Installing Air Throttle on 8V71TA

[ChuckMC8]

I'm attempting to install an air throttle setup on my 8V71TA. Thanks to a fellow bus nut, I was able to acquire servo  and mounting bracket that goes on the top of the governor that is specificaly made for 8V71.
  Oops, theres  the turbo !..... The right side exhaust pipe from the manifold to the turbo interfers with the mount for the air servo. I'm thinking that other turbo DD that are using the Air throttle would have already worked this step out. Anyone have a photo of an air throttle on a 6 or 8V92 that they could post or email to me? ( I need to see the governor setup)
  There is not a lot of air throttle info on-line (that I found) Anyone know the correct PSI to supply the treadle valve?
 Is it best to buy the air modulator for the Allison trans or try to incorporate the cable modulator in the linkage?
 Any air throttle tips to share? Thanks-Chuck

[TomC]

You can always position the air cylinder a ways away from the governor with either a short linkage or cable.  Personally, would change the cable throttle modulator on the transmission to the air modulator.  Will be more in synch with the pedal position-in my opinion.  I have the air modulator.  When I pull the transmission selector down to 1st, I can get converter lockup in 1st by flooring it to max speed, then bring up the accelerator about an inch and then you can feel the transmission bump into lockup.  Great for going up long grades without the heating of the converter, since it is locked up.  Good Luck, TomC

[edroelle]

Chuck,

I determined that I had to buy the Allison air modulator - but I also had some cruise linkage installed in the throttle area that took-up some of the real estate.

Jack Conrad gave me the lead on this.  The air modulator is a Williams Control unit PN WM775B.  It was $55

I looked at some old photos, but unfortunately, I did not take any of the throttle area.


Ed Roelle
Flint, MI

[rayshound]

Chuck;
   If you go to Tom Halls web site, coach conversions central the url is (Users.cwnet.com) there is a link on the front page that will show you the plumbing, and pictures of the actuator, modulator etc.   Ray

[JackConrad]

I have attached a photo of the air throttle installed on our governor (8V71N). I am also attaching a photo of the air modulator that we installed in the Allison 740.  We experimented with air pressure to the air throttle pedal. Too much pressure and the pedal is too sensitive (slight pressure on pedal gives a big increase in RPM). Too little pressure make the throttle sluggish and slow to respond. We ended up with about 45 PSI YMMV. When you install a tee to connect the air modulator, make sure the air lines from the tee to the modulator and the throttle assembly on the govenor are the same length. This is per Williams Control installation instructions.  Hope this helps, jack

[Stan]

One further note on Williams Air Throtle foot control. You have to specify everything in the order including whether manual or auto transmission and if the modulator is mechanical or air. They use a different spring in the foot valve  for the different modulators.

 Jack's problem with sensitivity sounds like he has the spring for a mechanical modulator. I went through this on an Eagle and although I ordered correctly, for an auto with mechanical modulator,they shipped with the wrong spring. The pressure range of the foot control is critical and along with the correct spring, you have a stack of shims that you juggle to get the correct range.

Many of things that we do or try to do on our buses have hidden snakes that jump out to bite us. Just read the posts on re-powering or changing to DDEC from the people who have done it and there seems to be an endless list of things to watch for. To get good results, you have to do it right, and the right way is usually expensive.

[JackConrad]

Thanks Stan,
   I purchased my air throttle used and do not know what engine/transmission it was used on. I recently realized that the return spring on the pivot pin on the bottom of the pedal was missing. This may have been a big part of my sensitivity. I ordered a spring from Williams. The parts list on their website only listed one part number for this spring. The throttle is much more responsive with this spring in place. I didn't see any shims on the parts page I looked at. Where are the shims installed?  Jack

[Stan]

Jack: Sorry I wasn't more explicit. The spring I referred to was the actual spring in the pressure regulator (the entire foot control is just an adjustable regulator),  not the pedal return spring. They use springs for different pressure rating  that are identified by color and then you trim the range by putting  shims on top of the spring.  Even different engines use a different spring.

To operate a modulator  with cable control takes more presssure than the  pressure needed for an air modulator. A standard transmission use even less pressure to move the throttle.  Proper operation is obtained when you get full travel on the throttle motor diaphragm  and the modulator when the foot pedal travels full stroke.

If you have a foot control set up for a cable control modulator and use it on an air modulator, you will have full throttle with less than full pedal travel. There should also be a return spring on the throttle linkage so that the throttle is not wide open for a long period of time before the pressure rises high enough to shift the modulator (slow shift). The cable control is easier to balance by adjusting the nuts on the end of the modulator cable.