FMX slams into D and R

[wodzu 0]

Hi. After a long time my car is almost ready to drive again (unfortunately I had to rebuild the engine).

I have  a problem with FMX - it is jerking when going into drive or revers. The hit is quite huge. Beside this it is working very fine. What could be the problem? 

[barnett468 418]

3 hours ago, wodzu said:

Hi. After a long time my car is almost ready to drive again (unfortunately I had to rebuild the engine).

I have  a problem with FMX - it is jerking when going into drive or revers. The hit is quite huge. Beside this it is working very fine. What could be the problem? 

Did it do this before?

I know very little about trannies, but my guess is that it is related to the valve body, which is fairly easy to remove, and disassemble to clean, otherwise if the problem it is inside the trans, it needs to be disassembled.

[RPM 1,190]

You can usually get a correct answer on the Bad Shoe farcebook page. Ken is the owner who makes and sells rebuild videos. Pretty sure you have to join to post a question. 

https://www.facebook.com/groups/badshoe/

[wodzu 0]

Yes it did it. I thought it was the drive shaft play but it was done and it is pretty much the same. What Valve do you mean?

[barnett468 418]

What rpm does your engine idle at?

If you have a high performance engine and a stock torque converter, the trans can klang or jerk some when you put it into gear and the engine rpm will drop some. If this is what it is doing, you most likely need a high stall torque converter.

If the trans shifts properly by itself thru the gesrs when it is in the drive position  the torque converter is likely the problem.

You need to check out youtube for ford c4 or c6 transmission valve body removal if you have either of those to see the assembly i am referring to, but this part is something that an inexperienced mechanic should not mess with. 

You can try lowering the idle as low as possible as a test then put the trans in gear. You can also take a video of the problem and post it here.

[Ridge Runner 1,112]

I thought he was talking about me ,i like a good FMX!

[barnett468 418]

2 hours ago, Ridge Runner said:

I thought he was talking about me ,i like a good FMX!

yeah, good trannies when they are built right. i think there is a wider high perf band for the drum, and maybe a different drum for the wider band, been so long i don't remember exactly.

[dcm0123 15]

FMX has a rod or cable coming from the carburetor to the transmission which controls transmission pressure.

Is it adjusted wrong or sticking?

Drive train play is another possibility. How did you determine there is none?

Did you check the play in the differential or just the driveshaft itself?

Bad spider gears or bearings in the differential can cause play as well.

[wodzu 0]

18 hours ago, barnett468 said:

What rpm does your engine idle at?

If you have a high performance engine and a stock torque converter, the trans can klang or jerk some when you put it into gear and the engine rpm will drop some. If this is what it is doing, you most likely need a high stall torque converter.

If the trans shifts properly by itself thru the gesrs when it is in the drive position  the torque converter is likely the problem.

You need to check out youtube for ford c4 or c6 transmission valve body removal if you have either of those to see the assembly i am referring to, but this part is something that an inexperienced mechanic should not mess with. 

You can try lowering the idle as low as possible as a test then put the trans in gear. You can also take a video of the problem and post it here.

hi.  I do not have the tach. the engine is matching number 351 with 4 barrel carb. the carb is Holley 750 with electrical choke.  when the engine is cold it revs quite high and when warm I think it revs still to high even we tried everything to get it lower. 

on the video you can here the engine warm  - one of first starts after rebuild

regarding the experience - I am living in Poland and my workshop has a lot of experience with oldtimers but unfortunately mostly Daimlers. They  forgot to check the under pressure lines and the gearbox didn't want to change to 2nd and 3rd... I had to tle them what to do... so I think it is not good idea to let them check the modulator...

[wodzu 0]

6 hours ago, dcm0123 said:

FMX has a rod or cable coming from the carburetor to the transmission which controls transmission pressure.

Is it adjusted wrong or sticking?

Drive train play is another possibility. How did you determine there is none?

Did you check the play in the differential or just the driveshaft itself?

Bad spider gears or bearings in the differential can cause play as well.

the driveshaft was renewed and now we see that probably we have to check the differential as well. But the play is not big. The hit by going into D or R was the same bevor the overhauling. 

[MN69Grande 203]

I second barnett468's suggestion at looking at the torque converter specs if you didn't rebuild the engine with stock parts.  In high school I put a performance build in with a stock converter with a stock transmission and had to stand on the brakes to keep the car from moving at a light.  Normally you can either talk to a good transmission shop or email performance torque converter manufactures with your engine and rear end specs and they can tell you the correct stall to use.

Also if you have a modified engine I would recommend getting an aftermarket tach.  They are easy to install with no modification to the car.  Just run 3 wires.  I've got one strapped to the steering column.  The more information you get about how your car is running the better you can trouble shoot and maintain the car.

@Ridge Runner I also thought he was calling FMX guys jerks!  I always found FMX owners pretty decent folk :)

[RPM 1,190]

16 hours ago, Ridge Runner said:

I thought he was talking about me ,i like a good FMX!

That took me a while to get :(

[barnett468 418]

1. It is idling way too high. This will cause it to slam into gear and you may very well damage the trans.

2. If there is a vacuum line going from the distributor to the carburetor or intake, disconnect it and plug the fitting on the carb or intake that it is attached to.

3. It does not sound like the cam in the engine is so big that it will not idle much lower, therefore, you must get it to idle lower somehow. There is a screw to set the idle with. It is located on the left side of the carburetor (as you are sitting in the drivers seat) and it pushes on the throttle arm. This screw needs to be turned counter clockwise (to the left) to lower the idle. Turn the screw out until the engine dies. If you can turn the screw out so the tip of it no longer touches the throttle arm and the engine still does not die, you have an air leak or there is something that is preventing the throttle blades from closing all the way. If this happens, disconnect the speedometer cable and try it again. If this does not close the throttle any further you need to find out why the throttle blades are not closing completely.

4. You can also try temporarily retarding the timing. It should around 10 degrees before top dead center when the idle is low. If the timing is set too high, it can prevent you from being able to lower the idle speed very much.

 

[1969_Mach1 333]

I agree, the idle speed sounds higher than it needs to be.  Cam sounds fairly mild so you should be able to drop the idle speed some.  

[dcm0123 15]

 

Corrected- FMX has both a rod and modulator, sorry for misleading you.

Check the shift rod setting since it may also control line pressure as noted below.

[1969_Mach1 333]

Been a while, but I believe the FMX uses both a vacuum modular valve and a rod from the carb linkage to the trans.  I'm don't know much about automatic transmissions.  But, I believe the vacuum modulator valve controls shift points under normal driving.  The other is to force downshifts, increase line pressure, or both (not certain) under hard acceleration from a normal cruise.

[lanky 44]

Fmx transmissions definitely have both a rod and a modulator. My FMX has always engaged in gear a little rough, but it doesn't sound as bad as the OP. It still works pretty damn well for an original unrebuilt transmission. My engine is 0.030" over stock 351w with stock converter and idle is set properly, and the shift rod adjusted properly.

[ralt962 11]

Sounds elementary, but oil level.  If you are low and running a higher idle, it will bang into gear.  

[Vicfreg 771]

Also suggest an idle adjustment.  That looks like an old school Holley.   Barnett has the right advice.  If the engine is still idling after you back out the curb idle screw, then the primary transfer plates are exposed and you need to adjust the idle mixture screws.  Plenty of YouTube and other Holley resources on how to do that. I use a Vacuum gauge.