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Used Wrong Drain and Fill Washers for Differential

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Used Wrong Drain and Fill Washers for Differential

 
Old 05-13-2019, 05:35 PM
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Default Used Wrong Drain and Fill Washers for Differential

Hi all. Had my S2000 serviced at an independent Honda shop. One of the things they did was drain and refill the differential with Amsoil 75w-110. Looks like the copper washer (90402-PCZ-003) was used for the drain bolt, while the aluminum washer (90401-PCZ-003) was used for the fill plug. The washers are reversed. Is this going to be a problem? There do not appear to be any leaks.

Go easy on me...
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Old 05-13-2019, 06:01 PM
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I don't know the reason for the difference but I think you'll be fine, they perform the same function of being crush washers.
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Old 05-13-2019, 06:26 PM
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I have an opinion, but I don't know the exact reason Honda chose those particular washers:

Both washers are crush-type washers, so leakage shouldn't be a problem. Some manufacturers use copper for both and others reportedly use aluminum for both. In a severely corrosive environment the aluminum drain washer could corrode preferentially over the steel plug because aluminum is less noble in the galvanic series. Pitting corrosion occurs as an electrochemical reaction between dissimilar metals in a saline aqueous environment. It's sort of a makeshift battery that attacks the least noble of the two metals. Since the aluminum washer is replaced with each fill, a little corrosion is no problem.

Copper is more noble than aluminum in the galvanic series, so in a very corrosive environment the corrosion would occur to the aluminum diff housing where it touches the copper washer. But since the copper washer is extremely small in volume compared to the aluminum housing, any galvanic cell would be insignificant. In my opinion, the Honda engineers chose an aluminum drain washer over a copper one just to be certain they don't have issues in extreme environments.

The fill plug isn't a problem.

If the copper washer on the drain plug bothers you, I suggest you dab a little grease around the plug and call it a day.

I'm a Metallurgical Engineer and have a lot of experience with corrosion issues, which is where I am drawing this info from, not from any specific knowledge on diff washers.
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Old 05-14-2019, 06:57 AM
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The bolts have the same thread but different head sizes (23mm fill and 24mm drain) for obscure reasons. I changed my differential fluid two days ago and was thinking to myself that perhaps the different washer material is just there to help identify the bolts during maintenance. My procedure is remove the fill bolt, remove and replace the copper washer, and set aside. Same for the drain and the aluminum washer. Easy to identify the bolts when time to replace and torque.

Trying some AmsOil 75W-110 GL-5 synthetic hypoid gear oil in the differential. The bottles have a wide mouth and the little bottle pump won't screw on! Some of this now comes in squeeze bags. But the diff takes less than quart so it's not debilitating. This oil is clear, unlike the red tint of LE-1605 which has been in the car for a couple of years. Barely a smudge of color on the magnetic plug in the differential after about 8,000 miles over the past couple of years. Same for the Royal Purple SyncroMax in the gearbox with an aftermarket magnetic drain plug. Wanted to try Amsoil there too (because we all know AmsOil will even cure cancer) but the boutique dealer was out of town and then never responded. No local source for the Royal Purple but the dealer had MTF. It really doesn't seen to matter a bit as long as "spec" oil us used. Sent an engine oil sample to Blackstone.

-- Chuck
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Old 05-14-2019, 07:04 AM
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Originally Posted by Chuck S View Post
The bolts have the same thread but different head sizes (23mm fill and 24mm drain) for obscure reasons. I changed my differential fluid two days ago and was thinking to myself that perhaps the different washer material is just there to help identify the bolts during maintenance. My procedure is remove the fill bolt, remove and replace the copper washer, and set aside. Same for the drain and the aluminum washer. Easy to identify the bolts when time to replace and torque.
-- Chuck
This is the reason. Maybe, the reason for that 3/8" female drive slot, for the transmission drain. Though, I believe thread diameter is different for the filler bolt. Prolly, just a old-time convention thing.
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Old 05-14-2019, 09:31 AM
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Both differential bolts have the same torque spec (not surprising as they have the same thread). The torque spec on the gearbox fill and drain bolts is different which indicates their threads are different (but I've not tried swapping them). I have to use a crow-foot wrench fitting on my torque wrench for the differential fill bolt.

-- Chuck
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