Yo,
Try a Self Test for Diagnostic Trouble Codes (DTC)s anyway.
by my pal, BroncoJoe19
http://broncozone.com/topic/14269-code-reader/?pid=74587&mode=threaded
Some basics;
The engine temperature must be greater than 50° F for the Key On Engine Off (KOEO) Self-Test and greater than 180° F for the Key On Engine Running (KOER) Self-Test.
Run it around to heat the engine up and shift thru all gears including Reverse.
Make sure A/C is off and transmission is in Park (automatic); or in Neutral for a Manual & release clutch.
Then turn off engine, all accessories/lights (close driver's door) , etc.
Do KOEO test First
Post Code(s) here according to:
KOEO
&
KOER
...
Check shift linkage at throttle body, could be obstructed, jammed or tight inside sheathing.
Have helper press pedal and observe throttle body butterfly to see if it fully opens.
http://web.archive.org/web/20130607121313im_/http://www.supermotors.net/getfile/488497/fullsize/change-oil-pan-gasket-and-valve-cover-gasket-009.jpg
here I am prying upward on the throttle cable with the ***** driver to remove it and I will next pry upwards at the throttle body and move the throttle cable out of the way.
...
http://web.archive.org/web/20131029112311im_/http://www.supermotors.net/getfile/488498/fullsize/change-oil-pan-gasket-and-valve-cover-gasket-010.jpg
Using the screwdriver again I pull the cable towards myself to slide the cable off the clip. Then using a pair of slip joint plyers I will squeeze the plastic clip on the sides which will allow me to slide the cable through the bracket.
by Waltman
. ..
Check vacuum at modulator
Pull the vacuum line off the mod. If fluid comes out of the vacuum line your modulator is not good.
Check vacuum line to modulator from engine intake manifold source
Vacuum Modulator; The vacuum modulator is a vital component of an automatic transmission. It tells the transmission what kind of load is being put on it allowing the transmission to react with the proper line pressures and shift points. Over time, modulators can develop leaks, get ruptured diaphragms, get bent, etc. Not only can this cause annoying drivability issues, it can lead to premature transmission failure.
Vacuum Modulator Adjustment; "...SOME Stock factory modulators are pre-set and most are sealed. TCI® StreetFighter® modulator-type transmissions are all equipped with adjustable modulators. By turning the adjusting ***** (found in the vacuum ******) counterclockwise, you will lower the spring pre-load. This will cause earlier shifts. By turning the adjusting ***** clockwise and raising the spring pre-load, the shift points will go up. The range of adjustability is only a few mph either way..."
Source: by TCI Automotive tciauto.com via web.archive.org
Source: by tciauto.com
is VERY IMPORTANT to verify amount of vacuum at the modulator with a gauge. Automatic transmissions typically need a minimum of 12 in. Hg. at idle. Throttle position increases should produce a quick decrease in the vacuum reading at the modulator. Not enough vacuum will cause late, harsh shifts. Slow response to throttle position changes due to a kinked or plugged line will not property boost line pressure and will BURN UP YOUR TRANSMISSION
by TCI
Check vacuum at modulator
Pull the vacuum line off the mod. If fluid comes out of the vacuum line your modulator is not good.
Cl vac line to modulator from engine intake manifold source
Also check for Vacuum leaks in HVAC system (to some doors), at PCV Valve, etc
Source: by tciauto.com
PCV Valve Location & Depiction in Parts Diagram in a 78 400M
Source: by 78brncoxlt at
http://www.supermotors.net/registry/media/646054
Also watch out that you don't loose the small removable pin in the end of the modulator, you need it for the new one. You will need to know the color band on the side of the modulator when you go to get a new one.
by Seabronc @
http://broncozone.com/topic/23087-c6-transmission/
C6 FAQs
Source: by Kenneth C at Bad Shoe Productions
http://badshoeproductions.com/trans.html
An excerpt;
"Q. Can the shift speed and firmness be adjusted?
A. Yes to a point. Most modulator diaphragms have an adjustment ***** through the vacuum tube hole. ***** clockwise for later/firmer shifts and counterclockwise for earlier/softer shifts. However if more than two or three turns don’t get what you want, you may have other problems... Q. Which way does the modulator valve go into the case?
A. Orient the valve so that the 2 machined lands go into the case first with long shaft end facing out. Then install the modulator pin (looks like a short finishing nail), and finally the modulator diaphragm...."
Vacuum Modulator Adjustment; "...Most modulator diaphragms have an adjustment ***** through the vacuum tube hole. ***** clockwise for later/firmer shifts and counterclockwise for earlier/softer shifts. However if more than two or three turns don’t get what you want, you may have other problems."..
Source: by Kenneth C at
http://www.badshoeproductions.com/trans.html
