
Bolt or spline is of no matter. You will need a different Ujoint to swap in a 9.5 and most have needed to shorten the driveshaft slightly.

I wasn't going to change the front or rear end size. Definitely sticking with the 7.2 in the front and the 8.6 in the rear. I was just trying to get a handle on what is what. I would ONLY be replacing the differential inside. It seems like the 8.6 has way more diff options than the 8.0. If the fullsize doesn't have 8.6, then what does? It doesn't make sense that they would make aftermarket options for the 8.6 and not the 8.0 when far more trailblazers have the 8.0... unless something else was using the 8.6 and lots of em?

Also that said, do I need to know bolts count, spine size, or anything else, if I'm just going to (have my mechanic) swap in just a new inner unit?

No on the front truetrac. Was a locker available years ago, but they are gone now. There is one guy doing a limited slip but it runs near a 1000 bucks. The front in the snow creates steering issue, hence I never wanted the front locked.
False. In loss of traction situations the truetrac would affect steering big time. Normally, it would do nothing, but you start spinning and loose any control pretty quick esp if off chamber at all, but even on pavement since you have nothing dragging and trying to grip.

$1000 well that makes it a very easy decision

I am not a fan of much but a full lock exactly cause of the one tire on ice BS. I like my ratchet, noisy but solid engagement and no worries about not engaging or needing to drive differently. Isn't torsen just a basic limited slip like the G86 in the SS and some of the AWD models?

Form what I understand, the Torsen is a gear based, clutchless LSD just like the TrueTrac. The Torsen promo video claims is locks FULLY when one wheel slips, but the commens on the video all say that's very misleading, and say that just like the truetrac, one zero traction wheel will prevent any spinning of the other wheel, and that theres no 'locking'.

Now that said, on the torsen or more likely, the truetrac... how slick does it have to be to turn into an open diff? It's not very often that one wheel is on ice and not the other. Usually it's snow or hard packed snow-ice. Having a wheel completely off the ground will probably never happen. It's more for traditional snow driving, or potentially slick off road situations, like beaches, wet grass pulling a boat, slimy boat ramps etc. I could still get another G80, both have strengths and weaknesses, I'm just not sure how they overlap with my actual driving conditions.

 

[Sparky]

A 1500 pickup has the 8.6" rear end in it, yes. The housing is different but the main guts are the same (carrier and gears at least).

A Torsen is a clutchless LSD, yes. I have one in my Camaro. It isn't hard to get it to transfer torque if one wheel truly has absolute zero traction - feather the brake slightly and boom you've got torque to the other side and you're off and running. I've not run into any cases where I've had to do that though, it seems to have had no problem throwing power around lol.

One thing I like about the G80 my truck has is it will not engage past 20mph or so, which helps reduce the chances of the rear end coming around on you as easily if you're giving it gas exiting a turn and you lose traction on one wheel in the back. The power transfer can cause the other to then lose traction and the rear trade places with the front (been there done that). The G80 essentially reverting to an open diff above 20mph helps keep that from happening as easily - sure in poor traction conditions like that you could still have it swing around on you, but I've just noticed it happens easier when the rear is throwing power around. G80 does let you get the forward momentum going easier from a stop or slow speed, like pulling away from an intersection etc.

G80 of course doesn't like getting slammed into engagement, so if I spin off the line I feather the gas a bit to get it to engage without banging the mechanism. I really don't want to blow it up. 167k miles and counting, so doing good so far

 

[HARDTRAILZ]

You just trying to get both rear wheels to twist at the same time then the truetrac is right up your alley. Auburn makes a good LSD as well. You shouldn't need to tell any decent mechanic spline count or bolt count.... but it is an 8.6 10 bolt with 30 spline axles

 

[l008com]

You shouldn't need to tell any decent mechanic spline count or bolt count.... but it is an 8.6 10 bolt with 30 spline axles

I'll most likely be buying the diff myself and delivering it to him so I need to know, or at least I assume I need to know.

 

[therealsethallen]

Yukon Duragrip would be my choice, I'm thinking about putting one in myself.
Cheapest option is swapping in a rear end from a 9-7x which is an 8.6" with the G86 Limited Slip.

Also, to corroborate what @HARDTRAILZ was saying about Torsen Diffs. In our platform the SS uses a Torsen Center diff, to split power equally between front and rear.

 

[cclarkk]

I ended up putting a Yukon Duragrip in my 08 Envoy and have been very satisfied with its performance in the snow. I originally wanted a True Trac, but thanks to an incompetent shop, I ended up with the Yukon. (Long story on why the switch ). 20k on the Yukon and no isues.