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Old 10-27-2013, 10:41 AM   #1
MrBob OP
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Tranny oil change, or not?

The auto transmission in my Astro is at a little over 180,000 miles. It seems to be working as it should. It hasn't needed any fluid during the 6,000 miles I've driven it and the fluid is reddish and doesn't smell burnt. I've been towing bike and trailer and for that reason wonder if I should give the tranny a flush, or just a filter change, or leave it the hell alone.
What's the consensus?
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Old 10-27-2013, 12:58 PM   #2
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I've always been told . . .

Either service it regularly, with fluid and filter changes, or leave it alone. That is, if it hasn't ever been serviced, a flush, filter, and fill can bring on problems. Could be an old wive's tale. Or not.
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Old 10-27-2013, 01:24 PM   #3
troidus
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Since you're towing with it, I'd drop the pan to replace the strainer and clean out the pan while you're in there. (Dunno if yours will have magnets in the pan or not. My Toyota has them and they were furry when I dropped my pan.) Then you can consider whether you want to do a complete fluid change or not.

I used the transmission cooler circuit and engine power to do my fluid exchange. I disconnected the cooler return line and put that in a bucket, then poured fluid in the fill tube while the engine idled. I pumped out three gallons of fluid.

Don't let it run dry if you do it that way.
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Old 10-27-2013, 01:43 PM   #4
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Change the oil. That old wives tale changing old dirty AT fluid will kill your trans is pure crap. Old dirty fluid eats your AT not the clean new stuff. AT fluid should be generally changed every 15,000-20,000 miles(read your owners manual). If that schedule is maintained you're golden. If it's been forever since yours has been changed you also need to change the filter and pump out the torque converter which holds and retains 50% of the fluid capacity. If you regularly swap trans fluid on schedule the converter fluid doesn't need to be changed each time but if it's holding dirty antique fluid it ALL needs to changed not just the fluid in the tranny pan. The little glovebox book you get with a car regarding how to work the radio, work the seat belt, lube/grease maint intervals wasn't printed to annoy you. It's meant to keep your car alive.
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Old 10-27-2013, 02:40 PM   #5
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Quote:
Originally Posted by usgser View Post
AT fluid should be generally changed every 15,000-20,000 miles(read your owners manual).
My owner's manual says every 100,000. More recent model years say "lifetime". I don't wait that long.
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Old 10-27-2013, 04:31 PM   #6
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How many miles? And what year? AWD?

Don't have it flushed. Drop the pan, change the filter and put some new fluid in it.

Older M vans used the 700R4 that had a replaceable gasket. Newer M vans used the 4L60 that could have had either a replaceable or, re-useable gasket

You can get a re-useable gasket for the 4L60 if you have the old style gasket. It is expensive but, it will last a life time.

Get the gasket from a GM dealer. Yea, it costs a little more but, it doesn't leak if installed properly. Don't over torque the pan bolts and don't slather any kind of sealant on the gasket. Just make sure the pan and mounting surfaces are clean and dry. Use brake clean and a clean rag to remove any fluid on the trans case.

Tech tip- Sometimes, it is easier to unbolt the center support on the trans and use a bottle jack to raise the trans about an inch. Stick a spacer between the mount and crossmember to hold the trans up about an inch. This allows you to slide the pan out from under the crossmember for servicing.

If you're towing, i'd change fluid & filter at about every 30K. Cheap insurance.

The Astro was a great van. The older LB4 4.3 TBI was a great engine and fuel system. I saw many that had well over 200K miles. Bullet proof engine and fuel system.

The mid 90's with the L35 4.3 CPI had lots of problems with sticking poppets in the CPI fuel injection. After about a million warranty repairs on the CPI fuel system, GM came up with a better solution in 96 with the SCPI for the 4.3
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Old 10-27-2013, 05:33 PM   #7
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Quote:
Originally Posted by Wasser View Post
How many miles? And what year? AWD?

Don't have it flushed. Drop the pan, change the filter and put some new fluid in it.

Tech tip- Sometimes, it is easier to unbolt the center support on the trans and use a bottle jack to raise the trans about an inch. Stick a spacer between the mount and crossmember to hold the trans up about an inch. This allows you to slide the pan out from under the crossmember for servicing.

If you're towing, i'd change fluid & filter at about every 30K. Cheap insurance.

The Astro was a great van. The older LB4 4.3 TBI was a great engine and fuel system. I saw many that had well over 200K miles. Bullet proof engine and fuel system.

