71 Mach 1 C6 only starts in 2nd gear?

dhvidston

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HELP!

My 71 Mach 1 with C6 automatic has developed an issue of not going into 1st gear... it starts out sluggish in 2nd gear.. goes to 3rd and 

seems to randomly drop back to 2nd.. but not to 1st as the car slows down.

I tried manually selecting 1st gear with selector... nothing happens... I can select 2nd, 3rd, neutral & reverse just fine.

I checked my trans fluid after warmed up & running.. level/color is fine.

Could this be a linkage issue or has my vacuum modulator gone bad.. or perhaps a worse problem?!

Thanks for your help and input... My M code Mach Mustang should be squalling the tires... not putting along like a Pinto!

Doug in Indy

 

bkdunha

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Sounds like your neutral safety switch is out of adjustment. You need to see if it has loosened and moved relative to the indicator being in park to allow you to start the car. I am assuming you are saying you cannot get the engine to start other than in second versus the vehicle moving forward only in second. If it is the later I would say it is an internal issue in the trans.

 

TheRktmn

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I think he means the car starts moving, not starting the engine. I thought he was talking NSS too.

:-/

 

dhvidston

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Sounds like your neutral safety switch is out of adjustment.  You need to see if it has loosened and moved relative to the indicator being in park to allow you to start the car.  I am assuming you are saying you cannot get the engine to start other than in second versus the vehicle moving forward only in second.  If it is the later I would say it is an internal issue in the trans.
Thanks.. motor starts fine and it goes down the road.. just launches in second instead of first gear... cant manually place in 1st either

 

TheRktmn

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I'm following this because my C6 has always tried to get out of 1st gear as quickly as possible. I have to come to a full stop to start in 1st.

I tried swapping valve bodies, no change. During the change I also switched shift kit vendors & types. I went from a no-name AT shop street and strip to a B&M HD/tow. No change at all. Changed vac mods, no change, tried green stripe mod, black stripe, changed mod rod, no change.

I just manually shift.

 
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Don C

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There's a valve in the valve body that may be the source of both of your problems, may be stuck, debris in it, or have a broken spring, or a plugged passage. It's called the "manual low / 2 to 1 scheduling" valve.

Low pump pressure could also be part of it.

 

dhvidston

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There's a valve in the valve body that may be the source of both of your problems, may be stuck, debris in it, or have a broken spring, or a plugged passage. It's called the "manual low / 2 to 1 scheduling" valve.

Low pump pressure could also be part of it.
Thanks for the input Don... if its just sticking.. is there an additive that can free it up? Sounds like replacing a valve is above my pay grade.. 

I have a new vac mod on the way... but sounds like maybe a waste of time?

 

Don C

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Doesn't sound like a vacuum modulator, it shouldn't have any effect when you manually shift into first, or when you start.

 

rvrtrash

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I would check the linkage first, just because it's the easiest and cheapest thing to do. I had a car once (with a C6) that wouldn't go into 3rd (drive). I discovered by accident that if I put it half way into neutral on the shifter plate, it would go into 3rd. After a linkage adjustment, everything worked fine.

Steve

 
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