Home » Public Forums » GMCnet » New Manny Tranny on hills (Question for Matt Colie re: engine "lugging")
| Re: [GMCnet] New Manny Tranny on hills [message #195323 is a reply to message #195317] |
Wed, 09 January 2013 20:50   |
James Hupy
Messages: 6806
Registered: May 2010
Karma:
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Senior Member |
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It has been my personal experience, also with a stock transmission with
3:07 final drive and a 403 with high mileage on those very same hills in
both summer and winter to downshift manually at 50 mph. My coach is a 78
Royale by Coachman and it weighs 11,000 and change. The 403 would pull down
to about 38 to 40 mph on those passes. When my transmission gave up the
ghost, I sprung for a Manny Transmission and at the same time installed Jim
K.'s 3:70 final drive gears. I have since pulled those same passes both
summer and winter both directions. The first trip I was extremely careful
because I had just installed the trans. the night before we left, and the
final drive was not broken in. The last trip was in November for the 49 ers
rally in Red Bluff. I also ran some 13% upgrades both uphill and downhill
in Canada. I can pull those passes in Oregon in high gear with the present
combination. The 13% stuff, 17 mph in first gear, running about 10 " of
vacuum to stay out of the secondaries. To address the lugging question, if
the rpm of the engine is below the stall speed of the torque converter, you
will have a greater problem with overheating the transmission than you will
with engine damage. Don't be afraid to rev the engine to 3200 or so,
especially if it is a 403. You won't hurt a good engine at that rpm.
JimHupy
Salem, Or
78 Gmc Royale 403
On Jan 9, 2013 6:03 PM, "gene barrow" <barrowgene@gmail.com> wrote:
>
>
>
>
> 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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