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-   -   5-4th Speed Shift - Air Throttle vs Cruise Control (https://www.wanderlodgeownersgroup.com/forums/showthread.php?t=18478)

Movin' On 12-11-2013 06:54 PM

5-4th Speed Shift - Air Throttle vs Cruise Control
 
My 84 PT36 shifts from 4th to 5th at about 54 MPH using the air throttle, but shifts from 4th to 5th around 45-48 MPH using the cruise control. I thought something in the air throttle is causing a difference in the shift point.

While using the air throttle to accelerate with the transmission shifted from 4-5 and then have to ease up on the throttle due to traffic, the transmission always downshifts to 4th at 53 or 54 MPH, even when the throttle is even gently pressed. If I re-engage the cruise control to speed up it does not downshift to 4th unless the speed has dropped below 45 MPH.

Does anyone have any idea what the cause could be. I thought maybe the air throttle has different pressures in the two lines from the air throttle and is causing the problem.

Randy Dupree 12-11-2013 11:00 PM

Shane is our resident PT expert.
He works on the Bendix cruise control stuff,maybe he can help?

Mike Hohnstein 12-12-2013 12:40 AM

Less throttle position angle on cruise control results in earlier upshift due to less transmission throttle valve (TV cable) motion. Best method is use cruise control at speeds over 55 mph. I've noticed that the MD 'puter trans in my FC and some other MD rigs I've driven will spin up a little on a 4/5 upshift on cruise, due to a more relaxed TV position.

Movin' On 12-12-2013 06:20 AM

Throttle vs Cruise Control
 
Mike,
Thanks for the information. Is there an adjustment for the transmission throttle valve cable?

Is this a separate cable from the air throttle cable or is there just the one cable that comes out of the cruise control and goes over to the engine throttle? I have not seen the second cable.

I would like to eliminate the downshift when using the air throttle that pulls the cable connected to the engine throttle.

Thanks
Dave

Rick 12-12-2013 08:16 AM

Dave, Can you take a picture of the engine? Since you have an Air Throttle you may also have and air operated kick down. We would know if you can post that picture.

Movin' On 12-12-2013 06:45 PM

Rick, Yes I would be glad to. Where would the air operated kickdown be located? Is it on the transmission or around the cruise control?

Rick 12-12-2013 06:55 PM

Dave, Open the engine compartment. Take a shot of the Johnson Control area. Let us see how the air throttle is hooked to the pump. We may be able to see if you have a cable there. If not you will need to take a shot of the transmission. The cable or air tube will be on the drivers side about 3/4 of the way back and right above the transmission oil pan.

sfedeli 12-12-2013 07:59 PM

Dave- There is a throttle position sensor which may need to be replaced on the side of your transmission. Our non-computerized MT654CR tranny has a "modulator" on the right side near where the shift cable is attached. It has a 1/4" air line going to it from above the trans and is used to "sense" the throttle air pressure- telling the trans to downshift or upshift. I have a spare one onboard the coach, but can't remember the part number. Maybe someone else has it and can chime in here....

Rick 12-12-2013 08:11 PM

Shane is right. For some reason I thought we were dealing with an FC. Sorry if I caused any confusion.

Movin' On 12-14-2013 02:01 PM

5-4th Speed Shift - Air Throttle vs Cruise Control
 
5 Attachment(s)
Shane, Randy, Mike - I have attached pictures of the cruise control panel with the actuator cable and pictures of the driver's side transmission.

I only see one cable from the cruise control to the throttle. Do not see a "modulator" on the side. I hope this helps in identifying the upshift components. I will try and read what looks like an ID plate on the side of the transmission which I noticed in one of the pictures.

sfedeli 12-14-2013 05:59 PM

Dave- the modulator is on the other side of the trans- near the tailpipe assembly. Looks like someone had a new throttle cable made at some point.

Bill Pape 12-15-2013 08:07 AM

this may not be your problem , but the throttle cylinder gets dirty & sticks, it may need to be cleaned and rebuilt, there is a kit available, the blue capped end is the rheostat, very fragile and obsolete, so be gentle,
the air solenoids mounted on the Bendix module may also need cleaned & lubed.

sfedeli 12-20-2013 09:24 PM

Here's the Allison shift modulator information-

The package has the numbers M-775-B on the outside. When you remove the bubble wrap, the instructions identify the module as a "WM775B Transmission Modulator". I was able to find one online-

http://www.wmco.com/getmetafile/6bcd...axsidesize=218

http://www.wmco.com/Products/Hydraul...Modulator.aspx

Don Meyer 12-21-2013 10:57 AM

Bill,
I'm not sure about lubing the air solenoids for the cruise control.

When I was in Dallas in 2011, I stopped at the outfit that repairs the
Bendix control modules to have mine checked. He told me at that time that the solenoids should be cleaned and reassembled DRY. With no lubricant. Some lubricants can become gummy over time. Causing problems with the solenoids. I keep mine clean and dry. No problems.

Movin' On 12-22-2013 01:04 PM

5-4th Speed Shift - Air Throttle vs Cruise Control
 
2 Attachment(s)
Shane,
I have attached a photo of the right side of the transmission and I can see the modulator towards the front of the coach and the shift adjuster towards the rear on the picture. When I replace the modulator is it a simple of removing the bolt I saw to the right on what looks like a retainer, pulling out the old modulator and replacing with the new one with the new O-ring. Is there any other gaskets needed and will the fluid start running out?

I have not traced the airline back to the treadle air valve yet. I have wondered of the treadle valve needs to be rebuilt. It looks like air may be leaking out of one seal, if it really is a seal. It looks like it would be a major project to get the treadle valve out.

Bill, Don & Jane
The CC5 throttle control valve was recently cleaned when the mechanic noticed that the air throttle was leaking air out of the valve and preventing full throttle application. When it was cleaned the coach went up hills mush better. However; I have not had the solenoids cleaned. Are there some procedures and a kit available for cleaning them?

Once again I want to thank everyone for the help. I would not be able to solve this problem without your help.

Mike Hohnstein 12-22-2013 01:08 PM

There will be oil.

sfedeli 12-22-2013 11:24 PM

Dave... there will be a little oil, but it should not be under pressure- just weeping. The solenoids on the CC5/Cruise assembly are meant to be assembled dry. I would suggest cleaning them with a can of compressed air- like you use on computer keyboards and a little denatured alcohol, not petroleum distillates like WD40 or paint thinner. Be very careful about the small springs and set screws. Count the number of turns in or out that you use to remove each one- you don't want to affect the settings as they were originally.


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