[RocktimusPryme]

So one of my projects has a th400 I bought used locally. Supposedly low miles, came out of his uncles race truck, performance rebuild etc. it was clean. It even has a B&M sticker on it!

Well I got around to installing the shifter today. Started the engine to see if it would go through the gears. It has all the forward ones, but no reverse. It was a little low on the dipstick so I added some fluid and tried again. No joy still.

I’m going to check the shifter calibration and make sure it’s actually getting into reverse by hand at the transmission.

Aside from that I’m going to ask two questions. One WILDLY optimistic.

1. When I googled No Reverse TH400 the first thing that came up was people with fresh transbrake rebuilds. Apparently you have to push a button to use reverse or something with a T Brake.

Let’s say this thing has a trans brake. I mean c’mon B&M sticker I am looking at you. One time for the people! How would I identify if that were the case? Drop the pan and look at the valve body? What am I looking for?

2. When that strikes out like it obviously will, can someone suggest a good rebuild kit. I watched a few videos, doesn’t look hard. Buy one $25 compression tool to make life easier. But the rebuild kits are all over the place in terms of pricing and what they come with.

Given my symptoms I’m pretty sure I’ll need a reverse band which it seems they don’t all come with. Other than that the big upgrade people do is the intermediate sprag right? That is also confusing as it said that you need a certain year drum to do that 34 element upgrade. I think I saw that you can do a roller upgrade which I guess would be in between the factory and 34 element in terms of strength.

https://www.oregonperformancetransmi...-TH400-RB.html

I kinda lean towards this setup. I just like that they start with a reasonably priced overhaul kit and then you can easily add what you need. In my case I would add the reverse band, probably a plate kit, a shift kit, and some kind of sprag upgrade.

[chuckies76ta]

On the trans break thing, it would have to have a solenoid to engage for trans break. Most of them are on the outside of the transmission. Would have to wires coming from it to activate it. The direct drum is the go to for an upgrade. I used the 4L80E drum as it excepts a 34 element sprag. Get Cliff's book on building TH400's. There are alot of videos online. I like Shawn at Mountain Garage. https://www.youtube.com/watch?v=W-0mK0Kn0zs and Richard at Performance Transmissions. https://www.youtube.com/watch?v=uJAc3iB0IOw
Another really good book is Ron Sessions. https://www.amazon.ca/Work-Modify-Tu.../dp/0879382678
Another resource is the ATSG manual. https://www.amazon.com/TM400-Technic.../dp/B071ZJCDN1
Get reading and watching videos. It's not that hard. But there are lots of little tricks and things to watch out for.

[RocktimusPryme]

Yeah I watched a whole rebuild series last night. I’m going to watch some more today.

It honestly didn’t seem hard at all. There are a lot of parts I guess, but looking at videos I would rather do that rebuild than I would plenty of other jobs I’ve done before.

So I guess I bite the bullet and buy the direct drum for the 34 element sprag. It looks like it’s about $250 from JEGS. Then maybe I get lucky and it already has one.

[Half-Inch Stud]

Probably already has a Good Direct Drum and Sprag.

Your "no Reverse" means the Rear Band Servo is leaking. No need to pull the Trans. Just drop pan, Valvebody, and rear servo cup, and renew the Servo seals. Maybe find a longer Apply Pin for certain apply margin.

After that, you may have a fully working TH400, that you can drop and do all you repairs and upgrades.

Remove the B&M sticker, and it should work even better.

[RocktimusPryme]

Originally Posted by Half-Inch Stud

Probably already has a Good Direct Drum and Sprag.

Your "no Reverse" means the Rear Band Servo is leaking. No need to pull the Trans. Just drop pan, Valvebody, and rear servo cup, and renew the Servo seals. Maybe find a longer Apply Pin for certain apply margin.

After that, you may have a fully working TH400, that you can drop and do all you repairs and upgrades.

Remove the B&M sticker, and it should work even better.

Oh nice!

So I could just buy this little kit and likely fix the situation?

https://www.amazon.com/dp/B09YM5MN7J...xpY2s9dHJ1ZQ==

[Sirrotica]

Originally Posted by RocktimusPryme

Oh nice!

So I could just buy this little kit and likely fix the situation?

https://www.amazon.com/dp/B09YM5MN7J...xpY2s9dHJ1ZQ==

If you're able to weld you can just add some length to the pin with a little weld on the upper end of it. I did the one in my 4L80E by just welding the pin up. I tried to get the free play down to roughly .100 when pushing the pin when assembled by hand. It worked like that for years in one of my duallies. The band had gotten so worn that I had little, if any engagement in reverse. I attributed it to moving my 5th wheel camper around in the backyard when I parked it for the winter. I had a fairly steep hill I backed it up, and that seemed to be when I started losing reverse.

