Technical TH350 Replace Fluid, Filter and Gasket or leave alone?

I'm sorry, I've never heard of not changing your transmission fluid! It's routine maintenance as far as I'm concerned. Aren't you already checking it and replacing fluid lost? My beef has always been: why don't transmission pans have a drain plug?

 

They are available , or you can retro fit one . The downside is not changing the filter or inspecting the particulate left in the pan.

 

Some of the early automatic transmissions pans came with a drain plug. Then the manufacturers realized they could save 50 cents by not installing one.

 

Naw, they decided to buy stock in oil absorbent and shampoo.

My ‘03 Chevy PU does have a drain plug tho

 

I'm actually remembering something now. I see the speedometer needle fluctuate a lot left and right when I'm driving, I think more at lower speeds but I can't remember and I also hear a light grinding noise perhaps in the dash as it's doing it. Maybe a stripped gear in the dashboard or related to the speedometer retainer missing on the trans?

I checked the speedo bullet and it's steel. It has a red gear which equates to 21 teeth. I checked the gear and stem and didn't see any ridges worn into it but a little play around where it rides. I've read the internal seal can be hard to replace so I just bought this assembly rather than to keep wasting time:

https://www.ebay.com/i/161276926451...g=2386202&algv=DefaultOrganic&brand=Chevrolet

No clue what rear end the truck has and whether someone deliberately chose the 21 tooth gear over other ones and whether I would need to change the internal drive gear to change to a different number of teeth so I ordered a replacement with same number of teeth.


I also spun the speedometer cable by hand and it spins freely so not sure if maybe a broken tooth on the drive gear inside the trans. or something in the dash.

 

Classic symptom of the speedometer needing to be oiled. On the back side just above where the cable screws in there is a small hole with felt/wick type material in it. That needs to be lubed, usually spray some WD40 or similar in there to get it loosened up. Sometimes there is a small brass cap in the hole that needs to be removed with a pick to oil it.
On some cars it's easier to pull the speedo and oil it on the bench rather than climbing under the dash.
I've attached a generic picture, they are all similar regardless of brand.

 

I'll give that a try thanks!

 

Changing the trans fluid, filter and pan gasket is one of those jobs that is less daunting now after years of experience working on cars than when I first was learning my way through it. I say with all respect to the OP, we all have to start somewhere. I think Bundoc Bob got it right in post #2. I'd do it if for no other reason than it's annoying to have a car that leaks fluid all over the place and louses up your driveway. My Jetaway leaks like a sieve and I'm always parking it nosed in over the grass. It sucks. If you're concerned about being able to true up the pan with a hammer and dolly, I wouldn't hesitate to buy a new pan, especially a cast aluminum pan that will be less likely to distort. I also like to wipe gasket sealing surfaces down with some lacquer thinner to remove residual oils that might inhibit gasket sealing. I too prefer cork gaskets. If you don't have one already, get yourself a 3/8" drive torque wrench (a $10 unit from Harbor Freight will suffice just fine), and pay attention to torque specs and tightening sequence. Go hand-tight first, and work incrementally up to final torque spec, which appears to be 12-13 ft/lbs, or 144-156 in/lbs.

Finally, I would also say that I wouldn't be surprised if after perfectly executing a filter and pan gasket change, you still get an annoying leak. It's been my experience that transmissions usually don't leak a whole lot from the pan gasket. The leak us usually somewhere else, and manifests itself in a way that makes you think it's the pan gasket. For example, a front pump seal that weeps and drips down the front of the trans, then hits the gasket lip and rides around the gasket to the sides, and leaks off there. If the front of the trans pan is wet, or if you remove the cover over the converter and it's wet or oily in bellhousing, I'd bet my ass you have a leak in the front of the trans. That wouldn't be a surprising occurrence if the trans is older, and especially how little you drive the truck, which only seems to exacerbate those kinds of issues. If that's the case, you're going to have to either replace the trans, have it rebuilt, or just learn to the deal with it. Don't be afraid of that job though.

 

Thanks for the advice, I'm going to give this work a go and if it still leaks it's not the end of the world but I will feel better having tried.

 

What Joe said.
And if you can, I'd crawl under and soak it down with some good degreaser, maybe simple green, and then go to the car wash and hose it down good. Not only because I hate working on messy parts, but it will also help you see where your leak originates from.

 

OP, get yourself a wide square pan. Twice as big as the pan on the transmission. What I do is take out two bolts opposite of each other on the front of the pan, put in two longer bolts with about a 1/4-1/2inch space from tightening. Then work back taking all the bolts out except a few at the rear of the pan.

then loosen the two at the rear a bit, break the gasket seal in the front where the longer bolts were, and lean the pan “tilt” down in front. Fluid should start dribbling. Then when the dribble stops I loosen the longer bolts some more. The idea is to keep the pan tilted and try to get as much fluid out as possible before pulling it off

Get a bag or two of cat litter as well

 

Could also be a dry cable ..

