Why would a 1975 C20 with a 350 trans not start out in 1st gear from a stop?

YOU CANT START A NORMAL AUTONATIC TRANSMISSION IN GEAR, HOWEVER YOUR DASH INDICATES THAT YOUR NOT IN GEAR. ONE CAUSE COULD BE DAMAGE TO THE LINKAGE BETWEEN YOUR TRANS AND GEAR SELECTOR. THIS WOULD INDICATE A DIFFERENT GEAR THEN THE GEAR SELECTED. YOU MAY ALSO CHECK THE PARK PINS IN YOUR TRANS. ...

If its a older trans sometimes the vacuum hose comes off the trans solienoid. ...

5th gear synro is inside the trans... the clutch has nothing to do with it. ...

You would need a ring gear for an automatic.

your trans axle has nothing to do with you losing 2nd gear

This problem could be the linkage in the transmission. The transmission could also be going out and would need replaced. ...

If it isn't slipping it is downshifting to 3rd gear

It is a switch that indicated what gear or gear range the trans is in.

If trans is jumping out of gear, that particular gear is worn from use. The beveled gears wear until they can not physically maintain contact. Split tractor at bell housing and again at rear differential to remove trans. remove top of trans and shifter. Remove main and counter shafts and replace worn gear and any bearings that show wear. ...

In the transmission tail housing where the speedo gear would be in an older version. ...

Low trans fluid, or internal trans failure.

I'm assuming you mean the inhibitor switch. ie the car shouldn't start in gear for auto trans. it's located on the passsenger side of the trans. it's the plastic unit which the gear shift selector goes through. ...

If it is a manual trans, the shift linkage might be loose, bent, or damaged. ...

Have the trans computer checked for trouble codes. That will give you a place to start diagnosing. ...

i would think it's a syncronizer inside the transmission

It is most likely stuck in second gear which is the "Limp" mode on the trans. There is something wrong with the trans and it should be taken to a good trans shop to be scanned for problems. ...

I have a 95 Lumina 3.1 and it would cut out of gear when I would stop, it turned out to be the sprag gear in the transmission. $$$$ ...

Depending on your car you have one of 2 things the speedo cable hooks to in the trans. It iether goes directly in to a gear in side the trans or hooks to a gear box which redirects a secound cable to the trans speedo gear. good luck Don ...

If your car has a automatic transmission, put car in neutral get a rolling start then switch to Drive. If car stays running your problem could be a solinoid switch in transmission. The trans. is stuck in second or third gear which would cause your car to stall out. ...

If it is 4WD, put put the transfer case in Neutral, leave the automatic in Park or standard trans in gear. If it is 2WD, automatic would have to have driveshaft disconnect, standard trans just put in Neutral. ...

if its jumping out of fifth gear the fifth gear syncronisers in the trans are shot ...

low trans fluid level.

Sounds like a vacum leak to me.

Is there park and nurtural?

That is the safety default (limp in) gear. The trans computer has detected a problem. You need to have the tcm checked for codes. The problem could be electrical or mechanical. ...