| New Manny Tranny on hills [message #195317] |
Wed, 09 January 2013 20:03  |
gbarrow2
Messages: 765
Registered: February 2004
Location: Lake Almanor, Ca./ Red Bl...
Karma:
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Back in August I posted the following:
"Coach, 1976 Palm Beach has 455 w/carb and 3:70. coach weighs~11,000 lbs.
Northbound on I-5 between the Oregon border and Canyonville (about 100 miles) you encounter Siskiyou Summit 4310' (highest point on I-5) 7 miles of 6% grade on both sides,
Sexton Pass (named for GMCer Dennis Sexton?) 1960', Smith Hill Summit 1730', Stage Road Pass 1830', Canyon Creek Pass 2020' the approaches to each of these passes have one to three miles of 6% grade
All of these hills except Canyon Creek Pass required downshifting to second for part of the climb. .
When speed drops below 50 mph and rpm drops below 2500 and vacuum is 5" or less I manually shift to 2nd."
In early November my old tranny died and I installed a new Manny Tranny and have now driven it almost 2500 miles, including a trip from Red Bluff, Ca. to Hillsboro, Ore. and back over the above mentioned grades/passes.
With the new Manny Tranny the coach runs "stronger' feels "lighter", peppier, more responsive to the throttle. Not my imagination.
On the trip to Oregon with one exception the coach made all these grades without falling below below 48 mph or 2400 rpm in 3rd gear. So I didn't manually downshift
The exception was the southbound 7 mile 6% grade.
Near the top of the hill the tranny automattically downshifted to 2nd at about 42mph and 2200 rpm.
So the question for Matt Colie or any one else who knows is this: At what speed/rpm at WOT on a long uphill grade does "lugging" occur and become detrimental to the engine or transmission? Or: Given the ~2700 rpm most efficient power point for the 455, what is the lowest "safe" rpm for the engine/tranny under heavy load?
Any Oregon Netters want to report their experience over these passes?
Thanks to all for your input.
Gene Barrow
Lake Almanor, Ca.
1976 Palm Beach
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