Allisonman I have retired a 1999 international schoolbus and want to turn it into an rv the problem Ihave with the tranny is that between 20-26 mph the trannt wants to shift back and forth between the gear it was just in, to the next gear. When I mean hunt and shift i mean it sounds as if the u-joints are going to be twisted out of the dang thing,its not a gentle hunting it is more like a gorilla with a club hitting the bottom of the floor. I have owned buses for a while and this is the first I have had of this problem with a 545.I have heard that if there are any air leaks in the turbo sys it would effect the shifting or if the throttle positioning switc on the accel pedal is bad this could be the problem of if the highpressure oil pump/fuel pump was going bad this could be a cause the tranny does not leak and if you go ahead and drive this thing like you are mad at it the hard shifting and the hunting is not as bad.before i spend any money i dont have what would you suggest to look for first before going to the local allison shop?any help will be most appreciated.
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at 545 transmission
- Thread starter wbsvc
- Start date
dbarton291
Senior Member
RE: at 545 transmission
I'm not Allisonman, but my suggestion is to get rid of the electric modulator and switch under the throttle. Replace that system with a mechanical modulator cable. The AT was designed to work with a variable throttle signal, not an on/off electric modulator.
wbsvc - 2/19/2009 9:26 PM
Allisonman I have retired a 1999 international schoolbus and want to turn it into an rv the problem Ihave with the tranny is that between 20-26 mph the trannt wants to shift back and forth between the gear it was just in, to the next gear. When I mean hunt and shift i mean it sounds as if the u-joints are going to be twisted out of the dang thing,its not a gentle hunting it is more like a gorilla with a club hitting the bottom of the floor. I have owned buses for a while and this is the first I have had of this problem with a 545.I have heard that if there are any air leaks in the turbo sys it would effect the shifting or if the throttle positioning switc on the accel pedal is bad this could be the problem of if the highpressure oil pump/fuel pump was going bad this could be a cause the tranny does not leak and if you go ahead and drive this thing like you are mad at it the hard shifting and the hunting is not as bad.before i spend any money i dont have what would you suggest to look for first before going to the local allison shop?any help will be most appreciated.
I'm not Allisonman, but my suggestion is to get rid of the electric modulator and switch under the throttle. Replace that system with a mechanical modulator cable. The AT was designed to work with a variable throttle signal, not an on/off electric modulator.
dbarton291
Senior Member
Re: at 545 transmission
Correction: Your vehicle may or may not have a throttle switch. Originally, the IH buses used a signal straight from the engine ECM to trigger the electric modulator on the transmission. Many of these vehicles were modified with a kit that put a switch under the throttle to bypass the engine ECM and trigger the electric modulator off this throttle switch.
In either case, I would still recommend the installation of a mechanical modulator on the transmission that is connected to the engine throttle with a cable containing a yield link. The yield link is to allow the engine to return to closed throttle in case the cable binds. There used to be kits available to do this because so many of these vehicles were changed to this system.
Any Allison outlet that has worked on school buses should be familiar with this modification.
Correction: Your vehicle may or may not have a throttle switch. Originally, the IH buses used a signal straight from the engine ECM to trigger the electric modulator on the transmission. Many of these vehicles were modified with a kit that put a switch under the throttle to bypass the engine ECM and trigger the electric modulator off this throttle switch.
In either case, I would still recommend the installation of a mechanical modulator on the transmission that is connected to the engine throttle with a cable containing a yield link. The yield link is to allow the engine to return to closed throttle in case the cable binds. There used to be kits available to do this because so many of these vehicles were changed to this system.
Any Allison outlet that has worked on school buses should be familiar with this modification.
dbarton291
Senior Member
Re: at 545 transmission
Have the service outlet reference Allison Service Information Letter 21-TR-02 which covers this issue. Keep in mind this issue is not new, so depending on demand, these kits may or may not still be available.
The process is rather involved, so I would not recommend attempting this yourself. Just my opinion.
Have the service outlet reference Allison Service Information Letter 21-TR-02 which covers this issue. Keep in mind this issue is not new, so depending on demand, these kits may or may not still be available.
The process is rather involved, so I would not recommend attempting this yourself. Just my opinion.