TH400 Rebuild suggestions

[Supersport350]

I'm going to be freshening up my TH400 trans this winter and am looking for some suggestions. I've scanned the net, and talked with a well known local mechanic/racer and it seems the consensus is just go with a good rebuild kit, add a transbrake or valve body if you want, and call it a day. The mechanic/racer even said I don't need to spend $250-$300 on a kit, suggested some company and said just get the good clutches and that's it.

This guy has a 69 Chevelle that I think has broke into the 8's now, and has been stood on its rear bumper, so he usually knows what he's talking about and is a good source for info.

My car has around a 700 hp BBC. I know the TH400 is world class, and aside from the 34 element sprag and a snap ring, it sounds like most don't do much beyond that.

So, I'm open to suggestions, as well as good quality kits that I won't spend more than I need to on. Also, my current setup has a modified valvebody so its manual. I'm not sure if I'm going the trans brake route, but what advantage does an aftermarket manual valvebody offer over a modified stock valvebody? I hope to FINALLY hit the track hard in 2014.

[anotheridiot]

I would never again rebuild another transmission without changing the pump. I am sure you can go thru it and rebuild by changing the gear, but all the little spring poppets in there are just too much to disassemble and not screw up. The entire transmission depends on hydraulic pressure created by the pump, and most aftermarket places like jegs or summit for about 100 bucks, or your rebuilding shop selling you the guts. If it feels like its slipping or getting lazy, theres a good enough chance its the tired pump than bad clutches not getting flushed of fluid.
If you are up in power you want to make sure your clutch hub is machined and not cast. Thats the first thing you are gonna rip apart with that power, another relatively low cost aftermarket part.
If you are happy with your valve body and its already manual, then no reason to change it. Why have anything different to worry about when you start on the track.
Transbrake, it wont get in your way if you dont push the button. If you think you are gonna want to launch the car with one foot or at higher rpms than your brakes will hold the car, its a good time to add it.

[squirrel]

I worked at a transmission shop for a little while, years ago....I know what goes into a rebuilt pump. I have never bought one, there's no need, unless your pump housing is worn, and even then you might be better off finding a good used pump and rebuilding it yourself. Just make sure there is no wear on the crescent, and buy new gears if the old ones are worn at all, they wear mostly on the ends of the teeth, and the tangs that mesh with the converter. It's not rocket surgery.

[Supersport350]

Thanks for the info. Now regarding a trans brake, what are the pros and cons of them? I realize they essentially put the trans in forward and reverse until launch. I have a roll control that will be going back on, which previously seemed to hold the car well. I have about a 4,200 stall, which allowed me to hold the car around 3500-3700 rpms staged. Will a transbrake hold whatever rpm you want? Or only up to the stall? If you rev it higher than the stall, do you risk damaging the trans or convertor? I think I know the basics, but not the specifics as to how they work.

[SuperBuickGuy]

the only upgrade I did (beside good parts) was to take the straight-cut gears from a TH475 and use them in my 400

[Loren]

If you rev it higher than the stall, do you risk damaging the trans or convertor?.

Stall is, by definition, the highest point you can rev the engine to against the converter...which is why engine power is a determining factor in rating a particular converter's exact "stall", beyond an approximate (and probably empirically-determined) number given by the mfr. At that point as far as the trans and converter care it's a matter of how much torque the engine is making, which is the same as it's going to be putting out at launch anyhow. Converters can balloon at least, if they're not up to it, beyond that I defer to anyone who knows more than I. Lucky me, the guy I paid to do my trans must've done it right. The only automatic I ever built myself didn't, uh, last so long.

[JeffMcKC]

I have a Big Sprag and a Cadillac high gear drum ( extra clutch pack) in mine as far it needs so far with red plates

[anotheridiot]

I get that, but its real easy to take them apart and even put the gasket on wrong and wreck the pump. For a first time build, I just suggested he get that professionally done. I remember the first pack we built, put the clutches in dry, checked for .070 between the snap ring groove and assembly, then took them apart and soaked the clutches in fluid and reassembling it. But when you are changing the clutch hub at the track, it would not even matter what clearance you have since you could not get any thinner steels anyway. So pay attention to the pump and make sure its working 100%. I dont know how you can check wear with standard calipers on a crescent but 100 bucks to not pull the tranny again and replace the clutches you just installed is insurance.

[squirrel]

I check wear by inspecting the parts. But it's hard to do that properly if you don't have experience.

[yellomalibu]

Thanks for the info. Now regarding a trans brake, what are the pros and cons of them? I realize they essentially put the trans in forward and reverse until launch. I have a roll control that will be going back on, which previously seemed to hold the car well. I have about a 4,200 stall, which allowed me to hold the car around 3500-3700 rpms staged. Will a transbrake hold whatever rpm you want? Or only up to the stall? If you rev it higher than the stall, do you risk damaging the trans or convertor? I think I know the basics, but not the specifics as to how they work.

Trans brake basics (which you probably know) : To launch your car with a trans brake (and a delay box), you put it in Low gear, stage, push the t-brake button, let off the brake pedal, and wait for the tree. Let go of the button, floor the gas, and the delay box will release the trans brake when the timer on the delay box runs out.

If you don't have a 2 step, the engine rpm will go to the stall speed of your torque converter. This builds heat, fast.

If you do have a 2 step (which I would recommend), the rpm will go to whatever chip you have put in the 2 step. You have a 4200 stall converter, but have a 3600 chip in the 2 step: the engine will go to 3600 until the delay box releases the trans brake, then the engine goes to your converter's stall speed for your launch.

I used a diode inline to my line lock (roll control) and tied it to the trans brake. With the diode, I can use only the line lock for burnouts, but when I hit the trans brake button it also activates the line lock. This helps ensure that my car doesn't roll into or out of the beams on the starting line.

As Loren hinted at - if you don't have a converter built with the intention of trans brake use (anti-balloon plates installed), it won't live very long with trans brake use, especially if you don't use a 2 step.


A major difference: your suspension is completely at rest when you launch, as opposed to being loaded up against the converter. My car launched much better this way. Results vary.

[anotheridiot]

Has anyone heard of JW rebuilding valve bodies that no longer use balls?