Should I swap in the 3.73 LSD for my open 3.55? Worth it?

[unpredictable1]

I just bought a 2001 sport that has 3.73 gears, LSD. (donor truck for its trans)

My 2000 xlt has an open diff 3.55. I plan on running 30 or 32 inch tires in the near future.

How much of a hassle is it to swap the front and rears? Is it worth the hassle?

 

[safn1949]

If you have the tools and jackstands not bad at all depending on the rust involved.Just remember to get NEW U bolts for the rearend,don't reuse the old ones. Lots of penetrating fluid a few days in advance and the rear will be a 2 hour job easy.

I have never done the front on one of these but it looks straight forward.

 

[99ex22]

The rears easy but on the front you basically have to take apart the entire front end. I wouldn't swap them enless you plan on lifting it and running larger tires. FYI it's perfectly fine to reuse the U bolts, I have done it many times.

 

[unpredictable1]

Would I just reuse my driveshafts? They'll be ok with a different differential? I would think the diff is the same, just the internals are different.

 

[techieman33]

you really are supposed to replace the u-bolts since the threads can strech. A lot of people do it anyway with not problems though.

The rear axle can take anywhere from a couple of hours to a full day depending on the rust levels and any other problems you run into. The front axle can be the same, a couple of hours or a really long day. You have to pull the driveshaft and cv axles, then it's just 3 bolts holding it in. Having a buddy around to run the jack is a huge help with this, especially getting it back in. For 30's, I would be 50/50 since the limited slip would be nice. For 32's I would swap the 3.73's in no question if you couldn't get 4.10's.

edit for your last question, yes the driveshafts are the same.

 

[unpredictable1]

Rust isn't that much of a problem for the most part.

I would probably get new u-bolts.

 

[4rd4life]

if your looking on getting bigger tires then i would say yes you should take the difs. i noticed a difference when changing to 31's with my 3.73. im looking on getting 4.10s for it now. so if you plan on going bigger then 32 you should probably consider at least 4.10s the l/s is a nice touch for the 373

 

[unpredictable1]

you really are supposed to replace the u-bolts since the threads can strech. A lot of people do it anyway with not problems though.

The rear axle can take anywhere from a couple of hours to a full day depending on the rust levels and any other problems you run into. The front axle can be the same, a couple of hours or a really long day. You have to pull the driveshaft and cv axles, then it's just 3 bolts holding it in. Having a buddy around to run the jack is a huge help with this, especially getting it back in. For 30's, I would be 50/50 since the limited slip would be nice. For 32's I would swap the 3.73's in no question if you couldn't get 4.10's.

edit for your last question, yes the driveshafts are the same.

Ok I think I'm going to tackle this soon.

Steps I've done and how I plan on doing the rear:

1. Vehicle is on jackstand, rear tires removed.
2. Jack on the diff.
3. I was going to let go the rear shocks, rear shackles and then lower it down.
4. Disconnect handbrake cable


5. Where to disconnect brake lines?

 

[4rd4life]

you can disconnect the brake lines at the calipers or there might be a block on the diff that a steel line goes into and then splits to both rear wheels. (unfamiliar with what it has sry)

 

[unpredictable1]

Will this swap throw my speedo or rpms off at all? I wouldn't think, other than when I put on larger tires then I know it'll be off.

 

[4rd4life]

when i changed to larger tires it only threw my speedo off about 2 or 3 mph at 75 mph, so if your getting bigger tires for it in the future swaping for the larger diff would only change in your favor

 

[unpredictable1]

So if I swap this in with my stock tires for now, it'll throw my speedo off?

 

[gavin]

FWIW, I just removed the calipers, and used plenty of zip ties to tie the calipers out of the way and support the metal brake line.

and yes, it will throw your speedo off. Your speedo will read about 5% faster than you are actually going, if I did math correctly.

 

[unpredictable1]

So after talking with a couple of my buds about this project - they said it seems like too much work for little gain - and that I would be looking to upgrade to 4.10s not longer after doing this.

I'm kinda on the fence now, tilting more towards holding out for 4.10s. There's a pick n pull close to me, and it's a matter of checking there every so often for a 4.10 set.

 

[gavin]

this is purely my opinion;
I didn't like the "sluggishness" of 3.73's when I upgraded to 33's. The jump to 4.10 was okay, but I'm on 4.56's now and much happier.

For 31's, 3.73 would be good. I didn't notice much of a loss when I upgraded from the stock 235/75/15's to 31x10.50's with the stock 3.73 gearing.

 

[TBMounty50]

The speedo on '98 and up reads off the raw vss signal from the rear axle. Different size tires will affect the readout but gears will not.

 

[kert0307]

I wouldn't swap them because 3.55 to 3.73 isn't that big of a jump. Plus, I would rather have an open diff because you have MORE options for putting a locker in the rear with an open diff than a LS because the carriers are different.

 

[gavin]

The speedo on '98 and up reads off the raw vss signal from the rear axle. Different size tires will affect the readout but gears will not.

der... forgot about that

 

[TBMounty50]

der... forgot about that

Don't worry, it got me too. I even spent time calculating a ratio that would compensate for the 31's and correct the speedo.

 

[Ray Lobato]

Want to save some money?

Keep your setup as is and take out both diffs from the donor vehicle, so when you are ready to go to 410's take the diff's from the donor truck and have them put the new gears into those, also this the best time to have a locker installed as you will only have to open up your diff once.
The gear guys DON'T like having to replace the gears in the front diff, because they have to take so much off to get to it. They will give you a better price because you already took out the differentials for them. The axles don't have to be on the truck for them to change them out, or even adjust them.