The mid 90's with the L35 4.3 CPI had lots of problems with sticking poppets in the CPI fuel injection. After about a million warranty repairs on the CPI fuel system, GM came up with a better solution in 96 with the SCPI for the 4.3
Thanks everyone for the information. Pulling the pan and topping off the tranny after installing a new filter seems to be the best move.
I didn't get a service history with the van so I'll assume no transmission servicing was done. The first service I gave it was switching to synthetics in the differentials and transfer case.
My previous 95 Astro had the injection issue and Chevy blew me off. Regular Sea Foam use minimized the problem.
While shopping for this one I noticed how many of the Astros had high-miles but were described as running perfectly and mine seems like a happy camper at 180'000 miles.
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Old 10-27-2013, 05:41 PM   #8
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Quote:
Originally Posted by troidus View Post
I used the transmission cooler circuit and engine power to do my fluid exchange. I disconnected the cooler return line and put that in a bucket, then poured fluid in the fill tube while the engine idled. I pumped out three gallons of fluid.

Don't let it run dry if you do it that way.
+1, it's how I do it. Remove the return line at the cooler, put on an adapter and rubber hose, run to pan. Place funnel in fill, start vehicle and watch it pump out the fluid, all the while slowly filling with fresh. When fluid looks like new stuff coming out, turn off engine, secure everything and top off. It's the easiest way to remove all the old stuff.
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Old 10-28-2013, 11:42 PM   #9
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Quote:
Originally Posted by troidus View Post
My owner's manual says every 100,000. More recent model years say "lifetime". I don't wait that long.
Forget that lifetime shit; car companies don't speculate on a lifetime longer than 200k miles or so. Mine had a lifetime filling too and after 110kk km half of the fluid was gone and the other half was an unusable smelly rotten mess. That stuff will get used up over time. Changing it regularly is th only right thing to do. Every 20k miles migjt be a bit overkilk, but better than not doing it at all!
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Old 10-29-2013, 05:56 AM   #10
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I have had problems with a flush. Never with drop pan and replace. Drive a little

You can then get another gasket and drop pan again, to change more fluid.

If it is AWD, change the awd fluid now.
You will notice a difference in shift quality as it relearns.

Rod
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Old 10-29-2013, 06:25 AM   #11
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If the fluid has never been changed the detergents in the new fluid will flush all the grit and buildup out of the transmission this could cause problems I have always heard if you want to change old fluid do it a couple qts at a time so it doesnt shock the system with to much detergent, just my 2 cents
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Old 10-29-2013, 02:56 PM   #12
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When you pull the pan and clean out all the accumulated crap and filter, consider plumbing in a drain plug if there isn't one already. As discussed, flushing it can aggressively loosen clogs of crap, but changing the fluid in the pan, then driving for a while and then changing it again, then again a month or two later will have replaced 90% of the fluid in the tranny and torque converter with new, in a couple of stages. Never had a problem with this way, but heard lots of anecdotal "data" on problems with flushes on poorly maintained ones.

Then go to a set maintenance schedule at 2x the owners manual frequency. If it's staying nice and clean you won't need to change the filter every time, just drain what's in the pan, which will be about half the capacity.
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Old 10-31-2013, 11:37 PM   #13
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Bingo. 100k is NO problem with a modern AT. However, after that, I'd consider swapping out at least 1/2 of the oil. I swapped about 1/4 of mine at 110,000 miles. Then another 1/4 at 120,000. It's nice and clean (red)....so that should last another 100,000 miles with no troubles.

If you tow stuff (the killer of transmissions), that creates a whole different set of considerations (cooler to start). But for regular highway driving.....a little maint. will go 500,000 miles.

Don't forget the differential (WAY more expensive than the transmission) and the zerk fittins (if applicable).
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Old 10-31-2013, 11:47 PM   #14
troidus
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I think the problem with flushing comes from power flushing, where an outside source is used to force fluid through the transmission. If all you're doing is pouring fresh fluid in the pan and letting the transmission circulate the new fluid under engine power at idle, I don't see how anything is going to be damaged.
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Old 11-07-2013, 08:27 AM   #15
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My experience with this is. Only high mileage automatic transmission i have owned is the current one i am driving. its a 2003 nissan xterra, 154000 miles. i bought it at 19000. I changed the transmission fluid at 105000ish as recommended. It came out clear red. I then changed it at maybe 125000 and it came out like new. and again at 140000. I consider this a flush. I only just drained the oil and put in new, no new filter.

Is this the right thing to do i don't know but it has worked for me.

But then again, it's not a GM so. I would just drain it and put new in and see what happens....
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