I'm putting a new M5R2 transmission in my 1991 F150 4x4 this
weekend and I'm wondering what you guys think of Mobil 1 synthetic
ATF for this tranny. The manufacturer recommends synthetic ATF for
this transmission and Mobil 1 is readily available here in North
Idaho. Has anyone had good results with Mobil 1? Thanks in advance.

91 F150 4x4
300 six 5 speed

 

It works great but its like $6.00 a quart in most places which can get expensive with a tranny that holds up to 16 quarts.However,if you do any towing then its probably worth it.

 

I definitely would put Synthetic in. Mobil 1 should be ok, although isn't Mercon V. If all you need is Mercon then go for it. The extra cost is worth it in my opinion for the high temperature performance. I personally use Amsoil synthetic ATF in my Explorer automatic 5R55 tranny and it works ok so far. You also might want to take a look at what Redline and Royal Purple offers.

 

I have also seen where Castrol now has a synthetic ATF.
Does anybody have any suggestions for the correct way
to flush an auto tranny?????

 

I switched the fluid in my M5R2 over to synthetic fluid...it was a bit expensive, but it's not too bad since you only need about 4 quarts. Poopey, are you sure you're not thinking about an auto tranny? Not many manual trannys need 16 quarts of fluid - at least, not in an F150.

As far as synth, I used Redline MTL - but in a colder climate, I'd probably recommend Redline D4 instead. I'm sure Mobil 1 ATF would also be a good choice, and you wouldn't have to special-order it. I switched over to synth to try and correct some synchro problems I was having...and to be honest, I really didn't notice much of a difference. It was perhaps a little bit better, and the shift linkage felt more...er, "mechanical" I guess would be the best word. I can't describe it all that well, but it wasn't a bad change - just a bit different.

In the long run, I think using synth in a manual tranny might be a good idea. They don't use much fluid, so the cost isn't a huge factor - and a tranny like the M5 can use all the help it can get. The only potential problem I can see is that the synchros need a certain amount of friction to work properly, and the M1 ATF might be too slippery and cause some problems...but I've never used M1 ATF in a manual tranny, so I don't really know if this would be a problem or not. If the manufacturer recommends it, I would assume that it wouldn't be a problem. Plus, if it is a problem you would know fairly quickly...not that it's fun to change the fluid back out (mine was a pain, even with a suction gun), but at least you'll have a good idea if you made the right choice.

However, I do have a co-worker that uses a mixture of motor oil, Marvel Mystery Oil, and Lucas in his M5 and his works great with over 235,000 miles - so maybe that's the way to go.

Oh, and Bob - the technical articles part of the site used to have an article Mark Kovalsky had written about flushing tranny fluid. Not sure if that part of the site is up yet or not, but from what Ken has said they'll be back on-line soon.

LK

 

Mobil 1 ATF would be an excellent choice in a 5-speed. The cost is very little for that quantity over a lifetme change interval. As far as "slipperyness" is concerned, that is a myth. Regular and synthetic ATF have to have the same friction characteristics or automatics would slip like crazy. If you have weak syncros, type "F" ATF, without any friction modifiers might help.

Jim

 

Per Mobil 1's web site:

"The product is manufactured from synthesized hydrocarbon base oils and a specially balanced additive system. The synthetic fluid is fully compatible with petroleum ATF products. However, it has better thermal and oxidation stability, a higher inherent VI, extremely low pour point, and improved low-temperature fluidity (down to -54°C or -65°F). The fluid provides unique advantages in long-term friction retention and air release."

And, as one of the advantages it lists:

"Heat and friction resistance increases fuel economy."

I guess the big question is what Mobil 1 means by "friction retention" and "friction resistance". I can guess that "friction retention" relates to the fact that the synth ATF retains its friction characteristics over time instead of breaking down like dino ATF. I'm not exactly sure what Mobil is trying to say with the last sentence though - from my understanding synthetic ATF normally has a lower coefficient of friction at high temperatures, so is that what they mean by "heat and friction resistance"? I'm not sure, though I did find several other synthetic ATF sites where the manufacturer specifically lists lower friction at high temperatures.

