What diff for a 400hp LQ9 in a 92 K1500?
Thread Starter
Staging Lane
Joined: Sep 2018
Posts: 86
Likes: 2
What diff for a 400hp LQ9 in a 92 K1500? Looking around for an LQ9 to swap into my K1500 for about a 400hp build. Truck has about 257k miles on it now and I can just about guarantee that neither differential has ever been opened. So, for the new setup, I figured let's look at some differentials that will stand up to the new power from the motor. From any of the other folks that have done this or a similar swap in a K1500 around this year, any recommendations on who to go with for a new posi for both ends? I figure gear ratio matters, and while I don't know it off the top of my head, I can check it if I can figure out where to look.
You will be fine with your stock diffs for now,as long as they are still in decent shape, as mentioned above look for some 2500 eight lug axles if you are serious about beating on it.
Thread Starter
Staging Lane
Joined: Sep 2018
Posts: 86
Likes: 2
285/75R16, or about 32.8 inches. I may be thinking of this wrong, but I thought the rear end was already a 6 lug or 12 bolt or however you call it? I could’ve sworn it was 6 lugs on each side. I’m looking through some photos I have from when the wheels were replaced and it looks like 6 lugs.
Teching In
Joined: Apr 2018
Posts: 25
Likes: 0
your rear should be 10 bolt and six lug. I have no experience with 10 bolts and decent power but i do with older 12 bolts and they hold together fine. id look 14b or D60 in 3/4 stuff but if you want to stay 1/2 id go 9" ford
Staging Lane
Joined: Sep 2018
Posts: 54
Likes: 3
From: In the mitten
The stock differential carrier or case is the weakest link in the 8.5 Corp axle. An aftermarket posi unit is something to consider if you stay with the 8.5. There are 6 lug 9.5 axle (14 bolt). Changing front axle doesn't necessarily require changing bolt pattern, because of half shafts.
Trending Topics
Thread Starter
Staging Lane
Joined: Sep 2018
Posts: 86
Likes: 2
The stock differential carrier or case is the weakest link in the 8.5 Corp axle. An aftermarket posi unit is something to consider if you stay with the 8.5. There are 6 lug 9.5 axle (14 bolt). Changing front axle doesn't necessarily require changing bolt pattern, because of half shafts.
Dumb question, but would the posi for the front and rear be different? I think the front axle and rear axle are different since the front is independent and the rear is leaf, right? Or does that not necessarily matter?
It’s not needing to be super beefy for pure off-road use. While it sees more off-road use than most pavement crawlers, it’s not hardly enough to warrant a serious off-road build on it.
Thread Starter
Staging Lane
Joined: Sep 2018
Posts: 86
Likes: 2
Ahh, that makes sense, the amount of lugs are not the same as the amount of bolts. What would the difference between the 10 and 12 bolt be? Just how many bolts it takes to secure it to the truck? This may also be a dumb question but I’d like to understand this a bit more, axles are somewhat like Greek to me.
TECH Senior Member
Joined: Jun 2016
Posts: 22,287
Likes: 3,615
From: Central Cal.
Coincidentally, a 12 bolt rear uses 12 bolts to hold the ring gear to the diff, AND 12 bolts to bolt the rear cover on. So look for 12 bolts on the diff cover for quick ID.
With a 32" tire you will be fine with an aftermarket 10 bolt posi unit as long as you aren't beating on it hard. The problem with a 12 bolt rear and your truck is that they do not have the same spring pad widths so a 12 bolt will not be a bolt in. You would need to cut off the spring pads and weld on a new pair in the right spots.
Thread Starter
Staging Lane
Joined: Sep 2018
Posts: 86
Likes: 2
With a 32" tire you will be fine with an aftermarket 10 bolt posi unit as long as you aren't beating on it hard. The problem with a 12 bolt rear and your truck is that they do not have the same spring pad widths so a 12 bolt will not be a bolt in. You would need to cut off the spring pads and weld on a new pair in the right spots.
Out of curiosity, are there other axles that would bolt in without welding done on the frame?
Thread Starter
Staging Lane
Joined: Sep 2018
Posts: 86
Likes: 2
It’ll probably see the extent of it’s new power rather rarely, as long as it can handle 4th-3rd-back to 4th when going over the countless hills we have here then it probably won’t see much more abuse. Maybe I’d get on it once every now and then just to smile but that’s about it.
Out of curiosity, are there other axles that would bolt in without welding done on the frame?
Thread Starter
Staging Lane
Joined: Sep 2018
Posts: 86
Likes: 2
For a front and rear posi for the 8.5”, is there a brand or part any of y’all recommend to run above others? I don’t want to think I found a great deal only to end up stuck somewhere with a busted knockoff from China.
I'll let you in on a little secret...you're gonna' blow through that old 700r4 transmission (if you spend the time and money to make it work) way before you have to worry about your diff... and they are such a pain in the *** to try and make work with the LS platform, your gonna' have to switch to a electronic 4l60e anyhow. So, yeah, a diff is the least of your concerns right now.
Thread Starter
Staging Lane
Joined: Sep 2018
Posts: 86
Likes: 2
I'll let you in on a little secret...you're gonna' blow through that old 700r4 transmission (if you spend the time and money to make it work) way before you have to worry about your diff... and they are such a pain in the *** to try and make work with the LS platform, your gonna' have to switch to a electronic 4l60e anyhow. So, yeah, a diff is the least of your concerns right now.
To be straight, I’m probably overlooking something huge that will cause it to break apart, so please pick at that relentlessly as I’d like to get it to work somehow.
