70 w-30

I'm looking for opinions to help me decide whether to rebuild this TH350 or just get another one to install. The seller said that the 2nd gear was inoperative and that the engine and transmission had been modified. I tore the transmission down using the Factory Manual and Cliff Ruggles book. What I found;

The torque converter is an aftermarket one that uses short bolts and nuts to secure it to the flywheel. Painted blue and a number was stamped on it, 20400 with an L and 8 or 6 to the right of the number.
Oil pan was filled with about an 8th inch of silver/grey gunk and there were small pieces of metal from the roller clutch. The gunk was also in the accumulators.
The 1-2 Accumulator spring was missing.
Only 1 ball was installed.
The intermediate roller clutch race was in 3 pieces. The roller clutch was destroyed. The retainer was bent and loose on the shaft. the snap ring was out of the groove.


Number on Torque converter

Bottom left ball was the only one installed.

Actual ball installation

Intermediate Roller Clutch as found

close up of roller clutch as found

Damage

another view

I was planning on replacing all bushings and bearings. Upgrading the center support to the 4L60. Upgrade the intermediate roller clutch and direct drum. Does anyone have a suggestion for parts and tech support to buy parts?

Thanks,
Ben

BrawnyMan

Check out my thread I started (copied URL below). There is a contact in there for a master rebuild kit/bushing kit out of Indiana for less than $200. They shipped it real fast.
I found most of the small pieces or other parts from various small trans parts websites and ebay. My TH350 also had a bunch of gunk and one check ball. I've been pouring over the Ron Sessions book and almost ready for assembly after bushings are replaced. You know how you are going to get out and install those bushings?

https://classicoldsmobile.com/forums...erhaul-156075/

Good luck,
Clay

70 w-30

Clay, Thanks for the link! I'll read through it. I have a bushing install set and was using a couple of punches like in Chris Ruggles book. He takes a long round tapered chisel and grinds the end at a 45 degree angle. I haven't got them all out yet but its working so far. Ron Sessions book is supposed to arrive tomorrow.

Ben

matt69olds

The roller clutch shatters because the intermediate accumulator spring was missing. Was the wave plate omitted in the clutch pack? That’s another sure bet roller clutch killer.

Either install a good stock sprag race, or buy a aftermarket replacement from a reputable dealer. Don’t use a EBay special!!! In the 25 years I have built transmissions, I have seen maybe a dozen roller clutch failures. I bet 11 of those 12 were cheap aftermarket parts.

Install a spring, I think orange was the factory performance spring color used in the Z28 and other performance calibrations. Good luck finding one, purple and green are the most common. I doubt you will feel much difference in shift firmness regardless of spring color. Install the wave plate in the intermediate if it was left out. Keep the intermediate clutch clearance on the low side of the spec, that helps the roller clutch from getting hammered from thr clutch slamming on. You can use a old low/reverse clutch as a shim under the intermediate piston. You need to scrape off the friction material from both sides of the clutch. Make a single cut in the steel backing plate. You can then spread it open enough to fit down in the piston bore of the pump, then install the piston.

What size are the feed holes in the plate? If your using a aftermarket higher stall converter, you can use 3/16 on 2nd and 3rd. If it’s a factory style, that’s definitely going to knock the dash out of the car when it shifts. In that case, .125 to .156 is better. A 350 will work with 1 check ball near the modulator, or you can follow the recommendations outlined in the Cliff Ruggles book.

Hope that helps.

70 w-30

Thanks for the advice and information! Is there a place that lists what the feed hole sizes on the plate should be so I can see if any were opened up? Or are they all the same size when stock? Is there anyway to tell what the stall speed of the torque converter are from that number on the outside? I have no idea what was done to the transmission before.

the spring was missing, there was a wave plate as the first plate in the pack.

droldsmorland

Replace the converter. It was in front of a blown trans. Blow out the lines and cooler too. Cheap insurance.

matt69olds

You might try googling the numbers on the converter, maybe you can some info. You might also try calling Hughes,Coan, or some of the other custom converter builders and see if they recognize the numbers.

