[rgunderm]

I have a 1994 Newell 45 with an 8V92 at HT740 Allison. My transmission is shifting late and I’m assuming it’s a modulator air pressure adjustment. Owner’s manual states it is in the passenger side engine compartment but I can’t find it. 

Anyone have any experience with this?  

Coach 349

[MrE]

Your coach has an ECU, I would suggest getting an engine monitoring system like BlueFire or SilverLeaf. They log any error conditions between the engine and transmission and will tell you what's happening.

Browse through this thread for more information Engine and Transmission Monitoring Systems

[BusNit]

There is a pressure regulator for the transmission modulator. The modulator itself is a wear item and needs to be replaced at each transmission oil change. Mine was bad and leaking air into the trans fluid. I could hear the gurgling when the coach sat. Pressure I believe is set to 60psi.

To find the line follow the air hose from the transmission modulator (right side) and see which regulator it goes to. There are two pressure regulators on the passenger side engine wall. One is for the tag axle (25-30psi setting) and the other is for the modulator.

[rgunderm]

Thanks Simon. There are two gauges on the passenger side engine compartment. Bottom one is definitely tag set to 25 per the manual. Top gauge is not connected to a regulator but is set to 90, it is plumbed out of the valve block with no way to adjust. I will email Newell service and see if I can get some sort of diagram.

[neverbored]

rgunderm,
Did you ever get a resolution to this? I have a 1988 with this transmission and it is slipping since my last tranny oil change. I don't think the modulator was changed.
Thanks,
Mark

[rgunderm]

rgunderm,
Did you ever get a resolution to this?  I have a 1988 with this transmission and it is slipping since my last tranny oil change.  I don't think the modulator was changed.
Thanks,
Mark

Hi Mark.The resolution for me was that I realized I have an HT741 instead of an HT740. HT 741 was the first year of complete electronic shift so the modulator was eliminated. In your case, if it’s slipping after fluid change, I’d verify the correct fluid was used and that level is correct. Next, I’d verify pressure to the modulator, then replace the modulator as I understand they failed often. 

[neverbored]

rgunderm,
Did you ever get a resolution to this?  I have a 1988 with this transmission and it is slipping since my last tranny oil change.  I don't think the modulator was changed.
Thanks,
Mark

Hi Mark.The resolution for me was that I realized I have an HT741 instead of an HT740. HT 741 was the first year of complete electronic shift so the modulator was eliminated. In your case, if it’s slipping after fluid change, I’d verify the correct fluid was used and that level is correct. Next, I’d verify pressure to the modulator, then replace the modulator as I understand they failed often. 

Thanks for the response.  Fluid is good.  I think the pressure is a little low.  I finally found the gauge in the water bay.  I'm driving on Monday so will test then.  
Mark

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Assuming they used the Williams WM-775b air modulator? This is the same as my 84 Wanderlodge. I believe they are to be replaced every 25k miles or something like that. I will try to find the documentation on it. I have been thinking about a replacement for these modulators when they finally become extinct. The replacement I think would be best is a cable operated modulator that could be connected to the cable that goes the engine governor. Wanderlodge used these on their Cat front mounted engines.