Cavu2u

Hi.

'73 Coupe with a stock TH400.
I'm dropping the transmission in order to R&R the leaking Oil Pump Cover Gasket and it's O-ring.

Is the only securement of the Oil Filler Tube the Case's hole it seats in, or does the tube have a welded tab and bolt (in a hidden and hard-to-reach place) holding it in position? Seems a little stubborn to move. I'm trying to drive it out from the bottom since the Pan is off, with a perfectly sized socket.

Thanks much.
Steve

bazza77

http://shop.docrebuild.com/1968-1973...0120NOS-1.aspx


please STOP hitting it

7T1vette

That bore it fits into AND the o-ring that is on it.

BTW, if you are getting oil leakage from the front of the trans, it's probably due to the oil pump bushing being worn out and allowing the lip-seal to wear prematurely.

Rodnok1

It is secured on tran to engine bolt. It'll pop right out then so stop beating on the end or it'll egg shape and never seal right again.

71VetteLover

Yes, it has a welded-on tab about 3" long and it is attached to one of the transmission-to-engine bolts.

Cavu2u

Thanks folks for "enlightening" me.
I'll find that bolt and remove it.


Steve

Cavu2u

Thanks 7T1.

Not sure, but if that lip-seal is leaking, would the oil show up coming from the area where the TQ fits onto the Transmission's Drive Shaft, with the rear face of the TQ and entire Oil Pump Cover (or at least the area from the shaft on down) wet? These areas on this transmission are dry.

Before I drained the tranny, I "watched" both leaks, they were so bad. With a paper towel, I blotted the areas; (1.) forward left corner of Pan-to-Case, and (2.) just the bottom of the round Oil Pump Cover. It took only seconds for the seeping from both areas to show. Am I correct in thinking it's the Pump Cover's big O-ring?
The '73 GM Shop Manual says the Pump Cover Bolt torque should be 18 Ft/lbs. and an instructional CD of the TH400 mentions 2 types of bolts: one with flat washers and one with O-rings. I wanted to find out which type I had, so I removed the lowest Cover Bolt (oil then drained out in a nice slow rate), and found it to be the steel washer type.
When I removed the Pan (BTW, I was wrong in earlier ID'ing the type gasket it had), the shop used a cork gasket with no sealer. And looking closely, yes, it did indeed have a very, very small cross-wise dent in that leaking forward left corner of the Pan's flange. So, I flattened out that area, maybe at least solving that leak.

Sorry again for the novel.
Steve

7T1vette

A leak in the torque converter area is nearly always the lip seal which seals against the converter input shaft. But, THAT seal gets worn out when the [internal] bushing gets worn. You can install another lip seal and reassemble it....but it will likely start leaking again in a few weeks/months.

If the trans has a lot of miles on it, it's probably time to have it rebuilt or swap in an overdrive unit (700-R4 or 200-4R). You can rebuild your THM-400 or swap it with another rebuilt 400, but that transmission is heavy and inefficient, though pretty much 'bullet-proof'.

There are a lot of parts that wear out in any auto tranny; I would surmise that it is time to rebuild or replace yours.

Cavu2u

Appreciate your thoughts!
Would that [internal] bushing you referred to, be pressed in the Oil Pump Cover, or is it the Center Support Bushing further in the Case? Wouldn't be a problem just taking the cover to a tranny shop to R&R it.

As far as what the odometer says, there are 70K miles worth of wear on the Speedometer Cable. Know what I'm sayin? Someone stripped a Transmission Pan Bolt Hole, so they Helicoiled it to the next larger sized bolt. I HATE THAT! So what else is modified on it? Lord knows.


Steve

7T1vette

It's the bushing in the [front] support/pump assembly. Yes, you could take it out and have a new bushing installed along with a new input shaft lip-seal. If the car only has 70K miles on it, the trans MAY last a long time that way. If someone rolled by the odometer.....maybe not.

