[8doors]

Rebuilding a 1968 th400 from a catalina for my 67 tempest.

Orginally this was a junkyard unit with new filter, midwest 2800 converter, deep pan with cooling tubes and b+m shift kit installed. Lasted about 2 days before i lost 3rd then second then everything.

Teaches me to cheap out again.

So i pull the trans and begin my rebuild
the th400 is hasn't been too bad to work on so far. Right now i have the planatary set assembled, and both the forward and direct clutches to together.

I'm a little confused on the sealing rings that live on the inside of the front pump and the inside the intermeadate clutch plates.

Do these usually get replaced? My kit looks like there could be some updated stile of pump ring but its weird its a little plastic lookin ring that is beveled and fits kinda loose. am i confusing some parts here? is this a revised design? Anyone run into this before re use old rings?

once i figure this out i can dump the guts back into the case and stop walking everywhere

thanks for the help guys

Brandon

[Half-Inch Stud]

Brandon,

Because of your failure-mode description, you may have another fix-it to do:

Check the cooler & lines for clogged material boy blowing them out and witnessing that they are not restricted by crap.

Was the Trans fluids red when this TH400 died?
----------------------------------------------
I trust you bought a Gasket & rubber kit, also new steels&frictions.

HIS

[screamingchief]

The sealing rings you are describing sound like the teflon variety with the scarf cut ends instead of the iron/chrome interlocking variety.

You'll find that most builders either love or despise one or the other of the two,but hardly ever will they like/use both.

I myself prefer the iron/chrome interlocking style for my own reasons,among them is I have'nt had many issues with wear on my cores equipped with them,and they are much more reliable when air checking the clutch assemblies,and IMO make assembly much easier.

I'm sure more folks will chime in with their $.02...

[8doors]

Yes the kit came with steels and frictions aswell as rubber and paper peices, i've also replaced all the bushings in the pump.

The fluid was red but had silver streaks in it after 25mi of operation

here is a pic of a seal on the intermeadate piston this is how it was wel i pulled it off

[Cliff R]

If you are going to use teflon rings, obtain them for the 4L80 transmission, they are solid instead of scarf cut. You will also need the correct tools to install them. The iron rings are easier to install and a better choice in my opinion. 98-up 4L80 units use plastic rings that snap together. Haven't tried any yet in a TH400, but it's tempting. I still use the hooked iron rings, they're old school, but they work.

Replace all the bushings during rebuilding no matter how good they look, same for the thrust washers. By minimizing up/down fore/aft play the trans will seal up better and run quieter after it is placed in service, aside from lasting about 10 times as long.

Air pressure check all of the drums before installation, then again after the trans is together. If you have any troubles with sealing rings or piston seals, it will be evident during the air pressure check. Do not put a unit into service that shows any leakage during the pressure check. This step is left out during most home builds. If you can apply the low band and the three clutch packs on the bench, it will short cut troubleshooting if you have problems once the unit is placed in service.....Cliff

[Half-Inch Stud]

Do not replace all the bronze bushing: Only replace bronze sleeve/bushings when you SEE an ofset wear pattern (typical to the Tail housing, Converter neck support) or feel play that would allow the rotaing mass to go offset.

Sometimes I use NEW iron sealrings, or NEW/OLD TEFLON seal rings depending on the seal surface and groove fit. I think the Front Pump-to-Forward Pack Must have a Teflon 1st-seal then an Iron 2nd seal for best results. Too much wear on the Forward pack sealing surface for 2 irons.

MOD: 2-3 upshift: Center Support gets 3 iron (teflon OK) sealrings, not 4. 2nd seal from end is leftout. Direct Pack middle DIA lipseal is leftout. Tiny feedhole in separatorplate is plugged (tiny screw&nut & peen it with a hit). Sometines I used a 1/4"dia shank from an old gring stone and plug the equivalent Center support feed instead of the tiny Separator plate hole.

Flip the protruding 2-3 accumulator puck within the Valvebody. That means flip the aluminum puck or grind the 3 tabs off the plasic puck&flip, and leave the coilspring out.

HIS

[Half-Inch Stud]

Must have the proper drift/unpress//press fixures to replace ANY bronze TH400 bushing.

Front pump seal and rear tail Yoke seal are 2 items that you can whack-out & tap-in with some skill mostly-unfixtured.

[Half-Inch Stud]

Intermediate seal is bad, yet I dunno about loosing all gears from that. 1st & Reverse should have worked. 2nd no-shift, 3rd might have worked on a moving car.

[OINK 1]

Call me and I'll tell you the easy way to get the sealing rings right. 1-303-776-0877. It's way too much to type, but I can start off by telling you, you use stainless steel shim stock. Pontiac Gregg

[Cliff R]

No doubt full bushing replacment requires lots of extra time and considerable expertise. We do not consider visual observation a reliable indicator of bushing wear. We see way too many bushings move or slide out of position aside from having a few thousands wear. On the TH350 tranmissions, for example, at least half of the ones we see, the sun gear bushings will nearly fall right out when tapped with a punch. Wear on the direct drum bushings cause the drum to ride pretty hard on the stator and make the sealing rings stick in the grooves. We've seen countless TH350's put back together and fail to work right because of this.

TH400's fair a bit better by design. We still consider taking the extra time/funds to see the job through by replacing sacrificial parts such as thrust washers and bushings. Would you put all the bearings back in your 455 after 100,000 miles, even if they looked fine?.....Cliff