Need help making a decision (regarding diff)

[ugaexploder]

Wanted to get your take on what I should do here. Car is in the shop to get a complete overhaul done for subframe, bushings, etc. Shop told me they found metal shavings in the diff fluid.

Placed an order for a diffsonline rebuilt M variable 3.62 ratio diff thinking they had a quick turnaround compared to the other options. Found out they are essentially made to order so I'm thinking about going 3.85 wavetrac since it will probably 80% road car.

Shop called me and said they have a slightly used OE diff they were able to scrounge up for $1k. Diffsonline turnaround is minimum 4 weeks from the sound of it.

What would you guys do in this situation?

[eacmen]

If you can wait for diffsonline I would go that route.

[S54330Ci]

Couple of thoughts:

1) If 80% of your driving is on the street - stay with the M Variable and save some money. Doubtful you will notice the difference between the M Variable and the Wavetrac on the street.
2) Bumping the rear drive ratio will improve the feel of the car off the line and through the gears so this is a good direction to go.
3) Use this link to download an Excel spreadsheet that will help calculate your gearing. This way you can play with final drive ratios to determine max speeds in each gear. Technical Information | Diffsonline (click on the Gearing Calculator)
4) Diffsonline differential will likely cost 4x what your shop is asking for theirs, so you'll need to determine if the extra money is worth it. Again, for 80% street driving I would go with the shop's diff assuming it is in good shape.
5) If you see yourself doing more and more track days then I'd opt for the Diffsonline diff. I'd opt for the 4.10 ratio but it will raise your engine revs and might be too uncomfortable on the freeway.

[ugaexploder]

If you can wait for diffsonline I would go that route.

I don't mind the wait but I feel bad having the car at the shop for at least another 4 weeks waiting for the diff.

[eacmen]

I don't mind the wait but I feel bad having the car at the shop for at least another 4 weeks waiting for the diff.

Is the shop giving you a hard time? Most shops this happens on a semi frequent basis

[ugaexploder]

Couple of thoughts:

1) If 80% of your driving is on the street - stay with the M Variable and save some money. Doubtful you will notice the difference between the M Variable and the Wavetrac on the street.
2) Bumping the rear drive ratio will improve the feel of the car off the line and through the gears so this is a good direction to go.
3) Use this link to download an Excel spreadsheet that will help calculate your gearing. This way you can play with final drive ratios to determine max speeds in each gear. Technical Information | Diffsonline (click on the Gearing Calculator)
4) Diffsonline differential will likely cost 4x what your shop is asking for theirs, so you'll need to determine if the extra money is worth it. Again, for 80% street driving I would go with the shop's diff assuming it is in good shape.
5) If you see yourself doing more and more track days then I'd opt for the Diffsonline diff. I'd opt for the 4.10 ratio but it will raise your engine revs and might be too uncomfortable on the freeway.

This is my thought process as well...although the wavetrac would be so sweet, not sure if I want to fork over the extra money plus my diff.

I'm going to head up there tomorrow to see what condition the diff is in. I asked the guy on the phone if it was rebuilt and he said yes...either way, i'm going up there to pick up steering rack and diff, and some other parts I need to return.

appreciate your thoughts on the matter!

[ugaexploder]

Is the shop giving you a hard time? Most shops this happens on a semi frequent basis

They've been super cool about everything so far, just worried they are going to get impatient with me since there have been a couple times we had to put a hold on things due to delay on parts

[TexaZ3]

They've been super cool about everything so far, just worried they are going to get impatient with me since there have been a couple times we had to put a hold on things due to delay on parts

Most shops deal with this every day.

[Altaran]

This is my thought process as well...although the wavetrac would be so sweet, not sure if I want to fork over the extra money plus my diff.

I'm going to head up there tomorrow to see what condition the diff is in. I asked the guy on the phone if it was rebuilt and he said yes...either way, i'm going up there to pick up steering rack and diff, and some other parts I need to return.

appreciate your thoughts on the matter!

When getting the diff rebuild I would definitely replace then locking body with a traditional LSD. GKN Viscolocks are not known for their longevity.
I have no experience with Wavetrac, that seems to be a stateside thing. The general feedback on this forum seems good with them.
In Europe the economical solution is the ZF 4 disc unit, I opted for a Drexler 8 disc unit which is a bit more spendy.

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[sapote]

When getting the diff rebuild I would definitely replace then locking body with a traditional LSD. GKN Viscolocks are not known for their longevity.

How? What could take place of the stock viscous pump lock unit and create the compression force on the clutch stack? A dummy big spacer and spider shaft ramp? This sounds like a major changing parts or mod.

[bmwfnatic]

How? What could take place of the stock viscous pump lock unit and create the compression force on the clutch stack? A dummy big spacer and spider shaft ramp? This sounds like a major changing parts or mod.

He means replacing the entire GKN LSD Core unit with a ZF one for which quality parts to rebuild it are readily available, this is the most common fix done in Europe.

[Feffman]

He means replacing the entire GKN LSD Core unit with a ZF one for which quality parts to rebuild it are readily available, this is the most common fix done in Europe.

This may be more expensive but long run it's by far, IMHO, the best long term and performance option.

[bigjae46]

Metal shavings? How much? It is perfectly normal
to find some metal in the diff fluid.

I’d replace if there were nuggets of metal or if you found pieces of a bearing cage or roller. If they found glittery diff oil then it’s fine.

Don’t go used if you have to replace. You’ll be right back at square one at some point soon. Get it torn apart, cleaned and rebuilt. Install new bearings, races and seals, throw in a RacingDiffs clutch pack. Be aware if it’s a V2 then the rebuild is more challenging. The V1 is easy.

Should be relatively straight forward as long as the ring and pinion gears are good.

[eacmen]

Metal shavings? How much? It is perfectly normal
to find some metal in the diff fluid.

I'd replace if there were nuggets of metal. If they found glittery diff oil then it's fine.

Is the glittery residue the clutch material from the LSD?

[bigjae46]

Is the glittery residue the clutch material from the LSD?

Partly. Also it’s bearing and race material.