Hello, we started the engine today after a long time after the 2nd attempt but the when we put the car in gear (3 speed auto) the wheels dont turn. Is it a problem in the transmission or is it due to the positive traction system since the car is on a jack and rear wheels aren’t touching?

 

Will the wheels turn by hand with the trans in neutral?

 

I will have to try tomorrow, what will this indicate?

 

The posi doesn’t have an impact on this.

 

If the wheels can be turned with the trans in neutral, the problem is not the rear axle. Are you sure there's fluid in the trans?

 

It will indicate that your brakes may be the cause. Transmissions don't cause the rear wheels to lock up. The only way the rear diff causes it is if it broke internally, not just being a posi.

 

The wheels turn by hand when in neutral

 

As Joe P. pointed out, you may be low on fluid in the transmission.

 

wOW... That is not right. If you are first of all in a GEAR reverse or 1st 2nd or 3rd....IN the air it will instantly start turning the wheels...even in the lowest of low idle speed. PERIOD.
Check the stall converter to the flywheel connection. IF you did not put bolts to connect these to items the rear will never get power.
Check the dumb easy things first.
EVEN low fluid that trans will move...BUT DO CHECK it while running...... If you do not have any fluid on the dip stick while the engine is running ...SHUT IT DOWN immediately and add 1-2 quarts
Another thing that could have happen and I hope not....DID you get the torque converter properly into the transmission pump drive slots.... that is why the torque converter has those two big slots in the snout of the converter neck
See how that goes ...
Jim
If you have all that good fluid converter stuff and in a correct gear.... then the trans has issues.
Do double check your transmission selector outside and inside the pan to be sure it is actually selecting a gear.

 

Was this car running at one time...??? or did you have it apart?
Jim

 

The car has been sitting since the 90s and is for my grandfather who was a GM mechanic so the car was perfectly maintained back then, we didn’t take anything apart just changed the spark plugs and wires and added oil to turn on the engine. I’m probably gonna take it to an expert and have it solved since I don’t want to do anything that might go wrong.

 

Please BE CAREFUL with the term Experts...lol. You would be surprised how many people think they know what they are doing and DO NOT.

WAS the car rolled into the shop ? Meaning the wheels and stuff rolls? Y/N?
IF the car can be pushed around by hand... you are talking about a transmission problem PERIOD.
IF you can not push the car and it was on the rack since 1990 ... well you would start to disconnect easy items... drive shaft now see if rear turns free... If it does then back to the trans again IF the rear still does not spin...it is in the rear end or the rear drums wheel bearings carrier bearings pinion bearings etc,

easy thing you can do is simply pull the cover off the rear see what things look like in there... if the fluid was low and humidity high the clutches could be stuck and bearing surfaces rusted too preventing them from spinning. You do not have a location of where you are in the USA But in the NORTH Ohio it is terrible to let a car just sit.... BAD NEWS ) you have to oil everything unless it is in a sterile environment.... a BUBBLE!

Jim

 

Jim is correct. Use some common sense here. If the car rolls in neutral, the problem cannot be in the rear axle or driveshaft. You have a transmission problem.

 

Been sitting for 30 years? Check fluid . Please let us know how it goes, Good luck!