engine revs like crazy when in gear?

[BigNate]

I have a 75 ish F250 4x4 with a 77 351M & C6 that I can't seem to explain the revving engine when it's put into drive. At first I thought maybe a loose wire was getting caught on the throttle linkage or something but eliminated that easily enough. It's almost as if the trans is trying to kick down so to speak but I don't much about auto tranny's.

How does the vac hooked to the trans effect it? Could the trans be causing the rev change? Has anyone else experienced this?

New distributor, control module, coil, plugs. Have new cap and rotor as well but not installed yet. I don't think the ignition is the fault as it was doing this before.

 

[BuzzGun79]

I know this maybe a longshot...but it happened to me long ago, Check your drivers side engine mt...if the engine mt broke the engine could raise while in gear pulling the accelerator cable/ pedal down..

 

[BigNate]

Never even thought of looking at the engine mounts! Thanks

 

[BuzzGun79]

Anytime Nate!!

 

[fatherdoug]

I believe the vacuum supply to the transmission is only used for shifting purposes.

I do know it will not shift when the vacuum is disconnected.

 

[Fellro]

Is it doing it before you move, or going down the road?

 

[BigNate]

It starts revving as soon as it goes into gear. It's a basket case of a project that I havn't driven on the road yet. I need to correct some steering issues before I'd feel safe going much of anywhere.

Take a glance at my photo album under The Hog. The steering mods before we got it were... interesting.

 

[m78]

I wonder if that transmission kick down linkage is binding with the shift linkage.

 

[BigNate]

I wondered the same except there is no linkage that I see, only a vac line to the back of the tranny. I'm at work till well after dark but am going to check out suggestions monday &tues.

 

[Fellro]

The linkage is a solid pipe linkage from the throttle to the transmission where the shifter also goes in.

 

[BigNate]

The only thing attached to the throttle is the throttle itself.

 

[BigNate]

The motor mount on the drivers side is split. Haven't been able to replace it yet but will let you know if it fixes it.

 

[Fellro]

That will definitely do it when you have solid linkage. As the motor rises, the linkage will move, increasing the throttle, then increasing the engine speed and raising the motor more, which then increases the throttle...

Quick poor man fix is to put something like a chin around the frame and bolt it to the motor such that it can't climb up. GM actually used to put a cable around the upper control arm pivot shaft and attached it to the exhaust manifold in the 60's.

 

[m78]

I think I still have a set of those cables off of something I dismantled.

 

[BuzzGun79]

That will definitely do it when you have solid linkage. As the motor rises, the linkage will move, increasing the throttle, then increasing the engine speed and raising the motor more, which then increases the throttle...

Quick poor man fix is to put something like a chin around the frame and bolt it to the motor such that it can't climb up. GM actually used to put a cable around the upper control arm pivot shaft and attached it to the exhaust manifold in the 60's.

Yep,agreed Roger..

 

[BigNate]

Thanks to BuzzGun! Mounts & alternator got done yesterday and the crazy reving dissappeared. Imagine that.

 

[BuzzGun79]

Thanks BigNate...Glad to hear it...