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Old 04-24-2019, 10:18 AM   #1
CJM72
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Swap Gears or Whole Axle

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.
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Old 04-24-2019, 11:56 AM   #2
Yukon Jack
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Re: Swap Gears or Whole Axle

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.
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Old 04-24-2019, 01:19 PM   #3
CJM72
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Re: Swap Gears or Whole Axle

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!
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Old 04-24-2019, 02:34 PM   #4
scott123
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Re: Swap Gears or Whole Axle

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.

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Old 04-24-2019, 05:40 PM   #5
SeventyOne
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Re: Swap Gears or Whole Axle

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.
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Old 04-25-2019, 10:31 AM   #6
Jesse B.
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Re: Swap Gears or Whole Axle

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.
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Old 04-25-2019, 01:57 PM   #7
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Re: Swap Gears or Whole Axle

Yes, I'm leaning that way at the moment based on all the replies. If I'm going to do it, I should just do it right. Might be a good winter project when I can pull the complete axles out. However, I can find dozens of threads where people advise others to just get it done professionally! We'll see how bad it is with the 3.08s. Maybe I won't make it until next fall if it's too sluggish.
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Old 04-25-2019, 02:49 PM   #8
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Re: Swap Gears or Whole Axle

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
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Old 04-26-2019, 04:26 PM   #9
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Re: Swap Gears or Whole Axle

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 !! :-(
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Last edited by hemi43; 04-26-2019 at 04:36 PM.
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Old 04-29-2019, 08:16 AM   #10
Mike C
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Re: Swap Gears or Whole Axle

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 80s when I re-geared the 1/2 ton axles.

My kids 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 DIYer. 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 2500HDs with the 6.0 run 33 or even 35 tires with no problems.
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Old 05-05-2019, 07:18 PM   #11
SmirchIs#1
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Re: Swap Gears or Whole Axle

Quote:
Originally Posted by CJM72 View Post
Yes, I'm leaning that way at the moment based on all the replies. If I'm going to do it, I should just do it right. Might be a good winter project when I can pull the complete axles out. However, I can find dozens of threads where people advise others to just get it done professionally! We'll see how bad it is with the 3.08s. Maybe I won't make it until next fall if it's too sluggish.
I feel sorry for you, reading these replies,some are good and a couple clearly don't have a clue.I don't like to involve myself,but it aggravates me to see people giving terrible info to another person who wants to know and doesn't know.I have been building rears for close to 40 years,when I sell a used or rebuilt rear it comes with a guarantee.I am in upstate NY and you can feel free to call me 518-234-2480 or 518-528-2646 cell Dennis I will say this Yukon and Auburn are products I will not use.I build rears with only quality parts
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Old 05-07-2019, 09:17 AM   #12
hemi43
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Re: Swap Gears or Whole Axle

Quote:
Originally Posted by SmirchIs#1 View Post
I feel sorry for you, reading these replies,some are good and a couple clearly don't have a clue.I don't like to involve myself,but it aggravates me to see people giving terrible info to another person who wants to know and doesn't know.I have been building rears for close to 40 years,when I sell a used or rebuilt rear it comes with a guarantee.I am in upstate NY and you can feel free to call me 518-234-2480 or 518-528-2646 cell Dennis I will say this Yukon and Auburn are products I will not use.I build rears with only quality parts
So you`re saying Yukon doesn`t make a quality part? I too have been building diffs for many years and find Yukon to be the easiest to setup and are the most quiet. Also, I have never had an issue with any Auburn products. Just because you found another product to use doesn't mean it's the only ones to use. Please don't tell me you use Richmond gears!!
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Old 05-07-2019, 10:24 AM   #13
Jesse B.
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Re: Swap Gears or Whole Axle

To the OP: At the risk I'll get flamed too, or maybe I already have, what I think this boils down to is you have a variety of folks offering to you their opinion. While I do not have as much experience installing gears as a couple of the posters claim to have, I have done it and I have paid to have it done. I currently pay to have it done (gear swaps), because it is a lot of work to do correctly, and because I simply have someone I know and trust to do it. In the gear swaps I have done, I've never been able to just swap gears without making changes to either pinion depth or ring gear location. Usually both have to be changed when new gears are used. In order to do this on your truck, not only will you have to buy set up bearings for both a 12 bolt and a dana 44 (you could do it without, but it is easier with the set up bearings) and also buy a dial indicator to measure backlash, and you possibly may need a carrier remover tool to pull the dana 44 carrier out of the axle. The carrier fits in TIGHT and it is difficult to remove without the right tool. Some use crow bars, but I would not. Also consider that since you are going from 3.08 to a higher gear ratio, you are going to need a new carrier for both axles, unless you buy a special gear to fit the lower carrier. With new carriers, you will most certainly need to adjust both pinion depth and carrier location from the factory set up. After you spend the money on acquiring these tools, and spend the time on setting up the gears, are you really going to save any money doing it yourself when you consider your time invested? As far as gear brand, I have Richmond and Yukon (as well as Motive, which I really like) and neither make any noise, because they are set up correctly. I also have an Auburn posi in the front of my truck, and I've had Detroit lockers, True-Trac and Power Locks. Each has its own benefits and drawbacks. My favorite limited slips are the True-tracs and Auburn units. I've broke one Power Lock. I dislike the Detroit locker as it was noisy and locked and unlocked at times on the freeway while changing lanes, which is unpleasant. Other folks may have their favorites too. For your purposes, if you are going to pay someone to do it, just go with your installer's recommended brand, right? They are the one who will be giving you the warranty, so go with what they think is best for you. My $0.02. Good luck with your truck.
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