The Great Debate

[Mike205]

If the ****** is shifting but has high mileage I will generally do filter service only unless I have evidence that it had been serviced previously. It's a tough choice if you don't know the history. Back in mechanic school it was explained to me like this; as the ****** wears the friction material from the paper clutches floats in the fluid. On a trans thats never been serviced that suspended friction material is part of whats keeping that ****** moving. The danger in replacing all the fluid is two fold; 1. you have removed the suspended friction material and 2. You now have a bunch of detergent cleaning off the plates and clutches and the result is a slipping ******.

 

[tommudd]

If the ****** is shifting but has high mileage I will generally do filter service only unless I have evidence that it had been serviced previously. It's a tough choice if you don't know the history. Back in mechanic school it was explained to me like this; as the ****** wears the friction material from the paper clutches floats in the fluid. On a trans thats never been serviced that suspended friction material is part of whats keeping that ****** moving. The danger in replacing all the fluid is two fold; 1. you have removed the suspended friction material and 2. You now have a bunch of detergent cleaning off the plates and clutches and the result is a slipping ******.

Back when I was doing trans rebuilds at a Ford dealership thats what we were told as well

 

[belvedere]

On a trans thats never been serviced that suspended friction material is part of whats keeping that ****** moving. The danger in replacing all the fluid is two fold; 1. you have removed the suspended friction material.

Folks who hold to this theory will generally tell you that if a trans has been regularly serviced, it's OK to keep servicing it, but if it's never been serviced, it may cause problems to remove the old ATF containing all the suspended friction material. Here's my problem with that: if the trans has been serviced over its life, then that friction material has already been removed (during previous ATF changes). So, shouldn't that trans be slipping, too? IOW, let's say two identical transmissions each have 120k miles, and trans A had its ATF changed at 30k mile intervals, but trans B never had a fluid change. They each have 120k miles worth of wear (worn friction material). So, it's OK to remove that amount of material a small amount at a time (trans A), but if you remove it all at once (trans B), it will kill the trans? Doesn't make sense to me.

 

[Logan Savage]

Folks who hold to this theory will generally tell you that if a trans has been regularly serviced, it's OK to keep servicing it, but if it's never been serviced, it may cause problems to remove the old ATF containing all the suspended friction material. Here's my problem with that: if the trans has been serviced over its life, then that friction material has already been removed (during previous ATF changes). So, shouldn't that trans be slipping, too? IOW, let's say two identical transmissions each have 120k miles, and trans A had its ATF changed at 30k mile intervals, but trans B never had a fluid change. They each have 120k miles worth of wear (worn friction material). So, it's OK to remove that amount of material a small amount at a time (trans A), but if you remove it all at once (trans B), it will kill the trans? Doesn't make sense to me.

I can't find fault with your thinking & I won't argue with anyone that's been to school to work on them but my thoughts are that changing fluid that's never been changed might cut loose crud hiding in all the nooks & crannys & clogging up fluid passages or the valves in the valve body .

 

[Dave]

If the ****** is shifting but has high mileage I will generally do filter service only unless I have evidence that it had been serviced previously. It's a tough choice if you don't know the history. Back in mechanic school it was explained to me like this; as the ****** wears the friction material from the paper clutches floats in the fluid. On a trans thats never been serviced that suspended friction material is part of whats keeping that ****** moving. The danger in replacing all the fluid is two fold; 1. you have removed the suspended friction material and 2. You now have a bunch of detergent cleaning off the plates and clutches and the result is a slipping ******.

This is what I always thought was true.

Folks who hold to this theory will generally tell you that if a trans has been regularly serviced, it's OK to keep servicing it, but if it's never been serviced, it may cause problems to remove the old ATF containing all the suspended friction material. Here's my problem with that: if the trans has been serviced over its life, then that friction material has already been removed (during previous ATF changes). So, shouldn't that trans be slipping, too? IOW, let's say two identical transmissions each have 120k miles, and trans A had its ATF changed at 30k mile intervals, but trans B never had a fluid change. They each have 120k miles worth of wear (worn friction material). So, it's OK to remove that amount of material a small amount at a time (trans A), but if you remove it all at once (trans B), it will kill the trans? Doesn't make sense to me.

This sounds reasonable too.




Not sure what to think???


Dave

 

[profdlp]

This is what I always thought was true.

This sounds reasonable too.

Not sure what to think???

Trust in The Force.

