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Author Topic: 77 Seville Update  (Read 630 times)

Offline 1977Seville

  • Keeping the legend alive....
  • Posts: 32
  • Proud owner of a 1977 Seville!
  • Name: Wesley Willison
77 Seville Update
« on: February 24, 2018, 05:17:18 PM »
So, on my 77 Seville I replaced the radiator, hoses, alternator, belts and smog pump and a fresh battery, I have finally almost run out of the old gas and am going to put in new. So, I took it for a spin around the block and the car does not want to go over 20 mph (though it can) and that noise that I mentioned gets worse, its almost like it does not want to shift out of 1st gear and the noise is holding it back, would the flex plate cause this? Or am I looking at a possible rebuild for the transmission?
1921 Chevrolet '490'- in the family since 1972
1941 Dodge Business Coupe- in the family since 1955
1948 Lincoln Continental- in the family from '75-'91 bought back in 2007!
1966 Ford Mustang - (2001)
1977 Cadillac Seville (2018)
1989 Buick Electra Park Avenue (2012;2017;2018)
1989 Buick Reatta (2013)
2004 Lincoln Town Car (2014)
2015 Chevrolet Volt (2017)
Wesley Willison

Offline TJ Hopland

  • Posts: 10188
Re: 77 Seville Update
« Reply #1 on: February 24, 2018, 06:52:53 PM »
That uses a 400 transmission.  The 400 has a vacuum modulator and an electric kickdown.   No vacuum signal reaching the trans or a bad modulator will make the trans think you are always flooring it so it will delay the shifts.   The electric kickdown gets a +12 signal when its floored so would be a similar result if its always getting a signal.   The rest of the Cads the kickdown switch was hooked to the throttle linkage near the carb.  Other GM's had it on the firewall near the pedal, not sure how the Seville was being that it shared more with other GM lines than a typical Cad.

No idea on the noise.  Flexplates will make strange sounds that will vary depending on load and speed but I don't think was an especially common issue with these.   

Did you get a look at the timing chain?   Borescope through the fuel pump hole?   Just rock the crank back and fourth while looking at the distributor rotor?
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

Offline bcroe

  • Posts: 3895
77 Seville Update
« Reply #2 on: February 25, 2018, 07:09:10 PM »
I am going to suggest, the ECU may be running quite lean, so power
is lacking, and you get the low manifold vacuum mentioned by
TJ Hopland.  That in turn is usually caused by a failing MAP in the
ECU.  Checking the mixture with a Wide Band OX sensor will tell
tell.  I also check the ECUs. 

The other thing to check, is a clogged Cat Converter, causing big
back pressure.  good luck, Bruce Roe


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