Shifting at high RPM - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Dead Parrot · 12-13-2023, 04:29 PM

From your description, sounds like you have a TH400.

Choke light on: Make sure the choke isn't stuck. Stuck choke can cause a way too rich condition which plays with vacuum and thus impact shift points.

Trans: Verify that the trans fluid level is correct. Low level can cause shifting issues.
One quick test - take a clean hose, pull off existing hose from modulator, attach test hose to modulator, suck on hose. If it keeps vacuum, modulator might be good. If it doesn't, modulator has leak and needs replacing.

12-13-2023, 04:29 PM	#2
Dead Parrot Registered User Join Date: Aug 2012 Location: Oklahoma City, OK Posts: 2,502	Re: ing at high RPM From your description, sounds like you have a TH400. Choke light on: Make sure the choke isn't stuck. Stuck choke can cause a way too rich condition which plays with vacuum and thus impact shift points. Trans: Verify that the trans fluid level is correct. Low level can cause shifting issues. One quick test - take a clean hose, pull off existing hose from modulator, attach test hose to modulator, suck on hose. If it keeps vacuum, modulator might be good. If it doesn't, modulator has leak and needs replacing.



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