 

[CactusJacked]

Folks who hold to this theory will generally tell you that if a trans has been regularly serviced, it's OK to keep servicing it, but if it's never been serviced, it may cause problems to remove the old ATF containing all the suspended friction material. Here's my problem with that: if the trans has been serviced over its life, then that friction material has already been removed (during previous ATF changes). So, shouldn't that trans be slipping, too? IOW, let's say two identical transmissions each have 120k miles, and trans A had its ATF changed at 30k mile intervals, but trans B never had a fluid change. They each have 120k miles worth of wear (worn friction material). So, it's OK to remove that amount of material a small amount at a time (trans A), but if you remove it all at once (trans B), it will kill the trans? Doesn't make sense to me.

Since you earlier made the comparison to changing the engine oil, let's try this. Take 2 similar engines, both with 120k miles. One had regular oil change intervals and the other one the oil was never changed, only added to as needed. Does that mean when you put new oil in both, they are equal again? Answer, no. The one that never got oil changes would be trashed by comparison, from running it's whole life on broken down oil. Same goes for the trans that has been running on degraded fluid it's whole life.

On the grit & grab scenario, I concur with the others, or is it the other way around?

I would probably change the fluid, but definitely not have a complete flush done. I know more than one mechanic as well who advise against changing the fluid at all on a high miles trans if it's never been done....or looks like it. With the old fluid, the clutch packs can have grit embedded in them which acts like a traction enhancer. New fluid, which is stronger in detergent than the worn out stuff, can flush the clutches clean, and chance causing slippage.

 

[Logan Savage]

Folks who hold to this theory will generally tell you that if a trans has been regularly serviced, it's OK to keep servicing it, but if it's never been serviced, it may cause problems to remove the old ATF containing all the suspended friction material. Here's my problem with that: if the trans has been serviced over its life, then that friction material has already been removed (during previous ATF changes). So, shouldn't that trans be slipping, too? IOW, let's say two identical transmissions each have 120k miles, and trans A had its ATF changed at 30k mile intervals, but trans B never had a fluid change. They each have 120k miles worth of wear (worn friction material). So, it's OK to remove that amount of material a small amount at a time (trans A), but if you remove it all at once (trans B), it will kill the trans? Doesn't make sense to me.

I'm trying to make sense of these theories as well . The only way it all makes sense to me is if regular fluid changes prevents wear by not having degraded fluid so would have a lot less friction material removed from the clutches than the transmission that didn't have fluid changes even though both transmissions have the same mileage . Don't know if I'll get a bingo or get sent back to the corner by the transmission guys .

 

[Leeann]

I think the theory of never changing the fluid comes from mechanics who are afraid of the voodoo of the automatic transmission.

My FIL, who is 84 and has been an automatic transmission expert for his entire life (because his father was John Maxwell's personal machine shop apprentice - look him up), says you change the fluid and filter regardless of how long it has gone without.

I've never had a ****** fail because I changed the fluid and filter when it hadn't been done in over 100,000 miles.

 

[belvedere]

Take 2 similar engines, both with 120k miles. One had regular oil change intervals and the other one the oil was never changed, only added to as needed. Does that mean when you put new oil in both, they are equal again? Answer, no. The one that never got oil changes would be trashed by comparison, from running it's whole life on broken down oil. Same goes for the trans that has been running on degraded fluid it's whole life.

Well, no. A trans can survive 120k on the original ATF (though it's far from ideal); an engine wouldn't survive 120k on the same oil.

Anyway, we obviously disagree. We've both made our points, and have different opinions. Nothing wrong with that. :favorites13:

 

[M38 Bob]

>>>>>>>>>>>an engine wouldn't survive 120k on the same oil.<<<<<<<<<<<<<<<<<

Afraid you're wrong on that one. Have a customer, owns a machine shop, not rich, but hasn't done too badly over the years. Semi-retired now, but when he was running hard, wheeling and dealing, partying hearty he'd get a new Chrysler every year or two. Trade em in when they hit 95k. They'd be on the second set of Michelins, AND THE SAME OIL THAT CAME IN IT!!! Add a quart when needed. Asked him WHY he'd never change the oil, said "Cause it'll run 100k on what came in it and I don't give a damn what happens after I trade. Folks waste a lot of money on oil." Honestly, they seemed to be running just as well as the ones that were babied.:emotions34:

Bob

 

[twowings]

I think the theory of never changing the fluid comes from mechanics who are afraid of the voodoo of the automatic transmission.

My FIL, who is 84 and has been an automatic transmission expert for his entire life (because his father was John Maxwell's personal machine shop apprentice - look him up), says you change the fluid and filter regardless of how long it has gone without.

I've never had a ****** fail because I changed the fluid and filter when it hadn't been done in over 100,000 miles.

They ARE the work of the devil!!!:gr_grin: