Should I service in anyway the transmission on my 1990 Suburban with over 200k miles?

[Giant Rock]

I bought this Suburban a few months ago, the truck shifts gears perfectly, but general wisdom says to change all the fluids because who knows what the PO did. However, I've been researching about the Transmission and I've come across multiple threads in other forums that say things like:

"At 200k miles it is entirely possible the tranny fluid has a bunch of the friction material in it that helps ensure your transmission still works. Drain the fluid and you may lose that friction material."

Or even more strongly:

"At 200k miles I wouldn't even pull the tranny dipstick... Your fluid could react with the fresh air coming from the dipstick opening causing the transmission to start slipping. Better yet don't even look at the transmission dipstick at all."

Is this truly one of the times to practice IF IT AIN'T BROKE DON'T FIX IT?

Thanks for any advice, here's a pic:

View media item 9406

 

[Bextreme04]

There is definitely something to be said for not touching it if you have LOTS of miles on a trans with no fluid change. If that is the case, you will likely have more and more wear until it finally gives out. Changing the fluid will do exactly what your first quote says and can actually make it start slipping. I would check the fluid and see if it smells burnt and to see what color it is. Try and see if the trans is painted some color or has any tags on it from a rebuild. Personally I usually flush and fill with new fluid, if it is gonna start slipping I'd rather know about it now rather than have a catastrophic failure down the road at some random time.

 

[Goldie Driver]

I bought this Suburban a few months ago, the truck shifts gears perfectly, but general wisdom says to change all the fluids because who knows what the PO did. However, I've been researching about the Transmission and I've come across multiple threads in other forums that say things like:

"At 200k miles it is entirely possible the tranny fluid has a bunch of the friction material in it that helps ensure your transmission still works. Drain the fluid and you may lose that friction material."

Or even more strongly:

"At 200k miles I wouldn't even pull the tranny dipstick... Your fluid could react with the fresh air coming from the dipstick opening causing the transmission to start slipping. Better yet don't even look at the transmission dipstick at all."

Is this truly one of the times to practice IF IT AIN'T BROKE DON'T FIX IT?

Thanks for any advice, here's a pic:

View media item 9406

I have heard that before, and horror stories when done.


The '91 I had got changed at around 120K - no idea about it's prior life.

I bought it used in '99, and never had a tranny problem.

Goldie had 93K on the clock or so when I changed it - tranny got rebuilt at around 103K NOT because of that, but because of leaks, and it would be stupid to pay labor to pull and reseal it and NOT rebuild it.

With 200K ?

I'd check the fluid levels and add if required and otherwise let it life out the rest of it's life.

Unless the fluid looks really clean like it has been done previously, in which case I would probably risk it.



If you are shy on funds or would have issues paying in case it does crap out, then I would revert back to leave it alone.


best of luck in your decision, and let us know how the science experiemtn goes if you run that route.

 

[Camar068]

Run it or have it rebuilt. If you're worried about funds for the rebuild later, stick some money aside to assist when it goes out.

In my life, they've always gone out when things are tight financially. With my history, if it's shifting fine....I'd run it.

 

[Matt69olds]

Good lord, I really wish this myth would go away!!!

If you have grit floating in your transmission fluid, your already in a world of hurt. Transmissions move a truck due to the friction on the clutch plates, the fluid provides the hydraulic force to apply the clutch.

People say changing the fluid will loosen up deposits in the transmission. ********!! If you have deposits of crud in your transmission, it was seriously neglected years ago.

Who in their right mind would consider NEVER changing the oil or filter on your engine a good idea??? You could apply any of these arguments to a engine, and yet as far as transmissions are concerned it’s acceptable.

Most people never consider changing the fluid or filter in their transmission until something doesn’t feel right. Maybe it’s slipping a little during shifts, maybe it’s lazy going into gear. They figure “hey, the fluid and filter has never been changed, let’s try that!!” Of course, the damage is done by this time. So when the transmission fails soon after, obviously the fluid/filter change caused the failure!!


Your not going to fix anything by changing the fluid. What you will do is prolong the life. If the transmission works now, it will continue to work fine after. The filter catches all the normal clutch and thrust washer wear debris, eventually the filter will become restricted. Once you starve a transmission of fluid, it’s all downhill.

 

[rt66paul]

If you plan to do nothing(that is me also, if it works and doesn't make bad noises, leave it alone), just be sure to have your AAA towing insurance paid up. Just 1 tow will cost about what 2 years of the insurance does, and you are good for 5-8 tows a year, which is nice if you have a lot of family living in your home.
Best money I ever spent. Just imagine breaking down on the freeway late at night near Compton and not having the cash to pay the tow truck driver(back in 1976 that was reality). That was a scary night out for me and my wife.

 

[Matt69olds]

Another “go ahead and change the fluid argument:”

Every engine (no matter how well sealed) uses a little oil. If you never change it or check it, eventually it’s going to run low.

Let’s say your driving along and notice the oil light is on,or oil pressure is low. Eventually, the engine is going to start making unpleasant sounds. You decide to change the oil and filter. Needless to say, by this point the damage is done. Soon the engine is making some really nasty/expensive noises. Is changing the oil to blame?

 

[Grit dog]

Been a while since I dealt with this, but I DO believe in not "flushing" IE power flushing the trans if it's real high miles, or ever for that fact, although that could be a wives tale too. I would and have changed the fluid.
Drop pan, change fluid and filter. Refill. Run it. That gets about half the old fluid out unless your torque converter is draining back.

What i prefer is drop, change filter, refill and before starting, disconnect trans cooler line from cooler back to trans. Start truck, pump out X amount (couple few qts) shut off, top up same amount, repeat a few times until remaining old fluid is out. Not 100%, but much closer than 50% and far less new fluid used compared to draining the pan multiple times and re-filling to dilute the remaining old fluid to "mostly" new.

Also depends on your budget and how much you rely on the vehicle. Drive around with nowhere to go on a weekend rig, leave it alone. If you rely on it and drive it regularly, prove to yourself it's reliable and in good serviceable condition (including the fluid).

Just my 2c, but I'm not a transmission mechanic. Let someone like vbb199 give his opinion, I'd trust him.

 

[AKguy]

Are we talking a TH400? I am a fan of changing my ATF and filter every 20,000 miles. Fluid and filters are cheap. I had the 4L60 in my old body style 2000 Tahoe rebuilt at 220,000. Not because it was not working right, it was. I did it because I do not need to be stranded in BFE. There are enough other things that can go wrong when you are out and who needs a high mileage tranny adding to the pile. I kind of laughed when the F150 I purchased new in 2016 did not come with a proper tranny dipstick, just a little tiny one down under at the pan. Sold that thing.

 

[Turbo4whl]

In my opinion the myth about not changing the fluid has to do with the wrong fluid replacing the original correct fluid.

Example: "Joe" backyard mechanic, goes to the parts house for his fluid service. The knowledgeable parts person sells Joe Dex/Merc. Says it is what Joe needs to replace his trans fluid.

Me... I'm still trying to figure out how one fluid can replace 4 different Ford Mercons and 3 different GM Dextrons.

The wrong fluid is what causes the high milage trans to fail quickly.

 

[Matt69olds]

The “best” way to flush a transmission is to first change the filter. Once the pan is reinstalled, disconnect to return line from the radiator, and run a hose from the radiator into a bucket. Have a helper start the engine, while pouring fluid into the full tube. Once the old nasty fluid going into the bucket starts to look like what’s being poured in, your done. That way you have changed the fluid in the converter, and the cooler

 

[Raider L]

@Matt69olds,

Matt, you're the guy who got me through all those dark months last year when I was having all those horrid trans problems. And yeah, it was right after having changed fluid when my intuition was telling me, "Don't fool with it. You'll start having problems!" Yep. And sure enough I did. But it wasn't because I changed fluid. It was I didn't know how much drained out of it the two says I had the pan off. And when I put the pan back on I under filled it and drove it around for a few days when it started messing up. Then I took the pan off, on, off, on changed filter every time, changed modulator valve, etc. until I had drained out 10 gallons!! of fluid not counting the 7 qts, I put in after changing the fluid the first time.

But up to when I changed it, it had been driving fine for years. And I did change my fluid about every 30 thousand or so because I wasn't driving the truck very much even after the truck got rebuilt. I think I let it go a bit to long and by the time I did change it, it probably had 50,000 on that fluid before I changed it this time. I still don't know what happened to it. I don't believe it just wore out from normal intown driving. My friends always said I drove, this hopped up race truck that never got raced, like a old woman.

That's okay. I've finally got the money to get it overhauled. We will see just what happened to it when they take it apart. If I burned it up, well that's what I get. But we'll see more when they look at the pump and the valve body of whether it's really been messed up. My money is on the pump and valve body are alright and all I'll need are plates.

What advice would you give me for them to look for. Yeah, it'll be a real trans shop, and no it's not a racing trans, just stock. But I think I might put that TCI Saturday Night Special 2000 stall converter back in again.

 

[SirRobyn0]

Good lord, I really wish this myth would go away!!!

