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FMX Transmission not shifting correctly- what should I do?

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Old 07-27-2010, 02:01 PM   #1
70MachU's Avatar
Join Date: Jun 2008
Vehicle: 1970 Ford Mustang
Location: NH
Posts: 19
Default FMX Transmission not shifting correctly- what should I do?

Ever since I changed my speedo gear my transmission hasn't been shifting correctly. It wouldn't shift back down to first gear at a stop and it wasn't manually shifting either.

I brought it to a transmission local shop and they replaced my fluid and messed around with it a little bit. They said it wasn't shifting correctly because the last guy didn't change the governor gear in the front of the transmission. When they pulled down my tranny pan they saw some metal filings, mostly crud and a some pieces to a plastic ring. No metal chunks.

When I got the car back the car now would shift manually from first to drive and occassionally would shift back down to first when I was at a stop, but not always and sometimes when it would shift down to first it would shift hard.

When I'm at a stop I can get the car back to 1st by putting it in neutral and then to drive and it's a hard shift when I do that or I can put it in Park and then to Drive.

Sometimes when I try to go from Drive to 1st at a stop I noticed that it just went to 2nd.

Also while in drive 2nd shifts to first almost right away unless I am stepping on it then they'll be a normal gap between shifts. Is that normal?

So, the mechanic thinks that rebuilding the valve body might make it shift better. The rebuild would be $350 to $400. But he also thinks the best way to go would be to rebuild the transmission and that would cost $1,500- 1,800. There's no gaurantee that the rebuild valve body would fix the shifting issues and I wouldn't want to do it to then spend another $1,500 to rebuild the transmission.

So, I'm at a loss of what to do. A little history on the car is I know that the engine was rebuilt in 2003- I'm not sure about the transmission and when that was last rebuilt since the previous owner took it as a quick trade before selling it to me.

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1970 Mach 1 351C 4v FMX- Numbers Matching - Whimbleton White
Eddlebrock intake, MSD Ignition setup with box, Headers, Electric Cutouts (crowd pleaser :-) FlowMasters, Holly Carb, Mild Cam, 3.73 gears, Original Shaker Hood Scoop.

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Old 07-27-2010, 02:44 PM   #2
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Join Date: Aug 2004
Vehicle: 69 Mach1
Location: ABQ, NM, USA
Posts: 2,250

I wish I was so lucky to get an excuse for a modern OD swap. Mine leaks a bit, but has not faultered in 41 years. I did add a shift kit over a decade ago...
69Mach1 - warmed up 395W (AFR 185s) and Gforce T5 with hydraulic clutch, 3.50:1 posi, rack&pinion/tilt, 235/50ZR17x8 front & 285/40ZR18x9 rear, American Racing Nova wheels, all MSD, Holley 750, custom paint, headlight relays, Shelby drop & 2" lower all around, Hotwheels Redline scale is 1 to 1.
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Old 07-27-2010, 05:41 PM   #3
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Join Date: Sep 2008
Vehicle: 1971 Mach1 351c Tremec TKO 5-speed- yea!
Location: The garage (near SF bay- Calif)
Posts: 469

Oh, Oh! I know the answer to this one:

A TKO-600 5-speed would be perfect behind that "C"!
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Old 07-27-2010, 05:41 PM
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body, cost, fmx, governor, location, mustang, overhaul, photos, properly, rebuilding, sale, shifting, trans, transmission, valve

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