904 transmission shift issues...

-
F

firefighter1

Well-Known Member
Joined
Jun 22, 2011
Messages
296
Reaction score
2
Location
California
So I've been having a transmission/carburetor issue for a long time. My car is running and driving fine, but first gear seems to shift very late at high rpm and my transmission does not down shift when I floor it. Furthermore if I am at idle at a stop light and I hit the throttle pedal to the floor, my car lags as if it is going to stall and then it kicks into gear and accelerates after hesitating for a second. I've played around with the transmission linkage a lot and nothing seems to help. Not sure maybe the transmission is bad. I have a 225/6 with a holley four barrel, 904 automatic transmission and 7.25 rear. I've tuned the carburetor and it seems to be fine. What's my problem guys? I am about ready to give up and send it into the shop even though that's against my religion to pay for something that I can do myself! Help if you can please. Thanks.
 
For sure you have a customized kick-down linkage since the slant didn't come with your Holley 4 barrel. If your 904 trans is OK, the problem is that your linkage is commanding kick-down even at low throttle. Is the kickdown pulled as far forward as possible (at the transmission), with a gap in the slot before the throttle starts to push it?

What size carb? If bigger than 370 cfm, you may have stumbling at first since it is likely too big for your engine. I doubt the stumbling has anything to do with the transmission.
 
I think you have two problems: poor adjustment and marriage of kick down linkage to carburetor; and carburetor type and tune issues.

First what carburetor are you using, and does it have vacuum secondaries?

Does the throttle plates fully open when accelerator is planted on floor boards?

When operating carburetor by hand, can you see the throttle lever on transmission fully swing its ark, and still allow full throttle plate opening (WOT)?

but first gear seems to shift very late at high rpm and my transmission does not down shift when I floor it.
Click to expand...
This is caused by too much throttle pressure, and rod needs to be adjusted to allow less pressure at low rpm. It may be that the carburetor’s throttle shaft geometry won’t allow your current setup enough travel to play nice with the transmission. You may need a Chrysler throttle adapter for your carburetor...can’t tell until more details on carburetor are reviled.

Furthermore if I am at idle at a stop light and I hit the throttle pedal to the floor, my car lags as if it is going to stall and then it kicks into gear and accelerates after hesitating for a second
Click to expand...
This is a carburetor tune problem. Generally a flat spot, or bog at off idle acceleration indicates a temporary lean condition during transmission from idle circuit to main jets, but can also indacate a too rich condion as well; I'm betting on lean. In other words perhaps a larger accelerator pump shot, or a longer duration shot will cure this. I’ll ask again, vacuum, or mechanical secondary’s? This is important because a light car with a small displacement engine is real hard to tune with a mechanical secondary because they can open too soon when there is not enough air moving through manifold to support proper air fuel mixture on a slant six. In other words it is a giant vacuum leak being introduced temporarily, or does the car blow black smoke on hard acceleration form a stop?

I need more information on your carburetor, and state of engine build to help much more.
 
Okay. I have a holley 390cfm carburetor. Brand new with electric choke. I have a 904 automatic transmission behind it with a stock torque converter. Yes you are right in that I have customs kick down linkage. I am trying to move the kick down linkage back and fourth but I'm obviously not having any luck. The throttle linkage is jimmy wrigged. Do you guys recommend a throttle linkage adapter that will make adjusting easier?


To answer your question, I'm not sure if I have a mechanical or vacuum secondar system in place. I think if anything I'm running too rich though. But maybe when I floor it, it gets too lean. I don't know. My skill and experience is lacking in this department. Sorry for the lack of information guys. I can only describe the symptoms.
 
About the kick-down:
It is best to consult a service manual and understand the correct adjustments, they change from year to year with linkage styles. It would help to know the year and model.

To get it to work the throttle bellcrank radius of the original carb, and Holley should be made to match with an adapter at the Holley 390 if needed. Then revised carb throttle location, may require a length change, of the throttle rod.

There is often an adjustment of the lower trans rod, using a jig holes in the kick-down bellcrank bracket. Then the upper transmission throttle rod, is adjusted to spec at curb throttle. Typically by pulling the rod forward, then extending by 4 turns. This varies by linkage style!!!

Danger: Transmission damage can occur with incorrect transmission rod adjustment!

About the throttle linkage:
It needs to have enough slack to insure carb can return to curb idle plus perhaps 1/8". It also needs to open the throttle fully when accelerator is fully pressed. It should operate without binding, and return quickly. The kick-down may need to be disconnected, for this test with engine "off". Reconnect kick-down.
 
Okay. I'll play around with that also. I have a 1971 dart swinger. The engine is from a '64 dart and is all stock except for the intake and headers. The transmission is a '71 904 transmission. I don't know if that information is helpfull or not...? Either way I will take all of your advice and keep working on it. I'm sure if one of you more experienced guys were working on it, it would've been fixed by now. But I guess you can't learn unless you screw things up first! Haha.

If you guys have any other recommendations I'm all ears. Thanks for all the help everyone!

Which service manual is best for this kind of information?(carburetor linkage and transmission kick down settings)
 
I have a Chiltons Barracuda & Challenger 1965-1972 Repair and Tune-Up Guide. ISBN 0-8019-5807-5. It has good pictures and instructions, for all the styles. It looks like 1968-1972 \6 had the same linkage design. The bell crank is bolted to the exhaust manifold. It looks like the throttle is mounted above the kick-down rod at the carb.
I have only worked with the common stud type.

The 1966 linkage looks nice to me since a single operating rod at carb. However the accelerator pedal has a rod, not a cable so will likely not install well in the 71'. It might be possible to use the 66' bellcrank at manifold, and set it up to work with the throttle cable.

