Diff replacement needed... Questions

[ChapterM3]

Hey everyone,

Well after 167k miles, I need a new diff and while its out looking to refresh the rear end. It's leaking very badly and is starting to grind while the gears are engaged. So I'm building a parts list and the seemingly endless "While it's out" list. I've researched and searched here but thought to ask this for 2026 opinions

History of the car that's relevant -
- Subframe already reinforced with Turner kit in 2017
- I believe most rear end bushings done also in 2017

Replacement parts list is the following -
- Diff replacement with OEM spec diff (Diffsonline is my go to right now)
- Diff cover with OEM bushings
- Driveshaft (will need center support soon anyway)
- Both Axles (22 years old at this point)
- Subframe bushings

Questions -
- Diffsonline OEM spec still the go-to for our diffs? I do not want to change gearing at all, just OEM spec
- What else should I do bushings wise considering the diff is coming out?
- Any other components you would add to do while this is out?

Thanks in advance!

Jonathan

[Cubieman]

Just a quick observation about your list, you mention replacing the diveshaft as the CSB is old.

The CSB can be replaced on its own, as can the driveshaft CV joint.

Refresh rather than replace that in order to help pay for any rear end bushes that may have not been replaced.

Also especially if you are pulling axles, if your rear wheel bearings are original I would definitely do those.

Edit: Also a good time for parking brake cables, as they are easy to replace and I think <$20 a piece.

[elrichmeister]

I just went through a diff upgrade. I highly highly recommend to get a unit to swap from diffsonline. I went a different route, even though i had some mods done, 3.91 and Wavetrac. In hindsight i should've just gone through factory spec replacement through Diffsonline, especially if you want to stay stock.

[sapote]

It's leaking very badly and is starting to grind while the gears are engaged.

where does it leak badly?
For 2004 I guess you have version 2 diff with the short output shaft on the left side; this would be the side that can leak

A diff should not grind while the gears are engaged (grind even when the car not moving but gear engaged?); sounds like a transmission with bad synchro. Or do you mean it starts to grind when you step on the throttle and put load on the rear wheels?

[uberchris]

I just went through a diff upgrade. I highly highly recommend to get a unit to swap from diffsonline. I went a different route, even though i had some mods done, 3.91 and Wavetrac. In hindsight i should've just gone through factory spec replacement through Diffsonline, especially if you want to stay stock.

Is it the ratio change that you don't care for, or the wavetrac?

[elrichmeister]

Is it the ratio change that you don't care for, or the wavetrac?

I like the ratio change, wavetrac not sure if im using it to is full potential. When i did my diff upgrades, i wanted to save some money, so i sourced the parts and i found a shop to do the ratio swap, i couldnt find a reputable source for the clutch discs, so the shop recommended that we do wavetrac instead.
Long story short i had to replace my axles, not sure if i can blame the shop if they messed up the outer boots, as they're original 20+ years old. In the end i did get what i wanted, but just a lot headaches to get there.
Unless you're doing the work yourself or a shop who knows these cars, go through diffsonline is my advice.

[Bob Sacamano]

I just went through a diff upgrade. I highly highly recommend to get a unit to swap from diffsonline. I went a different route, even though i had some mods done, 3.91 and Wavetrac. In hindsight i should've just gone through factory spec replacement through Diffsonline, especially if you want to stay stock.

Do you mind expanding on why you recommend that?

[elrichmeister]

Do you mind expanding on why you recommend that?

See my comment above is my personal experience. I was sourcing parts separately i think the diff rebuild was fine, but ended up spending more than i wanted to. Going through diffsonline is a lot easier with the core exchange and they have a good track record in terms of quality work.

[ChapterM3]

Just a quick observation about your list, you mention replacing the diveshaft as the CSB is old.

The CSB can be replaced on its own, as can the driveshaft CV joint.

Refresh rather than replace that in order to help pay for any rear end bushes that may have not been replaced.

Also especially if you are pulling axles, if your rear wheel bearings are original I would definitely do those.

Edit: Also a good time for parking brake cables, as they are easy to replace and I think <$20 a piece.

Thank you for this insight, I appreciate it. Currently exploring places in LA to rebuild all of these. Any suggestions in the US that you've used and can vouch for?

I just went through a diff upgrade. I highly highly recommend to get a unit to swap from diffsonline. I went a different route, even though i had some mods done, 3.91 and Wavetrac. In hindsight i should've just gone through factory spec replacement through Diffsonline, especially if you want to stay stock.

I appreciate this insight! I'm more thank likely going to go this route with Diffsonline

where does it leak badly?
For 2004 I guess you have version 2 diff with the short output shaft on the left side; this would be the side that can leak

A diff should not grind while the gears are engaged (grind even when the car not moving but gear engaged?); sounds like a transmission with bad synchro. Or do you mean it starts to grind when you step on the throttle and put load on the rear wheels?

It leaks heavily at the input for the driveshaft, and also a bit on the passenger side output shaft.

The grinding is not really grinding actually, I miss spoke - it's more like a friction sound that I'm hearing from the rear end that I haven't heard before

[adr_M3]

Thank you for this insight, I appreciate it. Currently exploring places in LA to rebuild all of these. Any suggestions in the US that you've used and can vouch for?



I appreciate this insight! I'm more thank likely going to go this route with Diffsonline



It leaks heavily at the input for the driveshaft, and also a bit on the passenger side output shaft.

The grinding is not really grinding actually, I miss spoke - it's more like a friction sound that I'm hearing from the rear end that I haven't heard before

I can vouch for EAS in Anaheim as they know the platform inside and out and are able complete repairs very quickly. I recently had my leaking diff and VANOS line fixed in day while the shop I used to use was going to take upwards of a week for the same job.

[sapote]

Thank you for this insight, I appreciate it. Currently exploring places in LA to rebuild all of these. Any suggestions in the US that you've used and can vouch for?



I appreciate this insight! I'm more thank likely going to go this route with Diffsonline



It leaks heavily at the input for the driveshaft, and also a bit on the passenger side output shaft.

The grinding is not really grinding actually, I miss spoke - it's more like a friction sound that I'm hearing from the rear end that I haven't heard before

Sounds like the input shaft bearings going bad hence the sound, and this causes the shaft wobble, destroyed the seal, leaking. Leaking on the R side output then likely it's V1 diff not V2 as I thought for 2004 year late months. Maybe you don't need a new diff or rebuild, but 3 seals, and bearings.