TH400 for dummies please

[DAN76]

Ok, can someone please take a couple of minutes and educate me on my TH400 trans!?
Treat me as a complete novice as i basically have very little idea how this works...

1. Would my 1965 Delta 88 have been installed with a Switch Pitch converter transmission? It's the 425 High Compression motor.

2. How does this pitch feature actuate in everyday driving?

3. If I have one, how can I tell if the converter is working or not?

4. I've heard of some people wiring it to an external switch somewhere on the dash, is this as simple as it sounds?

5. What is the fundemental difference between gear setting "L" and 1st gear in "D" or "S", because the pullaway in "L" with WOT is FAR more brutal than in any other setting (but still not burning rubber)?

I had been experiencing what appeared to be a lack of power when accelerating with WOT in "D" or "S". When i'm in 2nd gear for instance, I do get kickdown but when it steps down there's nowhere near as much pulling power as what i feel in "L". Is this possibly a clutch issue or is it completely normal?

I keep hearing tales of 100ft burnouts from a standstill with motors set up exactly the same as mine. Either we use grippier tarmac on our roads over here or there's something not quite right

The fluid level seems to be OK and when driving conservatively it seems to shift up gears when it should etc.

If it's something I can fiddle with myself then i'd like to give it a go before spending and ££'s at a Garage.

Thanks in advance!

[jaysun]

1. Very possibly, if the transmission has stayed original through the years. A easy way to check is to look for 2 wires on the drivers side and a switch on the throttle linkage

2. The high stall is activated when the the throttle is above 1/2 to 3/4 way. so driving the car lightly will not activate the switch.

3. Since you didnt mention any symptoms of a bad converter, i assume that you mean the switch pitch feature of the converter. Since it activates at about 1/2 or greater throttle, i'd find a nice stretch of road and try to get it to click on and off at 3rd gear. you should be able to hear or feel a R.P.M. difference. Alternitively, with the car off and with a helper slowly pressing the gas pedal, you might be able to hear the 2 clicks of the soilnoids. The first click is the soilnoid that activates high stall and the second is for detent (passing gear)

4.Yes, the easyest would be to either replace the switch on the throttle linkage or run a switch paraellel with it. If you remove the factory switch don't throw the bits away. They are expensive and hard to come by.

5. The difference between first (when selector is in drive) and first (when selector is in low) is internal. The rear band applys when the selector in in L. It however does NOT apply when in the drive range. In first gear,drive range, rotation of the reaction carrier is stopped in one direction by a mechanical clutch, in your case, a sprag. In first gear, selector in L., the carrier is held by the sprag AND the rear band. I suspect that your sprag is slipping when in the drive range. They are 3 things that could wear. the sprag race on the reaction carrier, the sprag or the race on the center support. I don't know which one is more likely to wear out first. The reaction carrier and sprag were for only 2 or 3 years and rare to find , but can be replaced with a later roller clutch and carrier. THe center support should be replaced with a latter style one, since its slightly thinner for an additional case snapring that prevents wear on the case splines.

If you want pictures or have more questions jusk ask.

/usual disclaimer. I'm not a tranny expert, but learning

Jason

[DAN76]

Thanks mate, that helps a lot!
I think this may confirm my fears and it's probably time to take it to see a specialist.

Is it possible that the change in RPM you describe at 1/2 or 3/4 throttle is what i assumed was the kickdown gear activation?

[DAN76]

Also, when using "L" for instance on pullaway, if I reach the maximum recommended revs for that gear and shift it into "S", would it be normal to experience a slump in the power delivery instead of continuation of acceleration?

[jaysun]

Originally Posted by DAN76

Thanks mate, that helps a lot!
I think this may confirm my fears and it's probably time to take it to see a specialist.

Is it possible that the change in RPM you describe at 1/2 or 3/4 throttle is what i assumed was the kickdown gear activation?

Yes, that should be the converter going into high stall mode. At full throttle, is when the kickdown for the passing gear kicks in.

I would say it's not normal for a slump in power delivery when shifting from first to second. Some things not right. Unfortunately I'm not sure what, right now. I'll think it over during work.

Do you have good power in 3rd? How many miles/km on the car? Out of curiosity does your speedometer read in km or miles per hour?
Jason

[DAN76]

yeah power in 3rd seems OK when running through the gears normally, but difficult to judge as I have nothing to compare it to.

Here's a scenario: I sometimes use "L" gear to pull away from lights because it's much quicker than starting with "D" or "S". When the engine reaches high RPM (about 50mph) i then shift it into "S" manually. This is when the slump occurs.

If I use "D" to pull away fast, when I floor the gas the transmission takes a second to engage, a bit like a clutch, and then the car takes off but with considerably reduced force than when pulling in "L". It runs through the gears smoothly but lacks low to mid range power. Once it hits 60+ the pulling power seems to be quite good.

Speed dial is showing miles per hour not KMPH.

[jaysun]

After pondering it for a couple days, I haven't come up with a solid conclusion for the 1st to 2nd gear slump issue. I'm not sure if its engine related, some sort of binding in the transmission , a line pressure problem , stuck, worn or broken parts. You'll need a shop to do the line pressure test, as it requires a 300psi gauge. They might be able to further diagnose too, hopefully without a teardown.

That being said , If your looking for something you could do yourself, you could drop the pan and take a look at the contents of the pan and fluid. Some sludge and metal is normal. but at this point I'd be looking for excessive metal. A filter is never a bad idea either but the early style filters are not made in quanity and are a little hard to find. However I've seen them on (us) ebay. A latter filter could be retrofitted. it would require a later pan, tube and a shouldered bolt, as well.

jason