Engine will not shift out of first gear

Asked by Oct 09, 2015 at 04:42 PM about the 1974 Cadillac Eldorado

Question type: Maintenance & Repair

I have a 1974 Cadillac Eldorado Convertible.  The big 501 V8 front wheel
drive automatic transmission.  The car had been sitting for years and I
restored it 2 years ago.  I recently had the engine completely rebuilt and
now the engine will not shift out of first gear automatically.  You can shift
from 1st gear to 2nd gear and to 3rd gear using the manual shifter on the
steering column but it will not shift when in "drive".
The engine will shift into 2nd gear automatically if the RPMs get high
enough.  The car has to be traveling about 25 mph before the RPMs get
high enough for it to shift.  Could it be a vacuum issue or a linkage issue?  I
had a transmission shop take a look at it and they say the vacuum
pressures are normal and say its internal with the transmission.  
Suggesting a $2500 rebuild. Doesnt sound right to me.  This is a completely
restored vehicle with an amazing paint job with airbrushed murals.  When I
bring it into an auto shop, I am always hesitant.  
Any suggestions??

4 Answers

72,435

The vacuum modulator would be my first suspect. It needs to be hooked up to intake manifold vacuum. Not carburetor vacuum. There should be a vacuum connection on the back of the intake manifold for this. If it's hooked up correctly and the vacuum modulator is working correctly then I'd suspect the valve body next. The passages may be gummed up. Also, check that the kick down switch on the carburetor is working as well as the kick down solenoid in the transmission. Of course inspect the wiring and the connections as well. These transmissions were VERY durable and long lasting. HTH. -Jim

1 of 1 people found this helpful.

I'm having same problem but mine will shift 1 an 2 but not into 3rd my vacuum is ran into carb on back already replace the modulator and still nothing it's shift Nice & Smooth no problems no jerks or anything the blood is bright red but my vacuum is ran into the back of the carburetor and I found were on the intake but I don't know where at on the intake can find any diagrams

Had customer same car same issue 74 elderado 500h thm-425 auto fwd disconnected throttle switch at car by fixed problem,switch was faulty.

Switch from gearbox to throttle position switch on carby.

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