904 Early Shift Points

[Jim Kueneman]

On my 360 block backdated to a 273 Commando with Edelbrock heads and Performer intake/1403 carb and a 904. I have 90% of the correct factory 273 kickdown and a few custom made parts. I have the geometry reasonably correct but it seems like this 904 shifts way to early. I have the correct length '66 lever on the transmission. The kickdown hits the end of its throw at WOT. It seems like the initial position of the kickdown needs to be at least 1/2 way to full throw at idle to have a reasonable upshift points. Right now it is in 3rd by the time I hit 15MPH. Also what was the year that the 904 included forced WOT 3rd to 2nd kickdown? It it won't kick down if I floor it either which may just be the older 904 that does not include that.

Any thoughts on what I can do? I could modify the linkage but that does not feel right since it's throw is close to seemingly to correct as it is using at least 3/4 of the full throw of the kickdown in a full throw from idle to WOT.

Thanks,
Jim

 

[Ricks70Duster340]

Try making your kickdown rod longer a little at a time. Start with 2 turns and see how that does. The older rods were screw in/out types.

 

[Ricks70Duster340]

The Fairbanks shift kit I use runs the valve body kickdown valve lever down so a 1/8 drill bit is all the lever needs to move before actuating the valve. This provides much improved kickdown performance because the external lever does not need to move as much before kickdown occurs.

 

[Jim Kueneman]

Try making your kickdown rod longer a little at a time. Start with 2 turns and see how that does. The older rods were screw in/out types.

It is as far as it can go without not allowing the carb to go WOT. I will probably have to modify the linkage geometry to do anything like that.

 

[Ricks70Duster340]

It is as far as it can go without not allowing the carb to go WOT. I will probably have to modify the linkage geometry to do anything like that.

I would work on the WOT issue after the kickdown problem is resolved. You don't use WOT very often but you'll shift all the time. The transmission could be damaged if the kickdown issue is not resolved.

 

[toolmanmike]

On my 360 block backdated to a 273 Commando with Edelbrock heads and Performer intake/1403 carb and a 904. I have 90% of the correct factory 273 kickdown and a few custom made parts. I have the geometry reasonably correct but it seems like this 904 shifts way to early. I have the correct length '66 lever on the transmission. The kickdown hits the end of its throw at WOT. It seems like the initial position of the kickdown needs to be at least 1/2 way to full throw at idle to have a reasonable upshift points. Right now it is in 3rd by the time I hit 15MPH. Also what was the year that the 904 included forced WOT 3rd to 2nd kickdown? It it won't kick down if I floor it either which may just be the older 904 that does not include that.

Any thoughts on what I can do? I could modify the linkage but that does not feel right since it's throw is close to seemingly to correct as it is using at least 3/4 of the full throw of the kickdown in a full throw from idle to WOT.

Thanks,
Jim

Do you have a photo of how your linkage looks at the carb?

 

[RustyRatRod]

It is as far as it can go without not allowing the carb to go WOT. I will probably have to modify the linkage geometry to do anything like that.

You may need to adjust the line pressure screw on the valve body. IT has an Allen head on it. I've had to before quite a few times.

 

[Jim Kueneman]

Do you have a photo of how your linkage looks at the carb?

Later today I can. It is just a clone of the 340 4 barrel linkage that I made with the Chrysler adapter for the Edelbrock. I am not using the original 273 snap on setup.

 

[Jim Kueneman]

You may need to adjust the line pressure screw on the valve body. IT has an Allen head on it. I've had to before quite a few times.

There is a port to install a pressure gauge to test it isn't there?

 

[RustyRatRod]

There is a port to install a pressure gauge to test it isn't there?

Yes, but you cannot always go by the pressure. Sometimes you have to adjust outside the box. You don't have a stone stock car anymore.

 

[Jim Kueneman]

I would work on the WOT issue after the kickdown problem is resolved. You don't use WOT very often but you'll shift all the time. The transmission could be damaged if the kickdown issue is not resolved.

It is not bad enough to hurt anything, it is just bad enough that it feels like a dog taking off from stop lights.

 

[RustyRatRod]

It is not bad enough to hurt anything, it is just bad enough that it feels like a dog taking off from stop lights.

If you're getting high gear at 15MPH, it's bad enough to make it slip.

 

[Jim Kueneman]

Yes, but you cannot always go by the pressure. Sometimes you have to adjust outside the box. You don't have a stone stock car anymore.

Does front band adjustment effect shift points?

 

[RustyRatRod]

Does front band adjustment effect shift points?

Not really, no.

 

[Jim Kueneman]

If you're getting high gear at 15MPH, it's bad enough to make it slip.

To clarify if you get on it off stop it will shift at close to the right points. It is when you are just lazily leaving a stop it jumps to 3rd quick.

 

[RustyRatRod]

To clarify if you get on it off stop it will shift at close to the right points. It is when you are just lazily leaving a stop it jumps to 3rd quick.

Might be normal, then. It's a light car. What gear is in it? Also, since you say it will not downshift, I must assume it's an early (pre71) transmission without the part throttle kickdown valve.

 

[Jim Kueneman]

Might be normal, then. It's a light car. What gear is in it? Also, since you say it will not downshift, I must assume it's an early (pre71) transmission without the part throttle kickdown valve.

Yea it’s the original 66 trans. So 71 was the start of that?

 

[RustyRatRod]

Yea it’s the original 66 trans. So 71 was the start of that?

I believe so, yes. I KNOW your 66 transmission does not have it.

 

[LooseInTheScrew]

This answers a lot for me too. my 904 from 66 does the same exact thing. Its so annoying ive thought about going mvb.

 

[RustyRatRod]

Those transmissions can be easily upgraded with the later valve body that has the part throttle kickdown valve.

 

[forphorty]

This answers a lot for me too. my 904 from 66 does the same exact thing. Its so annoying ive thought about going mvb.

I've got rmvb in everything , but I'm kind of a weirdo.

 

[Jim Kueneman]

Experiment. This is a bit too much. Probably if the bolt is slid back all the way it would be about right. Of course I can only get about 2/3 throttle now.

 

[RustyRatRod]

Well, that certainly won't work.

 

[mopowers]

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.

 

[toolmanmike]

Well, that certainly won't work.

I was afraid of that. I'm glad I asked for photos.