Harsh gear change on a FMX box

[Mach1 Ian]

Could any one please tell the reason why the gear change is very harsh and what is the cure when the vehicle is driven hard through the gears?

Thanks
Ian

 

[bnickel]

could be lot's of reasons. has the trans had a shift kit put in? is it full of fluid? could be a bad governor, could be that someone has adjusted the vacuum modulator in too far as well. an old trick for the fmx to get a firmer shift is to grind the vacuum modulator actuator rod down about 1/8" could be that someone tried to do that and went too far.

if can be a little more specific about when and how it shifts harshly we can help you better.

 

[geostang351]

could be lot's of reasons. has the trans had a shift kit put in? is it full of fluid? could be a bad governor, could be that someone has adjusted the vacuum modulator in too far as well. an old trick for the fmx to get a firmer shift is to grind the vacuum modulator actuator rod down about 1/8" could be that someone tried to do that and went too far.

if can be a little more specific about when and how it shifts harshly we can help you better.

I vote shift kit.

 

[69 Rustang]

Harsh? When my 69 had an FMX, after installing a shift kit it would get rubber going into second gear. I considered the shifts firm even at full throttle, but not harsh. It would bark the tires while rolling in first at about 25mph when opening the secondaries on the carb too--I kind of liked it like that...

What is your definition of harsh?

 

[bnickel]

the old shift kit in my car could have easily been felt as harsh. it would catch rubber on every gear change reagrdless of whether i was in the secondaries or not. i haven't driven the car since i had the trans rebuilt and the shift kit was supposedly removed but i had also done the actuator rod modification as well as adjusted the modulator for firmer/quicker shifts. it would pull the right front up to full travel on gear changes and would catch about 6-10 feet of rubber on full throttle 2-3 shifts when manually shifting. yeah it was pretty harsh by most standards.

i had the Ford shift kit installed and they used the higher level of the options in the kit. i used to tell people that 1-2 shift would make you see God, it hit so hard.

edit: oh yeah, the reason i had the kit removed on the last rebuild is because i was tired of having to have the 2nd gear band replaced all the time, it's only cast iron and has a tendancy to break under those conditions, i've gone through several. i also had them replace the cast iron badn with a steel "felx" band the last time around as well

 

[351carlo]

My FMX has all the goodies including a B&M Shift kit. The only thing not done was to remove the check valve (Stage III According to them).

Harsh shifting was never a problem for me with a properly adjusted vacuum modulator and a good vacuum source. I adjusted everything with my Ford Shop manual to shift at the proper RPM and the proper MPH. It was as smooth as it was when stock.

Now I could also spin straight through third at 60mph if I wanted to, from a roll or a dead stop.

If the vacuum modulator isn't connected (As mine isn't right now), the trans will go up and shift without using this as a reference. This will typically be far too high in the RPM, even though you won't be on the throttle. This will give a VERY rough shift.

Check the vacuum modulator, it's easy to put the rod in wrong too. Make sure everything is there, and the vacuum line is good down there (I use a gauge on the bottom to check it).

 

[Mach1 Ian]

Thanks for all your replies.
The best way of describing the harsh gear change is when i drive it hard in auto or using the box as a manual, when ever it changes up a gear there is a violent jolt which shakes the whole car, i have checked the prop shaft for any play in the uj's, that looks OK. As i haven't any history of the car, i am not aware of any modifications to the gear box.
I feel as though this problem needs to be rectified before any damage is caused.
I have owned it for 2 years and it has always had this problem, it has never bothered me until i spoke to a friend of mine who has a 390 and he commented on what a harsh gear change mine is compared to his.

Thanks
Ian

 

[bnickel]

it really sounds like it just has shift kit. i'd just check the vacuum line and make sure it's connected at teh trans and the engine and make sure that is all in good shape. wouldn't hurt to change the modulator either but it doesn't sound like you really have a problem.

also, your buddy with the 390 has a c6 and it's shift qualities are a little different than those of the FMX, so don't put too much stock in his opinion because it's not an apples to apples comparison.

how many miles have you put on the car in the 2 years you've owned it? if you've put a good bit of mileage on the car and haven't had any problems with breakage of any kind you're probably ok, just check the basic stuff i suggested and let us know what you find.

 

[bnickel]

here's another quick little test. a stock FMX will shift from 1st to 2nd gear at about 15 mph under light throttle and should be almost imperceptable, if it has a shift kit the light throttle 1-2 change would be closer to about 20 mph and be pretty noticeably firm but not necessarily hard or harsh, let me know.

 

[Mach1 Ian]

it really sounds like it just has shift kit. i'd just check the vacuum line and make sure it's connected at teh trans and the engine and make sure that is all in good shape. wouldn't hurt to change the modulator either but it doesn't sound like you really have a problem.

also, your buddy with the 390 has a c6 and it's shift qualities are a little different than those of the FMX, so don't put too much stock in his opinion because it's not an apples to apples comparison.

how many miles have you put on the car in the 2 years you've owned it? if you've put a good bit of mileage on the car and haven't had any problems with breakage of any kind you're probably ok, just check the basic stuff i suggested and let us know what you find.

I have done about 5000 miles since i first had it and it gets a good mixture of easy and hard driving conditions. As regards 1st to 2nd you can hardly feel the gear change, next time i take it out i will check it out and see.

Thanks very much
Ian

 

[bnickel]

I have done about 5000 miles since i first had it and it gets a good mixture of easy and hard driving conditions. As regards 1st to 2nd you can hardly feel the gear change, next time i take it out i will check it out and see.

Thanks very much
Ian

well in that case it sounds like what an FMX does normally. it may still have mild shift kit.

 

[Mach1 Ian]

well in that case it sounds like what an FMX does normally. it may still have mild shift kit.

Took the car out for a run today, it changes 1st to 2nd at about 15mph but with a definite clunk, nothing harsh though just sounds like it is taking the play up from some where, could it be play in the diff? Please excuse me as i know virtually nothing about cars:

Thanks
Ian

 

[bnickel]

was it a clanking clunk or more of a thud that kind of makes the whole car lurch? you could have a bad pinion bearing, to check it put the car in gear (foot on the brake) and then put it in neutral and then to reverse and vice versa and see if you hear kind of a ringing clunking noise, if so you may have a bad u-joint or pinion bearing. if you are really worried about it and not very knowledgable with cars you may want to take it to a mechanic to have it checked out

 

[Mach1 Ian]

was it a clanking clunk or more of a thud that kind of makes the whole car lurch? you could have a bad pinion bearing, to check it put the car in gear (foot on the brake) and then put it in neutral and then to reverse and vice versa and see if you hear kind of a ringing clunking noise, if so you may have a bad u-joint or pinion bearing. if you are really worried about it and not very knowledgable with cars you may want to take it to a mechanic to have it checked out

I have tried what you have suggested and it is a thud and the car lurches slightly, it is worse when reverse is selected. A friend of mine who is a UK ford mechanic is going to have a look at when he has the time.

Thanks
Ian