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Old 03-12-2008, 02:10 PM   #11 (permalink)
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75w90 gear oil is in the range of 10w40 to 20w50. The difference is in the additive package. The gear oil is designed for extreme pressure while engine oil is designed to withstand extreme temperature.

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Old 03-12-2008, 02:14 PM   #12 (permalink)
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Thanks for posting that, tjts1.
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Old 03-12-2008, 03:11 PM   #13 (permalink)
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Exclamation There is a Standard

Link for info on Motor Oil. www.api.org.



Last edited by H4MM3R; 03-12-2008 at 03:19 PM..
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Old 09-27-2008, 06:39 PM   #14 (permalink)
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Originally Posted by tjts1 View Post
Yeah, I think ur right. After reading further about transmissions that can run either ATF or gear oil, mixing traces of gear oil with ATF can cause the oil to clump up and destroy the transmission (or differential in this case). I think I'll just switch them both to synthetic fluids and leave it at that.
I run a Mazda MX5 (Miata) gearbox using gearoil mixed with20% ATF. I was advised to do this by a bloke who is the chief mechanic (has 50 plus staff) for a GM franchise. It immediately reduced crunching selector noise between first and second. He claims that putting ATF in gear is routinely done in his business to reduce noise and to make gearboxes less "sticky".

I wonder if I should cease this practise as I do not want to blow up my gearbox?
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Old 09-27-2008, 06:56 PM   #15 (permalink)
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I did that to an old sube..a 1987. same thing. fluid listed was bizarre thick. Tried synthetic against advice for the year (1987 didn't know what synthetic is) and as complicated as a synchrod, differential mounted dual range one piece tranny is...the synthetic really came through after a few months..dramatically. The key to winning is the wait...

I am going to seek that gm stuff...great test and thanks.
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Old 09-27-2008, 09:34 PM   #16 (permalink)
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Old 10-02-2008, 11:46 AM   #17 (permalink)
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GM Synchromesh Fluid (Made by Penzoil/Quaker State) is the best non-syn tranny fluid you can buy for a FWD Transaxle car. Civic dudes love it , made my other 2 Civic trannys shift like butter.

I had a Escort GT (Mazda 323) which called for ATF so I ran Mobil 1 ATF in the Manual tranny, shifted like crap, I put the Quaker State Synchromesh in and it shifted like BUTTER!

Guys who have DSM AWD Turbo car like Eagle Talons and Mitsubishi Eclipses swear by the Synchromesh fluid as it make this trannys shift so much better and they are VERY prone to grinding.

IMO I would run Synchromesh in any Transmission that specs ATF or Motor Oil for fluid
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Old 10-02-2008, 12:21 PM   #18 (permalink)
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I had the GM synchromesh fluid put in my Tracker transmission on its first change. These tranny's tend to grind the 1st to 2nd shift and that fluid was supposed to help. I have to say I didn't notice better shifting at the time. So for the next change I just went with cheap conventional fluid and noticed that it seems to make the 1 to 2 shift take slightly more effort but its less likely to grind.
I now just wait for the rpms to match before making the shift and it works fine. I have no stop and go traffic so I make the 1-2 shift about 10 times on the way to work so no big deal.

As for friction, I don't think the dealer put in synthetic fluid in the difs or transfer case but I think I am getting more rolling resistence after I put in all conventional oils. It amazes me how much better my neon rolls than the tracker and that extra friction only costs me 6 or 7 mpg. Next change I'm going all synthetic and thin as possible so I'll have to do an A-B comparison on rolling resistence. I imagine in winter the savings should be significant as you can feel all the fluid warm up and the resistence decrease!

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Old 10-02-2008, 04:33 PM   #19 (permalink)
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When the dealership first replaced the tranny fluid in my '99 Metro, it felt like I was rowing a spoon through peanut butter. (Two further synchro failures happened within 30,000 miles of each other following that.) I guess I'll ask before just trusting the manual from now on.

