Downhill with cruise control

[Y2008]

I've been wanting to post this one for a long time. When i'm driving down hill with the cruise control set, I feel the car braking to maintain the set speed. Is that true? Does it actually break or do I just get that feeling?

[mikepologti]

never tried it but you do have me curious.

[broady69]

I havent noticed the braking but I have def seen the speedo go above the set speed due to downhill/gravity so I don't think it brakes for you....unless mines tanked

[VWindahouse]

I feel mine braking down some of the steeper highway decents.

[Y2008]

I definitely feel the car braking in some way or the other going
down the westgate bridge. I wonder if the break lights come on ??? I keep looking in the mirror when i feel it clamping down to see if the break light is coming on

[gregozedobe]

It might be engine braking (or even changing down a gear if it is an auto/DSG). I very much doubt that it is actually applying the wheel brakes (that is a feature that is only just starting to appear in some of the more expensive "trend-setter" cars).

[VW GTI]

It might be engine braking (or even changing down a gear if it is an auto/DSG). I very much doubt that it is actually applying the wheel brakes (that is a feature that is only just starting to appear in some of the more expensive "trend-setter" cars).

Also known as BMW.

[STV4SYT]

Pretty sure mine doesnt, it will add on 15-20km'h thru the burnley tunnel if left alone. i normaly flick it down to 5th or even 4th to save the brakes a bit.

[pixl]

Definitely not braking. Cruise control is pretty much just trying to keep the speed of the car from the revs. If it starts to go downhill, it tries to keep the rev the same which you'll notice that slight pulling back. But gravity will eventually take over and there's only so much it can do to keep you at the speed.

If you're in 5th doing 80 down a steep hill, you'll be 20km over the speed limit in no time. However, if you're in 4th, it will hold the speed all the way down.

I do this on the Eastlink tunnel where the limit is 80 and I never have to worry about going over speed.

[seangti]

from my limited understanding, it tries to control it through the ecu, perhaps with timing or fuel delivery.

Certainly not through braking, only engine braking.

Must say mine does a pretty darn god job of controlling the speed, have never had it creep more than 10km/h on steep downhills - quite reasonable IMO.

[FL00DY]

It might be engine braking (or even changing down a gear if it is an auto/DSG). I very much doubt that it is actually applying the wheel brakes (that is a feature that is only just starting to appear in some of the more expensive "trend-setter" cars).

Yeah agreed, the car is definitely trying to slow you down. Not sure it's braking though.

Pretty sure mine doesnt, it will add on 15-20km'h thru the burnley tunnel if left alone. i normaly flick it down to 5th or even 4th to save the brakes a bit.

Tell me, what's the difference in price between a set of a brake pads or rotors and a new transmission?

[Grant]

i read in the manual that the car wont brake when using cruise control.

[gregozedobe]

Tell me, what's the difference in price between a set of a brake pads or rotors and a new transmission?

I think I might have a different opinion to what you seem to be implying ie :

It is cheaper to use only your brakes rather than your engine and gears to help slow you down.

IMHO using engine braking sympathetically is unlikely to prematurely wear out a transmission. It certainly hasn't for any of the 11 vehicles I've had for the last 37 years, and I did keep them most of them for long enough to notice if it was going to be a problem. And I don't recall any of my acquaintences needing to repair (let alone replace a complete) transmission because of engine breaking.

In fact, apart from outright abuse causing damage, the main issue I've seen with transmissions in recent years is people using top gear too much to tow heavy trailers using cars/vans with "weak" top gears (eg Turbo diesel Landcruisers, Bedford vans). Even there, it has been (admittedly expensive) bearing and shaft repairs, not totally new gearboxes.

Even VW's latest u-beaut DSG gearboxes do down shifts to provide engine braking to slow you down, so VW's transmission engineers must be pretty comfortable with the idea.

So some related questions for you :

How many examples of premature wear have you seen on manual transmissions that can definitively be blamed on using engine braking, and what percentage is that (of total worn manual transmissions) you've seen ?

How many of these have required a complete new transmission, rather than replacement/repair of the worn components only ?

[T Go]

Isnt this just abit more simple than what every1 is makin out 2 be?
When you lift your foot off the accelerator, dont you lose speed?
Thats all the car is doin in cruise control when its downhill, isnt it???

I dont think braking, electronics etc etc would come into it....

[gregozedobe]

Isnt this just abit more simple than what every1 is makin out 2 be?
When you lift your foot off the accelerator, dont you lose speed?
Thats all the car is doin in cruise control when its downhill, isnt it???

I dont think braking, electronics etc etc would come into it....

I think evry1 is saying exactly that : that the car is NOT braking, just using the engine to slow down