Being your transmission came out of a truck, you could have the same scenario. There might be hope to save it if the band isn't completely worn out, it's definiteley worth a shot.......

[RocktimusPryme]

I went ahead and bought that little kit. I do have a MIG but I figure if one of the seals is bad I would need the o rings anyway. I also bought a drain plug to install.

Honestly if it were free I would probably just rebuild it even if this fix works. I kinda want to try it. I just don’t want to spend the money on that kit right now if I can avoid it. I have other stuff I need for the Firebird. Stupid budgets always getting in the way of a good time.

[Schurkey]

Make the trans in the car work, by fixing reverse. Leave the rest of it alone, provided it's doing the job.

Buy a core transmission, overhaul THAT for giggles and grins. Then you're still able to drive your vehicle while playing with the guts of an automatic trans in your spare time. For that matter, you could rip it apart to see how it all works, and NOT put a seal kit in it--just cram it all back together.

[Half-Inch Stud]

Originally Posted by RocktimusPryme

Oh nice!

So I could just buy this little kit and likely fix the situation?

https://www.amazon.com/dp/B09YM5MN7J...xpY2s9dHJ1ZQ==

Yea, that's the ticket. Valvebody gaskets might be fried crispy so helps to have fresh ones inside or on a shelf.

[RocktimusPryme]

Originally Posted by Half-Inch Stud

Yea, that's the ticket. Valvebody gaskets might be fried crispy so helps to have fresh ones inside or on a shelf.

I thought about that. I’ll go ahead and order one of those and probably a new pan gasket. Even though the one in it is new. I put a filter in it when I bought it.

I have it slow draining now into a fresh drain pan so I can reuse the fluid. It’s brand new. Used a little trick I saw online with a self tapping screw to make a drain hole without a big mess. I’ll install the permanent drain once I drop the pan.

Hopefully this works and saves me some money I can use for new front tires for the Firebird. The band could still turn out to be trash. But if we can get engagement at all out of it so I can at least move the thing under its own power that would be a huge win. It’s been in the same spot for 2 years now.

[Formulabruce]

I would install a separate trans cooler as well. Try to preserve what you have

[Half-Inch Stud]

Rare to see a trashed rear band.

[RocktimusPryme]

Alright I need assistance with parts ID.

I was trying to be careful but I dropped the valve body. Thought I had a bolt with a few threads in but apparently I just spun it without it being engaged. Long story short the valve body fell into the catch pan when I pried out the metal lines from the case.

Stuff went everywhere. Mostly I need to know what this little metal tube is and where it goes. Also it looks like it bent a little on the edge so maybe I should buy a replacement if you guys can ID it.

[chuckies76ta]

Hmmm: That's an unknown for me. I would only guess that it somehow may how come from the actual 2 tubes that go to the tranny from valve body. As I'm writing this I'm thinking it may be a spacer that went between the filter and valve body. Check the bolt size if it fits through it, that holds the filter on.

[RocktimusPryme]

It is possible it was on one of the bolts that I had in the pan. I had everything separated into their own spaces. Then the valve body decided to start a mosh pit.

[chuckies76ta]

Take the bolt that holds the filter to the valve body. See if it fits through that tube.

[Half-Inch Stud]

That spacer tube is junk, except if you have a deep pan then it might be a Filter Bolt spacer.

[poncho447]

Originally Posted by RocktimusPryme

Alright I need assistance with parts ID.

I was trying to be careful but I dropped the valve body. Thought I had a bolt with a few threads in but apparently I just spun it without it being engaged. Long story short the valve body fell into the catch pan when I pried out the metal lines from the case.

Stuff went everywhere. Mostly I need to know what this little metal tube is and where it goes. Also it looks like it bent a little on the edge so maybe I should buy a replacement if you guys can ID it.

Its the spacer for the filter.

[RocktimusPryme]

Originally Posted by chuckies76ta

Take the bolt that holds the filter to the valve body. See if it fits through that tube.

I think you are onto something there. Looks like that’s it. It is a deep pan btw.

Next issue. You can’t make this stuff up. Sometime between when I took those pictures and came in to watch football, and just now when I went outside to check theory. That plastic piece exploded. I found parts of it 10 feet away. Had to make sure transmission fluid didn’t get on the paint of any of the cars.

So what’s that called? Because I clearly need a new one of those. I believe it’s the forward accumulator piston. Assume I should buy a metal one.

You can see it was intact a half hour ago in the first pictures.

[chuckies76ta]

Yes, it's the front band apply servo. I believe it's actives the band for engine braking. I don't use it in my valve body as I have a manual valve body without engine braking and reverse pattern shifting.