Date: Fri, 20 Jul 2007 11:49:01 -0400
Reply-To: Dennis Haynes <d23haynes57@HOTMAIL.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Dennis Haynes <d23haynes57@HOTMAIL.COM>
Subject: Re: Talk to me about AT's!
Content-Type: text/plain; format=flowed
Automatic transmissions have those manual controls because they are
occasionally needed. Even the computerized controls on my motor home allow
for forced downshifts as long as that won't over rev the engine. However,
you may also have an adjustment or control problem preventing the tranny
from working completely as it should.
For going up hills, when the accelerator is floored, a forced down shift
should occur automatically. In this condition, the lower gear should hold
until ~ 5,200 rpm. This will shoot you up most hills. If the hill is
extended or you find it hunting between 2 and 3, then manually down shift
and back off the throttle to maintain ~ 4,200 rpm. This will keep the engine
oil from overheating.
For going down hill, the rule of thumb is go down in the same gear as you
would go up. Since the tranny does not know you are going down hill,
manually down shift and definitely let the engine braking do some of the
work. If you are still going to fast, you want to use the brakes to scrub
off speed and then cost again. You don't want to ride the brakes all the way
down. There is some skill, art to doing this properly. THese conditions are
where larger brakes and vented rotors have benefit.
The transmission can make an awful lot of heat in these conditions.
Unfortunately a lot of this heat is getting dumped into the engine cooling
system. Lugging in high gear makes heat in the torque converter especially
if is is slipping. The lower the engine speed, the more it will slip. A
lower gear makes heat as there are now a lot of gears turning to make the
reduction. This also makes for a lot more wear but overall it is better than
forcing the torque converter and lugging the engine.
Dennis
>From: Michael Elliott <camping.elliott@GMAIL.COM>
>Reply-To: Michael Elliott <camping.elliott@GMAIL.COM>
>To: vanagon@GERRY.VANAGON.COM
>Subject: Talk to me about AT's!
>Date: Thu, 19 Jul 2007 21:53:37 -0700
>
>Mrs Squirrel and I just got back from several days of camping in the
>Sierra Nevada (spectacular weather, great camping, especially at site
>#32 at Highland Lakes) and Mellow Yellow operated flawlessly, even
>climbing the mighty 6% grade up highway 395 to Sherman Summit in 109
>degree (F) weather, loaded with camping gear, w/o overheating. This was
>at 7pm -- I tried to wait out the heat of the day but it hit over 105F
>at noon and just stayed there. I killed as much time as I could in the
>shade of a young sycamore at Tuttle Creek campground near Lone Pine, but
>it just never cooled off.*
>
>Anyhoo, on the way up, between watching the temp gauge, the tach, and
>rear-view mirror to make sure that I wasn't about to get rear-ended by a
>faster vehicle, I was very aware about how little I know about automatic
>transmissions.
>
>Uphill Question:
>
>If Mellow Yellow had a manual transmission, I'd think nothing of
>downshifting to second or even first gear as needed to keep the rpm's
>up. But there's just something about running an automatic transmission
>for long periods in lower gears that worries me. Maybe it's because the
>transmission sounds at a higher pitch than I am used to -- I don't know.
>I can't put my finger on it. Is it okay to stay in "1" or "2" with an
>automatic transmission as long as the engine isn't being over-revved?
>
>Downhill Question:
>
>Some of those Sierra passes have long downhill grades at up to 26%.
>Again, if I had a manual, I'd-a downshifted and used the engine to take
>some of the load off the brakes. Is it okay to do that with an automatic
>transmission?
>
>* Glad I had a Norcold refrigerator instead of the original Dometic --
>with its 45F max differential, the inside of the old reefer would have
>been 109 - 45 = 64F, which is too warm for food safety or cold beer.
>
>--
>Mike "Rocket J Squirrel" Elliott
>71 Type 2: the Wonderbus
>84 Westfalia: Mellow Yellow ("The Electrical Banana")
>74 Utility Trailer. Ladybug Trailer, Inc., San Juan Capistrano
>KG6RCR
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