Rear End Options

[burnie6bt]

Hey I am looking at getting 3.73 and posi in a rear end. A local shop quotes $2k to do that work. At that price I can get a 9" kit from speedway motors. My questions are:
-Does $2k seem reasonable?
-Should I just get a whole new rear axle?
-Is there a good late model swap, minimal modifications? 14 bolt, Dana 60, etc.

Basic requirements: posi/lsd, 3.50+ gearing (3.73 ideal will have a 4l80e OD trans), need to hold 600-700 hp at the crank (current engine going in will be about 500hp but want room to grow), street driven cruiser minimal strip time if any. So sticky tires and suspension with a ton of bite is not really in the plan of use.

Thanks in advance!

[jerry moss]

if the 9" is a real ford differential I would spend the money and beef up your 12 bolt, i've seen the stock 9" case break the cast support off on the rear of the pinion, there is a little bearing in there and the casting is thin. if it's an aftermarket case it will probably be stronger, the stock ford housings are known to twist so again if it's an aftermarket housing that is beefier you should be okay. 2 grand is very reasonable as long as they are using quality components. just my 2 cents worth.

[ZEKE68]

What ratio gears do you have in it now? I guess its not an open 3.73. I rebuilt my 12 bolt 3.73 in 2018, and added a limited slip. The new Eaton Limited slip carrier was just under $500.00. Add the bearings and seals and it would be over six hundred just for parts. I did mine myself so that's all I had in it beside the time spent. There is quite a bit of work rebuilding and setting up the rear end, so I also don't think that 2k is excessive. I am running a 454 big block, about 400 HP / 500 ft/lbs. with a 4L80e with shift kit. I push it some but don't try to do burnouts. I figured that the light rearend of the pickup would protect the 12 bolt, due to less traction. But you are going to be pushing more through it, and it all depends on how much you beat on it.

[LS short box]

Can't speak to the overall strength of the stock 12 bolt. On my 68 I used 30 spline axles from Moser and a TruTrac posi. Motive 4:10 gears. I was running only 400 rwhp.
But if you want a 9" I would contact the folks at Quick Performance in IA. They seem to have a good rep.

[burnie6bt]

Originally Posted by ZEKE68

What ratio gears do you have in it now? I guess its not an open 3.73. I rebuilt my 12 bolt 3.73 in 2018, and added a limited slip. The new Eaton Limited slip carrier was just under $500.00. Add the bearings and seals and it would be over six hundred just for parts. I did mine myself so that's all I had in it beside the time spent. There is quite a bit of work rebuilding and setting up the rear end, so I also don't think that 2k is excessive. I am running a 454 big block, about 400 HP / 500 ft/lbs. with a 4L80e with shift kit. I push it some but don't try to do burnouts. I figured that the light rearend of the pickup would protect the 12 bolt, due to less traction. But you are going to be pushing more through it, and it all depends on how much you beat on it.

Thanks for the input guys, I guess I was expecting closer to $1k. So that's a decent hit to the budget. The rear end is currently open diff with 3.08 gears. I would be fine leaving it as is currently but am a bit concerned about having too low of rpms at highway speed. At 70 it would be pretty low rpm, I think like 1600 when I calculated. OD+3.08+30" tall rear tire.

[Mike C]

3.08 and a 30” tire will be fine on the highway. My 307 in my 69 short step has plenty of gear for it’s pathetic output with 3.08’s in the back.

You should be able to get gears and a limited slip in your truck for $1000. $500 in parts and $500 in labor. Check out Quick Performance on eBay where they sell Yukon LSD but don’t say Yukon in the ad for the $300 range. Elite gears I have had good luck with as well.

Quick can build you a 9” as well if that’s how you plan to go. If you REALLY are going to make 500+ hp and hook it up, you need positive axle retention and beefier shafts. So 9” or Dana 60 is the way to go.

[burnie6bt]

Originally Posted by Mike C

3.08 and a 30” tire will be fine on the highway. My 307 in my 69 short step has plenty of gear for it’s pathetic output with 3.08’s in the back.

You should be able to get gears and a limited slip in your truck for $1000. $500 in parts and $500 in labor. Check out Quick Performance on eBay where they sell Yukon LSD but don’t say Yukon in the ad for the $300 range. Elite gears I have had good luck with as well.

Quick can build you a 9” as well if that’s how you plan to go. If you REALLY are going to make 500+ hp and hook it up, you need positive axle retention and beefier shafts. So 9” or Dana 60 is the way to go.

Mike, do you have an overdrive trans?

I will check that out, maybe I didn't type that originally as intended. The rear end won't likely hook up and take a ton of abuse. Because it's a truck, it will not have sticky tires, and the suspension isn't set up. I don't want a ford 9" just seemed a decent 9" could be had for 2500-3000 that was the only reason I mentioned a 9 inch. Thanks for the input I'll check it out.

[adf5565]

I'd look up the parts on rock auto or equivalent so you know what that cost is, but in general labor costs are getting out of hand. I've known people that have paid $1000 in labor to have the brakes changed on their vehicle.

[cj847]

-2k is reasonable.
-Should you get a new axle? I saw the speedway 9". I am not sure how/why there 9" is so much cheaper than, Currie, Quick performance, etc. The only issue with the 12 bolt is that it is a C clip axle. If I were running your HP I would switch to the 9" for C clip elimination and the huge aftermarket support.

[KQQL IT]

Originally Posted by cj847

-2k is reasonable.
-Should you get a new axle? I saw the speedway 9". I am not sure how/why there 9" is so much cheaper than, Currie, Quick performance, etc. The only issue with the 12 bolt is that it is a C clip axle. If I were running your HP I would switch to the 9" for C clip elimination and the huge aftermarket support.

