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Discussion Starter #1 (Edited)
How to Change Gear Oil/Differential Fluid​


Overview:
This tutorial will walk you through the process of changing the gear oil/differential fluid on the 124 Spider.

A note regarding fluid selection:
According to Ameridian's blog, FCA recommends a 75W-90 GL-5 hypoid gear oil with FCA's multi-vehicle limited slip additive (for the Abarth). I called AMSOIL's technical team and they explained that our 75W-90 Severe Gear actually has limited slip friction modifiers already formulated in the gear oil, and that I don't need to add any extra. I already had some additive on hand, but decided not to use it. If you end up using something else, ensure that it already has limited slip friction modifiers formulated in the oil, or plan to purchase FCA's additive. If you have a Classica/Lusso, you don't have a limited slip differential, so you don't have to worry about the limited slip additive. Use whichever fluid you feel comfortable with; this thread is intended only to provide instruction on how to change the fluid.

I used AMSOIL's Sever Gear 75W-90 because it has exceptional extreme pressure protection, it runs cooler than most fluids, is already formulated for limited slip differentials, and is now available (as of August 1st 2018) in a package that makes filling easier than anything else on the market. You can find it here:

https://www.amsoil.com/shop/by-product/gear-lube/severe-gear-75w-90/?code=SVGPK-EA&zo=5224266

A note regarding service intervals:
I like to change gear oil often based on the ISO particle count oil analysis reports I've seen of gear oils and the effects silicon have on metallic wear. Silicon is a contaminant that enters the differential through the breather. This wear is typically out of range of a typical oil analysis report (5-15 microns) and will not show up on cheaper reports until it's too late. I like to change the fluid to get the abrasive silcon out before it causes wear.

Tools Required:
- 23mm and 24mm sockets and ratchet
- Shop towels
- Torque wrench
- Ramps/jack/jackstands
- Oil pan

Part Required:
- 1 Quart of 75W-90 Hypoid Gear Oil (see comment above). Actual fill spec is 0.63 quart/0.6 liter.
- Optional: Replacement washers for the drain/fill plugs (Available on Amazon.com), part number 995-41-400 according to a thread on Miata.net. I generally replace these every other service or if I see one is damaged.

Procedure:
1. Lift the car securely and as level as possible. The differential is on the back. Note the location of the drain (blue) and fill (red) plugs.


2. Remove the fill plug first, and remove the drain plug only if the fill plug has been removed.


3. Clean the metal shavings off of the drain plug magnet. Reinstall the drain plug and torque to ~40N-m (official spec is 40-53 N-m).

4. If you're using the AMSIOL Easy-Pack, remove the nozzle, peel back the seal, cut the tip off of the nozzle, and screw the nozzle back on.

5. Fill the differential until fluid starts coming out. Wait for the fluid to stop dripping, and thread the fill plug back on. Note, keep your oil pan underneath while you're filling. I made a video of this one to show how easy it is.

6. Re-tighten the fill plug and torque to ~40N-m (official spec is 40-53 N-m).

Here's what my factory differential oil looked like at ~4700 miles.
 

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Wow, this is amazing XR, I was literally just about to ask about this process.
 
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Discussion Starter #3
Is this Abarth specific?
I don't think so. The non-abarth should have the same drain and fill plugs in the same location. I know for a fact the fill spec is the same.

Sent from my BBF100-2 using Tapatalk
 

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@XtremeRevolution

Slightly off topic, I know your car is a manual but would you happen to know what type of ATF I should use when changing out the auto trans fluid? The manual states the MOPAR brand but obviously I'd like to see if there is a more accessible/better off the shelf alternative.

Thanks.
 

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Discussion Starter #6
@XtremeRevolution

Slightly off topic, I know your car is a manual but would you happen to know what type of ATF I should use when changing out the auto trans fluid? The manual states the MOPAR brand but obviously I'd like to see if there is a more accessible/better off the shelf alternative.

Thanks.
I'm not sure about that to be honest with you. It looks like the fluid needs to meet JWS 3309 spec, which I don't think you'll find off the shelf. Our multi-vehicle OE and Signature Series ATFs meet that specification, if you're interested.
 

