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Discussion Starter · #1 ·
I ordered some Redline transmission oil from IPD here. I used their filter (my garage) and it showed up for my R. I thought I would try the Redline instead of the OE oil for something different. I've been running it for maybe 200- 300 miles now and not really any change other than the shifting has gotten a little harder or notchy. Upon further inspection, I see that it's GL-5. I thought we were supposed to run GL-4 in the M66, right? This concerned me, so I called IPD and expressed my concern about it being GL-5 and not 4 and also pointed out that the Volvo OE stuff was in fact GL-4. The tech basically told me my concern was invalid, and I don't need to worry. He used the analogy of mid-grade gasoline to premium and he also said someone that works at IPD uses the GL-5 in his R. Are you on here?

Are my concerns valid, and do I need to replace the oil again with GL-4? I'm a bit confused.
 

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http://www.widman.biz/uploads/Transaxle_oil.pdf


Edit:

From IPD's description:

Red Line's most popular gear oil, this is the preferred product in nearly all car and light truck differentials, both conventional and limited-slip. 75W90 is preferred for most racing applications. It contains friction modifier which is recommended for limited-slip units. 75W90 Gear Oil can be used in many transmissions and transaxles; however, other Red Line lubricants have better frictional properties for rapid synchronization. Exceeds API GL-5.

This, in addition to the article I linked, would make me hesitant to use this product. YMMV


Edit Edit:

I believe this is the more correct product that IPD offers - https://www.ipdusa.com/products/8602/109496-redline-mt-90-weight
 

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Discussion Starter · #3 ·
Hmm. Thanks for that.

I probably should grab some GL-4 to put back in there..
 

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I have the Redline in my transmission. I did notice it got slightly more notchy afterwards, only really when cold. It's been in there for at least 3 or 4 years now, with no issues whatsoever.
 

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There's a lot of good information out there regarding the GL-4 vs. GL-5 delineation as it applies to transmissions(and not just gearboxes in general) so I'll let you have at it. I'll just say that you were right to call IPD to seek confirmation and I'm surprised that you received that response. Granted, your transmission isn't going to implode but I would replace the fluid with GL-4 as soon as the shipment comes in.

Edit:
I missed R-Pow3R3d's post. That PDF pretty much sums it up.
 

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Discussion Starter · #7 · (Edited)
Does someone have the Volvo PN for the M66 oil? (don't have access to VIDA for a bit) I've seen a few different ones: 31280772, 31280771. Are these the same and the right ones to use?

Edit: I called the local auto parts store and gave the guy those numbers and he said the Redline stuff came up as the recommended to use..interesting
 

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The main concern for trans oil properties in the M66 is the brass hardware. Not all gear oils have the right moderators to be compatable with yellow metals and what you need to be concerned with.

Due to the age of my tranny and the mild scaring I have building on my sixth gear (whine), not to mention I frequently haul over a ton around with my R has me switching to Amsoil Severe Gear 75W-90 as part of my rebuild.

Its a GL-5 oil due to it meeting the higher standard, but its also compatible for trannys with brass parts so you can use it in vehicles with that require the GL-4 spec.

So yes, its possible for some manufacturer's GL-5 spec fluid being compatible with the M66.
 

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Correction, I have the Redline MT90, not the original linked Redline fluid the OP is talking about. So yes, mine is GL-4. Note the product page specifically discusses why using GL-5 is not a good idea for transmissions with brass parts:

http://www.redlineoil.com/product.aspx?pid=46

I had it put in before IPD had the "My Garage" compatibility tool and went off recommendations here in an older thread.
 

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Correction, I have the Redline MT90, not the original linked Redline fluid the OP is talking about. So yes, mine is GL-4. Note the product page specifically discusses why using GL-5 is not a good idea for transmissions with brass parts:

http://www.redlineoil.com/product.aspx?pid=46

I had it put in before IPD had the "My Garage" compatibility tool and went off recommendations here in an older thread.
I was going to ask which one, but you delivered. I PM'd [email protected] to get his input on the topic since it was their recommendation. Once he sees it, hopefully we'll get a response.
 

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Discussion Starter · #12 ·
I was going to ask which one, but you delivered. I PM'd [email protected] to get his input on the topic since it was their recommendation. Once he sees it, hopefully we'll get a response.
I'm not sure how I got that oil, or IPD has changed something. I'm positive though it was a recommendation, I don't know why or how I would have bought it otherwise.
 

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Some GL-5s are not brass compatible, some are, so the above statement isn't always correct. Many late model manual transmissions with brass synchros and shift forks also specify either GL-4 or GL-5, so some really outdated assumptions are being passed off as fact here.

I'm giving the right GL-5 severe duty that is brass compatible a try because I stress my tranny more than most people here do because I tow stuff. My main concern will be if its too slippy and changes they synchro action in a way I don't like. If so all I have to do is drop back down to a GL-4.

With 6th gear being a little noisy after the volvo dealer didn't top my tranny back off after pulling the AG (was almost a half a quart low and scarred the gear on a top speed run in top gear) I'm hoping the pros will outweigh the cons.
 

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Stealthy, the only thing that worries me about what you are using is what the oil itself says it's compatible for use with:

Recommended for use in differentials, manual transmissions and other gear applications requiring any of the following specifications: API GL-5, MT-1, MIL-PRF-2105E, Dana SHAES 234 (Formerly Eaton PS-037), Mack GO-J, or the differential (hypoid) gear oil specifications from all domestic and foreign manufacturers such as GM, Ford and Daimler Chrysler. Can also be used in axles where an API GL-4 lubricant is recommended.

I don't think the M66 explicitly meets any of those, does it?

I doubt it's going to do any damage and like you said, it only takes swapping back to OEM to be sorted out. If it was me I'd just go OEM, the correct Redline product, or this Amsoil product, but that's just my $0.02 and they are both irrelevant. lol
 

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I've done my research and its actually more yellow metal safe than many GL-4s so I'm not worried about any kind of damage to the transmission. The only risk is that it may make synchro engagement too soft because it has better slip properties and will effect their bind rate. Then again it is considered safe for synchro-mesh manual transmissions. Its also popular with import rebuilders who are trying to keep their old trannys going as they get long in the tooth. Only real complains are people living in sub-zero temps having a harder time shifting in cold weather before the car warms up. It rarely gets below freezing where I'm at so I'm willing to give it a try.

At this point I rather give my old gears and bearings a little extra slip and cushion since I'm not speed shifting everywhere, lol.

So basically if I'm happy with my synchro engagement I'll be good to go.
 

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I think you're dead on. It's not "quite" the same, but not so different that it's a damage risk. It is yellow metal compatible, but it's not a GL-4 Transmission Fluid replacement, by it's own description. If you like it, great. If not, swap back. Likely, no harm no foul.

Edit:

Practically speaking, what would "too soft synchro engagement" feel like? Would it just be more clutch slip into gears under load?
 

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The synchro prevents you from going into gear for a certain delay time that is directly related to the shift pressure. With a slicker lube I may find that for a certain pressure on the shifter it takes longer for the shift to occur. Then again one advantage of this lube is that it has some friction modifiers in it just for that purpose that also makes it popular with the porsche crowd that have limited slips. Some reviews say that thanks to them it shifts just like a GL-4, though stiffer when very cold.
 
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