GL4 vs. GL5 gear lubricants

[wood_e]

At 94k on my audi a4 I changed the trans lube. I have 102k on it now I don't know what was in it before. I used castrol syntec 75w90. I didn't know that Audi says to use a GL4 lubricant. The castrol is GL5.

Now... whats the difference? Should I switch the stuff out? It was a total mess changing the lubricant... and its cold as all heck outside.

Will there be any problems with the GL5 in my transmission?

Any comments are appreciated!

Thanks!

 

[RogerKlugerAus05]

If Audi says use GL-4 then use it. Some manual transmissions suffer corrosion using GL-5 oils. Personally I use Redline MT90.
Roger

 

[Wrehch]

GL5 gear oils can cause problems with some of the yellow metals used in light duty synchronized transmissions. Unless it's a multi spec (GL4 and GL5) gear oil I would change it out to a GL4 oil.

 

[Pablo]

The real problem isn't that all GL5's will attack brass and bronze, because modern synthetic GL5's won't.

The problem is related to the additive pack and FM's to be a GL5 are NOT what you want at your MT syncro interface. Yes you need FM's but no you don't want nor need the EP additves. Too slippery in the wrong kind of way.

 

[wood_e]

So, bottom line: Change it NOW, change it when time permits (and it isn't cold), or leave it for a while?

I'm not sure if the castrol is a multi spec....

 

[bmwtechguy]

Change it when time/weather permits. I can't see how you will do immediate damage to anything. Pablo's comments are right on. If you notice any negative effects relating to shifting, get it out sooner than later. Redline MT-90 and Amsoil MTG are both popular 75W-90 GL4 gear oils for manual gearboxes.

 

[Brogy]

I had the mobil 1 gl5 in my gl4 application. Drove on it for 10k miles no problems. However I did notice when I went to amsoil gl4 it made a BIG difference. All grinding has vanished, and it's no longer notchy when cold.

My guess is that since the GL5 has twice the pressure additives as GL4, too much pressure forced oil off of the syncros not lubricating them properly. Just my uneducated guess. That or the stuff is slippier.

 

[wood_e]

I love this forum. Thanks guys! I haven't noticed any ill effects but I'm leaning towards amsoil. I need my trans to last a while...

 

[wood_e]

BTW: other than cold I haven't noticed any problems in my trans... once warmed it shifts fine. When its warmer out though I'll put some amsoil in

 

[wood_e]

well I decided to put in some synchromesh - HUGE difference! Smoother shifts, especially from 1-2 cold

 

[unDummy]

Sychromesh is not a 90wt and won't protect a transmission that calls for a 90wt.

 

[mechtech2]

There are 90 weight oils that won't protect as well as the thinner Pennzoil Synchromesh.

 

[PT1]

Quote:

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The real problem isn't that all GL5's will attack brass and bronze, because modern synthetic GL5's won't.

The problem is related to the additive pack and FM's to be a GL5 are NOT what you want at your MT syncro interface. Yes you need FM's but no you don't want nor need the EP additves. Too slippery in the wrong kind of way.

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This is 100% correct....have seen many torn down failures because of failure to read the oil spec.