Question about "gearing down"

Discussion in 'General Motoring' started by Pat Durkin, Jul 26, 2004.

  1. Pat Durkin

    Pat Durkin Guest

    I've got a 2001 S80.

    I live in a pretty hilly area that has up to 12% grades and puts a pretty
    big load on brakes.

    My owner's manual seems to endorse engine braking and maybe I shouldn't
    worry about pulling the gear lever into 3 or even 2 to take a load off the
    wheel brakes but I can't help but wonder if I'm putting a lot of stress and
    strain into my transmission and cooling system.

    In other words should I resist the temptation to gear down and just let my
    wheel brakes do the job?

    I don't need speculation. I can do that myself.

    Anybody actually have some real information to kick in here?

    TIA

    Pat
     
    Pat Durkin, Jul 26, 2004
    #1
  2. I strongly support downshifting a manual shift. Don't use it to slow down -
    the brakes do that job. Use the engine to keep the car from speeding up on
    a downhill slope.
     
    Marvin Margoshes, Jul 26, 2004
    #2
  3. Pat Durkin

    Boris Mohar Guest

    You are putting a lot more stress going uphill.
     
    Boris Mohar, Jul 26, 2004
    #3
  4. Pat Durkin

    Guest Guest


    A good rule of thumb is to go down a hill in the same gear you went up in.

    chuck
    73ES
     
    Guest, Jul 26, 2004
    #4
  5. Pat Durkin

    Rob Guenther Guest

    I put our 1993 960 into "3" and sometimes even L for descending larger
    hills.... We *needed* L, in the lowest possible gear (meaning we had to stop
    the car, and let it engage first, not just let it use second) when towing in
    the moutains around Nova Scotia... the brakes would have cooked - we used
    1st gear to get up the hill.... a slow 45kph in first, all the way up,
    12-14% grades.
     
    Rob Guenther, Jul 26, 2004
    #5
  6. Pat Durkin

    Larry_Horse Guest

    | I've got a 2001 S80.
    |
    ..
    |
    | In other words should I resist the temptation to gear down and just let my
    | wheel brakes do the job?


    Someone once told me that it's cheaper to replace brakes than it is to replace
    a transmission.
     
    Larry_Horse, Jul 26, 2004
    #6
  7. [Larry_Horse] (Mon, 26 Jul 2004 19:36:58 GMT):
    How about when your brakes are boiling..

    Is your life easily replaced? ;)
     
    Svein Tore Sølvik, Jul 26, 2004
    #7
  8. Pat Durkin

    Peter Milnes Guest

    How do you "gear down" (use the gears to slow the car under ordinary conditions)
    when they only have an automatic gearbox?

    Cheers, Peter.

    :
    : : | I've got a 2001 S80.
    : |
    : .
    : |
    : | In other words should I resist the temptation to gear down and just let my
    : | wheel brakes do the job?
    :
    :
    : Someone once told me that it's cheaper to replace brakes than it is to replace
    : a transmission.
    :
    :
     
    Peter Milnes, Jul 27, 2004
    #8
  9. Pat Durkin

    Pat Durkin Guest

    Silly question.

    To all those who answered I thank you.

    The term "gear down" applies as much to an automatic as it does a manual
    even though there is admittedly some slippage in the torque converter. When
    you pull the lever down into 3 or 2 while descending a grade there is
    unquestionably a slowing effect on the vehicle - just as there would be if
    it were a manual gear box. Maybe not as dramatically but yeah...it slows
    the car and it saves brake lining.

    But I have heard the following statement myself - more than once:
    And that's what prompted my question.

    Am I money ahead to slow the car as well as stop the car with brakes alone -
    because brakes are cheap and transmissions are pricey?

    Or is it relatively harmless to the trans? Is the transmission designed to
    take this kind of usage or will it shorten the life of the component?

    Well, okay, I can answer part of that myself --- anytime you use something
    you're burning up part of its useful lifespan.

    But some things can be used for a millennium before you ruin them. A
    thimble can take a lot of needle pokes before it wears out.

    On the other hand brakes (in my neighborhood) can only be used 3 or 4 months
    before they've got to be replaced.

    Hence, my question: Can I safely and PRACTICALLY use my trans to slow the
    car without risking extremely expensive transmission repairs?

    Refer to my original question. I'm a pretty good speculator myself. I can
    imagine a LOT of scenarios - all of which make a certain amount of sense.

    What I'm looking for is some EXPERIENCED advice on using the automatic
    transmission to slow the vehicle on a steep incline.

    TIA.

    Pat

    PS - Just so that there's no misunderstanding of how my car is equipped ---
    it is a 2001 US-Spec'd S80 with the standard 197 or 194 HP 2.9 non-turbo
    engine and the REGULAR auto trans ---- which, correct me if I'm wrong ----
    is (was) originally purchased from the Oldsmobile division of GM and was
    identical to the front drive transaxle used in an Olds mid-size car before
    Olds failed and Ford bought the Volvo car division.
     
    Pat Durkin, Jul 27, 2004
    #9
  10. Pat Durkin

    sno Guest

    I have been driving volvo's since 1970 and have always
    "geared down"......never have had any transmission
    problems....and get very very very good mileage on
    brake pads.....