I’d suggest either replacing the converter, or at the minimum having it cut open for cleaning. Any time you reuse a converter after major transmission failure it’s a roll of the dice. Any trash from the trans could be pumped into the converter, any trash from the converter will be pumped into the trans.

Each transmission calibration had its own spacer plate, valve body code, and accumulator spring colors. There is a code stamped into the plate, and usually a code painted on the valve body, but unfortunately that’s usually unreadable after all this time has passed. And unless you can find documentation telling what all the codes mean, that info is kinda useless.

If your running a aftermarket higher stall converter, and want a good bang/screech shift, go 3/16 on the 2rd and 3rd clutch feed. It’s definitely going to have a hard full throttle shift, and very noticeable part throttle shift. If you want a little more conservative, go 1/8 inch. As long as you keep the accumulator functional and keep the wave plate in the 2nd clutch pack, you should be fine.

You can delete the 3rd gear accumulator by installing a 3/8 freeze plug in the valve body, under the accumulator piston. Leave the spring out, and if the piston is plastic, throw it away and get an aluminum replacement.

I don’t use the wave plate in the direct stack unless it’s a stock rebuild. Machine the direct piston to install a 5th clutch disc. You can machine the pistons on a brake drum lathe. Dual feed the directs either with a shift kit or by blocking the reverse feed in the case and omitting the seal in the center of the drum.

If you can find it, the Ron Sessions book on the 350 is a much better book than the Cliff Ruggles version. Cliffs book isn’t bad, but doesn’t have nearly the good tech tips.

I have built many 350s for low 11s/high 10s cars using theses tricks,

Hope that helps.

oddball

That's a 12 inch converter, so won't have a stall higher than 3,000.

Sonnax has a new intermediate race that looks like the hot ticket. You need a replacement anyway. Check out Sonnax's info - looks like their race might be stronger than the sprag setup.

I'm not convinced that replacing the direct drum is worthwhile, unless that one was damaged when stuff came apart.

matt69olds

The direct drum will almost certainly be trashed. Sometimes the shrapnel destroys the pump as well.

I haven’t used the Sonnax sprag race yet, if Sonnax makes it I’m sure it will do what they say it will. I have used several 350 drums modified with sprag races from other transmissions. Last time I checked, those drums were about $325. Not really cheap, but much cheaper than the damage from roller clutch failure.

About the best you can get from a 12 inch converter is 2400ish rpm. If you need more stall speed than that, look into the 10 inch converters.

70 w-30

I've finished the complete teardown and inspection of the transmission. I'm going to order a rebuilt one. Besides the problems listed in previous threads;
It appears that the transmission was operated for a while with the damage.
The valve body valves look like they were cut across the faces with a fine grit (like I found in pan).
I couldn't remove the 2-3 shift valve, the control valve sleeve was jammed in the valve body.
The direct-clutch-accumulator spring was missing and the piston was jammed.
All the bushings are worn well below the babbit.
Most needle thrust bearings are worn and rough turning.
The steel sleeve on the pump was worn, pump gears had deep scoring on the sides.
The intermediate roller clutch assembly, race, outer race, retainer and ring are shot! These parts appear to have been pushed out of place into the bolts holding the pump halves together and wore the top of the bolts off.
Direct clutch pressure plate is deeply scored.
Forward clutch input shaft has a groove where it rested in the bushing.
The forward clutch pressure plate is badly scored.
Both output-carrier assemblies have at least one pinion end plays over 0.030in.
The governor bore and valve are scored and "sand blasted" on sealing surfaces. It was jammed before disassembly.

The grit did a lot of damage to the hard steel parts and I have to assume the aluminum case may have erosion in the passages and the oil cooler in the radiator may be blasted also.

I've got 2 TH400's to overhaul after the Cutlass is done, so I'll have plenty of chances to learn transmission repair.

Thanks to all of you who offered advice! BTW the 20400 on the torque converter is code for the B&M Torque Master 2000

matt69olds

If the governor bore is chewed up, either find another case, or have it fixed with a repair sleeve. The only other option is a manual valve body that doesn’t require the govenor, not really an option for most street cars.

it sounds like you might be better off finding a different core to build.