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Old 04-22-2009, 04:59 AM   #20 (permalink)
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Some Gear Lube and ATF Data

I pulled this together for a VW TDI forum. Last update was Oct '07. Most data comes from manufacturer spec sheets, but has been validated and/or expanded with oil analysis. Sorry...it's heavily weighted to Euro and VW fluids.

There's been a steady shift from 80-90 gear lubes to fluids that are basically automatic transmission fluid with some extreme pressure additives in order to improve corporate average fuel economy...so manufacturers can sell more trucks... You can see that the lightest fluids are off the chart...

When it comes to improving fuel economy thru changing fluids, the differential is the largest factor, with tranny second and engine last.

Changing from petroleum to synthetic - even with the same viscosity - can make a significant difference. For example - a class 8 truck (semi) tractor with dual drive axles, when moving from petroleum fluids to real synthetics, can gain 8.3%. 5.25% is the differentials, about .5% is the engine.

I did some highway testing with my old VW diesel - moving from the factory 75W-90 synthetic, to a synthetic synchromesh fluid, down to VW G52, and back up. The move from 75W-90 to the really thin G52 was worth 1.8mpg. In the end I moved back to 75W-90 to keep my 390,000 mile transmission a bit happier.

VI is viscosity index and speaks to viscosity stability as temperatures change. Higher is more resistant to change with temperature.

Transmission fluid viscosity is normally rated at 40C, while engine oils are rated at 100C. And, as already pointed out, the viscosity scales for gear oil and engine oils are different.

Viscosities are in cSt - centistokes - and are essentially a timed flow thru a cup with a hole in it.

(Manual Tranny Fluids)

VI Vis@40C Vis@100C
128 159.0 18.3 = AMSOIL CTL SAE 50 Powershift GL-1
..............16.7 = Motul MOTYLGEAR 75-90 GL-4/-5
..............15.6 = VW G50/G51 GL-4
185 90.0 15.6 = Redline MT-90 75-90 GL-4
..............15.2 = Mobil 1 Synthetic 75W-90 GL-5
..............15.2 = Motul Gear 300 75-90 GL-4/-5
..............15.0 = Elf Tranself Synthese FE 75-90 GL-4/-5
132 116.0 14.9 = AMSOIL AGL 80W-90 GL-5
177 84.5 14.7 = AMSOIL MTG 75-90 GL-4
..... 76.6 14.2 = VW G052-911
133 76.2 11.0 = AMSOIL CTJ SAE 30 Powershift GL-1
183 56.2 10.6 = Redline MTL 70-80 GL-4
194 47.1 9.6 = AMSOIL MTF Synchromesh Trans fluid (GM/Chrysler) GL-?
208 41.6 9.1 = Penzoil Synchromesh trans fluid GL-?
198 34.0 7.5 = Redline D4 ATF Dexron III / Mercon / API GL-4
138 40.5 7.1 = AMSOIL CTG SAE 10W Powershift GL-1
..... 31.2 6.5 = VW G-052-171-A2 GL-?
..... 35.1 6.4 = VW G-055-726-A2 GL-?
..............6.3 = VW G52 (part numbers G052726A2 / G05272601) GL-?

(Automatic Tranny Fluids - except for Redline D4 dual-use)

VI Vis@40C Vis@100C
.............8.3 = Honda CVT Fluid
.............7.6 = Mobil 1 Synthetic ATF

198 33.5 7.5 = Redline D4 ATF Dexron III / Mercon / API GL-4
.............7.4 = Mobil 1 Synthetic Dexron/Mercon
197 32.5 7.2 = Redline Synthetic ATF Dexron II / Mercon
.............7.1 = Mobil 1 Synthetic Multi-vehicle ATF
138 40.5 7.1 = AMSOIL Ford type F auto trans fluid
168 37.4 6.8 = AMSOIL Automatic Transmission Fluid ATF
..........5.5-6 = Ford Mercon SP

Last edited by AndyH; 04-22-2009 at 05:12 AM..
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