TF998 Fluid Question.

Just about to fire up my '88 RAM for the first time. The engine was yanked in 2016, and I've spent the last few months putting it back together. Transmission was drained when the engine was removed.

Can't find and have been told Dexron III is obsolete. I was pointed to this Mobil brand stuff called D/M and on the back, it claims to be the modern equivalent of Dexron/Mercon III and is compatible with vehicles designed for that blend.

Anybody else run it? Good to go? Thoughts?

atf4 supersedes most mopar atf's its available anywhere

Type F is still available if you are looking for a non synthetic.

Kevin

hi

type F if it were me !

Why anyone would run type F is beyond me, that specification is so old you may as well pour ditch water in the trans.

If the trans has a lockup converter (likely) then ATF+4 is the correct fluid. For a non-lockup 3-speed, Type F is fine.

It is a lockup 998, 100% correct.

If the shaft torque applied exceeds the clutch friction holding torque,
which depends on the ATF friction coefficient,
how quickly do the clutch frictional surfaces wear to the point that they must be replaced in a rebuild?

Can it happen in one or a few dragstrip passes,
or one or a few maximum highway accelerations?

I ask because I once changed out ATF+3 to ATF+4 on a high mileage 46RH.

After the change out I did a few full throttle accelerations up a steep high hill.
Everything seemed OK,
but a few hundred miles later the TC clutches began slipping,
and a few hundred miles after that the overdrive unit clutches began slipping.

I later read in an SAE technical paper co-authored by Lubrizol Company and Chrysler
that ATF+4 has a lower clutch friction coefficient than ATF+3,
although ATF+4 has other numerous advantages.

Why did you change the fluid to start with?

ATF+3 has superseded to +4.

Late model trans, stock, lock up, daily driver, ATF+4.

Performance, race, non-lock up, something else. Type F probably, Or synthetic Type F. Or Dexron.

The old ATF+3 was at the 30,000 mile interval.

Neither Torque Converter Clutch or Overdrive Clutch was slipping before the change,
but every now and then the trans was “bump shifting” while the truck was coming to a stop.

After the ATF+4 and a new filter went in,
the bump sifting was not felt anymore.

Did it set any codes?

What makes you think the OD was slipping?

When the TCC started slipping it set a OBD-I code and turned on the CEL.

I was on a trip and I had the transmission rebuilt at an AAMCO on the East Coast of Florida.
The OD unit was not rebuilt then because AAMCO said they would have to wait on a part that had already delayed the trans 11 days.

Looking back I wish now I had the truck towed over to Fort Walton Beach Florida to Suncoast Performance.
The towing bill, the wait for the repair to complete, and the total cost would have been less, as AAMCO charged $3300 without touching the OD unit.
I had friends and a place to stay at Pensacola.

When the OD clutches started slipping, first only on uphill grades, it initially confused me,
because I would see rpms jump up suddenly in the Tach at the same time MPH on the Speedometer would stay nearly stable.
After awhile I experimented pressing the button on the dashboard that turns OD off and found that RPM and MPH now stayed normal.

I was surprised to see my dipstick is stamped "Use Type 7176 or Dexron II " Yes, Dexron II.
So, if this Mobil says it's the direct descendant of Dexron III / Mercon III.... I guess I'll give it a try.