BrawnyMan

Hello,

I have a '71 Cutlass Supreme with 140k miles on original equipment. The engine is somewhat tired but plugging along and so was the transmission until it started to slip, fluid got dark, and continued to slip more often. Luckily, I have been expecting this since I have bought the car and just finished reading the rebuild book written by Ron Sessions as well as collecting tools to prepare for a rebuild. About a week ago, I parked it in the garage and dropped the pan and found some shiny, aluminum-colored sludge of what I think (based on what I read) is parts of a failed torque converter and also all sorts of gunk from frictions and metal in the filter.

Assuming I need a rebuild, does anyone have any suggestions for full rebuild kits (w/ new bushings), a shift kit, and torque converter? My goals are to wake up the engine and get it a little faster off the line; I would describe it as factory plus? Could I achieve this with same stall as the factory torque converter? I am also interested in doing any mods or upgrades while I am in there for durability and performance. Any and all advice is welcome and I am looking forward to the challenge.

Thank you,
Clay

matt69olds

This is where I get most of my transmission stuff, ask for Cheryl.


A properly built TH350 will easily handle 500-600 hp with stock parts. You don’t need fancy Kolene steels or high dollar friction materials. Get a overhaul kit with the Borg Warner or Raybestos high energy friction material (they are kinda greenish gray colored, the stick frictions are tan colored paper). Make sure you get an extra direct friction and steel. Get a bushing/thrust washer kit with the overhaul kit, make sure you get a wide direct drum bushing. Machine the direct drum piston the equivalent of one steel and friction plate, that will allow you to install 5 frictions in place of the stock 4.

Don’t spend money on a shift kit, it’s easy enough to get a firm shift with some simple free internal mods while it’s apart. Drill the 2 and 3rd clutch feed holes to .156-.185 depending on how firm you want it to shift. Block the 2-3 accumulator by driving a 3/8 freeze plug into the feed hole in the valve body, under the accumulator piston.

Dual feed the 3rd as outlined in the Ron sessions book. Assuming nobody had messed with the transmission in the past, and it’s the original unit, it should have an aluminum accumulator piston. If not, get rid of the plastic piston!

Keep the 1-2 accumulator functional. Most likely the factory accumulator spring is broken. I think the factory performance was orange, purple and green are the most common color.

Keep the end play on the low side of spec. They make thicker thrust washers for the carriers to reduce endplay. I have used pinion berating shims from rearends under the stock thrust washers to reduce clearance on really sloppy units.

Don’t scrimp on the converter. A good quality converter won’t feel mushy at part throttle. A good quality 2500ish stall speed will drive and feel basically like the stock unit did, until you stand on the throttle. The difference will be petty obvious.

Hope that helps

joe_padavano

I've built several TH400s using the B&M Trans Kits. Very complete and excellent step-by-step instructions.

olds 307 and 403

The stock converter stalls around 1600 rpm, too low. As Matt said, get a decent quality 2000+ stall. The Jegs 2000 to 2300 stall is a B+M converter, decent for around $100. Any kit with name brand frictions and steels should be good.

Inline

Its easy to rebuild in my opinion. I used MAKCO Transmissions or something for my parts back then, i have a faint memory they went under.
So far i have almost 2.5k miles on the trans of hard abuse, and it wont show any marks of giving up. I managed to cut some lip-seal and therefore had to buy whole new sealing/ rubber parts kit.

Hardest part was fabricating the tools to install all the bushings. Of course you can buy one, but $$$. I bought two cheap generic aluminium bushing install kits, and cut them to size.

I strongly suggest you to do it yourself, always something to learn.

matt69olds

Before I had the fancy tools, I used a camshaft bearing installation tool to install bushings. It’s still an expensive tool, but at least it’s a tool that will install many bushings in many transmissions.

Inline

I went totally ghetto
I grinded the aluminium discs with wood chisels, and lathe was an variable speed bosch angle grinder attached to table vice, with improvised axle to attach the discs for grinding

You can make anything work if you want, as long as there is an sound idea behind.

BrawnyMan

Small Update:
Dropped the pan to see what I can see and found all of this:




From what I can gather from the Ron Sessions book, he states any aluminum-colored putty in the pan to be parts of the fins of the torque converter. This goo definitely feels thick like a putty. As for the metals bits in the filter, I'm assuming this isn't normal steels/frictions wear. Could these be pieces of worn bushings, and debris from an original 140k-mile, 50 year old transmission finally crapping the bed?

I appreciate the help and wisdom,
Clay

matt69olds

That’s definitely not normal clutch/bushing wear. Will the debris stick to a magnet? If not, it’s aluminum.

The only parts of that transmission capable of generating that much aluminum is in the converter, or from the case. If the case is ground up, it’s obviously not worth rebuilding.

The 350/400 transmissions internals are all steel. The only aluminum in the trans is the case itself, or the pistons.

