Best ATF Type for old th350 trans

[demian5]

Ok Transmission guys (not tranny guys), I am going to service the fluid and filter in my unknown mileage th350. I want to know what would be the best trans fluid type to use. And Id like to try and pick it up locally.

Im not having any transmission issues or leaks either, drives and shift great. Downshifts like it it supposed to. No excessive clunking when putting into drive or reverse.

And in your experience, with a stock depth pan, its 5 qts for a filter change if I remember correctly.

Keep in mind, I don't want to stick "royal purple" $30 dollar a quart stuff in there (that's what the ZF fluid for the wife's BMW costs, so I'm good).

I will also change the dipstick O-ring while I am under there.

Any other tips? I mainly need the best trans fluid type for my old, unknown mileage, transmission. And maybe you know of a good additive.

Thanks!

[MARKDTN]

Why not just Dextron III from WalMart or the parts stores? No additives. I like a genuine GM filter mainly because the gasket is not folded to go into the box.

[demian5]

Originally Posted by MARKDTN

Why not just Dextron III from WalMart or the parts stores? No additives. I like a genuine GM filter mainly because the gasket is not folded to go into the box.

Agree, but seems can only go grab dext/merc

[garyd1961]

You might want to think twice about changing it if it has a lot of miles on it. You could cause trouble where there is none. If you change the fluid you should do it every 30,000 miles or don't do it at all. The new fluid will loosen up all the crud and deliver it to places it has no business being.

[Alex V.]

Valvoline Maxlife "Multi vehicle" Dex/Merc ATF.
The "every 30K or not at all" rule seems a little much - on any transmission with an unknown history you run the risk of dislodging gunk, but if the fluid isn't terribly dirty or burnt already chances are it won't hurt it. If nothing else, siphon out about 2 quarts every thousand miles for a while (freshen up fluid slowly) then do a normal pan drop.

[garyd1961]

Where I work we don't recommend a fluid change if it has over 60,000 on it.

[demian5]

Originally Posted by garyd1961

Where I work we don't recommend a fluid change if it has over 60,000 on it.

Yes I believe this is an OG 93k mile trans in a 69 driven by an grandma... It has a drain plug, and I had to add 3 qts to get it driving, but its OK and doesnt seem to leak. I replaced the tailshaft seal, my concern is the dipstick o-ring is going to leak soon as well.

[toolboxchev]

Originally Posted by Alex V.

Valvoline Maxlife "Multi vehicle" Dex/Merc ATF.
The "every 30K or not at all" rule seems a little much - on any transmission with an unknown history you run the risk of dislodging gunk, but if the fluid isn't terribly dirty or burnt already chances are it won't hurt it. If nothing else, siphon out about 2 quarts every thousand miles for a while (freshen up fluid slowly) then do a normal pan drop.

I have used this product on a very old transmission with very good luck. I flush the entire unit out by simply disconnecting a line off the Transmission cooler and place a section of hose into a 5 gallon bucket. Beforehand, drop the pan, replace the filter, and seal up the pan and gasket with some Permatex.

Lots of miles here, over 100k. So far, so good. I have flushed my unit over 5 times since ownership 12 years ago.

The Turbo 350 is a very solid design.

[Rich69shortfleet]

If it was a completely dry fill I'd say good ole Type F fluid. Firmer shifts which helps it run cooler. A GOOD shift kit is easy to install and helps firm things up to help with longevity. GM Dextron fluids are fine, but are softer, slower fluid which allows the clutches to slip more, therefore wear faster.

If it is just a drain and filter change, put in whatever is in there now. If you don't know, chances are it is probably a Dextron fluid and I'd stick with that.

Not changing the fluid on a trans that hasn't seen a fluid change in a long time or many, many miles makes no sense to me.

As far as sealing up leaks, the speedo bullet is often a leaky point. Consider putting new o-rings in that as well if you see even a little wetness in that area.

[68Gold/white]

Use plain old dexron III, Walmart brand, that's all you need. There are 2 types of filters for a TH350. One has a screen type filter, it is the preferred one to use. It will not clog easily. They also make a fiber element filter. I would not use one, if possible.

I would not use any Royal Purple products, ever.

Drive it!!!

[WorkinLonghorn]

Rich69 shortfleet says;

"Not changing the fluid on a trans that hasn't seen a fluid change in a long time or many, many miles makes no sense to me."

I used to work in a few shops in the early 80's and people used to show up with vehicles with very high mileage and what looked like original fluid all the time. It was quickly learned that changing the fluid (just what is in the pan) would cause some of these vehicles to start malfunctioning. Customer would scream that "It worked OK when I brought it in!! You guys did something to it!" - and call the State Bureau of Auto Repair.