If you have grit floating in your transmission fluid, your already in a world of hurt. Transmissions move a truck due to the friction on the clutch plates, the fluid provides the hydraulic force to apply the clutch.

People say changing the fluid will loosen up deposits in the transmission. ********!! If you have deposits of crud in your transmission, it was seriously neglected years ago.

Who in their right mind would consider NEVER changing the oil or filter on your engine a good idea??? You could apply any of these arguments to a engine, and yet as far as transmissions are concerned it’s acceptable.

Most people never consider changing the fluid or filter in their transmission until something doesn’t feel right. Maybe it’s slipping a little during shifts, maybe it’s lazy going into gear. They figure “hey, the fluid and filter has never been changed, let’s try that!!” Of course, the damage is done by this time. So when the transmission fails soon after, obviously the fluid/filter change caused the failure!!


Your not going to fix anything by changing the fluid. What you will do is prolong the life. If the transmission works now, it will continue to work fine after. The filter catches all the normal clutch and thrust washer wear debris, eventually the filter will become restricted. Once you starve a transmission of fluid, it’s all downhill.

Been a while since I dealt with this, but I DO believe in not "flushing" IE power flushing the trans if it's real high miles, or ever for that fact, although that could be a wives tale too. I would and have changed the fluid.
Drop pan, change fluid and filter. Refill. Run it. That gets about half the old fluid out unless your torque converter is draining back.

What i prefer is drop, change filter, refill and before starting, disconnect trans cooler line from cooler back to trans. Start truck, pump out X amount (couple few qts) shut off, top up same amount, repeat a few times until remaining old fluid is out. Not 100%, but much closer than 50% and far less new fluid used compared to draining the pan multiple times and re-filling to dilute the remaining old fluid to "mostly" new.

Also depends on your budget and how much you rely on the vehicle. Drive around with nowhere to go on a weekend rig, leave it alone. If you rely on it and drive it regularly, prove to yourself it's reliable and in good serviceable condition (including the fluid).

Just my 2c, but I'm not a transmission mechanic. Let someone like vbb199 give his opinion, I'd trust him.

These guys are right on and it is how I advise my customers at the shop. Besides if the trans fluid is black it's near death anyway. If it's so fragile a fluid and filter change is going to kill it it's on it's death bed anyway. I changed the tranny fluid on my 1984 when I got it 2 years ago, no idea the history. Check the fluid if it's not terrible looking change it now and get it on a regular schedule. If the fluids terrible, it might possibly kill it, but it's near death anyway, and if it's still shifting good you might just save it. A tranny with black fluid is doomed anyway so seems like little risk. Don't power flush it, if you feel the need to clean up the fluid do multiple changes in a short period or do the trans line disconnect method.

 

[Matt69olds]

A 700 will live a long life with a upgraded 3-4 clutch kit, wide band, and decent shift kit. That’s assuming the shop pays attention to the potential wear items. The accumulator pistons are bad about wearing where the alignment pin goes thru the piston, any slop here will result in a hydraulic leak. The later 4L60E are bad about wearing the valve body bore for the converter clutch, lucky for you that’s a problem you don’t have to deal with.


The key to long transmission life is getting rid of that “soccer mom soft shift” GM so carefully designed into the transmission. That greasy sliding shift is great for comfort, but over the long haul wears out friction material. A good solid thud when the trans shifts is what your wanting. Most girlie-man drivers would think that’s too hard a shift.

Occasionally, I’ll get smart ass people asking me how many transmissions I have put into my diesel Ram truck. I always reply “including the one it came with? Let me think, ONE!!” I do have some power upgrades, nothing crazy. I have 220k miles on it, the fluid is clean, there is never more than a light dusting of clutch material in the pan, and the band adjustment never moves. I installed a shift kit early in its life.

This is off the subject, I’m convinced the reason Chrysler transmission have such a lousy reputation is because of how easy it is to make some serious power with the Diesel engine. You can add 150-200 pounds of torque without even raising the hood. The problem is you can’t crank up the power like that and expect the transmission to handle. Same thing with the 700. It was originally designed with a really low first heat ratio to help get heavy trucks moving with the highway gears they had to use in a effort to improve fuel economy. Combine that with the lame underpowered engines GM was forced to use (due to emissions) its a recipe for driver dissatisfaction. Due to the step first gear and the big drop in gear ratio when it shift to 2nd, it’s really hard to get a smooth shift. I think people loosened up the TV cable trying to soften the shift, which leads to other problems.

Build it right, know the limitations, install and adjust it correctly, the 700 will live a long happy behind pretty stout engines.