Governor/ inaccurate speedo issue- only does 25mph

[Flipmode]

Hi guys, reaching out for some direction on troubleshooting this issue I got: Bus has been sitting all summer while i did a roof raise. Finally took it out and it runs great but it tops out in the 25mph range in 3rd gear i think at about 1700rpm. The speedo is obviously off because at slow speed(~15mph) it reads 45mph and when the engine starts cutting out power the speedo reads 65mph but the actual speed is prob 25mph. My governor is set to 65mph so I'm guessing it is cutting out due to the faulty speed reading. I drove it down the road about a mile, put about 20gal of diesel in it, and then drove it back home. It accelerated good until it reached "65mph" on the dash then stayed at that speed.

Anyone have thoughts on what I should troubleshoot? I have decent mechanical ability but need direction sometimes, lol. I'm definitely going to pull the gauges and check the solder joints but not sure if I should be looking at the speedo pickup on the trans or...?

**I held off posting this until i could drive it again. When I took it back out it drove fine and the speedo seemed accurate. I drove it about 15 miles and everything was good like when I drove it 200 miles home. So I guess it is an intermittent problem which I recall the mechanic for the previous owner mentioned it had intermittent gauge issues. Havent looked at the dash yet.

[cadillackid]

im guessing allison 2000 series transmission?



i nthat year the dashboard speed is generated by the computer which gets its speed signal from the allison transmission TCM.. se we have a loit of things at play here..



the ultimate way to troubleshoot this is to be able to read at least the ECM computer data.. most likely the engine computer is getting a messed up signal fro mthe transmission.. the fact its intermittent speedo issues are often tough to troubleshoot. it very well could be the speed sensor on the allison as well.. are you getting a shift inhibit or check trans light?


if this is an MT643 or AT545 then life gets easier as the only control is the speed sensor on the back of the trans which feeds the ECM and it is notorious for picking up metal from the trans and going wierd..

[Flipmode]

Thanks Chris. Yes I have an allison 2000 series trans. I think its intermittent to the point if it gets shut off and turned back on itll reset. When it was acting up I didn't want to turn it off for fear of it not starting back up. I wasnt paying attention to the lights on that trip but when I took it back out again that night the range inhibited light was on but it seemed to be shifting fine(I only drove about a half mile). The next day was when I took it for a longer drive and I had no lights on for that trip. Is this something that can be trouble shot with a Bluefire?