TF 904 Auto slipping 2nd to 3rd when manual shifting @ higher revs

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Jason Maitland

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Hi everyone, so I'm in the middle of hooking up a Lokar type cable kickdown system, and have it connected at the trans, but not yet hooked up at the carb end. Anyways, whilst waiting to get new brackets etc to hook it all up I've been driving my car (68 Dart w 318) around, to test other recent work etc.
I usually shift manually through the gears, and have been doing that now, and all is good if I drive sedately - i.e. rev normally up to 3500/4000 and shift up; Trans shifts nice and smooth as per normal. However, IF I stomp on the gas, in 2nd gear, then go to shift up to 3rd , at say 4500 or higher it slips as if I've shifted into Neutral!... Is this because I don't have the kickdown connected? Or is it something more sinister y'all think?... Welcome any feedback/.insight as I don't really wanna drive it around whilst it's doing this... thanks
 
Don't drive it until you get it hooked up and adjusted correctly or you'll be rebuilding that 904 transmission! 65'
 
Without the kick down hooked up, your line pressure is very low. A cooked transmission will result. Do not drive until it's fixed.
 
Thanks everyone for your input... I asked several guys here about driving without the kickdown hooked up as I was concerned about driving it without being hooked up and they said it would be fine, you can simply manual shift it (as I often do anyways)... And it seems fine except that actual issue I've described... Can anyone explain what is actually happening/ not operating correctly to cause my issue? I appreciate it may be due to the kickdown not being hooked up and I'm not going to drive it anywhere till it's hooked up, but just curious to know the exact reason it's slipping only when accelerating aggressively VS normal, thanks
 
That. Cable/linkage that connects to the lever, which int turn contacts a valve in the valve body, to increase the line pressure of the trans. Proper adjustment is when carb at wot, the lever fully moved. So when you're at wot, the trans has the pressure it needs to function correctly and SURVIVE!!
 
Without the proper pressure the trans will not only slip on the shift but it will be slipping in gear. The result is excessive heated fluid and internal parts. Once you cook the clutch packs and or Bands due to slippage it will only get worse. If its slipping on the shift its slipping in gear . Don't drive it with out the throttle pressure.

When others state you can, It will only work if you tie the trans back to wide open position and shift it with wide open throttle. Many do this to race the car but they are always at wide open throttle. Letting it down shift with the lever tied back can break the band at the strut. Ask me how I know. The band will spin in the case destroying the case and many other parts. Not to mention parts and pieces getting into the converter.

I have many extra 904's when you need one.
 
It is not really a "kick down" it is more of a line pressure adjustment based on where the throttle is.

At light throttle you do not need as much pressure while shifting so it has less. The shifts are relitivly soft.

At more throttle you need more pressure to have the shift feel about the same.

At WOT you need max pressure.


What you are doing is using the minimum pressure at WOT and as such slipping the clutches and or bands during the shift.


That's why folks are saying you will cook your transmission.


On Ford C4 for instance there is a vacume valve that (IIRC) does the same controls, and a real kick down linkage that actually shifts the trans down one gear under the correct conditions.
 
Thanks everyone for your input... I asked several guys here about driving without the kickdown hooked up as I was concerned about driving it without being hooked up and they said it would be fine, you can simply manual shift it (as I often do anyways
If they are Mopar guys I would stop taking advise from them.


If they are Ford / Chevy guys, well you get what you pay for.

:rofl:
 
That. Cable/linkage that connects to the lever, which int turn contacts a valve in the valve body, to increase the line pressure of the trans. Proper adjustment is when carb at wot, the lever fully moved. So when you're at wot, the trans has the pressure it needs to function correctly and SURVIVE!!

If they are Mopar guys I would stop taking advise from them.


If they are Ford / Chevy guys, well you get what you pay for.

:rofl:
 
Thanks everyone for your advice/insight... Luckily, I'd only literally driven it about 10 miles and only light cruising (except the 2 times I made it slip)... I'll definitely leave it parked till the "kickdown" is hooked up now
 
Make sure you have the correct amount of oil in the trans too.
 
Yeah shall do... I've actually got the cable hooked up and working well right now, however....I think I'll end putting in a forward pattern manual valve body... So will probably post a thread asking for best recommendations for one of these soon
 
Hate to rain on your parade, but I think the damage has already been done. Whether the damage is due to insufficient line pressure at WOT or the trans is just worn out from a lot of miles.
In my opinion, the trans should not spin up on the 2-3 shift even with the KD disconnected. It would eventually fail with continuous use like that. I suspect the front clutch is worn or seals leaking & it is slipping under WOT load.
 
Hi Bewy, thanks for coming in , nice to hear from a local... The trans is not that old from a rebuild, and now I have the cable connected and working well, there is no slippage whatsoever... Anyways, I'll definitely upgrade to a forward pattern manual valve body, so if you have any good local recommendations in Oz, happy to hear
 
If you've driven it enough that's it's now slipping, chances are it's done. Without the throttle pressure cable or linkage (the correct name) the transmission will burn up in short order, starting with high gear, then second and finally first. Slipping going into third tells you high gear is probably done. You can get the cable on and sorted out, but there's little chance of that fixing it alone. Find new friends that give good advice, because the ones you have now don't.
 
I do not know anybody here that does man VB conversions. Doubt there is a 'market' for Chrys.
I have a GM car which has a T350 trans. I bought the man VB from Summit, who are great to deal with. It comes as a bolt in deal. Another option is a Transgo manual shift kit, that converts your existing VB into full manual operation. I have used many of these, good product.
 
Thanks Bewy... With the transgo kit, does it retain forward pattern? I'm after a forward pattern and so as to retain the original shifter console set up etc...
 
Yes, it keeps the fwd/factory pattern. From memory, the kit is designed so that it can be returned to full auto mode if desired. Clever piece of kit!
 
Thanks Bewy... With the transgo kit, does it retain forward pattern? I'm after a forward pattern and so as to retain the original shifter console set up etc...
Yes. The forward pattern is retained. I don't know of any kit or any way a kit could convert the stock valve body to a reverse pattern.
 
Yes, it keeps the fwd/factory pattern. From memory, the kit is designed so that it can be returned to full auto mode if desired. Clever piece of kit!
You treed me. dork. lol
 
You could just stage 2 the valve body with a shift kit and also keep the auto function.
 
Why do guys like to leave stuff disconnected or leave parts out of a trans just because somebody told them it was a smart idea? Is it because they're just lazy? I guess so. An automatic transmission clutch is NOT designed to slip; like a manual trans clutch. Slipping KILLS an automatic. It either wears down the frictions or scorches them so they just turn to mush. Compare a 904 clutch to a 727 one and lmk how much slipping it could take...
 
Cuda,
I can see why people do it with the 727/904 trans. [ leave the linkage off ] Once the engine is modified, it can be a lot of messing around to get the linkage/ratio just right for part throttle shifting and the WOT shift. The GM Turbo 400 system is much better.
 
I like the th350 kd the best. It's almost self explanatory, is a pull system instead of push, and it's complemented by a modulator. About half of the th400 customers think that plug on the side is for the reverse lights. I've been trying to figure out a simple way to make the tf kd a pull system.
 
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