I guess the question then is if a manual tranny under load (say, towing on a hot day) will run hot enough that the difference in friction will come into play - I don't know if it would or not, and I am having a heck of a time finding technical data which lists the friction characteristics of synthetic ATF at different temperatures.

Basically, in an automatic transmission all the differences Mobil 1 lists are advantages, but I'm not sure how these would affect the performance of a manual transmission. I'm not saying it'll be worse - all I'm saying is that synth ATF does perform differently in manual trannys, and in particular it affects the synchros. I noticed the change in my M5R2 the first time I drove it - it felt more 'mechanical' and the synchro engagement was more obvious. I wish I could describe it better, but I can't. There wasn't much of an improvement, but there was a definite change in the shift feel compared to the dino ATF. Of course, this was Redline and not Mobil 1.

ATF in general is just not well suited towards use in a manual transmission - like 5w20 motor oil, they traded durability for a little more gas mileage. However, I'm not sure I'd be brave enough to start experimenting with different fluids in a new transmission...though I do know some tranny guys that recommend taking out the ATF and using a non-detergent 30w motor oil instead.

I'll agree that saying one is more 'slippery' than the other isn't really accurate - I should have found a better way to say it.

LK

 

>"The fluid provides unique advantages in long-term friction retention and air release."

>"Heat and friction resistance increases fuel economy."

An automatic transmission is a fluid drive and uses a fluid coupling for the engine to transmit power through the transmission. For the fluid to act as a coupler, it needs to have 'frictional' qualities. If you think of air as a fluid having 'zero' frictional qualities, then as you increase the density of the fluid, you increase the frictional qualities.

On the flip side, excessive friction between fluid clutches, gears and bearings requires more power and builds up excessive heat, further stressing component materials.

So for a power fluid to work most effectivly, it's a balance or a trade-off. Depending on how you look at it.

*edit* It is my understanding that manual gearboxes that specify ATF instead of gear oil rely on a pressurized lubrication system instead of splash and dip lubrication. At least this was the case with my BW 1345 transfer case. So the less viscous fluid not only pumps faster, but because of the higher flow rate carries away more heat.

Scott

 

[QUOTE]Originally posted by horsepuller
*edit* It is my understanding that manual gearboxes that specify ATF instead of gear oil rely on a pressurized lubrication system instead of splash and dip lubrication. At least this was the case with my BW 1345 transfer case. So the less viscous fluid not only pumps faster, but because of the higher flow rate carries away more heat.

Does the M5R2 use a pressurized lubrication system? I don't think it does, but I'm not a tranny expert and never had mine apart.

My understanding (from a close friend who owned a tranny shop) was that the switch to ATF was done primarily for fuel economy, and that it wasn't due to any internal changes. If he was still around I'd ask him about it, but he passed away a few years ago. I'm not sure how the pressurized lubrication system would change the situation...I would still think that motor oil would do just as good a job as (if not better than) ATF. I suppose that the overall best choice for long-term durability might be a synthetic gear oil...assuming that it's thin enough to be able to shift in cold weather.

My co-worker (who runs the odd mix of tranny fluid) called a local transmission shop about a year ago, because he and I were discussing whether or not he should be running motor oil in his M5 tranny - and the transmission shop said that they recommended motor oil rather than ATF for that tranny.

All I know is that now I have an auto tranny and it takes Mercon! Or was that Mercon V?

LK

 

LK, I'm no tranny expert either. How I found out about the pressurized lube system in my xfer case was by looking at an exploded diagram in my 'Motor Manual'. I wondered about using ATF in a gearbox too. But seeing it was a pressurized system made me feel a lot more comfortable.

You should be able to find an exploded diagram of your M5R2 in a 'Motor Manual' or 'Mitchell Manual' in your public library. They are both good books. More detailed than Chilton's, IMHO. A pressurized system should have a gear pump and a dip tube or pickup.

I can see how the ATF recommendation could be driven by CAFE fuel economy ratings. However, an automatic transmission still uses gears and bearing same as a manual gearbox and automatics can go as many trouble-free miles as a manual. But...automatics rely on a pressurized lubrication system...

Scott