TH350 Tranny Fluid Filter Change

[72BlckButy]

I would like to hear everyone's opinions... According to this past thread, people have stated that it is a bad idea to flush a transmission. I have owned my truck for almost 3 years, and have never had any service done to the tranny. First off the tranny is leaking from somewhere, where it's hard to tell, but I would like to replace the gasket/filter and just refill with new fluid.

Does anyone see any problems that might arise from doing this? I have heard speculation that this may bring out other problems by changing the pressure in the tranny, moving things around... and so on. This thing is leaking like a sive, and I would like to do some preventative maintenance, but now I'm a little worried to clean it out. I wasn't planning on flushing it, or using any chemicals to clean it out, it would mainly be just to replace the gasket/filter and add new fluid. I'm hoping the new gasket will help to minimize the amount of fluid lost...

Anyway, thanks for your experiences and information!

[BigDaddyDave]

What you want to do will not hurt anything, in fact that is considered regular maintenance. Flushing one can leave particles behind,that can get into places that can cause problems. I change my filter,fluid and gasket about every year.

[Longhorn Man]

Moved to correct forum


If the tranny is on it's last leg with black burned fluid, I would skip it.
If the tranny has red, or dark red oil in it, and doesn't smell burned, then chainge the fluid.
It's not only considered reg maint... it is outlined in the owners manual

[RicksTrucks]

My 69 SWB is still on it's original TH350 and I flushed it late last year and it is doing fine.

[71big block]

My experiance has been the th350 and th400 suffer no ill effects from flushing. for some reason the high milage 700r4s that I have flushed have experianced problems afterword, concidence????

[WorkinLonghorn]

Where's it leaking from? If it's the front seal it's got to come out anyway. Remove the cover and dry and clean the front of the trans, run it around and look again. Wet=front seal.Dry=maybe just the pan.
The 350 doesn't really have a "filter",just a screen which is easily cleaned.
Like LM says,change fluid unless really burnt.

[DavesRide]

Also check the seal where the dipstick tube goes in.

[cowboymike51]

I am going to Mechanic school right now, and i just rebuildt my th350, my Instructor told us, that you should change the filter and fluid every 30,000 miles or so. But he said that it the tranny has burnt fluid then it will do more damage to flush it and put in new fluid becuase the new fluid has deterngent in it that will basicaly make things worse for the old tranny. But it the fluid is still good than go ahead and change it out.

[Jered33]

Change the fluid and filter it's not hard. make sure to use a new gasket. When mine started to leak it was from the front pump seal, had to rebuild tranny.

[arkracing]

I would clean it all up and then run it to find out where it is leaking from. If it is comeing from the hole in the inspection cover, then it is the front seal. It may be coming from the dipstick, the pan gasket, or even the shift linkage (there is a little o-ring in there).

If you do change the tranny pan gasket and filter, be sure to loosen up all but one side and then slowly loosen those up so that you can tilt the pan to one corner. No matter how hard you try, you will probably spill some, so have plenty of rags AND speedy dri ready

you're only draining a few quarts when changing the pan gasket. They hold about 9qt total. TH350's are pretty forgiving, so if it is shifting fine that you shouldn't have a problem.

If it is the front seal, the tranny has to come out. You don't have to rebuild the tranny though, you can get a seal for it and put it in - I've done it several times before.

[Longhorn Man]

if it's the original tranny, it should have a drain plug. It's pretty cool, it doesn't leak like that Mr Gasket piece of crap drain plug kit they sell.

[72BlckButy]

What types of buckets or pans do you guy's use? I have the 5 or 6 qt oil bucket that I had planned on using, but I figured I would fill that in a hurry. Do they make a 9 to 10 qt. bucket?

Hey thanks for the info guys. I guess I got a little confused on the definition of flushing the tranny. Looks like I will have a weekend project to keep me busy then. I will let you guy's know how it turns out.

[DennyB]

If your just draining the pan then your drain bucket is fine.
I would not recommend draining the torque converter unless your pulling the trans.

I also use a synthetic blend trans fluid. The blended fluid is compatible with regular fluid and I noticed it firmed up the shifts a slight bit. I like the stuff and have used in all my vehicles.

I use Valvoline Durablend trans fluid. I won't use Valvoline oil but like the trans fluid.

[RicksTrucks]

Originally Posted by 72BlckButy

Hey thanks for the info guys. I guess I got a little confused on the definition of flushing the tranny. Looks like I will have a weekend project to keep me busy then. I will let you guy's know how it turns out.

I did my flush with a machine at the local votech. I am taking a 7 week class just to be able to use all of their equipment. (Cleaned the fuel injection on the van the other day - saved at least $100).

I think I bought 12 quarts for my TH350.

[Longhorn Man]

In all reality, if you want to run synthetics, there is no point in a blend, that is only a little better in quality. Plus, in all reality, there is very little point in pouring it in a used tranny. There is no way prectical way to get all the oil out, so it gets diluted with the old stuff, decreasing the benifits even more.
I use mobile one dextron in the longhorn, took 11 quarts (I have a TH400 converter that is bigger than a TH350 converter) and it took $75 to do (with an extra quart on my tool box). But I know I have absolutly no mineral based oil and the stuff is almost like insurance.
I gotta say, it sucked when I had to replace my converter though. Another $75 in oil.

[72BlckButy]

Dumb question... it takes Dexron III or Mercon right???