Hopefully the transmission is still rebuildable. Most likely the pump will be trashed, along with the bushings.

BrawnyMan

When I take the transmission out and start disassembly, do you know what you look for to determine whether it is worth saving? If it can be saved, I want to try to but I don't want to waste time if its impossible.

Thank you,
Clay

matt69olds

Either buy a factory service manual, or the Ron Sessions book on the TH350. There are other books available, and countless online articles and YouTube videos.

Basically, you need to look for excessive wear. The 350 is a very forgiving and durable trans. Properly built, they will take abuse far beyond what the original engineers ever imagined. Even sloppy rebuilds usually work pretty well.

Keep the end play on the tight side. GM originally had some pretty loose clearances, they continually tighten them later in the production years.

If you need to replace parts, you need to be careful. There were a few production design changes. This is an advantage the aftermarket books have over the factory manual. The aftermarket books will detail the changes, and what works and what won’t work together. The later years used bearings instead of thrust washers, as long as the parts are compatible there is no problem. You can’t put a thrust washer on a part originally intended for a bearing, or the other way around.

I have helped many people on this forum with their transmission rebuilds. The 350 trans is one of the simplest transmissions to build. You need minimal special tools, and those special tools are easily fabricated with stuff most people have sitting around their shop. Work slowly, work cleanly, don’t force anything. Air check every clutch assembly before installing the part.

There are some almost free performance/durability upgrades you should plan on doing, even if racing or performance isn’t a concern. They just make a good trans even better.

BrawnyMan

I own and have read both.

Vintage Chief

Clay - Good for you on reading the material and going for a rebuild. I've rebuilt several motorcycle transmissions over the years & they were rather simple & straight forward. I look at an automobile automatic transmission (the internals) and I quickly run away before I allow the slightest thought of rebuilding ever enter my head.

Schne442

I recently rebuilt my 72 350 Trans
I used the book mentioned along with a lot of help from Matt69olds (Matt)
and a few Youtube videos
working on anything like this looks a lot more confusing than it actually is, once you lay it all out and slowly work through each unit (clutch set)
it is simple. Just pay close attention to how it all fits together and ask questions, answers will come
Good luck

BrawnyMan

Thank you for the advice and the encouragement, I looked over your '72 rebuild and the pictures and write up were wonderful. I wish I had the time and patience to document it that well for others.

matt69olds

It helps if you have a large work area, one that won’t be disturbed. Start with the oil pan and valve body, put all the parts in the oil pan IN the pan, abd set it off to the side. Then pull the pump, clutch drums, gearsets, etc, and lay them out in the order they were removed. Get large pieces of cardboard, set the part on it, write notes about the location/orientation of bearings (which way went up, things like that).

All this info is covered in the book, but the bearings and other related parts look similar. Anything to make it easier to remember or understand how things go together will help.

BrawnyMan

Hello!

Progress has been going slowly due to waiting on parts, getting a parts-washer setup, and cleaning the parts I have already removed. For background information, this was removed from a '71 Cutlass Supreme and believed to be the original with 140,000 miles on it. All parts seem to be original with '71 stampings on aluminum pieces. In posts above, aluminum was definitely present in the pan.

So far I have found a few oddities:

- I can't seem to find the two steel check ***** in the valve body although I have found the two viton ones.
- One of my valve body filter screens was completely blown out leaving behind its frame and some bits of mesh.
- I found what looks like a small piece of gravel inside of the case. It is non magnetic nor metallic as far as I can tell.
- I found, upon disassembly, that the intermediate clutch band was not clipped together and was able to rotate until stopping against the case which can be seen in the picture below:



I believe this clip finally failed and the pieces may have wiped out my screens in the valve body, could it have caused the possible damage I describe below? What affect would this have on function? EDITED: Nevermind, I just learned today that this band is supposed to be loose.

A few things of concern I have are three "holes" that can either be from casting flashing or damage. I have seen similar cavities on some other cases but I wanted to check with more knowledgeable folks. I have highlighted these in pictures below:





Thank you,
Clay

matt69olds

Stock 350s have 4 check *****, technically they will function with just one in the case, near the modulator valve. I think they were all used steel check ***** thru the the entire production run. If they are plastic, most likely someone has been into it.

There are numerous holes cast into the case, some are pretty rough looking. Rough enough that you would swear something came apart internally and broke the case. Rest assured, if something internal broke bad enough to leave exit wounds, you would find lots of shrapnel.

There are 2 screens that I can recall, one is a filter on the suction side of the pump, near the manual valve. I think it was eliminated in the mid 70s. I don’t know if it’s available in the aftermarket. Since GM eliminated it, safe to assume they considered it unneeded. The other filter goes in the governor feed passage near the rear of the case. You shouldn’t have too much difficulty finding that one, they are included in every 4L60 seal kit. I think they are also used in the 4L80, and maybe other transmissions. Go to your nearest trans shop, maybe they have one.