So it's a rear guard action by the shops. Personally I feel that if a fluid change causes problems then it would not have been good enough to trust in the first place and was well on it's way out.
We always used Type F in all the GM Transmissions -BA

ps. I saw a heck of a lot of TH400s starved of fluid and burnt up due to a clogged fabric filter (the fords all had screen filters iirc) so the advice above from 68 gold/white seems logical.

[GASoline71]

Do not use Type F... There is a thread in here somewhere about why not to use Type F in Turbo Hydromatic transmissions. I'm too lazy to search for it, but in a nutshell if you use Type F in a GM transmission that has been running Dexron it's whole life, you'll shorten the life of the transmission.

Plain ol' Dexron III or DexIII/Mercon will be the best. You can use the cheap parts house brands...

Gary

[demian5]

Awesome info.
I have a WIX filter and gasket. The filter is a screen, and like I said, to get it moving I had to add about 2.5 qts of fluid (used cheap dex/merc then) , so whatever would go wrong with new fluid, has hopefully passed. I have driven it about 100 miles since topping off and it shifts a little lazy into 3rd under a hard accell but I feel its ok. Ill ball peen the pan holes and put some permatex on the pan side for the gasket. Ill pull the speedo bullet and change the O-ring and maybe the modulator too and do the o-ring there (I have a nice assortment of O-rings.

Another thing, when I got it, the TV cable wasn't connected. When I topped it off, I connected and adjusted the cable and that works great as well.

[7 Devils]

Ok, I gotta chime in on this one.... Over 60k don't do a trans service/flush. Wholeheartedly disagree. If the fluid in it is burnt and has particulates in it then yeah a flush is probably going to cause it to stop working. The reason being is because those particulates are the only thing in the poor thing causing enough friction to work in the first place! Flush them out and yeah it'll die. On a trans in good working order that doesn't have a bunch of gunk in the fluid, flush away, BUT, let the pump in the trans do the work to flush and don't use a power flush machine. Done it lots of times under those guidelines and not once had a problem. Gm/Ford/Dodge/import, etc. Also, do your research as some manufactures clearly instruct no to power flush the trans. Honda is common for that. Drain and refill several times for most of them.

Dextron/Mercon III is fine for your TH350 and other such models (pre 86). In addition, anyone ever run B&M Trick Shift in a GM tranny? Its spendy and its much cheaper by its other name....Type F. I have run Type F in nearly all of my drag racing automatics with fantastic results. Exceptions being Lencos and Jericos. In DD stuff it works quite well if you want a firmer/quicker shift. This only applies to TH350/400/200R4 and the likes. Newer stuff is a bit more sensitive.

Its a common sense/wives tale thing. Sure a nearly dead, badly maintained trans with semi-metallic ATF (LOL) will die if you flush it. One in decent shape that needs serviced or has fluid starting to burn will be fine done correctly. Think about it, your running dirty/old fluid out and filling it with correct fluid at the same time WITHOUT a power flush machine and guess what? That new fluid is running through the very same lines/valving/clutches/band/steels/spags/etc, as the old fluid. What about that inherently causes "stuff" to be dislodged?

I've been building my own for years and have yet to personally see that take place. Not trying to ruffle any feathers or shoot any sacred cows and I know I'm a newbie on the board but that's my 2 cents.


Dan

[garyd1961]

I have seen a lot of transmissions run 250,000 and 300,000 without a fluid change.

[WorkinLonghorn]

I think it was more a matter of adding fluid that has much higher viscosity than the ancient stuff being replaced causing slippage. I'm talking about 35 years ago. We did around 10-20 a day so I do have some experience (well a little that I think I still remember anyway). -BA

[WorkinLonghorn]

Originally Posted by garyd1961

I have seen a lot of transmissions run 250,000 and 300,000 without a fluid change.

If we got a very high mileage vehicle in one of the shops with fluid that looked and smelled old with very little viscosity the shop owner would tell them to leave it alone if it was working well. I think we collected $19.95 or $29.95 for a fluid change (the pan fluid) so for a shop in those days, we would not risk messing with them. Talking 1979-82 -BA

[Grumpy old man]

cheap dollar general trans fluid . dex/merc . Type F is for Fords .

[demian5]

And......... its now leaking from the front of the pan

[Steeveedee]

If you had the pan off, just snug the bolts a little more. Do it a bit at a time, if you aren't sure that you have a real feel for the torque. The bolts just may need a little more.

[garyd1961]

If I had to drain the pan for some reason I would go ahead and change the fluid and screen then hope for the best but if everything was working fine I would leave it alone.
Pan leaks on these transmissions can be a real pain to stop. Be sure to straighten the pan and use a good gasket. If you use any sealant be sure it states that it is trans fluid resistant, trans fluid will eat most sealants. Don't over tighten the bolts or you will cause more leaks.
It took me a while to stop mine from leaking.

[Steeveedee]

If you haven't had the pan off yet, and the flywheel cover is still installed, take it off and see if the leak is at the front seal.