Swap Gears or Whole Axle

[CJM72]

I'm nearing the end of my LQ9 swap with 4l65e transmission. At the moment, my Blazer has a 3.08 gear ratio and 33" tires. Pretty much a recipe for making overdrive sluggish at best. I had always assumed I'd end up changing the gears to 3.73 or something similar in the future. I have an opportunity to buy a complete set of 3.73 diffs from rippen. Is it better to just swap the axles out entirely? Re-gearing what I have would probably be left to a driveline shop and cost $2k or more I'm guessing. However, I'm concerned I'd basically need to rebuild the 3.73 axles as well and end up in the same cost range by the time I'm done.

What's the collective wisfom of the group? Regear what I have or swap both axles out? Thanks.

[Yukon Jack]

If the axles you have available to swap in need to be rebuilt it will still cost a lot less than $2k to rebuild them. I'd swap in axles. Factor in whether you need to do the brakes too. Even doing a rebuild and brakes shouldl be well below that $2k figure.

[CJM72]

I should add a few details. The axles would be $500 shipped. No locker. Condition is generally unknown as they are coming off a non-running 72 blazer. It would be hard for me to install them without at least freshening them up (i.e seals, bearings, u-joints, brakes, etc.). I'd have to store them outside under a tarp for the next 6+ months until I can play with them this winter. It still may be a better idea then swapping the gears in what I have. I don't actually know what it will cost to get new gears set up and I'd probably end up freshening up what I have since it is apart.

I guess the question is, can you swap the bearings and seals on an axle without having to do a complete set-up? If the answer is 'not exactly' then I'm potentially paying $500 for the gears themselves (which are in unknown condition). If I can just clean up the outer bearings, seals and brakes, maybe it's worth it. If I'm dead set on getting a posi, then I'm probably better off holding out and just rebuilding what I have.

I imagine my estimate of $2k for both axles is probably quite low if I'm paying for the labor. I don't have access to case spreaders, but could get dial gauges and certainly have hand tools. I'm an engineer by trade, so I'm tempted to just give it a go and see how bad I can mess things up!

[scott123]

I'd re-do what I had in the truck/blazer now. I take more of the 'bird in the hand' approach.

Pros and cons to both choices.

Setting the gears up in a housing is easier outside the truck than inside. So re-doing the other set would be easier.

If you are currently driving the blazer re-building the other set and doing a weekend swap would be less timely. If your Blazer is apart and not moving, I would do my own sets.

I have did it both ways and each time I guess my thought process was, 'which route gets me back riding first?'.

As far doing the work your self it is not all that hard of a job. Brain surgery is about the only thing left off of the 'how to section' on youtube.

There are tons of sets of rear ends out there with millions of miles that were set with a handful of shims and a can of spray paint. Tools optional.

Best of luck. I am not sure there is a right decision across the board, the right one will be what best fits your forward plan.

S

[SeventyOne]

Pay the money (or attempt it yourself) to have new fresh gears installed in your existing axles. Gears are not a place to try to squeeze value especially from an axle of unknown condition. You're just asking for issues to crop up down the road.

[Jesse B.]

I'd re-gear for the reasons above, and because 3.73 is too low. A 4L65 has an OD of 0.70. With 33" tires and 3.73 gears, you will be turning 1861 RPM at 70 MPH.

I think 1861 is too low for 70 MPH. You'll be too far below your torque curve and will be lugging the engine. In addition, when driving around town at speeds above about 40 mph, the trans will shift into OD, so you will be lugging even worse at lower speeds.

With 4.11 you'll be turning 2051 RPM at 70 MPH. I have a 4L60 in mine with 4.11 gears, a RamJet 350, and 33s and it cruises at 70. I would never go down to 3.73.

Lastly, if you are going to open up the case, I recommend installing an LSD in the rear.

[mongocanfly]

With 33s,3.08s, and a od of .7 you'd be turning 1427 at 65mph....you definatly wont like it..
I agree with the 4.10s....I have 4.10s with 31in tires..its a great combo...
My current truck is getting 4.56s with 33in tires...
Here's a rpm calc that might help...I use the column at the bottom...
http://www.csgnetwork.com/multirpmcalc.html
A locker is a must in my opinion
Ag 65mph heres what you'll get
3.08=-1427rpm
3,73=-1728rpm
4.10=-1899rpm
4.56=-2113rpm
If you've never done gear swaps youd be better off finding axles with what you want...gear setup can be hairpulling

[hemi43]

Just buy new gears and put them in. Only use Yukon as they are IMO the best and easiest to install, and they wont whine like Richmonds. 4:10 is a perfect ratio for a larger tire and OD.
I have 33's and 4:10s with a 4L60E and 5.3 Vortec. Tons of acceleration and the best part is I get 24.9 MPG (imp)

Installing gears is not difficult to do if you're shown how to do it properly. The secret to an easy install is to make yourself a setup bearing.
With today's close machining tolerances, the shim pack that was in the original set is usually perfect for the new gears.

Changing the whole axle is absurd, and a total waste of money and time. Chances are if you even find used axles (good luck), they will be junk inside.
Also like someone mentioned, install a new diff section like an Auburn unit. The week point of the 12 bolt diff is the spider gears, and they are known to explode. Ask me how I know !! :-(

[Mike C]

On my Jimmy I converted to 8 lug axles from a 3/4 ton Suburban. 4.10 gears and a semi-float 14 bolt in the rear. I found the Sub for $300. After breaking 12 bolts a half-a-dozen times it was time for more beef. Should have done this in the late 80’s when I re-geared the 1/2 ton axles.

My kid’s Jimmy project we did the same. His is a TH350 and the $200 3/4 parts Sub had 3.73. Both trucks running 35” tires.

For $2000 you should be able to get a set of CUCV axles. Full float 14 rear most likely with a Detroit and a Dana 60 front. 4.57 gears are the norm.

Yes, you can rebuild diffs without setting up the gear set again. This is a fairly straight forward project for the competent DIY’er. It is possible to cut old pinion bearing off and use a drift (pipe) to drive the new pinion bearing on. A press makes this job easier along with a bearing separator.

I would go for the used axles for $500 if it were my money, but I agree that you would really like more gear with an OD trans. But many 2500HD’s with the 6.0 run 33” or even 35” tires with no problems.