My '69 Cutlass Convertible had a 3/4 restoration in 2015 with a complete engine (350 Rocket) rebuild. I've owned the car since '87, have about 155,000 miles on the automatic transmission w/just over 10,000 on the new engine.

The transmission leaks, and my mechanic says he's replaced every seal/ring etc. His suggestion is A.) pull & rebuild the old one, or B.) buy and install a 'new/rebuilt' one.

I don't have a posi rear end (my '70 Delta 88 with the 455 did!) and I can count the times I've spun the tires on the Cutlass on 2-hands.

Looking for suggestions / thoughts from guys who may have been down this road already. I appreciate any input......as I wait for some good Summer weather here in Maine!

TY!

 

How original is the car? Which transmission is in it now, a 2 speed auto or a 3 speed? If it is a 2 speed I'd definitely considering replacing it with a 3 speed TH350, if it is currently a TH350 have the one in it rebuilt.

 

OK--Was hoping that my lack of knowledge about my cars mechanics wouldn't pop up----but here goes---I have Drive, Super, and Low (and Reverse of course) ---so does that qualify as a 3-Speed?

If I do have that rebuilt, do I need a new drivetrain and rear end? I'm a 'cruiser' vs a 'hot rodder' --- the car has always been more 'torquey' than quick.

Thanks again!

 

Yes, that is a 3 speed TH350. Only the transmission needs to be rebuilt not the entire drivetrain; however, it would be a great time to check the universal joints (2) in the driveshaft, replace the transmission mount and change the oil in the rear gearbox/differential.

 

Sometimes transmissions leak significantly at the connection point of the speedometer cable.

Yes, lucky man. Most automatic 69 Cutlass Ss are 2 speed.

With your wants and needs I wouldn't do more than necessary. I'm assuming 2bbl carburetor, is the air cleaner housing black ?

If so that would explain the sleepy throttle response. 2bbl 350s came with a 2.56 rear gear standard. Very sleepy.

 

Sugar Bear is bang-on with his advice, I would only add that since you seem a little disappointed with your car's performance, an alternative transmission might wake it up a bit. A four-speed overdrive (TH200-R4) is a fairly easy swap and the lower first gear will give you more dig off the line and the overdrive will reduce RPM on the freeway leading to better fuel mileage and quieter cruising.

Not a good choice if originality is a concern but might be worth considering if the car is to be a driver.

 

Does the transmission work fine? Go to a different shop and get it fixed. No need to rebuild something that just leaks. Also, what kind of a leak are we talking about and over what period of time? If you let it sit for a month and there's a paper plat sized spot on the ground, it barfed some out a vent or somewhere when the torque converter drained a bit over the month. Checking fluids should be done before every period of use.

Now, if it puked a quart on the floor from tire to tire, sure, that's an issue.

 

I agree w/ John, T350 is great trans, but lots of spots to leak- Speedo, shift linkage, Kickdown cable, etc. I actually sprayed (fogged) the whole bottom of my trans with plant pesticide and finally found my leaks!! Sounds weird I know, but the powder shows where fluid comes from. Wifey happened to be dusting plants that day and light bulb went off....

 

Thanks to all chiming in. Here's what I do know.
Car is very original-I'm the 3rd owner (purchased in '87 w/72,000 mi ($2,500!!!) and I know the previous owner was not a street racer!
Carb is original 2 bbl / w black cleaner housing.
No AC - Bummer- If you've ever driven a flop-top with black interior in the middle of the summer----anywhere----you know!

Like I said, I do trust my mechanic. He's got 2 separate shops on his property--1 out front on the street where he does his day to day work and the other up the driveway near his house where he works on the classics. He's got both a beautiful '67 Camaro and an '87 Buick GN that are to die for!!!

Including the rebuild, he's dropped the tranny at least twice to address leaks etc. We did investigate the leaks via the speedometer cable and fixed that. The car is stored in a garage --usually from mid-Nov to mid-April and I measured last years drippage with a solid 12 OZ in a plastic drip pan on the floor. I'd say I put 3000 mi (+/-) on her each year. I check the fluid at least 3x a month in between, adding a half quart here and there. Since the engine rebuild in '15, I've only taken one trip of 5+ hours with it with no issues.

I THINK the transmission is working well---maybe a little slippage here and there but nothing egregious that I can detect.

