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Hello everyone, I would like to understand how the th400 transmmission works, and particularly the vacumm modulator, what exactly is it for?
My problem : I have a big clicking sound when I switch to R on the TH400 gearbox. I don't have any other noise when I shift to neutral in park or on 2 or 1.
Do you also have this clicking sound?
The vacuum modulator controls pump pressure , it relaxes the pump at low throttle high vacuum driving situations , give it gas and when vacuum drops the pump pressure increases so the clutches don't slip under acceleration ..... the adjustable modulators help fine tune the shift points during a light throttle cruise and or light throttle acceleration.
Not sure on the clicking noise but it seemed that the T400 has either a Center Support or one way clutch that used to wear a groove in the case when applying reverse gear making a one time knock noise . I’ll have to get my book out to verify
Is your vacuum modulator line hooked to full manifold vacuum?
Have you pulled the line to see if there is trans fluid inside? A bad vacuum modulator will pull trans fluid through the port......
Thank Jebby, it is well connected but the rubber elbow is cracked ! I m going to change it . But i doubt that's what produces the clicking when it goes into R in the transmission.
Im having a similar issue. Most of my problem went away when I changed the rubber bushing at the front of the differential however I still get that same noise when going into R from Park though now is much less.
Th400 vacumm modulator and