    I talked once to a transmission man I trust about this,
    as have people through the years tell me I would ruin
    my transmission.....he said it is the same as when you
    press the accelerator and go into passing gear....the
    transmission is built to handle it.....

    thank you for listening to my thoughts.......steve

    --
    Seen it all, done it all, can't remember most of it

    This tag line is generated by:

    SLTG (Silly Little Tag Generator)
     
    sno, Jul 27, 2004
    #10
  11. Pat Durkin

    Pat Durkin Guest


    Was it called the "Aurora"? I think so.

    I wonder if the current production standard 2.9L S80's are still being built
    using the same transaxle purchased from GM. Probably not. I'm aware the
    turbo models have a fancier transmission.

    Pat
     
    Pat Durkin, Jul 27, 2004
    #11
  12. Pat Durkin

    Pat Durkin Guest

    I just posted a couple of photos of this car on alt.binaries.pictures.autos

    Pat
     
    Pat Durkin, Jul 27, 2004
    #12
  13. Pat Durkin

    Pat Durkin Guest


    Thanks for offering them. That's exactly the kind of feedback I wanted.

    Pat
     
    Pat Durkin, Jul 27, 2004
    #13
  14. Pat Durkin

    Bob Noble Guest

    Hi, Pat - - -

    *Years* ago, Road & Track magazine had an article on the subject -
    pointing out that brake linings are a lot cheaper than clutch linings.
    That said . . .

    The obvious consideration is clutch engagement - wet or dry. A small
    effort to get the different masses rotating at the same rate will pay
    big dividends. There is no significant stress on the engine in
    operating at a higher-than-normal rate in a braking mode; no likelihood
    of overheating or etc.

    From recent experience with our two Volvo's (98 V70XC and 02 S60AWD), I
    find that a mild increase in accelerator pressure as the lever selects a
    lower gear allows the engine to speed up enough to synchronize the
    clutch and gears (again - manual or auto) so that input/output speeds at
    the clutch involved are close enough to stop any obvious synchro
    problems.

    bob noble
    Reno, NV, USA
     
    Bob Noble, Jul 28, 2004
    #14
  15. Pat Durkin

    mrhuntnpeck Guest


    that's one reason I would always prefer a manual , you approach a
    corner, double clutch down into 2nd or 3rd, this synchronizes the
    motor with the drivetrain. ( take it out of gear, adjust engine speed
    to match drivetrain, re enguage then shift.) this puts the energy from
    the braking effect into "spinning up" your engine and flywheel,
    saving your brakes and not wearing your synchromesh. What you are
    doing is making the gears inside the box match speeds. then when you
    come out of the corner you can then get a free boost of power as you
    shift back up. in other words you can reuse that energy, rather than
    waste it.
    the smooth roll in and out of gears also makes the car handle better
    because the forces you are transferring to the road , braking, gearing
    down, acellerating, gearing back up are one smooth motion

    it takes practice to drive smoothly, more to doubleclutch smoothly
    but it saves gas and your drivetrain. I have bought cars with
    transmissions that were stubborn to shift , and worn them back into
    operating smoothly, through another 50 k of driving them smoothly.

    one can take things a step further in a sporty sense, and combine
    this action with rolling off the gas and onto the brake and back on
    the gas while doubleclutching down and back up. it takes practice to
    get this right and the gas and brake pedals need to be situated right,
    but it gives one a great feeling when it comes together into one nice
    fluid motion.

    In my opinion it is the "twisting action" that wears your drivetrain.
    Every time you jolt it by either accellerating or decellerating with
    sudden force it makes every part involved from your pistons to the
    tires on the road reverse forces with their mating parts from a
    "driving" mode to a "driven" mode. this causes a wee bit of wear to
    all mating parts, splines, ujoints rear axle gears transmission gears,
    clutch. Even all the bearings involved are affected because the load
    on them changes direction. lets not forget all the rubber parts , like
    your transmission mounts etc. in lower gears you are able to stress
    these parts much more than in higher gears, because more torque is
    involved.
    and of course the greater the force on every part , the more wear.

    so my opinion for what it is worth is:
    of course, use your transmission to slow you , but the harder you
    "jolt" your drivetrain, and the quicker it will wear, so if it goes
    down into a lower gear with a great big thud it probably isn't a good
    thing. same goes for flooring it in first.

    also since it is a proven fact that if one chooses roads which go
    downhill, one will save gas. so if you have a choice , go downhill in
    mexiican overdrive (neutral) :)

    Phil
     
    mrhuntnpeck, Jul 29, 2004
    #15
  16. Pat Durkin

    taff Guest

    So, you are driving down this steeeeep hill in high gear, and the
    brakes fail ( Unlikely I know, but not impossible) PANIC.

    Now your are driving down the same hill, in the correct gear, and the
    brakes fail, "Damn, have to sort that out at the bottom of the hill."

    Which do you prefer.

    Taff...........



    www.sounds-pa.com | www.thecomputerworkshop.com
     
    taff, Jul 29, 2004
    #16
  17. Pat Durkin

    Pat Durkin Guest


    Unlikely to say the least. Nowhere that dramatic.