I am concerned (overly?) with the originality / matching numbers for the engine / tranny etc. as I'll mmaaaayyyyybbbbeeee look to sell it (unless I use it for my casket) when I head off to that final Cruise-In in the sky ( in 15 years or so) ! My guess is that none of my 3 boys will take it on...........

BTW- I won't sell it as long as I can drive it!

Thanks again for everyone's input!

Rick

 

(1) Determine "where" it's leaking - I wouldn't start to think of removing the trans. & having it rebuilt until you determine where it's leaking. As John (Koda) suggested - does the transmission work? Any automotive service supply house sells a small bottle of fluorescent dye (and a small UV flashlight). Clean the transmission well, add dye, drive car, examine w/ UV pen light where the oil is leaking;
(2) The transmission has a vent hole (see image below). The transmission must be vented - as heat builds, pressure builds, vent allows pressure to escape in normal operation(s). This vent hole must not be clogged w/ 50+ yrs of driving road sludge. I've known others who've plugged the vent hole not knowing what it was for - it's a vent. It does not go straight through into the trans. case, it makes a quick 90° after entering the trans. case. It must be open to vent. The vent hole originally contained a plastic tube, yours likely is broken off, it happens to many transmissions. The key point here is the vent must be open & operative. If the vent hole is plugged (not open) for any reason, as heat builds pressure in the trans builds, this pressure must be vented, if the pressure is not vented it can/will cause trans. fluid to leak from other areas e.g. seal(s) - that pressure has to go somewhere. Sometimes a tell-tale sign of a plugged vent hole is the inability to adequately/properly fill the transmission from the trans. fill tube - often times taking forever to fill properly as there's no venting of the trans. at the vent. Another sign of a plugged vent tube can be trans. fluid creeping UP the trans. fill tube w/ trans. fluid leaking from the trans. fill tube itself. Finally, if the trans. vent hole is working properly & the trans. was/is overfilled w/ trans. fluid, it will leak from the vent hole. Find out "where" it's leaking before deciding to have it rebuilt;
(3) As Greg mentioned there are other areas it can be leaking - the automatic transmission modulator valve assembly can be suspect, as well. Again, add dome dye, find the leak.

 

Haven't tried it yet, but a friend suggested using baby powder to detect and trace leaks. Clean the area, apply powder and watch for the trace.

 

These guys (mud dauber) are known to create havoc - they'll get into anything. You can take a piece of 10 GA electrical wire (w/o the insulation), insert into the tube and jiggle the wire removing any debris. Remember, the vent tube inside the trans. case makes a quick 90° turn. Any debris will fall to the bottom of the trans. pan and be caught by the trans. filter. Again, add some dye, find the leak first.

 

Sound advice.

Much appreciated.

 

Also check the dipstick seal.

 

Here's one thing with a pretty much stock TH350 or TH400. If you're using the stock torque converter in these they will drain back and overfill the transmission. All of mine with aftermarket converters do not drain back overfill and leak.

 

X2, 12 ounces from Nov-April could very well be the torque converter draining back into the pan causing the leak.

The transmission may not need to be rebuilt but, if the mechanic is trusted and the car is over fifty years old with 155,000 miles, going through the unit would probably be a good move.

 

x3 Valid point. Ensure you're filling trans. fluid to designated (appropriate) level. There's a significant difference between filling the trans. w/ fluid in a cold vs. hot engine. I don't know the exact statements/markings on your trans. fluid dipstick, examine the image (below). This is often done incorrectly; yet, it's important. I check trans. fluid level with engine running at normal operating temperature AFTER taking it for a ride, cycling through each of the gears, brief run in reverse & then in park (engine running).

It's a messy job removing trans. fluid from an overfilled condition since there is no drain plug on the trans. pan.

THEME: Check where the leak is before tearing into this further. You may well be surprised to find the fluid is exiting the vent hole (overfilled condition). If you aren't in the mood to dropping the trans. pan to remove excess trans. fluid (preferred method), you can (without harm) continue driving the vehicle normally. Eventually the fluid will subside to a level below the vent & stop puking fluid in an overfilled condition without harm to the transmission. You're going to end up w/ more oil in the system than is normal, which is not ideal, but it won't be puking oil out the vent. It will take some time & miles driven to reach an equilibrium before it stops puking. Again, put in some dye, find out location of the leak - first.

 

What that picture says. I scratched the stick above the centering bulge for a cold, off level. I may have to check trans after the drive. That's a good idea.