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Found on:
http://forum.thedieselpage.com/ubb/ultimatebb.php?ubb=get_topic;f=3;t=007648
Contributor
Member # 10887
posted 04-19-2004 11:02 AM
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Driving this weekend with 20200# gross, on 6% grades at 50-65mph, when I would break, the transmission would downshift for engine grade breaking. Some times, it would shift to a low enough gear it would go well into redline, like 4000+ rpm.
Is it normal for grade breaking to let the engine redline? Should I be concerned about damaging the engine at these high RPM's?
I found I could prevent this by maintaining the speed where a downshift wouldn't redline and by using occasional light breaking to drop a couple MPH. Is there anything else to be done?
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2004 D/A 2500HD
Line-x bed liner, Black nerf bars Prodigy, B&W Turnover Ball, Amsoil air filter and FireStone air bags.
2004 Charmac 9x13 3H LQ trailer.
Wish List: 265x70R17 Revos, Wheels, Juice/Attitude.
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Posts: 104 | From: Boise | Registered: Sep 2003 | IP: Logged |
Inspector
Contributor
Member # 226
posted 04-19-2004 11:32 AM
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It is my understanding that the TCM won't allow overspeed of the engine. It will cause an upshift if sees an overspeed.
Denny
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2003 Pewter One ton Dooooley Ext cab LT.
Everything but XM and DVD.
Not stock. Transynd trany and transfer case. Post Kennedy Mega filter.
Honda Aspencade. If you gotta ask I'll tell ya.
93 still in the family and well taken care of.
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Posts: 379 | From: Layton, Utah, USA | Registered: Mar 2000 | IP: Logged |
mdrag
Moderator
Member # 5016
posted 04-19-2004 11:40 AM
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Rockin,
Inspector is correct. If you look at your tachometer closely, you will notice that the redline limit is marked in two different patterns - one is the limit for normal throttle input, and the higher limit is for the grade braking feature. The electronics will not allow the engine to overspeed during grade braking.
Check out the ALLISON GRADE BRAKING TECH TIPS on Kennedy's website for a detailed explanation of this feature.
http://forum.thedieselpage.com/ubb/ultimatebb.php?ubb=get_topic;f=3;t=007648
Contributor
Member # 10887
posted 04-19-2004 11:02 AM
--------------------------------------------------------------------------------
Driving this weekend with 20200# gross, on 6% grades at 50-65mph, when I would break, the transmission would downshift for engine grade breaking. Some times, it would shift to a low enough gear it would go well into redline, like 4000+ rpm.
Is it normal for grade breaking to let the engine redline? Should I be concerned about damaging the engine at these high RPM's?
I found I could prevent this by maintaining the speed where a downshift wouldn't redline and by using occasional light breaking to drop a couple MPH. Is there anything else to be done?
--------------------
2004 D/A 2500HD
Line-x bed liner, Black nerf bars Prodigy, B&W Turnover Ball, Amsoil air filter and FireStone air bags.
2004 Charmac 9x13 3H LQ trailer.
Wish List: 265x70R17 Revos, Wheels, Juice/Attitude.
--------------------------------------------------------------------------------
Posts: 104 | From: Boise | Registered: Sep 2003 | IP: Logged |
Inspector
Contributor
Member # 226
posted 04-19-2004 11:32 AM
--------------------------------------------------------------------------------
It is my understanding that the TCM won't allow overspeed of the engine. It will cause an upshift if sees an overspeed.
Denny
--------------------
2003 Pewter One ton Dooooley Ext cab LT.
Everything but XM and DVD.
Not stock. Transynd trany and transfer case. Post Kennedy Mega filter.
Honda Aspencade. If you gotta ask I'll tell ya.
93 still in the family and well taken care of.
--------------------------------------------------------------------------------
Posts: 379 | From: Layton, Utah, USA | Registered: Mar 2000 | IP: Logged |
mdrag
Moderator
Member # 5016
posted 04-19-2004 11:40 AM
--------------------------------------------------------------------------------
Rockin,
Inspector is correct. If you look at your tachometer closely, you will notice that the redline limit is marked in two different patterns - one is the limit for normal throttle input, and the higher limit is for the grade braking feature. The electronics will not allow the engine to overspeed during grade braking.
Check out the ALLISON GRADE BRAKING TECH TIPS on Kennedy's website for a detailed explanation of this feature.
Last edited by a moderator:
