I believe that the M1008 uses a TH400 and a NP 208 from what I've read, what I'd like to know is what kind of a modulator does the trans use. Is it a vacuum or mechanical modulator?
Gus
Gus
CK5
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M1008
- Thread starter Speedo
- Start date
Vacuum
Thanks.
Gus
Gus
I've read some military TH400's used mechanical modulators (cable operated,that use a 700R4 TV cable to operate it)..never seen one myself yet though..you can buy those modulators ,but they are not cheap,125 bucks or more last time I looked one up..
I've worked on several different applications where TH400s were used with diesels and no vacuum pumps so a mechanical modulator was necessary. I have a friend who has a M1008 and from his description it sounded like his modulator is failing but I didn't know if it was vacuum or mechanical.
Gus
Gus
What is it doing?..(or not doing!)..?
I've had my share of experience with TH400's and TH350's that had modulator issues,my '82 diesel pickup included..
I put a used vacuum pump "can" on it recently,the original was dead,not making any vacuum,the one I put on seems to work,but on a vacuum gauge it pulsates rapidly between 5 and 15" of vacuum..
The transmission seems to shift sooner into 3rd now, with it producing vacuum ,and a bit less firmer than it did with just the dead pump,and the re-worked govenor Greg Ducato here set up for me..actually I liked the way it shifted with "no" vacuum,relying just on the govenor to upshift it--it was much firmer--but it not wanting to go into 3rd until 35 mph and lack of engine braking in second gear, is kind of irritating in city driving..
I've had my share of experience with TH400's and TH350's that had modulator issues,my '82 diesel pickup included..
I put a used vacuum pump "can" on it recently,the original was dead,not making any vacuum,the one I put on seems to work,but on a vacuum gauge it pulsates rapidly between 5 and 15" of vacuum..
The transmission seems to shift sooner into 3rd now, with it producing vacuum ,and a bit less firmer than it did with just the dead pump,and the re-worked govenor Greg Ducato here set up for me..actually I liked the way it shifted with "no" vacuum,relying just on the govenor to upshift it--it was much firmer--but it not wanting to go into 3rd until 35 mph and lack of engine braking in second gear, is kind of irritating in city driving..
Delayed shift, firm and most noticeable in first gear. I was guessing that it was a vacuum modulator so I told him to pull the hose and look for ATF inside the hose. I haven't seen the truck yet but I probably will soon.
Gus
Gus
Usually if the modulator is not getting enough vacuum or its diaphram fails,(yes,you'll see ATF in the hose ! )-- it will shift later and harder,and is most noticeable when it goes to upshift into 3rd from 2nd while accelerating..it may have to be wound out to as much as 40-50 mph to get it to finally go into 3rd gear,and it'll bang in pretty hard ..
Also,if your in "drive" and it is in second,if you let off the throttle,it will feel like you shifted into neutral,no "engine braking" effect--if you manually downshift it into 2nd, you'll feel the engine braking return to normal..
The govenor also controls upshifts ,it can strip the plastic teeth on its drive gear and cause the shifts to delay,and eventually it will refuse to upshift out of 1st gear entirely..if the valve in the govenor spool gets crud in it that too can affect the upshifts..
The detent "passing gear" solenoid and switch can also cause issues with upshifts too,so I'd see if the transmission will downshift when you floor the gas pedal,to ensure that is working right..there is a fuse for that circuit I believe..
Also,if your in "drive" and it is in second,if you let off the throttle,it will feel like you shifted into neutral,no "engine braking" effect--if you manually downshift it into 2nd, you'll feel the engine braking return to normal..
The govenor also controls upshifts ,it can strip the plastic teeth on its drive gear and cause the shifts to delay,and eventually it will refuse to upshift out of 1st gear entirely..if the valve in the govenor spool gets crud in it that too can affect the upshifts..
The detent "passing gear" solenoid and switch can also cause issues with upshifts too,so I'd see if the transmission will downshift when you floor the gas pedal,to ensure that is working right..there is a fuse for that circuit I believe..
Well I finally got to talk to the truck's owner and it was a modulator problem in a way. He found a hole in the vacuum line to the modulator. Line repaired, problem cured.
Gus
Gus
Glad he fixed it and it was so simple!..how come I'm never that lucky ?..
Glad he fixed it and it was so simple!..how come I'm never that lucky ?..
Don't feel like the Lone Ranger, my junk would've been internal trans problem.
Gus
