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Differential Oil-GL-1, GL-4 or GL-5?  Rate Topic 
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 Posted: 09-27-2017 01:35 am
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Steve Duncan
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I've been spending way too much time trying to figure out what type of 90 wt oil to use in the differential.  It seems EP qualities are a must, but I'm unclear about concerns that these additives will harm yellow metals. Are there any brass or copper components in the differential to be concerned about? If not, then GL-4 or GL-5?

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 Posted: 09-27-2017 10:12 pm
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Esprit2
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Use a GL-5. It's specifically formulated for use with hypoid gears, such as those used in the final drive's crown wheel & pinion. It's consistent with the EP requirement.

GL-4 is formulated for manual transmissions, and it's synchro friendly... ie, those yellow metal parts you're concerned about. It is NOT for the hypoid gears commonly used in crown wheel and pinion of rear axle assemblies.

Back in the day, the JH manual recommended the following gear oils for the rear axle:
Shell Spirax 90EP
BP Gear Oil 90EP
Esso Gear Oil GX 90/140
Castrol Hypoy
Fina Pontonic MP SAE 90
Mobil Mobilube HD90
Texaco Multigear Lubricant EP90
Duckhams Hypoid 90

Note that all those oils are decades old and probably no longer available. But you can use them as a starting point to cross-ref to a modern gear oil.

Or, just shop for a GL-5, EP90 gear oil.

Many modern full synthetic gear oils are dual-rated for both GL-4 and GL-5. One of those would be fine as well.

Back in the old days, most GL-5 oils used compounds of sulfur to provide EP protection for hypoid gears. It was those sulfur compounds that would attack brass components. Many modern gear oils have replaced sulfur with other compounds for EP protection. It's that brass compatibility that allows some EP oils to be dual-rated GL-4 & GL-5.

Regards,
Tim Engel

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 Posted: 09-27-2017 11:10 pm
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Steve Duncan
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Thanks for the information. Just so I'm clear,there are no "yellow metals" in the differential? All the shims are steel?

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 Posted: 09-28-2017 07:14 am
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Frank Schwartz
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Just in case:
20W50 in the four speed trannys
90W gear oil in the five speed trannys

Don't use the wrong ones..

Frank

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 Posted: 09-28-2017 04:15 pm
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Steve Duncan
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Thank you for your response. I have a four speed and have always used Valvoline 20-50 racing oil in it. My question has been what to use in the differential. I know it calls for an EP 90 wt. But I am unclear if I need to be concerned about sulfur content. As I understand it, sulfur content can affect "yellow metals": any bronze or brass parts. I know the four speed transmission has bronze syncos in it, but I can't seem to get a clear answer if there are any bronze or brass parts in the differential. I've never rebuilt one, so I've never seen the internals. Thanks

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 Posted: 09-28-2017 04:25 pm
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Frank Schwartz
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From the owner's manual, there are a number of choices...both for below 32F and above 32F...so assuming you live in a temperate zone you would choose above 32F..
the choices are:
Shell Spirex 90EP
B.P. BP Gear oil 90 EP
ESSO Esso Gear Oil, GX90/140
Castrol Castrol Hypoy
Fina Fina Pontonic MP SAE 90
Mobil Mobilube HD.90
Texaco Multigear Lubricant EP90
Duckhams Duckhams Hypoid 80

So...you have a large number of choices...and my take on it all is that any quality 90 weight gear oil will work just fine.

Regards to all,
Frank Schwartz

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 Posted: 09-28-2017 07:46 pm
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Frank Schwartz
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Oops...I see Espirit2 already listed the recommended gear oils. So,good with a good quality and you should have no problems...
Frank

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 Posted: 09-28-2017 08:04 pm
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Steve Duncan
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No worries. But I'm still hoping to get an answer from anyone who knows if there are any bronze or brass parts in the differential.

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 Posted: 09-28-2017 08:18 pm
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Frank Schwartz
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If I remember correctly, there are no bronze or brass gears in the rear differntial. I remember some years ago, we took one apart...only bearings and steel gears.
Frnk

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 Posted: 09-28-2017 10:37 pm
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Esprit2
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Steve Duncan wrote:
Thanks for the information. Just so I'm clear,there are no "yellow metals" in the differential? All the shims are steel?The Jensen-Healey rear axles have no brass/ bronze parts, and a GL-5 gearoil is to be used.

The J-H 4 & 5 speed transmissions do contain brass synchro rings, and they should not use GL-5.

20W50 motor oil in the 4-spd (high ZDDP is a plus)
90W GL-4 gear oil in the 5-spd. Redline MT-90 is good.

*~*~*~*
Not directly applicable, but...
Yellow metal corrosion due to sulfur-based EP additives is not instant death, or even over-night. No more than wear due to a lack of EP or anti-wear additives is immediate. The long term life expectancy will be greater if the correct gear oil is used, but failure won't happen right away without it.

Sometimes certain synchro transmission applications are given GL-5/ EP gear oil recommendations because of the high loads being imposed on them. Any damage due to corrosion will take place at a much slower rate then any damage due to a lack of EP protection, so the lesser of two evils is chosen.

Don't get too paranoid about "NEVER" =8<O putting GL-5 gearoil in a synchro transmission. Follow the manufacturer's recommendation. I have several sporty cars that require a GL-5 in the synchro transmission... but no J-H does.

Regards,
Tim Engel

Last edited on 09-28-2017 10:38 pm by Esprit2

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 Posted: 09-28-2017 11:43 pm
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Steve Duncan
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Thank you for providing the answer I was seeking. I got my '74 Mk 2 in 1986. Back then there was only the sub-par manual and a lot of calls to Delta. In the first few years I tried a lot of different oil weights in the 4 speed transmission. I ended up using Valvoline 20-50 racing oil because that's what I was using in the engine (it was more about constantly topping off the gearbox due to the unfix-able rear seal). Sounds like that was a good choice. Guess it's better to be lucky than good. I did change the differential oil back then. Know it was 90 wt. And know it must have had "hypoid" on the label. But never considered sulfur and yellow metals. Having now learned of them, it is reassuring to know it is not a consideration with regard to the differential. As I now find myself going back through the car doing things for the second and third times it is great there are so many more resources to tap (especially this message board).

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