904 Early Shift Points

[toolmanmike]

Here's some different photos you may find helpful. The lever extension is listed in this thread. 2-Barrel to 4-Barrel Conversion Correct the topside than see where you are at on the bottom.

 

[Jim Kueneman]

How long is the TP lever on the transmission? Sound like you may need a long lever on that side to allow for higher pressure but not limit WOT on the carb side.

Going shorter on the carb side would do the same thing.

Doing a mind experiment in linkage geometry... are you sure that is not reversed? The problem is I have too much total throw for the pressure control. I need to reduce the overall throw of the lever.

 

[mopowers]

Doing a mind experiment in linkage geometry... are you sure that is not reversed? The problem is I have too much total throw for the pressure control. I need to reduce the overall throw of the lever.

A longer lever on the trans side would mean you could bottom it out at WOT and the movement back down to idle wouldn't move the trans side as much because the lever's now longer - equaling more pressure. At least that's how my brain is seeing it. Could be wrong though. I'm like you though - I'd probably just start experimenting and taking notes. You'll get it.

 

[Jim Kueneman]

Here's some different photos you may find helpful. The lever extension is listed in this thread. 2-Barrel to 4-Barrel Conversion

View attachment 1716468489

View attachment 1716468490

View attachment 1716468491

View attachment 1716468492

View attachment 1716468493

What am I suppose to be seeing here that is different than what I have? The catch here that I did not explain is the lower bell crank I had to fabricate as I could not find an original 273 one. I am sure it's dimensions and geometry is not 100% OEM.

 

[toolmanmike]

What am I suppose to be seeing here that is different than what I have? The catch here that I did not explain is the lower bell crank I had to fabricate as I could not find an original 273 one. I am sure it's dimensions and geometry is not 100% OEM.

First of all, put the throttle spring in the middle of the throttle cable clevis. It won't help your transmission but it is correct. Take the hardware out of the slot and adjust the kickdown do that the slot is touching the throttle pin. That's where you need to start. If you run out of threads to get there, you will have to get the right lever, modify that one or use an adapter extension like I pictured. Like I said above, once you get the top side right, then you can work on the bottom side to get full travel at WOT.

 

[Jim Kueneman]

First of all, put the throttle spring in the middle of the throttle cable clevis. It won't help your transmission but it is correct. Take the hardware out of the slot and adjust the kickdown do that the slot is touching the throttle pin. That's where you need to start. If you run out of threads to get there, you will have to get the right lever, modify that one or use an adapter extension like I pictured. Like I said above, once you get the top side right, then you can work on the bottom side to get full travel at WOT.

No that bolt and nut I JUST put in there to see how far back I need to have the rod back at idle to shift the way I want from. I will slide that back and forth to see where the "zero" position of the rod needs to start from when the throttle is at an idle. If I thread longer (right now it looks like I need to extend it about 1/4") then I loose WOT. When you say work on the bottom side? Clarification? The problem is the current throw of the kick-down is too much compared to the carb throw (recall I fabricated the lower bellcrank). I need to have "zero" position with the rod holding the transmission arm about in about 1/3 the total range the lever can travel and then the right bell-crank ratio so that the remaining 2/3 throw of the transmission lever equals the the total range of the carb pin can move.

 

[RustyRatRod]

How long is the TP lever on the transmission? Sound like you may need a long lever on that side to allow for higher pressure but not limit WOT on the carb side.

Going shorter on the carb side would do the same thing.

But he's said the lever is all the way back at WOT. Although a longer lever at the transmission may get him there quicker, it won't make any ultimate difference, I don't believe.

 

[RustyRatRod]

Yall go back and read post #1 real good. He clearly says the KD is at the end of its travel at WOT. He cannot get anymore OUTSIDE the transmission. He is going to have to drop the pan.

 

[Bewy]

It is all about 'ratios'. Two examples:
- you change the carb to one that has larger primary bores. The throttle does not need to be moved as far to let ther same amount of air into the engine. So the rod to the k/down lever does not move as far & you get earlier shifts.
- different carb has different length throttle lever than original. Depending on whether shorter or longer, distance the K/down lever moves will be shorter/longer.

My comments assume that the 904 is ok, no internal problem.
I presume your k/d linkage has the typical pivoting lever with two arms at the rear of the engine. One side connects to carb, other side to 904. The carb arm: the connection to it needs to be slightly shorter, closer to the pivot pin.

 

[Jim Kueneman]

It is all about 'ratios'. Two examples:
- you change the carb to one that has larger primary bores. The throttle does not need to be moved as far to let ther same amount of air into the engine. So the rod to the k/down lever does not move as far & you get earlier shifts.
- different carb has different length throttle lever than original. Depending on whether shorter or longer, distance the K/down lever moves will be shorter/longer.

My comments assume that the 904 is ok, no internal problem.
I presume your k/d linkage has the typical pivoting lever with two arms at the rear of the engine. One side connects to carb, other side to 904. The carb arm: the connection to it needs to be slightly shorter, closer to the pivot pin.

2 arms on the bell-crank that bolts to the back of the head (273 style), then another bell-crank on the pivot pin on the transmission so 3 linkages and 2 bell cranks. Yes the transmission was rebuilt during the restoration by someone who has done hundreds of them and I trust.

Correct to make less throw on the KD but that messes with the geometry of the throttle cable and makes it harder to get it to go to WOT as you are sort of pulling straight back once it gets close to WOT. It is all about getting the geometry right.

Thanks,
Jim

 

[mopowers]

But he's said the lever is all the way back at WOT. Although a longer lever at the transmission may get him there quicker, it won't make any ultimate difference, I don't believe.

I fully understand that. But it should still make a difference. A longer lever on the transmission side would mean he can run further back during "cruise mode" and still have the trans bottom out at WOT. It shortens the throw on the trans side. Not sure how else to put out. It's just a matter of playing with the lever ratios at this point. He's oustide of the bounds of adjustment if he's bottomed out at WOT and still not enough at cruise. Sounds like he's got a mish-mosh of bell crank levers and such. I'd bet that's what's cause him to be where he is.

 

[mopowers]

First of all, put the throttle spring in the middle of the throttle cable clevis. It won't help your transmission but it is correct. Take the hardware out of the slot and adjust the kickdown do that the slot is touching the throttle pin. That's where you need to start. If you run out of threads to get there, you will have to get the right lever, modify that one or use an adapter extension like I pictured. Like I said above, once you get the top side right, then you can work on the bottom side to get full travel at WOT.

I think the bolt thing was him just experimenting to see if the added pressure would result in high shift points, while acknowledging it would result in him not being able to reach WOT.