Subaru Hill Assist and clutch (?) smell

I recently bought a 2019 WRX. These have a "Hill Assist" system that operates by default.

I really like the way this operates. It uses the brake to keep you from rolling backwards when taking off on an incline, similar to how some people use the handbrake.

Unfortunately, I find that using this system results in an odor that's definitely some sort of burning friction material. This is particularly true of a steep hill that I cross at the very beginning of my commute. (So it's possible the odor is associated with a cold clutch.)

My hunch is that I'm slowly burning up my clutch with this thing, so I've turned it off and am yo-yoing (to varying extents) up inclines as I always had.

It surprises me that Subaru would install such a device. Even if they don't, as a rule, replace clutches under warranty, it doesn't make sense to add a "feature" that slowly destroys the clutch.

So I'm wondering whether the smell is really clutch smell, or am I burning up my rear brakes (which I could accept). Maybe this problem goes away after a while?

I've also been pondering the physics of the situation. Is making the clutch fight a stationary, braked driven member really worse than making it fight against one that's spinning the wrong way? (Or have I misunderstood what's going on inside the clutch assembly somehow?)

The issue confuses me. Wondering if anyone else has dealt with it.

I’ve had hill holders on three Subes (older than yours) that didn’t do that. There was a valve that held the brakes on as long as you kept the clutch pedal down. As soon as the clutch began to come up, the brakes were released, and off you went. I know that after a clutch change (around 200,000 miles, so no, the hill holder wasn’t wearing the clutch), the hill holder needed to be adjusted so that the engagement worked as intended. I’m wondering if yours is out of adjustment, or if your clutch is dragging slightly when the pedal is fully depressed. Also, check to make sure the mats aren’t preventing the pedal from going all the way down.

In reply to Turboeric :

Thank you. That makes a lot of sense. There are at least two adjustments in play here.

The mats should be OK. Seems like they came with an almost-Velcro type surface on the bottom.

You probably should not be smelling anything if it is working properly. I just hold the brakes with my right foot, transmission in neutral. Time to go left foot clutch pedal down,put in gear, off the brakes, on the throttle and drive off.  What is yo yoing? 

The hill holder only affects the brakes, not the clutch.  The clutch works normally, the hill holder keeps the brakes applied until you engage the clutch.   If you're smelling clutch material, that's probably because manual transmissions and steep hills suck, and Subarus are heavy vehicles with tiny clutches.

My '88 had a mechanical device with a cable that slaved off of the clutch fork, and it was angle-sensitive so that it only worked when pointed uphill.  It was nothing more than a line lock.  If you had your foot on the brake, applying the clutch would keep one of the brake circuits engaged until you engaged the clutch.  The modern Subarus just use the ABS to do it, using software instead of a huge mechanical device underhood.

Incidentally, Buick Regals with a manual trans also have a hill holder function:  You can apply the electric parking brake, and it will automatically release when you go to drive away.

Do Subies still have dual mass flywheels?  Our '05 Legacy GT didn't have hill assist, but it SUCKED at hill starts (and in traffic) until I put an aftermarket clutch/flywheel in.

Can you put the hill assist into other cars ?

It might be interesting in an old VW

In reply to californiamilleghia :

You could with the 80s version.  It was literally nothing more than a cable operated line lock.  There's plenty of room under an ACVW to place it at the right angle (since it was also pitch-sensitive), and since ACVWs are cable operated, there's that nice long clutch fork that would be simple to stick the hill holder's actuation cable to. 

If you're on a steep hill and don't want to roll back or use the hill holder, use the parking brake instead. As you feel the clutch engage, let off the parking brake. On my 2015 WRX I've smelt minor clutch smell a few times after aggressive starts. I think it's probably just a bit of a weak clutch combined with a clutch action that's quite hard to be smooth with that's contributing.

Studebaker had a hill holder back in the 50s.

Looking on Google it seems that Studebaker started using them in the 30s !

and lots of other companies have used them thru the years , 

Hill Holder

https://en.wikipedia.org/wiki/Hill-holder

pilotbraden said:

What is yo yoing? 

I hope he’s not talking about using the clutch to hold the car on the hill. I  cringe whenever I see a car moving forward and backward slightly on a hill.

I feel old. I never had a manual car that did that. You just need faster feet. Hill starts we’re never an issue for me with out one of those and clutches were never an issue either  

I can see a few pluses for the hill assist , if you live in areas with lots of hills and stop and go traffic , 

or for cars that eat clutches that are hard to change ......

But are there negatives ?   since I do not think you can turn it off and on ,  

Thanks for your ideas....

rustybugkiller said:

pilotbraden said:

What is yo yoing? 

I hope he’s not talking about using the clutch to hold the car on the hill. I  cringe whenever I see a car moving forward and backward slightly on a hill.

That would account for the burning clutch stench. 

I'm thinking he's talking about letting off the brake and the car rolls backwards a bit before he's able to engage the clutch to go forward.

In reply to RX8driver :

That is also what the handbrake is for...  and technically, you're supposed to have the handbrake on any time you are stopped and the foot brake is not applied, otherwise you are "not in control of the vehicle".

At least, that's what they taught us.

pilotbraden said:

rustybugkiller said:

pilotbraden said:

What is yo yoing? 

I hope he’s not talking about using the clutch to hold the car on the hill. I  cringe whenever I see a car moving forward and backward slightly on a hill.

That would account for the burning clutch stench. 

Good God no, I'm not doing that. I'm generally pretty easy on clutches. I've driven more than one standard transmission car for years and years without smelling the clutch. Smelled it once at the drag strip and another time when I was much younger, trying to get out of a ditch before the Mounties arrived. That's it.

"Yo-yoing" just means I roll back a few inches before moving forward when I take off on a very steep hill- which is what the "hill assist" prevents completely.

Since I posted this thread, I've turned off hill assist and I haven't smelled the clutch at all. This is what puzzles me. My starting-off technique feels the same to me: foot off the brake, and then quickly use the gas pedal a little bit while releasing the clutch. It's the same thing I do from a level surface, just a bit more urgently.

How soon do you smell burning clutch after using the hill holder? Could it be a brake not releasing completely? It seems to me that the clutch would smell regardless of hill holder use if it's the clutch.

pilotbraden said:

How soon do you smell burning clutch after using the hill holder? Could it be a brake not releasing completely? It seems to me that the clutch would smell regardless of hill holder use if it's the clutch.

I start smelling it around 1 or 2 seconds after I start moving, and it peaks maybe 2-3 seconds after.

I have a hunch it's brake-related, but if so those brakes are getting used a lot more than they ever have when I've used the handbrake on a hill.

In reply to b13990 :

the handbake is cable operated , 

if the hill assist is hydraulic and drum brake could the brake cylinder be sticking or the return spring weak ?

just an idea......

I autoxed an '08 STi at a test and tune and when the pads got hot and sticky, the hill assist would sort of stick in place.  When you launched you'd get a wierd chatter and/or a massive thunk from the rear end about 30ft after the start.  It was annoying.

/derail