Are old-school auto transmissions with non-lockup torque converters harder on AT fluid?

[SumGuy]

Is having a lock-up torque converter a factor for oil longevity in auto transmissions?

Meaning that if it is, then you want to look at oil heat or shear stability for the older auto transmissions from the 60's and 70's ?

 

[Creekside]

Is having a lock-up torque converter a factor for oil longevity in auto transmissions?

Meaning that if it is, then you want to look at oil heat or shear stability for the older auto transmissions from the 60's and 70's ?

I think so. The medium duty Allison AT545 is not a lockup trans and they are known to heat up on long pulls-think mountains. These are common in busses and are to the age where they're being used for conversions, toters, toy haulers, etc.

 

[MolaKule]

The older non-lockup AT's sheared the fluid less than do lockup torque converters but heated the fluid more.

However, most of the temperature rise in AT fluids come from the torque converter, so if you can lock it up, the temps should go down since you are not transmitting torque through the fluid. But it is during lockup and release where you get fluid shearing in a lockup type.

 

[barryh]

I ran a non lock up auto for 21 years. It was noticeable by doing quick stall tests just after a fluid change and then again a few weeks later, that new fluid sheared down quite quickly. I know that too low a stall speed is not necessarily desirable but if stall speed on new fluid rises after only a few weeks that seemed to me to be an indication that viscosity had dropped.

I don't think I'd want to run a non lock auto again in terms of efficiency and MPG.

 

[Fordiesel69]

Yes! My C6 in my 1986 F-250 Diesel gets roasting hot. On a near identical truck we bypassed the radiator cooler, and plumbed in an external tranny cooler and the fluid got too hot. We had to have a shop braze in a new fluid cooler into the bottom of the factory radiator (back when real radiator shops existed).

In simpler terms a large external tranny cooler was not enough!

 

[tnt_motorsports]

Non-lock up automatics are essentially a heat pump so IMO, yes they will be harder on ATF. If there is no lock-up that means there is slippage and no 1:1 drive.

Just my $0.02

 

[burbguy82]

The older non-lockup AT's sheared the fluid less than do lockup torque converters but heated the fluid more.

However, most of the temperature rise in AT fluids come from the torque converter, so if you can lock it up, the temps should go down since you are not transmitting torque through the fluid. But it is during lockup and release where you get fluid shearing in a lockup type.

what is worse?

 

[SC Maintenance]

Yes, they ran much hotter. The fluid back then was not as good either. Service intervals for the fluid were much shorter. Transmission shops where everywhere.

 

[350Rocket]

I had a local transmission rebuilder tell me once (about 20 years ago when I was young) that he would much rather have a TH200C transmission (despite their terrible reputation) than a non lockup TH350 (which I was considering swapping into my 87 Oldsmobile Cutlass in place of it's TH2004R overdrive transmission because the oldspower.com forum discussions had me convinced I was going to blow the transmission up one day and that a th350 was much more reliable.

20 years later that car is gone to a junkyard but many of its parts including that never rebuilt transmission with over 300k miles is still going in my 84 Cutlass that replaced my first car.

Glad he talked me out of that swap. The transmission rebuilder actually passed away before either my 2004R or 4L60E ever needed a rebuild.

 

[MolaKule]

what is worse?

What is worse for what?

 

[burbguy82]

What is worse for what?

heat or shear? for the trans

 

[MolaKule]

heat or shear? for the trans

They are both bad for ATF. Extreme heat oxidizes the fluid and shear thins it.

In the case of the non-lockup torque converters of old, fluid slippage meant the fluid consumed more energy and thus resulted in a larger temperature rise.

However, modern additive chemistry and better base oils, starting with Dexron VI, has improved both to the point where we see much less shear thinning and oxidation, and we cannot forget the more stabilized friction modification chemistry as well.

 

[burbguy82]

They are both bad for ATF. Extreme heat oxidizes the fluid and shear thins it.

In the case of the non-lockup torque converters of old, fluid slippage meant the fluid consumed more energy and thus resulted in a larger temperature rise.

However, modern additive chemistry and better base oils, starting with Dexron VI, has improved both to the point where we see much less shear thinning and oxidation, and we cannot forget the more stabilized friction modification chemistry as well.