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Discussion Starter #7
Sure, I'd be interested. I guess what I mean by off the shelf is anything on Amazon or I could buy online that's not OEM/dealership only.
It looks like Mobil 1 has a 3309 ATF also: https://amzn.to/2MaDBAb

Shoot me a PM with what you'd be interested in ordering and I can get you a quote shipped.
 

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Are the replacement washers the same dimensions as the ones that go on the manual transmission fill and drain bolts? I still have a few of those kicking around.
 

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Discussion Starter #9
Are the replacement washers the same dimensions as the ones that go on the manual transmission fill and drain bolts? I still have a few of those kicking around.
I think so but don't quote me on that.
 

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Are the replacement washers the same dimensions as the ones that go on the manual transmission fill and drain bolts? I still have a few of those kicking around.
Per this tutorial, the diff & trans crush washers are the same for a M18 bolt.
http://revlimiter.net/blog/2017/02/nc-mx-5-miata-2006-2015-oil-trans-diff-fluid-change/

I found some M18 washers on eBay for a few bucks. https://www.ebay.com/itm/M18-18mm-Crush-Solid-Copper-Washers-Solid-10-Pieces-OD-24-mm-ID-18-1-mm/223081029844?ssPageName=STRK:MEBIDX:IT&_trksid=p2060353.m2749.l2649
 

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I don't think so. The non-abarth should have the same drain and fill plugs in the same location. I know for a fact the fill spec is the same.

Sent from my BBF100-2 using Tapatalk
Having already changed the diff (and fluid) in my Classica, I can verify there's no difference from what you have.

Edit: as a side note, I installed a complete "pumpkin" from an Abarth, and used Mopar 75W85 GL5 synthetic w/ LSD additive. It's been doing fine since early this spring with both race and street use. I'll examine the fluid closely this fall.
 

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Discussion Starter #12
Having already changed the diff (and fluid) in my Classica, I can verify there's no difference from what you have.

Edit: as a side note, I installed a complete "pumpkin" from an Abarth, and used Mopar 75W85 GL5 synthetic w/ LSD additive. It's been doing fine since early this spring with both race and street use. I'll examine the fluid closely this fall.
By "examine" do you mean send it out for oil analysis?

How hot does your differential get?
 

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How to Change Gear Oil/Differential Fluid​



Overview:
This tutorial will walk you through the process of changing the gear oil/differential fluid on the 124 Spider.

A note regarding fluid selection:
According to Ameridian's blog, FCA recommends a 75W-90 GL-5 hypoid gear oil with FCA's multi-vehicle limited slip additive (for the Abarth). I called AMSOIL's technical team and they explained that our 75W-90 Severe Gear actually has limited slip friction modifiers already formulated in the gear oil, and that I don't need to add any extra. I already had some additive on hand, but decided not to use it. If you end up using something else, ensure that it already has limited slip friction modifiers formulated in the oil, or plan to purchase FCA's additive. If you have a Classica/Lusso, you don't have a limited slip differential, so you don't have to worry about the limited slip additive.

I used AMSOIL's Sever Gear 75W-90 because it has exceptional extreme pressure protection, it runs cooler than most fluids, is already formulated for limited slip differentials, and is now available (as of August 1st 2018) in a package that makes filling far easier than anything else on the market. You can find it here:

https://www.amsoil.com/shop/by-product/gear-lube/severe-gear-75w-90/?code=SVGPK-EA&zo=5224266

A note regarding service intervals:
I like to change gear oil often based on the ISO particle count oil analysis reports I've seen of gear oils and the effects silicon have on metallic wear. Silicon is a contaminant that enters the differential through the breather. This wear is typically out of range of a typical oil analysis report (5-15 microns) and will not show up on cheaper reports until it's too late. I like to change the fluid to get the abrasive silcon out before it causes wear.

Tools Required:
- 23mm and 24mm sockets and ratchet
- Shop towels
- Torque wrench
- Ramps/jack/jackstands
- Oil pan

Part Required:
- 1 Quart of 75W-90 Hypoid Gear Oil (see comment above). Actual fill spec is 0.63 quart/0.6 liter.
- Optional: Replacement washers for the drain/fill plugs (Available on Amazon.com), part number 995-41-400 according to a thread on Miata.net. I generally replace these every other service or if I see one is damaged.

Procedure:
1. Lift the car securely and as level as possible. The differential is on the back. Note the location of the drain (blue) and fill (red) plugs.


