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Old 10-12-2019, 09:44 AM   #1
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Allison AT542 shift Problem

Hello,I`m new here and i`m from Germany(sorry for my bad english)
I have a 1995 Georgie Boy Swinger on Spartan Chassi with chevy 6.5TD ( manuel Injection Pump no PMD) with an Allison AT542 Transmission.
I have buy the RV with broken engine (86000mls) I change the engine with a new one and change Transmisson Fluid and Filter(the old was not black and not like burning)

On testdrive i see the Transmission was not shift up.I check Oilpressure at the checkpoint it was arround 145PSI then i take the Transmisson out and make a Overhole with all Parts new but not the Torque Converter.
Next testdrive the same Problem no shift up
Have you an idea ?

The governor is OK.Can the Problem com from the Torque Converter ? It`s make no noise or Vibration or something
The Original Converter have a stall speed 1200-1400
Can i take one with 1000-1200 ?
Thanks Paul

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Old 10-14-2019, 09:29 AM   #2
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145 PSI for main pressure on an AT542 is okay.
What is the assembly number on the side of your transmission?
How many RPM will the engine turn? The original stall speed sounds very low.

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Old 10-15-2019, 12:38 AM   #3
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Tanks for Answer
I have a chevy 6.5TD with 187 HP at 3400 rpm
Allison AT 542N
Model. AT542N 94J26
The emty wight of my Motorhome is 14660 lbs
In the Allison Handbook are two Converter for the AT 542N listetd.
TC275 1.96:1 Stall 1200-1400 this was OE

TC290 1.72:1 stall 1000-1200

I hear something from " Converter slippage " if the Converter is inside brocken.It feels like an slipping Clutch insinde the Transmission
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Old 10-15-2019, 09:40 AM   #4
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That part number is a 3400RPM valve body so not a mismatch causing your problem.
The torque converter in an AT series transmission has no lockup clutch. It always slips some comparing engine RPM to transmission input RPM.
Usually the causes for not shifting up from first gear are:
1. Engine not making power up to its correct specification.
2. If the torque converter is failed, the only thing to fail would be the stator freewheeling. If that is the case the vehicle will try to move very, very slowly. It is obvious.
3. Stuck governor or stripped governor gear.
4. Incorrect valve body components (shift springs or stuck valves).
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Old 10-15-2019, 10:18 AM   #5
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I have take a masterkit for the Transmission so all inside is new(seals,Liprings,Clutch and steel plates) I have take all Valves out of Body and no sticking Valves,all Springs in OE Position.No buddy have open the Transmission brfore me.
It`s my first Motorhome,before i drive only Chevy Pickup with 6.5TD Engine and there if i pusch down the Throttle the Truck gos fast forward.
On the Motorhome i pusch down the Gas and it goes slowly forward so i think it can be the Stator is slipping.
Do you think i can change the TC275 to the TC290 Converter with no Problems in Acceleration ? because the lower Stall Speed ?
thanks Paul
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Old 10-15-2019, 10:48 AM   #6
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Stick with the TC275. The 290 is made for the lower speed heavy duty diesel engines that turn at lower RPMs than the 6.5. Your peak torque is at a higher RPM than those engines and needs the higher stall speed.
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Old 10-15-2019, 09:08 PM   #7
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OK thanks

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