High Mileage Auto Transmission Fluid Change Question

jcolby · October 1, 2007

I have a Sierra 1500 5.3L with 115,000 miles. I'm guessing that the automatic transmission fluid has never been changed. I just bought it and it feels like it's shifting pretty hard. So I'm wanting to drain the fluid and put an additive in. I'm wondering if I would do more harm than good. I've heard that changing the fluid this far along can cause problems. Should I change the fluid and then change it again in 5K miles, leave it as is, or do one of those total tranny flushes? Thanks for any advise.

luminaapv3 · October 2, 2007

I have a Sierra 1500 5.3L with 115,000 miles. I'm guessing that the automatic transmission fluid has never been changed. I just bought it and it feels like it's shifting pretty hard. So I'm wanting to drain the fluid and put an additive in. I'm wondering if I would do more harm than good. I've heard that changing the fluid this far along can cause problems. Should I change the fluid and then change it again in 5K miles, leave it as is, or do one of those total tranny flushes? Thanks for any advise.

Drop the pan and drain the oil, put it back together, add enough fluid to top it off, just remember that there is still fluid in the converter, I can't remember how much it holds, something like a quart or two, maybe someone else can remember on here.

Anyways run it for about a week, drop the pan, Change the trans filter, put new fluid back in and bolt it up.

You can try to get away with using the same pan gasket for the first time, I DID and it did leak a little, but not enough for any great concern, use your own judgement, you can always use a new one each time if your concerned, I'm just cheap , but I did check it every day.

I say to do it this way so that the first time it has time to mix with some of the old crap left in the converter and the second time make sure you change the trans filter, Don't do it on the first round or you'll be just defeating the purpose!

Also most shops won't touch a truck with over 100,000 miles on it, against policy, this is the part that could do more harm than good, seals aren't strong enough to handle the flush pressure. Good Luck and have fun, I'm in the middle of a project myself.

jcolby · October 4, 2007

Thanks for all the advice. I feel more confident changing out the fluid now. I've got a stripped out drain plug right now, I'm going to hook up some vice grips and try to get it off. I think the plan I'm going to do is drain it without changing the filter and then drain it again in a week or so and change the tranny filter. Also adding some Lucas tranny additive, hopefully smooth things out a bit. Thanks again.

spartus · October 5, 2007

Good idea of hooking up hoses to the tranny cooler. I'll probably go that route. Didn't even think of that. Thanks.

That is what I was going to suggest, and the way I do it. I usually buy 16 quarts. Most GM cars and trucks with the 4L60E have a capacity of around 12-14 quarts, and there are 4 quarts to a gallon. I take a bucket with graduations on it, and drain 1 gallon at a time, then pour 1 gallon of fresh fluid back into the trans.. Once all 16 quarts are gone, I know I've flushed most of the used fluid out of the complete system.

Norseman · October 4, 2007

Thanks for all the advice. I feel more confident changing out the fluid now. I've got a stripped out drain plug right now, I'm going to hook up some vice grips and try to get it off. I think the plan I'm going to do is drain it without changing the filter and then drain it again in a week or so and change the tranny filter. Also adding some Lucas tranny additive, hopefully smooth things out a bit. Thanks again.

When you get that drain plug out ( I used vise grips from the inside after I took the pan off) go to CarQuest and get a regular oil plug bolt to replace it with. I don't really understand why a regular bolt wasn't used in the first place.

RCH · October 4, 2007

Thanks for all the advice. I feel more confident changing out the fluid now. I've got a stripped out drain plug right now, I'm going to hook up some vice grips and try to get it off. I think the plan I'm going to do is drain it without changing the filter and then drain it again in a week or so and change the tranny filter. Also adding some Lucas tranny additive, hopefully smooth things out a bit. Thanks again.

I would be leary of additives, I have never had one work. If you drop the pan and replace the filter, then refill with a good synthetic you would be better off. When I switched to synthetic that's what I did and it worked out fine. I also disconnected the transmission cooler return line at the transmission, clamped about 5ft. of clear re-enforced hose and drained it into a 5 gallon bucket. I had my wife start the truck and run it for about 2 or 3 seconds then turn it off and I would add more fluid. We did this until clean fluid came out of the hose, then removed the hose and reconnected the cooler line. Just be sure not to run too much out at a time, you don't want to run the transmission dry. it was very easy, and you get a clean pan, new filter and fresh fluid. (Just my .02) LOL

C & A s Dad · October 5, 2007

This is how I did my flush as well. I was upgrading my trans cooler, changing the fluid and filter all at the same time. While I had the cooler lines off, I flushed it one qt at a time with my Wife starting it while I watched the glass catch container. I used a glass container so I could watch the color and clarity fo the fluid change as I went through the process. I initially got the instructions off the Amsoil website which is a good blow by blow for someone who may be a little unsure.

As far as the drain plug. It is installed at the factory with a medium strength thread locker. If you have a drain plug that is not already stripped. Use a good quality 6 pt impact style socket and make sure it is on the plug good and straight. Also a small amt of heat from a propane torch will melt the threadlocker and allow the plug to come right out.

If is already stripped, heat it a little with the torch and then use vise grips if there is any head left to grab.

jcolby · October 2, 2007

Thanks for the advice. It was kind of what I was thinking. The reason I think the fluid has never been changed is that the tranny drain plug immobile. I've already rounded off the hex head trying to get it off. I'll probably have to put a drill bit through the plug and hope that it comes off. But will probably end up having to get a whole new drain pan. So frustrating yet so fun at the same time. Thanks for the advice. Anybody else have $.02 on the subject?

Draenor · October 2, 2007

Jared, If the fluid already smells burnt and looks dark or has small clutch particles in it, I would save up and have it rebuilt. If you flush it in that condition the transmission will not last too much longer.

If not definitly changed the fluid and filter.( A flush is OK, ONLY if the filter is changed also.) If you do it yourself, take note on how dirty the bottom of the pan is, this will be an indication of how long the fluid has been in their. Also hard shifting may be caused by sticking soleniods, probably crud from the lack of maintenance. You can always pull out the valve body, clean out the passages and solenoids. Depends on you faith in your skills.

As Mark mentioned you may want to run it a week or two and change it again.

C & A s Dad · October 4, 2007

Jared, I would have to disagree with your thinking that 115,000 miles is "high mileage". There are many of these trucks running around with a lot more miles. I would agree with John, drop the pan, change the fluid and filter. You will get approx 5 qts out of it doing this. If you want to change all of the fluid, you could have a flush done but be sure they drop the pan and change the filter. Some shops want to do a flush and call it done. This does not change the filter and is not a complete job.

If it were mine, I would just drop the pan, change the filter and put it back up.