Need help in understanding & correct choice of MTF

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The additive packs vary somewhat but are similar.

Pennzoil is composed mainly of mineral oil bases, but have a special viscosity index improver.

The others such as Amsoil, Redline, and GM are composed of synthetic bases.
 
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@MolaKule:

I studied your recommended link. Although there remain questions:

1. Why is the shiftability not only a matter of the correct friction but also of the viscosity ?
2. What is the danger of too low viscous oil in hot temps ? In many threads thicker oil at higher temps is claimed as more save

On my last trip over 1 hour I observed the 2nd gear shiftability more detailed. If gearbox is cold there is the rubber block feeling mentioned previously, effort is most. If it is warmed up the first part of shift act is easier and smoother but at the end of the shift act I can feel something like teeth in the shiftstick.
All this is worse at low rpms. After about 1 hour shifting is very smooth up and down.

btw: pennzoil is sadly not available for me
 
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Busfreak:

In answer to your first question:

Quote:
The shifter forks have a bore so they can slide on the guide rods. There is a specified clearance between the shifter forks’ bore and the shifter fork guide rods. Lubricant effects: Too high a viscosity lubricant and the shifting will be hard and sluggish. More force will be required to go from one gear to another. Too thin an oil and the forks will wear, the clearances will increase, and the shifting will become sloppy and uncertain. The correct mix of base oil viscosities is needed here to insure good cold weather and hot weather shifting. Synthetics excel here because of their high viscosity index.


Second question:

"What is the danger of too low viscous oil in hot temps ? In many threads thicker oil at higher temps is claimed as more save"

Thicker oil is not always better. If the base oil in the MTF specific oil has a high viscosity index it should not allow the protective film to get too thin. Also remember that there are AW additives in there to keep wear to a minimum in case the hydrodynamic film does thin too much.

On the other end of the spectrum, a low viscosity oil without the proper MTL protective additive package can be detrimental.

Formulating an MTL with the just the right base oils and protective additive package for a specific horsepower range and heat load is a balancing act.
 
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So Penz synchromesh and Ams mtl have the proper additive packs for gl4 apps that call for these viscoaitiea?
 
Those and Redline MTL75W80 and others.

Most of the Manual Transmission specific lubricants have a protective additive package with a protection rating of GL-4.
 
MolaKule:

saying RL MTL 75W80 you mean MTL 70W80 ?

due to your answer to my 1st question I reason:
- friction is important for the synchronizers
- viscosity for forks and rods

How does the tribologist decide the best viscosity scope for a gearbox. Providing that he determined the correct visco range, isn't it not careless to leave the range e.g. in order to improve the cold shiftabilty, while on the other hand e.g. the forks wear out more. In other words: May / should I trust in the manufacturer oil visco recommendation as best compromise ? Dave from RL told me to go not too far from recommended visco. In my case I think to go from 75W85 to 70W80 is not too far, isn't it ? 75W85 --> ATF would be too far !!
My problem is most of the fine oils discussed and recommended here (pennzoil, amsoil, RP) are not acquirable in Germany. The only available is Redline.

to your 2nd answer:

the ticker the oil film is the less often the EP/AW additives must prevent the worst, isn't it ?

btw: in hot temps when the oil is more slurry, in this case isn't the centrifugal force of the rotating gears a issue in respect of the adhesion of the oil ?

Does friction value of the oil decrease with increasing temp ?


a lot of questions to specialist, thanks a lot !
Gear oil is a very interesting subject for me :)
 
Ok, let's try and separate out one question at a time:

BTW, what does your vehicle specify as the viscosity or SAE grade? I don't remember you stating that.

Quote:
to your 2nd answer:

the ticker the oil film is the less often the EP/AW additives must prevent the worst, isn't it ?


The GL-4 AW additive package is the same, no matter the viscosity. Higher loads from higher HP and torque require a higher viscosity. That's how viscosity is determined.

Quote:
btw: in hot temps when the oil is more slurry, in this case isn't the centrifugal force of the rotating gears a issue in respect of the adhesion of the oil ?


No. MTF does not tack like dfferential fluid does. Oil sling is not a problem. Defoamer additives keep foaming to a minimum.


Quote:
Does friction value of the oil decrease with increasing temp ?


No. The friction modifier provides consistent static and dynamic friction over the life of the oil. The friction modifier is not affected by heat.

[/quote]
 
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Quote:
75W85 is recommended from car manuf.
HP: 200
torque max.: 450 NM


OK, recommend you try the Redline MTL 70W80 GL-4 Gear Oil.

It has plenty of AW additives and the shifting should improve in cold weather.

I would never use any ATF because the AW additive level is less than 30% that of a dedicated, application specific GL-4 MTL.
 
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OK , thanks

Two more questions are rising up in this moment:

- Why is 2nd gear shifting at higher rpms smoother than at lowers ? How can this be explained ?

- One of my initial proposals of this thread was, to mix 70W80 with RL 75W90NS in order to improve friction value in cold and improve protection in hot. What would probably happen, what would be to expect using this mix ?
 
is it right, that really warm oil could be easier squeezed out between synchronizer and konus ? another reason for smoother warm shifts ?
 
Quote:
Two more questions are rising up in this moment:

- Why is 2nd gear shifting at higher rpms smoother than at lowers ? How can this be explained ?


Transmission design.


Quote:
- One of my initial proposals of this thread was, to mix 70W80 with RL 75W90NS in order to improve friction value in cold and improve protection in hot. What would probably happen, what would be to expect using this mix ?



This not needed. Use the 70W80.
 
Quote:
is it right, that really warm oil could be easier squeezed out between synchronizer and konus ? another reason for smoother warm shifts ?


The friction modifier determines synchronizer engagement characteristics.
 
What about this additive for those who must fill in ATF in their gear box:

gear oil additive

Is it a solution to combine very low viscosity of ATF with EP/AW concentration of a MTF ?
Would would happen using this mix ?

It's not for me but generally interesting.
 
After playing with the viscosity in my f250s ZF5 manual, I have ranged from maxlife ATF, amsoil ATF, pensoil synchromesh, and at last Redline MT-90.

The trans called for mercon from the factory, but ATF functioned terribly both balky syncro engagement and gear whine. I thought I had found the holy Grail with the synchromesh as the syncros finally worked like they should, but gear whine on first through third remained.

Finally, MT-90. Shifts great, quieted the gear whine. Perhaps a "younger" trans wouldn't like the viscosity? The trucks 351w is rated at 200hp/300tq I believe.
 
Originally Posted By: MolaKule
Two more questions are rising up in this moment:

- Why is 2nd gear shifting at higher rpms smoother than at lowers ? How can this be explained ?


Transmission design.


In regard to using a much thicker 15.6cst redline MT-90 instead of what is called for ( mercon ATF), I noticed in another mtf thread you posted that the fluid needs to be able to penetrate the bearing cage for low horsepower applications. Should I be concerned about starving my tapered roller bearings on my application using MT-90?

It's shifting remarkably well, but I am considering moving down to redline 70w-80 when fall arives or maybe thinner? What would you recommend? Thank You.
Click to expand...
Click to expand...
 
Quote:
In regard to using a much thicker 15.6cst redline MT-90 instead of what is called for ( mercon ATF), I noticed in another mtf thread you posted that the fluid needs to be able to penetrate the bearing cage for low horsepower applications. Should I be concerned about starving my tapered roller bearings on my application using MT-90?

It's shifting remarkably well, but I am considering moving down to redline 70w-80 when fall arives or maybe thinner? What would you recommend? Thank You.



Either flluid wil get to the bearing cages. I think the Redline MTL 70W80 will serve you well.
 
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