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Snow580 09-28-2017 04:12 AM

AT-545 Lockup??
Hey everyone long time lurker but finally joined!
My skoolie is a 1995 3800 Carpenter with the T444E/545 combo and from what everything I've read is that the transmission does not have a lockup torque converter but I swear mine does just from watching the tach while driving. It definetly seems to drop suddenly about 100 rpm when it levels out down the road.
Is that possible?
There is a sticker from Allison which says AT-500 series transmission and it explains when you should use each shifter position and in each of the 4 selections it says lockup. I don't have a picture of it right now but I can get one tommorow.
If it's not a 545 what other 500 series could it be?
Thanks and I really have been enjoying this site!!


cadillackid 09-28-2017 07:44 AM

on one of these mechanical transmissions, the easy way to check for lockup is at light-medium load. feather the throttle up and down.. if you notice your RPMs are pretty steady and only varying slowly as you speed up or slow down then its locked.. if you can make your rpms move up and down quite a bit with very little speed change you are likely unlocked.

you can also look at the tag on the side of the transmission as well.. I havent found any documentation of a 5xx having lockup, but doesnt mean there wasnt one made..

Iceni John 09-28-2017 10:37 AM

AFAIK no AT5xx-series transmissions have any lockup: only the MT6xx-series (in 3rd and 4th) and the big HT7xx-series (in 2nd, 3rd and 4th), plus all the newer Allisons, have lockup. For low-speed around-town driving an AT is OK, but for long distances and especially in the mountains a lock-up transmission is preferable.


Snow580 09-28-2017 09:13 PM

2 Attachment(s)
Thanks for the responses!
I do really believe the torque converter does in fact lock by doing the test like you said.
It definetly is a 545 transmission according to the tag on it. I'm going to attach a couple pictures. One of the transmission tag and one of the sticker on the dash.Attachment 16169

Attachment 16170

Snow580 09-28-2017 09:26 PM

2 Attachment(s)
Hey there thanks for the replies!
It is definietly a 545 and it sure seems to lockup when doing the test like was mentioned.
If these pictures attach correctly one is of the sticker on the dash and one is the transmission tag.

Attachment 16171

Attachment 16172

Tango 09-28-2017 10:21 PM

If it is indeed an AT 545, then there is no lockup.

jazty 09-29-2017 08:39 AM

Funny that the AT 500 tips sheet mentions lock-up...

turf 09-29-2017 09:20 AM

the AT1545 and the AT545 share a bunch of parts, service bulletins, tech info. i beleive its just an inclusive (both series) sticker as to the driving ranges.

find the longest steepest hill you can and try these 2 tests.
floor it on the way up - keep the rpms pegged to the max, then look and see if you slow down? if you do and the rpms stay max, its not locked up.

on the way down the hill, go fast. get rolling fast and take you foot off the pedal. do you slow down, does engine braking kick in, or do you just keep rolling downhill? the 545 can engine brake a bit, going slow, but fast with lots of mass quickly overcomes the clutch pressures, the trans makes noises like its fallling apart and you go screaming down the hill.
down a steep grade is scary in a 545 because it doesnt engine brake very well or not at all. thats the lockup's function.

the uphill is probably the safest way to tell. imo thats what kills the 545. slippage going up a hill.

if you have lockup, you would have a 1545. thats the difference, as far as i can tell.

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