Turbo 400 Build

[hotrodpc]

So now its time for a little pause in the build and a short lesson in the Intermediate Sprag. Here is a pic of all 3 differant Intermediate Sprags to choose from for the THM400. Notice the drum on the Left is notched to make way for the roller sprag. The roller sprag is used from 1970 and up applications. Its not a bad design, still works great and does have some strength. But, it is not near as strong as the drum on the right with the smooth race that accepts the 16 element dogbone sprag, aka wedge sprag. And naturally the 34 element sprag is even stronger yet. Why is it important to have this part beefed up? Because the sprag is overunning in 1st gear, or free wheeling for a better term. Then the second the trans hits 2nd gear, that sprag stops instantly and grabs the drum and starts spinning the direct clutch drum. Imagine how much force is put on that sprag when hauling a heavy load, or hitting 2nd gear at high rpm. And even more force if you have added a shift kit, and trans fluid pressure is raised for a firm instant shift. Picture something spinning at 3000-5000rpm and have to stop instantly with the wieght of a vehicle behind the force and then carry on with the weight of the drum and cluctches that outweight the sprag probably 10X. Sprags take alot of abuse. So its best if you can upgrade them if you expect to using high performance applications, or towing more weight than what a normal truck would be towing. I think the pictures show the obvious differance. So my upgade in this transmisison from from the roller sprag to the 16 element dogbone sprag and drum from the donor trans. Then, since the 34 element sprag fits the 16 element drum, I bought the 34 element sprag off of eBay for $25 which usually in itself is about a $70 part at trans shops.

This is what was originally in my transmission and was destroyed. This is what its supposed to look like unharmed. Mine was far from this.

Here are both the 16 and 34 element sprags side by side. Even the 16 element is stronger than the above roller sprag. But the 34 is even much stronger. I would not have a problem running at least 600hp and slamming into 2nd gear with that 34 element sprag which is what I installed in my transmission.

 

[hotrodpc]

While on the supject, of sprags and upgrades. I have found and robbed 2 pics for explanation purposes. First will be the spiral spring upgrade on the Intermediate Sprag of the Direct Drum. This spiral snap is sure not to come off and is much better at holding the sprag gear on the sprag to the drum. You can see the standard C snap ring above in previous pics. The differance is obvious. I advise using this snap ring even on a standard trans build with the roller sprag. It is possible that this trans failure of the broken sprag, is that this C snap ring popped off and that is what caused the sprag to break. If this spiral snap ring was used, that would not have happened. Just so happens, that this spiral snap rings is stock OEM equipment for a 4L80-E. So, where do you get one?? Call up the dealer or trans shop and tell them you need a snap ring for the intermediate sprag on a 4L80-E trans and this is what you get. They are about $13 at any GM dearlership. It doesn't do a bit of good to updrade to a 34 element sprag if this snap rings pops off, so best to be sure and insure it doesn't.

 

[hotrodpc]

The other updgade, which is a very rare hard to find part. Is the reaction carrier drum for wedge or dog bone element type one way clutch similar to a sprag. Realistically, it is not a necessary upgrade in a Turbo 400. This is what is used for 1st and Reverse. Where does something come in handy or where you might want to prefer the use of it??? If you running a drag car, and you launch hard off the line, or if you are using a trans brake in a high performance application. Being that in most cases, and even if towing some weight, you are not leaving very hard in first gear, the roller type is quite strong and effective, just that the wedge element type is even better. Here is a pic I robbed of the differant styles side by side. Again the differance is easy to see. This part is rare and hard to find because it was only used on early Turbo 400's. The first year of THM400 was 1964 and this carried thru only to 1966 for sure and some 1967 models had it. How many 64-67 THM400's do you think are still around??? I do happen to have one that is still OEM and never been cracked open. Its a gold mine transmission. I haven't had the need yet to use it, but will someday. Its also a variable pitch aka switch pitch torque converter trans. It has a solenoid in it to change the stall of the torque converter. It has the standard 1400-1600 stall, then by hitting a switch, the vanes in the TC will adjust and the stall is now 1800-2200. There are also aftermarket converters or you can have one built to your own specs. So lets say you want 1800 stall and then flip the switch and you can now have 2500 stall. NICE idea. Perfect for making a sleeper and that is exactly what I intend to use that trans for someday. Here is the pic of the differant reaction carriers. One on the Left is after 67 for sure, and the better on the right is early 67 on back to 64. Something else you find really fascinating, but I find quite scrary, is where you can find this wedge style low/reverse clutch. You call a GM dealership, chances are they don't have it in stock but can order it and its expensive. BUT, you can right down to your local FORD, yes, I said FORD stealership and they will likely have it in stock, and because its more common there, it will not cost an arm and a leg compared to the GM stealership. The part is used in 4R100 and most likely E4OD FORD 4 speed overdrive transmissions which are very common models these days. Keep in mind, I am just reffering to the dog bone wedge clutch, not the drum itself. So if you have drum already, go the FORD dealership and get the clutch. You're now set up strong enough for mega hp and a hard launch off of a trans brake. Mind Blowing isn't it???

