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Old 05-21-2010, 09:40 AM   #1
70MachU
 
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Join Date: Jun 2008
Vehicle: 1970 Ford Mustang
Location: NH
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Default Shifting problems with my FMX Auto Trans

Ok so I beefed up my rear end to 3.73s (from 3.25) a while back and I've been meaing to fix my speedometer for a while. Last fall I found the right gear. A 19 tooth white Speedo gear and installed it. It was a manual gear since they didn't make a auto gear in that tooth size (the difference is the numb on the end- so I had to cut the wire slightly to make if fit- which I was told wouldn't be a problem).

So, now my speedometer is working right, but the car was shifting hard into 2nd and then into 3rd right away. When I would come to a stop the car would stay in third not shifting back down to first. I also couldn't even manually shift down to second and 1st for some reason, but when I stepped on the gas my kick down rod would make it down shift.

- I should note that before I changed my speedo gear the car was shifting fine -

So I bring it to a tranny shop to take a look. They told me it was because the governor gear wasn't changed as well. They change that and played around with my bands in the transmission, replaced the fluid and I saw some crud build up in the bottom of the tranny pan. No metal chunks, just a gray type of sludge under the fluid coating the bottom of the pan and a couple pieces from the seals. They fixed my rear seal leak and put in a new front govenor gear and played with the bands.

Now the car will shift from 1st into 2nd and then 3rd when I come from park or neutral into drive. When I am still in drive and stopped at a light or a stop sign it doesn't always go back to first, but it has gone back to first a couple times after I put it into neutral then back into drive. It will shift correctly for a little while and then it will stay in Drive when I am stopped again for most of the time. The shifting is also smoother now but 3rd gear still follows 2nd fairly quickly but now immediate (with regular driving).

My Questions:

1. What could be the causing the trans to not shift back into first all the time when I am at a light or stop sign?

2. What are the shifting points? When should my car be shifting into 2nd and then 3rd? Should it be shifting at a certain speed?

3. That crud in the bottom of my pan. How much life do you think I have left to my fmx before a rebuild is needed? (This is the first time I flushed my fluid since I owned the car - 5yrs- I drive around 2,000 miles a year- The engine was rebuilt in 03 but I'm not sure if the trans was touched then as well.)

4. Ever since I changed out the speedo gear my speedometer needle vibrates when driving under 30mph. What's causing that?

Thanks!
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Old 05-21-2010, 04:16 PM   #2
rtintwo
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Vehicle: 1970 Mach 1
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Ok it sounds like you have multiple problems to me.

http://www.familycar.com/Transmission.htm This site has a basic explanation of the govenor and the vacuum modulator about half way down. The FMX only uses throttle possition for high load downshifting(passing gear).

The modulator is on the rear left side of the tranny. Take a real close look at the rubber hose on the bottom, trace the line up and make sure it is attached to the vacuum T on the back of the intake manifold, make sure the rubber is not cracked or leaking and that it is hooked up properly. Work was done in that area and the line might have been knocked off.

You say in your sig that you have a mild cam. Most mild cams will still produce enough vacuum to operate the modulator. However if you have a vacuum leak and a cam then you might not have enough vaccum. Spray the intake down with carb cleaner to make sure you dont have any vacuum leaks.

Double check your transmission fluid is full when the car is idling and engine hot.

The gray build up is from the clutch packs and is perfectly normal to have soem in the pan. Wouldnt be a concern to me unless there is metal chunks or the fluid has a burnt smell.

I would say that after you have covered the basics with fluid, modulator hooked up and good vaccum then i would say it is time to head to a tranny shop so they can look at possible sticking servos, band adjustment, etc...


The speedo fluxing is most likely from the new gear being modded to fit.
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Old 05-21-2010, 04:41 PM   #3
Waffles
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The problem is that you have an FMX.
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Old 05-21-2010, 04:41 PM
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2011, auto, clunks, downshift, fluid, fmx, ford, gt, light, modulators, mustang, slipping, stop, trans, type, vacuum

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