From: jws@billy.mlb.semi.harris.com (James W. Swonger)
Newsgroups: rec.autos.tech
Subject: TH350 rebuild followup
Date: 5 Jan 93 22:27:09 GMT
Distribution: usa
Organization: Harris Semiconductor, Melbourne FL


 I had somebody write me with a bunch of questions; I thought the exchange
might be of interest (potentially) so, with permission...



I am very glad you decided to share your experience with rebuilding your TH350.
I have an 81 Buick Regal with one that I beleive to be slipping.  It does
shift nice and hard into gears, but when I floor it at about 40mph, the engine
seems to rev up and down and the car goes no faster until I let off.(This all
takes place after it downshifts to first)  I've been thinking it could be the
gaps on my plugs(.080), but that is what a number of sources recommend for my
year engine.

- I think this is a slipping clutch. I get the names of the different ones
  mixed up, but it sounds like engagement is poor. This could also be a
  result of low hydraulic pressure due to a plugged filter, worn seals, etc.


1    I haven't really asked anyone this, because I haven't been that serious
     about doing it, but do you think I'll have to lift the engine and tranny
     to do this, or is it possible to drop the tranny from the bottom, and
     how hard is it to get those bolts out holding it on the engine?

- You can do it from underneath, leaving the engine in place, but it's a
  pisser without a lift and tranny jack. The trans bell bolts are down in
  the tunnel and hard to apply decent torque to. You'll need at least 2'
  of ground clearance to work underneath. That's the main reason I pull
  them as a unit and separate them later. A bit of plumbing and wiring, 
  exhaust and the motor and trans mounts vs. the effort of separating the
  trans and, worse yet, lining the torque converter back up to the oil pump
  while holding it up. I've done it the "easy way" and it was harder.

2    In your article, you let on that you replaced everything that the kit
     gave you.  This is probably a stupid question, but if nothing else
     was bad but the clutch plates and the band, could you just get away
     with replacing them?  Of course being more or less a perfectionist....
     ok, ok...my curiosity would drive me to strip the rest apart.

- I could see the differencr in thickness between the original and new seals,
  so they were pretty worn I guess. I took it down all the way to see if there
  was an identifiable source for the shavings in the pan. 

3    Was that spring compressor a spur of the moment thing or did you know
     about it ahead of time?

- The shop manual showed the use of special GM tools for compressing the
  different spring retainers, which I didn't have. I just figured what I
  had to pull on and against and went through the scrap pile until I found
  stuff that'd work. I have a very well stocked scrap pile.

4    What brand of kit did you buy and were the parts made in the USA?

- The clutches were Raybestos, yellowish in color. I know there are also
  blue ones for higher performance uses. No brand name was evident on the
  box. I had to call around to find a local supplier. The big name places
  had no interest in selling me the means to compete (scAAMCO, e.g.) but 
  this hole-in-the-wall rebuilding place didn't seem to mind.

5    About how many hours did it take to rebuild the tranny?  Including
     all fumbles and tool making.

- Took me about 12 hours for the tranny teardown, parts replacement and
  reassembly (one (long) day). Another day on either end for pulling the
  engine/trans and reinstalling. 

6    You say the planatary gears were ok?

- All of the gears, castings, etc. were in amazingly good shape; all edges
  looked like new. Pretty good for 130K miles.

7    Were there any type of timing marks you had to watch out for?

- The rearmost clutch pack only goes in in one orientation, as well as its 
  piston. That's not too bad to figure out. The only thing that really has
  to line up radially it the oil pump drive; it has a pair of ears which 
  have to engage the torque converter outer hub in order to (1) slide all
  the way on and (2) spin the pump. The pump gasket is pretty busy, and
  needs to be lined up properly with holes that don't really match the
  cutouts. The inlet passage is the identifier to key on; it's big and 
  unique.

8    Aren't there bearings instead of bushings?

- there are a few thrust bearings and two roller clutches, but the spinning
  parts use simple bushings for the radial loads (similar to the crank 
  and rod bearings in an engine, but one piece). They are journal bearings, 
  not roller or ball types. Only one of mine was worn down into the copper
  plating. That's the tail bushing, as I noted.

9    Whats the chance of a torque converter going bad and how would I know it?

- Not much, I think. I've never heard of one going bad. They're pretty simple.
  I think failure would be either an extremely high RPM to move at all, or a
  condition of no idle slip (tries so hard to creep that the engine dies).
  If your idle in drive doesn't rise past 1500 with one foot on the brake and
  one lightly on the gas, it's doing its job.

10   Did you clean any of those channels and passages in the valve body?

- Yeah, I cleaned them with mineral spirits. I didn't take out the captive
  valves though. Had to clean out all of the gasket scraps left when I
  separated the valve body from the case. This is one area not to leave
  chunks lying around.

11   Were there any parts that when you took them out, they just sort of
     exploded little pieces all over the place?

- Not really, but the snap rings are a bit happy. Watch for the check balls
  inside the valve body.   

12   Did you use any liquid sealants anywhere?

- No. The trans filter kits say it's a bad idea, and after disassembling
  I have to believe them. I had sealed the pan gasket on one side with a
  permatex "Liquid Copper" sealane and the other with silicone. The non-
  silicone was completely missing, and the RTV wasn't looking too useful 
  either. This was from the last change maybe 20K miles ago. So one went 
  into solution and the other was worthless. This time I just followed
  instructions and used grease to coat the pan and gasket. No drips so
  far. The front and rear seals seem to be a tight enough press fit that
  sealants are not necessary there either.

13   I know putting a power steering pump back together with that new big
     o-ring is a bitch.  Any similar circumstances with the transmission?

- The reassembly of the pistons into their cavities with the new seal rings
  is more of the same. The key is to hold some pressure on the piston with
  one hand and poke the seal lip down into the chamfer around the cavity lip
  with something very thin (I used a .010" feeler gauge) that won't damage
  the seal material. When the seal is entirely down in its cavity the piston
  can be pressed in without excessive effort. I didn't want to force things.

14   Finally, what did your wife think when you told her you were going to
     rebuild this thing?

- She took it in stride. I've done and am doing other major car projects
  so it's not too much of a shock to her.

These are good questions. Maybe this exchange is worth posting as well. Any
objections?


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