2. Remove the fill plug first, and remove the drain plug only if the fill plug has been removed.


3. Clean the metal shavings off of the drain plug magnet. Reinstall the drain plug and torque to ~40N-m (official spec is 40-53 N-m).

4. If you're using the AMSIOL Easy-Pack, remove the nozzle, peel back the seal, cut the tip off of the nozzle, and screw the nozzle back on.

5. Fill the differential until fluid starts coming out. Wait for the fluid to stop dripping, and thread the fill plug back on. Note, keep your oil pan underneath while you're filling. I made a video of this one to show how easy it is.
https://www.youtube.com/watch?v=SoG26Tj_SM4&t=

6. Re-tighten the fill plug and torque to ~40N-m (official spec is 40-53 N-m).

Here's what my factory differential oil looked like at ~4700 miles.





Xtreme, when you say you like to change the fluid often, how often is that? I am just at 2900 miles. I am not sure what all the issues with shifting and such. Best I can tell, Spidy shifts just fine, and any shifting issues are definitely operator induced
 

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Discussion Starter #14 (Edited)
Xtreme, when you say you like to change the fluid often, how often is that? I am just at 2900 miles. I am not sure what all the issues with shifting and such. Best I can tell, Spidy shifts just fine, and any shifting issues are definitely operator induced
With regard to service intervals, I was talking about differentials alone. The issue here is the constant heating and cooling, while the breather is exposed to road dust on a regular basis, causing silicon contamination that is abrasive. This, combined with a low sump volume, causes wear over time. This isn't as much an issue for transmissions as it is for differentials, which are closer to the road and lower to the ground. I will most likely change my differential oil every 2 years with my driving. I drive around 3000 miles a year.

As for when to change the MTF, you'll start to notice shifting quality degrade over time, but generally I recommend every 30,000-45,000 miles. Changing it early won't hurt, and getting the break-in oil out early on the initial change will certainly help as well.

Keep in mind, as a bit of a perfectionist, I'll recommend people do what's best for their vehicles, not the minimum necessary.
 

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Extreme
changed my MTransmission Oil today, with the pump it took 2 1/3 QUARTS. Mechanic asked me if there was a OIL gage for the trans, I told him mostly likely NO. Anyway when he drained it the bold had metal on it. Once finished screwed the draining bolt and started to fill from the above bolt till it started to overflow.

Is 2 1/3 quarts what's needed. tia
 

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Extreme
changed my MTransmission Oil today, with the pump it took 2 1/3 QUARTS. Mechanic asked me if there was a OIL gage for the trans, I told him mostly likely NO. Anyway when he drained it the bold had metal on it. Once finished screwed the draining bolt and started to fill from the above bolt till it started to overflow.

Is 2 1/3 quarts what's needed. tia
Yes that's approximately correct. The method you described is the way it should be done.
 

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I tought I would get some metal chunks on the bolt, but were very fine. One last mode, waiting for the REMUS axleback, I told him to slack the exhaust bolt which he did and re=tightened them.
 
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By "examine" do you mean send it out for oil analysis?

How hot does your differential get?
1) no, but that's not a bad idea, come to think of it.

2) I haven't measured it. What kind of use do you think would produce the highest peak number or a consistently high number, for sake of measuring? I have thermocouples and thermally conductive grease, so I can put a probe just about anywhere on the diff. I'm guessing somewhere out of airflow would be good, but not quite sure where the best place to be to get closest to the "inside view."
 

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Discussion Starter #19 (Edited)
1) no, but that's not a bad idea, come to think of it.

2) I haven't measured it. What kind of use do you think would produce the highest peak number or a consistently high number, for sake of measuring? I have thermocouples and thermally conductive grease, so I can put a probe just about anywhere on the diff. I'm guessing somewhere out of airflow would be good, but not quite sure where the best place to be to get closest to the "inside view."
Back of the diff, lower half. That would be about the best place you could put it. As for driving conditions, high load, low speed, with low airflow and little cool-down time. Auto-x racing would be a good example.

Let me know if you want to get oil analysis done and I can get you a kit with a good ASTM Certified lab.
 

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I did this and the MT fluid change tonight. This is a no-brainer and couldn't be simpler with the Amsoil pack with spout. Your shipping is ridiculously fast. I took 10 mile test drive and the rear end didn't seize up so I must have done it right.
 
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