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mj007nz
New Member
United States
1 Posts |
 Posted - 10/05/2008 : 11:26:08 AM
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Hi all,
I have a '97 Chevrolet Blue bird handy bus with GMC 6.9L(?) diesel.
More frequently now, the bus' automatic transmission will not select top gear (overdrive). It usually selects this gear when doing about 55 mph. Without this gear the bus is slow and is a hazard on the highways.
There seems to be no pattern as to why it sometimes does it and other times not. If it stops selecting top gear i usually have to pull over or something. I try turning off and on the engine. Letting it rest. Temperature gauges are normal. AT fluid level is fine.
Any ideas anyone?
Many thanks,
Mike |
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International-9.0
Advanced Member
USA
459 Posts |
Posted - 10/05/2008 : 12:48:28 PM
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I"m no mechanic and not familiar with GM, but here are some very basic ideas on trying to find the problem. Does anybody know if this engine/transmFirst off, GM made a 6.5, IH made the 6.9. Are there problems shifting between any other gears? How does the fluid look (a nice pink? dark? burnt smelling?) Have you tried wiggling the shifter back and forth within the overdrive "notch"? (or adjusting it?) If the vehicle has a modulator cable attached to the accelerator pedal, try adjusting it. If the fluid level is correct level/clean, and changing the modulater or shifter cable position does not have an effect, I would suspect internal transmission problems. Unfortunatly, I'm not sure whether this setup used a cable or electronics for the shifter and modulator.
On some vehicles with elecronically controlled engines, the transmission will not allow the engine to shift into overdrive until the engine temperature has climbed to a certain point. If electronic, you could also be having problems with certain sensors on the transmission such as the turbine speed sensor.
After looking around a bit, it does appear that GM used an electronic throttle of some sort in place of the stanadyne DB2 in later years. Anybody know if the transmission had any electronic controls implemented into it?
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ModMech
Top Member
USA
948 Posts |
Posted - 10/05/2008 : 1:37:12 PM
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It has a 6.5L turbo in it, the 6.2L (turbo) was replaced with the 6.5L in about 1994/5. It cannot have a 6.9L, the last year for that Intenational engine (never in a GM) was 1987.
This vehicle most likely (1997 MY engine) have the DB2 "drive by wire" IP. The trans is a 4L80E and well known for electrical problems between the DRAC, ECM, TCM and Dash that can cause shift problems of many types. |
If you want customer service, you NEED an International! |
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origcharger
Top Member
United States
619 Posts |
Posted - 10/05/2008 : 1:42:31 PM
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| Not sure about this particular vehicle either but sometimes whats percieved as the lack of shifting into high gear is actually the transmissions torque convertor not going into "lock up". This can be caused by brake lamp switch defects or maladjustment or other sensor or engine issues like discribed in previous post. |
Operating; Seven T444Es, One MaxxForce 7, One VT365, Four DT466s, One E-450 6.0 and one Mercedes in a C2. |
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Wolf0r
Top Member
USA
2181 Posts |
Posted - 10/06/2008 : 07:46:15 AM
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| If it's a 4L80E GM it may be shift solenoids leaking. I would plug a scan tool in and watch TCC slip, etc. |
“The good thing about science is that it's true whether or not you believe in it.”
Neil deGrasse Tyson |
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LPSMECH
Senior Member
90 Posts |
Posted - 10/09/2008 : 10:52:44 AM
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| We've had this happen before with the 6.5's. Replaced the throttle position sensor on one and a brake switch on the other. A transmission shop scanned them for me. |
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Bluebird auto often won't select top gear
