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?
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.
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,
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.
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.....
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.
*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.
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) :)
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.
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.
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.
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.
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