 

"...referring to the whine, what causes this? I have a th350 with a whiney 1st gear and the trans mount was failed when I bought the car - the misaligned crossmember has been reworked and the mount replaced..."

If the 1st gear whine doesn't go away when the rear mount is changed, you have another issue, but generally 350 planetaries don't fail for any reason. It is normal to have some 1st gear noise with any Simpson type 3 speed automatic, as both planetaries are transmitting torque in 1st.

 

Quick question, I'm looking online at th350 pans and most of the ones available look like this one:


I'm better off just using the stock and flatten? I have access to vices, hammers, punches, all sorts of shapes of metal plates at my work and can take the stock one and flatten with patience. I read in other forums the aftermarket ones can be worse. It seems anything under $50 are these chrome plated steel ones.

Secondly, should I change the accumulator seal? I can't tell if it's leaking much, its dirty around that area on the trans but not sure that's a difficult seal to change. I forgot to add that one to my list.

 

Stay away from the inexpensive chrome pans. It was mentioned before, but a good cast aluminum one is a much better option. Reason being they won’t flex, tweak the mounting holes, etc

 

That's basically the exact same thing you have except chrome. Personally, I think it's actually a downgrade in terms of sealing ability since a chrome surface is smooth and shiny and a difficult surface to get a liquid-tight seal on, whereas a bare steel surface has more bite and adhesion to the gasket material. Same would hold true for cast aluminum, which will remain flat and not be as susceptible to warpage or distortion with tightening. The only benefit to the chrome pan is that it's shiny.

This is more or less what I was referring to. https://www.jegs.com/i/JEGS/555/601...5SxIb-LZFlzDkv3oJjflaJ_k5zApLf_0aAmqXEALw_wcB

I wouldn't change the accumulator seal off the top. Change your filter and pan gasket first.

 

Thanks, I found one on ebay just like it for a little less:
https://www.ebay.com/itm/Chevy-Alum...rand=Unbranded&_trksid=p2047675.c100005.m1851

So it's probably better for me to just buy another pan vs. trying to straighten the stock one? Another thought I have is to use button head socket cap screw, that might allow me to use an allen key with ball end and maybe can take the bolts out for next time around without needing to take the trans cross member off. Only thing is might be hard to get a socket in there to use a torque wrench for future work so maybe that's pointless.

 

I often use Allen-drive cap screws for places where I can't or have difficulty getting a socket around a nut. Exhaust headers and oil pan bolts come to mind immediately. Your trans pan would also be an ideal application.

 

I installed a chrome 350 TH trans oil pan with a drain plug in my previously owned Model A Roadster along with a new filter. I was careful to clean the gasket surface on the trans. Installed the new pan and gasket and never had any leaking problems. I like to cement the gasket to the removable part and then spread a very thin coat of grease on the exposed side. This allows the gasket to stay in place when installing and allowing some movement to match up bolt holes without disturbing the gasket. Also, this will allow the pan to be removed in the future without the gasket sticking to the component surface.

 

Thanks, I went ahead and ordered the polished cast aluminum pan. I might be able to straighten the stock one with patience but I've never done it so better to just skip that part of the job so I don't have to remove the pan twice possibly.

 

Its difficult to use a wobble on a Allen drive .
OP , straighten your pan rail if its not rusted
Isn't there a rubber pan gasket with torque limiters ?..

 

Thanks, I went a head and ordered a polished aluminum pan to make it a little easier.

 

That's true that it can be difficult to use a universal on a Allen but you can also just use ball-head Allens and get some articulation that way in lieu of the universal.

 

That's what I was thinking. I'm going to use some button head 5/16-18 bolts and hopefully can find a ball end allen socket combo that I can use on a torque wrench.

 

Hi, does anyone recognize the blue grease in the photo for the speedo bullet assembly? I bought a new one with new red gear and it came with blue grease but I'm not sure if that's supposed to stay or I'm supposed to clean that off.

 

It looks like assembly lube, you can leave it.

 

Dropped the pan, so much fine metal particles! I'm hoping everything works as it did after I change the fluid. I'm not going to clean this pan up as I got a new cast aluminum one.

 

I'd say your problems with that trans run much deeper than a leak.

 

The entire pan isn't full of that much just pockets of it but almost guaranteed. I was just trying to take care of it leaking on my driveway or at least lessen it. I don't drive it far from where I live so I was hoping to keep hopping along until it completely died. With that mindset, I'm not sure changing the fluid in it's current state is a good idea or not. I saved the old fluid in a big pan I could reuse I suppose. I'm not looking to put big money into this truck otherwise I wouldn't care about rolling the dice and having a shop rebuild the trans if I made it worse.

 

Take the fluid to the recyclers. Don't reuse it.