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Discussion Starter #1
Ok, here we go.......

2006 GTP, manual trans, got the car in September 2013, as of now 47k on the clock. I am looking for the best fluid to put in it. Yes, I have all the similar F40 complaints that everyone seems to have (notchiness, 2-3 shift, blah blah blah.....). And yes, I am aware that GM has their "special" fluid that is "lifetime." I'm looking to change the fluid out to see if that can help with some of these issues, and to maintain it. I want to know if anyone has had any experience with something different that doesn't involve me going to a dealer. Redline MTF? Synchromesh? Royal Purple gear oil? Anything different that gave better performance than OEM? I've been searching for a while (this forum, Saab forums, etc.) and cannot get a good, solid answer to what would be best.
 

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I haven't used Amsoil manual transmission fluid, but their auto trans fluid is top of the line and I have no complaints with it over the decade I've been using it between four vehicles. It's lower cost than anything the dealer tries to sell you. http://www.amsoil.com/shop/by-product/transmission-fluid/manual/

Manual trans fluid is often overlooked, as it should be changed every 60K miles depending on driving style. Lexus also offers a "lifetime" fluid - bad marketing for those who own, instead of lease for a few years.

Almost all light vehicle manual transmissions are synchronized, so you should use a full synthetic fluid that matches GM's grade/viscosity (knowingly 5W30) and you'll be fine. It should specify the fluid in the owners manual.

The reason you won't get an answer to 'what is best' is because there are so many options out there. Just stick with a full synthetic and you'll be fine. If the current oil drains black and/or seems dirty, it's wise to change it again after 5-10K miles just to drain any crud out of the transmission. I know a 9-5 Aero owner and he has no clue what the local shop (not the dealer) puts in his transmission but with 370,000kms on the original transmission, changing the oil regularly is key.
 

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I use nothing but the recommended ac delco trans fluid. Its 32 bucks a qt.
 

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...you should use a full synthetic fluid that matches GM's grade/viscosity (knowingly 5W30)...
Getting confused with the engine oil? The manual trans fluid specified by GM has a GM part number and also a Castrol number. I've looked it up before and the Castrol product is a 80-90 GL4 duty rating gear oil, with a red tint though. It looks like ATF but it is NOT.

...Just stick with a full synthetic and you'll be fine. If the current oil drains black and/or seems dirty, it's wise to change it again after 5-10K miles just to drain any crud out of the transmission...
:agree:
Lucas Synthetic 75-90W Gear Oil

This is what I put in when I replaced the clutch in my '07. When doing this, I removed the '07 trans that came in the car and installed a brand new F40 (ebay) with the '06 gearing. For this new trans, I filled it with Lucas. I can't really say that the new/old trans had any different shifting feel, but it seems like my new one warms up quicker(idk if that's really the explanation). Just like everyone else, I have noticed that when it's very cold out, my trans doesn't like going into 1st & 2nd gears. But after driving for 30 seconds, this clears up. My old '07 trans needed more driving time than that before it would shift normally.

And for what it's worth...
The '06 MT2 gearing is MUCH better for a daily driven car. The gears are spread out more, allowing you to reach higher speeds per rpm which means less shifting during normal driving, and never using 6th gear unless on the highway. 5th gear in the MT2 trans is about equivalent to 6th in the MU9 trans. MU9 = 65mph @ 2100rpm in 6th. MT2 = 69mph @ 2000rpm in 6th. I'll take the lower cruising rpm. But that's just me and I will also say this: the MU9 trans will make the car accelerate FASTER. I noticed right away that acceleration was affected, but it's only a slight difference.
 

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Discussion Starter #5
Thanks for the feedback. Been very busy and haven't had the chance to reply. After searching the ends of GM forums (Saab, Vauxhaull, even Cobalt forums..........) ended up going with Redline MTL (75W80), seemed to be the best fitting fluid for the F40 trans. Ran $16 a quart, and sweet baby jesus it made a great difference. It's a dedicated manual trans fluid and closest to factory spec, but shifting is greatly improved, getting better economy, and feels next to a brand new trans! Yes I do still get a rough shift once in a while, but I'm thinking it's just the way the trans is. Shifts with a LOT more ease now, mainly from 1-2 and 2-3. 100% recommended, 100% satisfied.
 

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Oh, and fluid looked decent when it was drained, good red tint to it and not too dirty. And for what its worth, I have no idea what correct viscosity is for the ACDelco, OE Castrol Burmah, whatever-they-want-to-call-it is. From what I have read it's gear oil rating is a 75W85, but its true viscosity is closer to a motor oil weight, 5W30. I was worried that gear oil would be a little too thick, and sychromesh a bit too thin. But I got something that works. The F40 sounds versatile enough to run anything synthetic, and everyone has and will get different results for different fluids. My stuff works, and I like it. I'm very sure Amsoil, Lucas, RP, anything higher quality will be ok.
 
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