P.S. It looks like you can buy the book on amazon from $5 to $265 (new) :)
 
I'll look into buying the manual. I'm about to go tinker with the linkage. Wish me luck. Here we go again. I'll let you guys know what happens.
 
Do you guys recommend a throttle linkage adapter that will make adjusting easier?

Yes absolutely needed; Holley part # 20-7 http://www.summitracing.com/parts/HLY-20-7/

I have an older Holley 390, 904 automatic transmission, Holley part # 20-7, and Bouchillon kick down cable kit, this combination is fully adjustable. The only thing you need to be sure of is that the accelerator pedal when floored will fully open the throttle plates in carburetor. I had to place a 3/16th inch between the accelerator bracket and floor. If throttle plates won’t open fully the secondaries will not open. There are other cables the work as well.

http://www.bouchillonperformance.com/BPEtkdc.asp

Get a factory service manual for the year of your car. They are available in print, and on disk; personally I prefer print copy as one can mark it up with notes, and drag it under the car while working.

As for rigging up non stock carburetors, manifolds etc. you’re kind of on your own relying on us here, or that other /six site dot org.
I install an o2 sensor to help tune the old holly, it helped. You may want to take a look at this site for a few Holley tuning tips http://www.bob2000.com/carb.htm , and get this book covering Holley 4160 (390) carbs; http://www.mre-books.com/fuel/hp473.html

005.jpg
 
He'd probably be fine if he just got the right conversion parts like you suggested.
 
Bouch? Where can I look at some conversion parts?

I tried messing around with the kick down linkage and it helped out. The car is now able to accelerate at a full stop without hesitating, but it still does not shift at the proper time because it revs really high before down shifting to second. Also when I am coasting or moving and I hit the throttle more than half way down, the car still lags and hesitates before accelerating. I tried leaning the carburetor out as well as making the mixture more rich and none of those changes helped the situation. I think the lag definitely has to do with the secondaries opening up, but not sure how to fix it or test that theory out.

Also while the engine was off I floored the throttle pedal and checked to make sure the throttle linkage was opening the choke all the way... It is.

Other than that I'm trying to take it step by step and not get ahead of myself. I did make a little progress, but still have issues with the shifting at slightly higher rpm when I push down 1/2 way on the gas pedal.

What should I do next guys?
 
Wjajr, where did you get the adapters that link the throttle cable to the kick down linkage? My setup is super Jimmy wrigged. It looks about the same in terms of where everything goes, but it's just not that pretty. Also it may be causing some obstacles with tuning. I think. it's okay for now, the real problem lies elsewhere. Also thanks for all the great links to info!
 
Give Lokar a call and tell them what you have.
They can hook you up.

Call us Toll Free 1-877-469-7440
Lokar Performance Products
10924 Murdock Drive
Knoxville, TN 37932
865-966-2269
FAX 865-671-1999


firefighter1 said:
Wjajr, where did you get the adapters that link the throttle cable to the kick down linkage? My setup is super Jimmy wrigged. It looks about the same in terms of where everything goes, but it's just not that pretty. Also it may be causing some obstacles with tuning. I think. it's okay for now, the real problem lies elsewhere. Also thanks for all the great links to info!
Click to expand...
 
firefighter1 said:
Wjajr, where did you get the adapters that link the throttle cable to the kick down linkage? My setup is super Jimmy wrigged. It looks about the same in terms of where everything goes, but it's just not that pretty. Also it may be causing some obstacles with tuning. I think. it's okay for now, the real problem lies elsewhere. Also thanks for all the great links to info!
Click to expand...
if this is as you say jimmy rigged thats your prob buy the right parts and hook it up right if its worth doin do it right and it will work right
 
jimjimjimmy said:
if this is as you say jimmy rigged thats your prob buy the right parts and hook it up right if its worth doin do it right and it will work right
Click to expand...

Thanks for the advice jimjim. Youre very insightful. I'll head your words of wisdom instead of doing everything jimmy wrigged.
 
Also while the engine was off I floored the throttle pedal and checked to make sure the throttle linkage was opening the choke all the way... It is.
Click to expand...
Not choke, though it has to be fully pulled off when engine is warmed up, but the throttle plates that the throttle cable operates.

Other than that I'm trying to take it step by step and not get ahead of myself. I did make a little progress, but still have issues with the shifting at slightly higher rpm when I push down 1/2 way on the gas pedal.
Click to expand...
You have to have the Holley adapter 20-7 for Chrysler that I hot linked from Summit… Any place that carries Holley parts will have this item. Until you have the right adapter, 20-7, to synchronize KD cable & throttle cable travel the or car will not shift correctly.

Boulchillon (see hot link in previous post) sells the compound factory like cable mount that is bolted to the carburetor. Their kick down cable is basically Chrysler factory parts used to operate later model rear wheel drive vehicles such as PU trucks, so the whole shoot’en match bolts right up with no messing around in about a half hour, and can be adjusted in a few test drives.
Mancinni Racing sells a similar KD cable conversion: http://chucker54.stores.yahoo.net/kiccabkit1.html As well as Lokar cables.

Once you have the transmission shifting better, we can work on tuning the carburetor.


Wjajr, where did you get the adapters that link the throttle cable to the kick down linkage? My setup is super Jimmy wrigged.
Click to expand...
Look at the hot links in previous post for these parts, and forget about Jimmy. Jimmy ain’t cutt’en it. LOL
 
Got it. Thank you for all the help. Im trying my best to get it all worked out and I will. Try try again. I ordered the proper brackets for the carburetor and linkage. I guess I'll have to wait until it get here.
 
You must log in or register to reply here.
-

Back
Top