There is so much talk about transmission temps having to do with direct relation to the tranny itself, and not the improvement of the fluid. Modern fluid is so much better than older fluid, but this never gets brought up in the conversation, nor the temp ceiling of the trans. Recently, I got to 240f outgoing temp with a 19k GCWR setup in the mountains of Kentucky and West Virginia, maybe 10 different times. Fluid look unscathed, nearly no visible color or smell difference. Not scientific I know, but I counts for something.

When I got home, I did a pan drain and fill, just to be overkill.

Trans over temp on my 99 GM powered Motorhome is 266f. At least in the computer.

 

[meep]

I think I saw those temps or close to them in my gen iv Chrysler T&C, 2002, 3.8L, steep uphill in July heat. Sucker got hawt.

 

[supton]

I think I read somewhere that a non-lockup TC is about 5% slippage. But when the lockup TH350 was introduced, in order to fit the clutch, the TC wasn't quite as good, and so it had more slip when not locked up? not sure that applies to any other transmission, since any new clean-sheet design should make space for the TC to have lockup. So I tend to think that most TC's operated past stall speed is "low" slippage, but still 5%, give or take.

Interesting that 5% slip (since pulling hills no engine & TC setup should be near stall speed--should be well past it to make the hp to pull the hill) would create so much heat... I guess 5% of 200hp is still 10hp of heat, or 7.5kW of heat. A 1,500W space heater aimed at my feet is pretty warm! let alone 5x that.

The good old days apparently weren't as good as we (like to) remember them them.

 

[SumGuy]

I started this thread because I wanted to understand if the recommendation to use Dexron 3 or 4 in a 1960's era Chrysler 727 Torqueflite was valid. Instead of, say, ATF+4. Other BITOG threads have compared the viscosity changes and shear stability of these oils:

P

Thread 'Atf+4 vs Dexron vi'

May 10, 2015

I've got a non lock up A-518 chrysler transmission in my 91 dodge power ram truck. The transmission was re-built in October of 2011 and it came with a 2 year warranty, the transmission has 5500 miles on it right now, I only use the truck for hunting and sometimes go for a little drives here and there. The builder told me he put dexron III in it, and he told me that's what he recomends to run in it.
So i followed his advice and ran the dex III he put in it since he was giving me the two year warranty, the warranty has been expired since October of 2013. I have been wanting to get rid of the...

• pjc360
• Replies: 45
• Forum: ATF, Differential, Trans, Brakes, P/S

Am I wrong that ATF specs today heavily focus on what's needed for computer-controlled clutches and lock-up converters (when it comes to their additive packages) but meanwhile the old torqueflites need a different focus for their oil? Is heat and shear stability the most important spec when the oil is going into these old transmissions?

The old standby "read the manual" is useless today for those of us that have these cars / transmissions. We're left reading between the lines of what's said and discussed and speculated about using today's ATF in our cars.

 

[nascarnation]

I think so. The medium duty Allison AT545 is not a lockup trans and they are known to heat up on long pulls-think mountains. These are common in busses and are to the age where they're being used for conversions, toters, toy haulers, etc.

I think we built the last ones in production in 2003 so they're old enough to drink now.

 

[nascarnation]

There is so much talk about transmission temps having to do with direct relation to the tranny itself, and not the improvement of the fluid. Modern fluid is so much better than older fluid, but this never gets brought up in the conversation, nor the temp ceiling of the trans. Recently, I got to 240f outgoing temp with a 19k GCWR setup in the mountains of Kentucky and West Virginia, maybe 10 different times. Fluid look unscathed, nearly no visible color or smell difference. Not scientific I know, but I counts for something.

When I got home, I did a pan drain and fill, just to be overkill.

Trans over temp on my 99 GM powered Motorhome is 266f. At least in the computer.

At Allison we ran our durability tests with 250F sump temperature. That would give Dex III a workout but wasn't very damaging for the PAO based TranSynd.

 

[MolaKule]

...Am I wrong that ATF specs today heavily focus on what's needed for computer-controlled clutches and lock-up converters (when it comes to their additive packages) but meanwhile the old torqueflites need a different focus for their oil? Is heat and shear stability the most important spec when the oil is going into these old transmissions...?

These fluids have the high-stability DI additive component chemistry and the same era viscosity (~7.3 cSt) so they should provide sufficient protection for ye olde tranny:

HPL BlueCC

Amsoil ATF

Redline D4

 

[97prizm]

Yes, they ran much hotter. The fluid back then was not as good either. Service intervals for the fluid were much shorter. Transmission shops where everywhere.

That, muffler shops, and custom car audio installers.