    Okay. My fault. I didn't adequately describe my thoughts.

    I'm not afraid I'll burn up my brakes in long one panic stop while
    descending one of our hills around here. They are HILLS (steep ones, yes,
    but hills nonetheless) not mountains - and I'm driving a CAR, not a
    commercial truck with an 80,000 pound GCW pulling me down a long mountainous
    decline at ever increasing speeds while I desperately scan the road ahead
    for an emergency off ramp.

    None of that applies.

    What DOES apply is that in this neighborhood I burn up a set of front brakes
    every 4 or 5 months. Every third reline I replace the front rotors too and
    they're about $120.00 each and of course now and then I've also got to do
    the rears --- so my brake maintenance costs over time are quite a bit higher
    than somebody who just toodles around on flat ground. Right?

    That's issue number one.

    Issue number two is that I try to take some of the braking load off my wheel
    brakes by pulling my automatic gear selector into 3 or even 2 while
    descending these steep local grades.

    Which leads to my QUESTION:!: "Am I wise to continually use my engine's
    compression braking effect to slow the car and extend brake life over a
    period of time - or will this inevitably result in early and
    catastrophically expensive transmission failure and ultimately COST me more
    in the long run than I'm trying to save in the short run?"

    That's all. That's the whole question. Pretty straightforward.

    I have no interest in debating whether or not a manual is better than an
    automatic or any of that stuff...not that I had any choice in the matter
    because a US-spec'd 2001 S80 with a naturally-aspirated 2.9L engine only
    comes with ONE transmission 'choice' and it happens to be an automatic. So
    it is what it is. If ya like the whole car ya buy it automatic and all, and
    I did.

    Pat
     
    Pat Durkin, Jul 29, 2004
    #17
  18. Pat Durkin

    Tim Hobbs Guest

    I use the auto selector to get engine braking all the time. My wife
    says I'm just being fussy, but the car is easier to control and I
    drive with little use of the brakes. It's also a habit from my
    off-road driving, where braking down steep hills is a very bad idea!

    The force through the gearbox to go downhill at a steady speed is
    exactly the same as going up the hill at the same steady speed. If
    you accelerate up a hill then you put far more force through the
    transmission.

    I don't worry about the transmission - if you generally drive smoothly
    and get it in low gear before you start the decline I can't see why
    there should be any extra wear.


    --

    Tim Hobbs

    '58 Series 2 88" aka "Stig"
    '77 101FC Ambulance aka "Burrt"
    '95 Discovery V8i aka "The Disco" (FOR SALE)
    '03 Volvo V70

    My Landies? http://www.seriesii.co.uk
    Barcoding? http://www.bartec-systems.com
    Tony Luckwill web archive at http://www.luckwill.com
     
    Tim Hobbs, Jul 29, 2004
    #18
  19. Trouble is, I don't think it really is very straightforward. No matter
    what you do there will be a cost. If you save your brakes you will
    load the transmission, but I doubt anyone other than you can resolve
    the equation of which method will save you most money. Other variables
    that will affect your answer are the current condition of the car, how
    long you plan to keep it, its value, your annual mileage, labour
    costs, inconvenience of maintenance...

    Under normal conditions, using engine braking will not unduely stress
    the transmission, so 1 - 200k maintenance-free miles should easily be
    possible (other than fluid changes). But your conditions sound far
    from normal. Your brake wear rate is extremely high, so it may be
    worth trying out different types of pad.

    Under the sort of conditions you suggest, I would have thought it was
    imperative to slip the lever into 3 or 2, just to maintain good car
    control. Remember also, that a very hot brake will have impaired
    efficiency, so your braking ability may be reduced. I guess this could
    in turn lead to greater wear.

    Incidently, it is not the compression of the engine that provides the
    braking effect, but the vacuum in the inlet manifold.
    --

    Stewart Hargrave


    For email, replace 'SpamOnlyToHere' with my name
     
    Stewart Hargrave, Jul 29, 2004
    #19
  20. Pat Durkin

    psyshrike Guest


    Howdy,

    As I understand it, heat generated during high load conditions is the
    primary killer of transmissions, not direct mechanical stress. The
    stress that causes failure is indirect, caused by reduced lubricity,
    and reduction of the strength of parts due to heat.

    If you are particularly concerned about it, get an auxillary oil
    cooler for the transmission. Can't do harm over the long run, and is
    relatively inexpensive. If you are _really_ concerned about it, you
    can have a oil temp quage installed for the transmission. This fairly
    common practice for people who regularly pull trailers.

    Truckers use engine breaking, and they run their equipment to millions
    of miles. You will find every truck has that does any substantial
    loading has a some sort of auxilary heat management system for the
    transmission oil.

    The old adage "better to replace brakes than a tranny" is sixpack
    wisdom IMHO. The point here is how not to have to replace _anything_.
    Which is a matter of keeping yourself inside manufacturer tolerances,
    not a matter of prioritizing failure.

    -FWIW
    -Matt
     
    psyshrike, Jul 30, 2004
    #20
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