AT540 shifting 2400 rpm questions?

[OneOneNone]

First post, but have rolled past this site several times as this seems to be one of two places on the internet information for my transmission comes from.

Short version 1979 Ford 429/AT540 40k original miles. When I bought the truck I notice I have very low shift points at WOT throttle. First gear comes out at 2600, the next two shifts are 2400 rpms shifts. The factory 429 from Ford makes peak power at 4400 rpm (this particular truck did not have a factory 4k governor when new). Is there anyway to modify/upgrade the factory Allison trans to shift at 5000 rpm or at least near it??

Couple of notes, have verified tach speeds with multiple gauges and timing light. Have checked and verified WOT.

[cadillackid]

Originally Posted by OneOneNone

First post, but have rolled past this site several times as this seems to be one of two places on the internet information for my transmission comes from.

Short version 1979 Ford 429/AT540 40k original miles. When I bought the truck I notice I have very low shift points at WOT throttle. First gear comes out at 2600, the next two shifts are 2400 rpms shifts. The factory 429 from Ford makes peak power at 4400 rpm (this particular truck did not have a factory 4k governor when new). Is there anyway to modify/upgrade the factory Allison trans to shift at 5000 rpm or at least near it??

Couple of notes, have verified tach speeds with multiple gauges and timing light. Have checked and verified WOT.

the MOST likely culprit is the original transmission died and someone installed one from a diesel. diesel versions shift at 2400-2600 WOT.. the governor is different than a gas versions.. the trim rings may be set different also.


they probably put a governor part 461 in.. a 462 or 463 is higher shift points for gasoline engine... you can trim the governor wit hthe valve body trim rings but going as high as you need then you need the other style governor..



the governor is a bubble on the side of the transmision, you remove the cover and the govneror pulls out, it will be stamped with a number, 460,461,462 and the likes... 461 is what I see in most diesels... I havent had the governor off of my AT540 which shifts at about 3600 RPM.. I suspect its a 462 and the trim rings are turned up a it... I do know the spare one i have laying in my garage from a 545 i scrapped is a 461 (diesel).. that shfted out max throttle at 2700 RPM..




on that engine you should have a vacuum modulator on the side of it.. looks like a little can with a vacuum line going to it... if you remove and plug the vacuum lhose then try to drive, the transmission should have rough and very high shift points all the time regardless of throttle position.. and will have very rough downshifts.. (dont drive far like this)..


that tells you the modulator isnt stuck.. if not change then it could be the modulator is stuck in the full vacuum (low shift point) position...



most often if. vacuum modulator goes bad the transmission shifts high and rough all the time.

[s2mikon]

I think that the at 540 series were limited to 4000 rpm. I was told by a long time Allison mechanic, it was because of the size of the planetary gear sets.

[cadillackid]

Originally Posted by s2mikon

I think that the at 540 series were limited to 4000 rpm. I was told by a long time Allison mechanic, it was because of the size of the planetary gear sets.

somewhere i have a spec sheet that mentions max RPM of 4000... but he appears to have a doesel governor in his it seems vs the higher governor..

[OneOneNone]

Originally Posted by cadillackid

the MOST likely culprit is the original transmission died and someone installed one from a diesel. diesel versions shift at 2400-2600 WOT.. the governor is different than a gas versions.. the trim rings may be set different also. they probably put a governor part 461 in.. a 462 or 463 is higher shift points for gasoline engine... you can trim the governor wit hthe valve body trim rings but going as high as you need then you need the other style governor.. the governor is a bubble on the side of the transmision, you remove the cover and the govneror pulls out, it will be stamped with a number, 460,461,462 and the likes... 461 is what I see in most diesels... I havent had the governor off of my AT540 which shifts at about 3600 RPM.. I suspect its a 462 and the trim rings are turned up a it... I do know the spare one i have laying in my garage from a 545 i scrapped is a 461 (diesel).. that shfted out max throttle at 2700 RPM..on that engine you should have a vacuum modulator on the side of it.. looks like a little can with a vacuum line going to it... if you remove and plug the vacuum lhose then try to drive, the transmission should have rough and very high shift points all the time regardless of throttle position.. and will have very rough downshifts.. (dont drive far like this)..that tells you the modulator isnt stuck.. if not change then it could be the modulator is stuck in the full vacuum (low shift point) position... most often if. vacuum modulator goes bad the transmission shifts high and rough all the time.

First of all thank you. Tested the Modulator, seems good as described. Pulled the Governor housing, 460 stamped clear as day on the head. Where can I buy a 463 that isn't $1200 or what kind of RPM increase can I expect from the governor I have if I modify it??

[s2mikon]

Have you tried Dartco?

[cadillackid]

here is the parts catalog i found online..
460 appears to be the governor you are supposed to have for what you want to do... it is the highest shift point range..


https://www.transtar1.com/download.a...alog_FINAL.pdf


catalog page 42 (PDF page 4) shows the 3 available governors..



I had thought the 462 was the highest but its a few hundred less RPM than the 460..
so you likely have something else going wrong ..perhaps a line pressure issue or maybe a broken spring...



the governor is centrifiugal with its weights.. hydraulic pressure opposes the springs of the inner weights.. stronger the spring the less likely for the spring to be overcome and trigger a shift.. the hydraulic pressure applied is different with each gear as the governor keeps increasing in speed with the output shaft speed..


I tried to attach the AT540 / MT643 service manual but the file is too big to upload apparently to the forum post..

[Booyah45828]

With the governor being the correct one, and the fact that's it's shifting at all, I'd say it's fine. I'd circle back to the modulator/circuit not being functional, as it can cause early/low rpm shifts too.

Just my 2 cents.

[cadillackid]

Originally Posted by Booyah45828

With the governor being the correct one, and the fact that's it's shifting at all, I'd say it's fine. I'd circle back to the modulator/circuit not being functional, as it can cause early/low rpm shifts too.

Just my 2 cents.

entirely possible as those vacuum modulators are often adjustable or it could be sticking