That choice is yours, of course; and I understand not doing more work than is necessary. I suggest you make that decision based on how long you intend to keep that car. If it is a long-term 'keeper', you might consider getting a full rebuild so that you will never have to mess with it again. (Yeah, sure...) If you only plan on keeping it a few years, the stop-gap fix might work fine for you.

P.S. Keep in mind that the plastic/Teflon piston seals, etc. tend to harden and shrink over TIME, as well as wear due to actual use. And the seals in your trans are well over 30 years old....

gungatim

^^ what he said. the seals and things can harden over time even with few miles. if it were me, I'd have the entire thing gone through once it's out of the car. new seals clutches and bushings are cheap insurance short of just buying a new rebuild...you could even do much of the work yourself with improvised tools (do a search on how to make them from c-clamps and threaded rod), but the bushings you'll need to have done at a shop most likely.

Cavu2u

7T1 & Tim,

Yeah, it's a keeper. I sort of feel compelled to do things the right way anyway, mainly because I've inherited some pretty bad things/fixes associated with used vehicles myself.

The transmission was running ok (shifted normal, no unusual noises), just leaking badly. Right now though it's got 400+ horses driving it, up from the stock 190.

I've decided: I'll drop it and take it to a shop and have them overhaul it. It should be done right. For a valid warranty, most shops understandably require tranny installation by them, so I guess I'll miss out on that (unless I can figure out a way to hold up the engine's rear during the tow process).

I'm installing the new filter and pan, and now I'm about to disconnect everything on it. Plan on building a wooden holding jig for the jacking process, as it appears to me the pan isn't a good choice for supporting the whole thing. It's an adventure, and besides that, it keeps me outta the bars.

Thanks for the inputs.
Steve

71VetteLover

I started overhauling my automatic transmissions when I was a kid back in the early 1960's. With a Haynes G.M automatic transmission manual and readily available tools anyone can overhaul an automatic transmission. Or you can easily make your own tools like I did.

Cavu2u

71VL,

Ya know, your not the only one I've heard say that. I'm tempted, but I ain't a kid anymore. And I admit my frailities too, for I've been known to "miss" things on assemblies, which usually come back to bite. Thanks for the input anyway.

BTW, when I installed the pan today (original), it seemed "wavy", or the contact surface with the case seemed uneven (sorta like "No wonder it tends to leak!"). I'm seriously considering buying a new pan (with a drain plug too).

Steve

Cavu2u

Gee, there seems to be a lot of good TM400 do-it-yourself YouTube vids out there.


Steve

gungatim

I did the same, only it was the '80's, and I got the Haynes manual from the library, lol...made my own tools as well. TH350's, and TH400's are pretty simple. not as many critical tolerances like the the ones that use TV cables.

OP: the pan being wavy is because someone over-torqued the pan bolts. you can flatten it out with a body hammer gently tapping on a flat surface or dolly. like doing sheet metal work, you don't hit hard, just sort of slap it and let the hammer head lightly vibrate if that makes sense.

Around here, warranty usually does not require they install, many shops accept drop-off's and pick'up for owner install, so you may check around. also It used to be pretty price competitive to just order a mail order rebuild but I haven't priced one in a very long time...

Cavu2u

King's X!

I'm changing my mind about taking the tranny in for major rebuild.
In one of the boxes of parts I received when I bought the project, was a used internal Transmission Bushing. Along with the fact that the transmission is operating great, I believe it has been rebuilt before. Therefore, I'd say, as some foreign maintenance shop manuals describe it to be, false economy to have it rebuilt again. After all, it was only seeping oil from the Pump Cover (not the Shaft Seal) and the Pan Gasket.

And, by working on it myself, got a nice warm fuzzy in finding the transmission's stamped serial number matches the car's VIN.
Kinda cute the tranny's side tag is pink too.

I have spoken.
So it shall be.
My Car.
Steve