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Thread: HI Please Help Th400 vacuum problem maybe????

  1. #1
    gsautotech's Avatar
    gsautotech is offline Cadillac Owners Member
    Automobile(s): 1968 fleetwood brougham, 1969 coupe deville
    Join Date
    Jun 2009

    HI Please Help Th400 vacuum problem maybe????

    hi Guys and gals, i have a 69 coupe deville with 472 , factory manifold and eldebrock carb and th400. i will describe the
    symptoms am having to the best of my ability, any input would be greatly appreciated, thanks everyone in advance.
    one day i noticed when i floor the gas my car beings to choke as if theres wasn't enough fuel going to the carb… i
    changed the fuel filter and fuel pump. i did a test run, and yet the same problem so i changed the carb from a quadrajet to an elderbrock 1405. before the carb swap, the transmission vacuum line was ran to the front port on the quadrajet and the tranny shifted normally. now that i have the eldebrock carb, i got the vacuum line connected to a port on the
    manifold behind the carb. the transmission seems to stay in one gear. i drove the car and reached speeds of 60+ in this
    one gear…rpm was about 3-4k and yet nothing changed. please anyone help i been trying everything i can think of.

    -i tried disconnecting the module at the manifold;the drive test...the transmission felt as if it was in 1st gear.

    -i tried removing the module and doing a vacuum test;i used a brake line vacuum pump and the module did not leak, the diaphragm is good. plus there was no trace of trans fluid on
    the nipple side on the module.

    -i removed the governor and inspect it for and sign of damage; no sign of damage

    -i sent 12v to the solenoid to test if it was working; i head it click as i connected 12v/disconnected 12v

    -trans fluid level is good

    am stumped, the trans worked well before the carb was swapped

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  3. #2
    cadillac_al is offline Cadillac Owners Connoisseur
    Automobile(s): 70 Deville 77 Fleet 78 Seville 92 Deville 03 Deville
    Join Date
    Feb 2007

    Re: HI Please Help Th400 vacuum problem maybe????

    There has to be a problem with that vacuum hose now. If that modulator is getting full vacuum it has to work. I would verify the vacuum at the modulator with a gauge. It is supposed to be connected to a manifold port anyway. Maybe you got the hoses mixed up and it is actually hooked to the ported vacuum on the carb? I'm sure you will get it sorted out quickly.


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