Transmission Hosed Y/N Maybe?

[MattinLA]

hmmm, bought a used 96 4runner 2WD with a rebuilt engine, runs GREAT but MUCH maintenance required, all fluids filthy, especially transmission! The guy who checked it said "Matt, the fluid is so filthy with flecks of dirt, it's your clutch packs they're hosed and your tranny may be fine now, but it will die soon! My Tranny guy however said to just change it, he did a thorough maintenance filter change blew out the coolant hoses, then I did a thousand mile trip to ZION NP, NO PROBLEMS whatsoever, got home, fluid somewhat dirty, drained 3 quarts replaced it with new, ABSOLUTELY NO SHIFTING PROBLEMS right now or ever.... ok, can I consider my transmission SAVED? Should I keep doing partial changes? Not clear if I am on borrowed time...all opinions respected thanks!

 

[Uneek]

Typically the consensus is, if the transimission fluid is dirty and smells burnt, the transmission is on its last legs and about to go. From what I've read, do NOT change the fluid. It's not if it will fail, but when.

I'm not a mechanic, but from what I've read my understand of it is because the clutch materials have worned out and is suspended in the fluid and increasing friction allowing the transmission to function. But when the fluid is changed, the materials are gone and slipping begins.

I could be wrong though. Hopefully someone with transmission knowledge can correct me if I am.

 

[TechWrench]

Typically the consensus is, if the transimission fluid is dirty and smells burnt, the transmission is on its last legs and about to go. From what I've read, do NOT change the fluid. It's not if it will fail, but when.

I'm not a mechanic, but from what I've read my understand of it is because the clutch materials have worned out and is suspended in the fluid and increasing friction allowing the transmission to function. But when the fluid is changed, the materials are gone and slipping begins.

I could be wrong though. Hopefully someone with transmission knowledge can correct me if I am.

I too have heard people say that changing the fluid in an auto trans if it is already burnt, will cause it to fail sooner. I can't, for the life of me, figure out where that 'myth' (imho) comes from. The only reason new fluid in a failing trans might hasten the eventual failure would be if there is a lot of varnish coating the inside of the trans. The new fluid may cause the varnish to break loose, and that would then clog the filter, and cause a loss of pressure, which isn't good. If the trans is already that far gone, I wouldn't recommend changing the fluid, only because it is a waste of money. The trans needs to be overhauled. As for the clutch material suspended in the fluid increasing friction and keeping it working, that is definately not true. The clutch packs in an auto trans are applied by fluid pressure, and if the clutch disks (friction plates) are worn, there is NOTHING that will replace that missing friction material. All the suspended clutch material in the fluid will do, is accelerate bushing and bearing wear that the fluid is trying to lubricate, clog the filters which will eventually cause a loss of pressure, and accelerate the clutch disk wear. Clutch disk wear is caused by one thing, loss of pressure to the clutch piston that compresses the clutch pack. The pressure loss can be due to several things. The seals between the piston and clutch pack housing are failing, allowing fluid to flow past and cause a presssure loss, low fluid, faulty pressure regulation from the pump or valve body, or clogged filters, which cause fluid starvation to the pump.

If the fluid has become burnt, because of heat, caused by heavy towing, or inadequate cooling, and internal damage hasn't begun, then by all means change the fluid as soon as possible. It's not a guarenteed fix, but certainly better than continuing to run with the burnt fluid. But, you should also try to solve the overheating problem, or the fluid will just burn again. Fresh fluid, in addition to providing new lubrication media, helps keep the internal seals pliable so they work properly. But, if the internal seals have become hard and brittle, the new fluid wont fix them, they need to be replaced.

 

[MattinLA]

Ok!

That is the most authoritative reply I've had. It seems the fluid was NOT burnt, it just had not been changed in YEARS. It was just brown filthy. However how do you distinguish plain fillthy tranny fluid that needs to be changed from something much more ominous - or is it all one and the same?

thanks...........

 

[TechWrench]

Re: Ok!

That is the most authoritative reply I've had. It seems the fluid was NOT burnt, it just had not been changed in YEARS. It was just brown filthy. However how do you distinguish plain fillthy tranny fluid that needs to be changed from something much more ominous - or is it all one and the same?

thanks...........

If the fluid is 'burnt', it will be obvious by the smell, there is nothing quite like it. It is not something you will forget, when you have seen it before. As for just plain dirty oil, that hopefully is just because of age. If you are not having any mechanical problems, then a complete change of fluid is a good idea. But getting a complete change is not as easy as it sounds. If you remove the pan, and collect what drains out, you will only get about a third of the total amount of fluid in the trans. The torque converter holds the rest, and it does not drain when the pan is removed. You are left with two choices. Have the system flushed by a shop, with the proper equipment to do so. Try some of the dyi methods of performing a flush. Or you can replace what is drained from the pan with new fluid, run it for a week, and repeat the process. It will take 3-4 drains and refills to get the majority of the fluid changed. A complete flush is more effective, but more costly.