 

[hotrodpc]

Back on Track to Donor Trans Disassembly

Now removal of the Center of Support. Notice the differance of the center support in the 69 Model vs the 86 model. The one on the left is from the 69 THM400 the 2 pics on the Right of the 86. Remember, the 86 center support is a little thinner than the support in the 69 to make room for the case saver spacer. This also makes a differnace where the retaining snap ring fits in the case, so the 2 cases are machined differantly in this area. That means the older center support is not interchangable.

Center Support out of 69 THM400.

Center Support out of 86 THM400. Same part, same purpose, just differant syle and NOT interchangable.

Center Support apply piston removed. Notice the familiar destroyed part. Lucky, I have to have some 400 hard parts laying around, and this was one of them. Now put to good use.

 

[dirtyoldman]

Just caught up on your build,fascinating.I kind of see the differences in the parts as far as how they're made and how one is stronger than another

Still doing a great job on the write up

 

[hotrodpc]

Thanks Gramps. Auto transmissions have always been fascinating to me. And the more complicated they get, the more fascinating they get. Sure glad someone appreciates the write up. Taking much more time than I had thought. And really, I am not going deep into detail, although it may appear so.

 

[hotrodpc]

Moving along on the disassembly of the 69 Chevelle Donor trans. Now down to the wire and almost to a stripped case. Here are pics of the planetaries removed, and nothing left the but the rear band and the output shaft assembly.

Planetaries Removed.

Output shaft assembley removed, aloing with the rear selective thrust washer. Only thing remaining now is the band which is just sittining in the case on its lugs. Very nice, clean, rebuilable case.

 

[davbell22602]

Speaking of the TH400 I have one in my 77 XJS Jaguar. Its was the first year jaguar start using GM transmissions in there XJS model.

 

[SILVER HAIR DEERE]

great rite up , 1st class with pictures , but if i may change some words here to help you out

Thanks Gramps. big ugly women have always been fascinating to me. And the more ugly they are, the more fascinating they get. Sure glad someone appreciates the write up. Taking much more time than to find one than I had thought. And really, I am not going deep into my preference, although it may appear so.

and remember we here spare no expense for laughter here !

 

[hotrodpc]

Again, we come across some differant style parts. The needle bearings, sometimes reffered to as Torrington Bearings are differant in both transmissions. I think its obvious by the color which ones came out of which transmission. The one that looks burnt in color is from the 86 model, and the nice clean one is out of the 69 model. So that is an obvious upgrade along the years. The newer 86 bearings is the ones I'll be reusing since other than color, they still appear to be in great shape. If memory serves, there are 3 differant places where these bearings are used. There is also known aftermarket torrington bearings to be used in place of some thrust washers. In very high performance applications, and for a very talented builder with knowledge of how to work a machinists lathe, he will use the lathe to modify certain drums to grind out a notch for space of a torringting bearing rather than a thrust washer. You will not find a thrust washer in the transmission at all. It will be all torrington bearings. This is what is reffered to as a rollarized transmission build and is usually quite expensive, but also have many other parts upgraded for strength.