X2

C clips and power is a recipe for disappointment.
Not to mention 3.25" .250 wall tubes are available and a multitude of ratios.
buy the best and only cry once or something.

[HO455]

Is it coil springs or leafs?

[MikeB]

About the stock truck 12-bolt, it's rare that I hear about breakage, especially with street tires and auto trans. $2K to replace the R+P in your 12-bolt does seem high to me. For that much I would expect high quality gears and all new bearings, along with dinner and drinks for two!

If the price is just for labor, that seems really high, seeing as how I have done it in my garage, on my back in around 8-10 hours. A pro with a lift should be able to knock it out in half that time. And he'd better be a pro, with lots of R+P swaps under his belt.

As for the 9-inch from Speedway, is it complete--axle flange to axle flange--and designed to bolt right into your truck? Also, how much torque is it designed to handle? Is it a stock Ford case, stronger nodular iron case, or what?

You should also check with Currie and Strange.

Edit: Is your engine a big block? What displacement? 600-700hp at the crank is massive, at least in my world. Can the trans handle that much?

[KQQL IT]

Originally Posted by MikeB

You should also check with Currie and Strange.

Edit: Is your engine a big block? What displacement? 600-700hp at the crank is massive, at least in my world. Can the trans handle that much?

6bt in the user name

And it's rare but they break. However they do when you try to hook the tire
Wish I could find the pic of the twisted splines.

[MikeB]

Originally Posted by KQQL IT

6bt in the user name

I had no idea what 6BT meant until I looked it up! I thought those things were all about massive torque at low RPMs, and don't rev high enough to make 500-700 horsepower. What am I missing here?

[KQQL IT]

Originally Posted by MikeB

I had no idea what 6BT meant until I looked it up! I thought those things were all about massive torque at low RPMs, and don't rev high enough to make 500-700 horsepower. What am I missing here?

I'm assuming a lot by a 6bt swap.
But it's easy to make big power with them.

[Mike C]

Originally Posted by burnie6bt

Mike, do you have an overdrive trans?

No, TH350.

[HO455]

Personally that fact that you're planning on that much horsepower with a 6BT changes the whole equation. You're going to be making close to double the torque with a diesel engine than a gasoline engine of similar horsepower would make. Torque is going to be what breaks things in the drivetrain. I would figure out how much torque your expecting to make and then plan your axle, transmission and driveline around that number. Ask Currie or Doug Williams what axle they recommend for 1000 lbft's of torque.

It's easy to think "I'll be fine if I don't put big sticky tires on it" but the reality with making that much torque while running small, hard tires is that those tires lead to unexpected wheel spin in 2nd gear or 4rd gear at speed. Think about having the boost come on in while passing a car on a curve at 55 mph and both rear tires suddenly break loose. At the least you get an eye opening pucker! And in the rain better hope you've got plenty of real estate around you.

My 09 Ram 2500 4x4 had factory wheels and tires on it when I got it and it also had had a bunch of work done to the engine. It was pretty much able to smoke the tires at will at any point below 60 mph which made it not much fun to drive most of the time and scary the rest of the time. That truck tipped the scales at 7200. Which i'm guessing is about 1500 more than your truck weighs.

I ended up spending a couple grand on wheels and tires as I would prefer to accelerate hard and never spin a wheel. Of course shortly after that I destroyed the carrier bearing.

[Joyridin]

Here is my suggestion, and it is cheap. Go find a rear axle from a Ford Explorer around the model year 2000. They have 3.25" diameter axle tubes, 31 spline, and all were LSD. On top of that, you get free rear disk brakes. If you want a big tire, all you have to do is shorten the passenger side housing, then take a left axle and install it on the right. Now you have something close to 52" wide and you can put a 13" tire or more with ease.

[sixty8HDC30]

14 bolt all day! the AAM 14 bolts form the early 2000's have disc brakes if that's something you care about. I wouldn't build a 12 bolt or a 9", those belong in cars. I'm super confused how a Chevy truck forum hasn't recommended a 14 bolt???

[LS short box]

I have a 98 Wrangler with a LS6/4L60E combo. I swapped in a Explorer 8.8. Fairly typical swap for the Wranglers. Stock 4:10, posi and disc brakes. The pinion is offset a bit but I forget how much. I cut off the Explorer axle mounts and added the aftermarket Wrangler 4 link brackets. It's been 15 years with zero issues. I think the Explorer axles are 31 spline. The offset has not caused any vibration or u-joint issues. I think I paid $400 for it complete back 15 years ago.

[Richard]

Had a high pinion D60 built by East Coast Gear for the front of my K10 truck. A lot less than Currie or Dynatrac which did not even seem interested to build my axle. Put an AAM 11.5 in the rear of my truck from a 2006 HD2500, will set up myself. Gears, air locker and master rebuild kit were about $1,800 for parts. Does not include any parts to actuate the air locker. Stuff does not cost what it used to. If people can get parts cheaper, let others know. Had to strip all the mounting brackets and install new in the correct places. A Trutrac or posi will be a bit less for parts, without added costs for the air. My axles are 3/4-1 ton 8 lug now, if wanting different there will most likely be added costs. I am running 5.13 gears with a 37" tire which will put me close to 2k rpm at 65 with the 6L90. My 94 is right there and I like it.

[KQQL IT]

Parts in my 9in been together 10yrs at least. 500hp sbc
Hundreds of passes down the strip and probably 10k miles
Maybe I'm just partial