Alexandre Dubé

Power loss after hard braking

13 posts in this topic

Hello everyone, this is my first post :P

I bought a Spark 2016 2LT a couple of months ago, and I wanted to check if what happens after a hard braking is normal for a CVT.

It happens sometimes, but not always.

 

I've found a similar case to mine on a Nissan Forum.

So, when I do a hard braking on my Spark (emergency stop, or because of a sudden stop in traffic), and that I come to a complete stop, if I press the accelerator immediately after, I have almost no power and the car feels sluggish. Then after a couple of seconds (sometimes less, sometimes more) it will accelerate. Sometimes after a hard braking, it will accelerate but very slowly. Sometimes not at all.

I was wondering if that was normal with a CVT. My guess is that after a hard braking, the engine uses compression to help stop the car, and the CVT stays in "high gear". When I press the accelerator immediately after, the car computer hasn't had the time to adjust the CVT ratio and that is why there is a delay in the acceleration.

However, that can sometimes be dangerous: for example if I need to accelerate quickly after stopping, and am unable to do so.

 

On a similar note, I've found that when coasting, if I'm at 40 km/h (25 mph) or lower the car seems to brake on its own as though it was automatically using engine braking. Has anyone had something like that happen with their Spark? Is it a feature of the car?

 

Thanks a lot for your answer!

Edited by Alexandre Dubé

Share this post


Link to post
Share on other sites
   


I have noticed both.

The car (2014) seems to try to start in second gear frequently,  and coasting, i have noticed it feel like it engine brakes itself. It's done that since day one.

 

Im sure gearhead will be in soon. He seems to have the best understanding of the cvt and its odd shifting patterns.

Share this post


Link to post
Share on other sites
On 7/28/2016 at 6:13 PM, Alexandre Dubé said:

I come to a complete stop, if I press the accelerator immediately after, I have almost no power and the car feels sluggish. Then after a couple of seconds (sometimes less, sometimes more) it will accelerate. Sometimes after a hard braking, it will accelerate but very slowly. Sometimes not at all.

     Most likely the CVT is not engaging 1st gear fast enough. Remember that first and last gear (overdrive) is accomplished by the main CVT unit engaging the attached aux conventional auto tranny to extend the gear ratio/range from 5 steps to 7. So this is most likely something that can be resolved by someone who is able to properly reprogram the CVT to correct factory specs or if the factory setting to spec is incorrect some new mechanical or electronic setting is what the manufacturer needs to come up with and direct GM on how to apply that...that's my take on that issue..seems like that is the most widely reported issue..no first gear when needed.

 

     I know how the Jatco-7 works..but certainly no idea on how to correct these issues. I think some engineers who worked on that new design CVT need to issue a clear repair directive to GM, since from what I gather, most dealership techs don't have a clue on how to proceed with this unit or the directive how to correct this is incorrect.

     As far as the braking effect on coast..that is part engine braking and part tranny resistance and most likely totally normal as it cycles down the gear range.

     Only good thing about all this is your powertrain warranty that I believe is still 5yrs/100Kmi on the Spark. I have never heard of a single tranny with so many people having the exact same issues and no clear cause or fix..Those who have had the CVT replaced seem to be satisfied...Sorry, wish I could suggest some logical and accurate solution and I really thought the 2016 with the new flat torque engine would resolve the issue, but apparently some problems are still there.

Edited by Retired old Gearhead
VegasSpark likes this

Share this post


Link to post
Share on other sites

Thanks for the answers!

I'll try to film the issue so I can show my dealer what I mean, because they'll want proof.

I don't know yet if they have a fix for that.

 

I've looked around on the web, and from what I can find the 2016 Spark uses the same transmission model as in the previous years. As you said, The model is Jatco CVT7 JF015E.

 

I've found the product brochure on their website (File attached to my post). From what I can see on the description, I think this problem is related to how the gearbox on the CVT works:

 

"Utilization of the gear for switching between moving forward/reversing as auxiliary gearbox CVTs originally have planetary gears used for switching between moving forward and reversing. Those gears are utilized as an auxiliary gearbox through adding two-step shift transmission elements. On top of the original CVT function of shifting from low gear to high gear, this new function makes it possible to shift  from first speed to second speed while driving.
In order to ensure that the driver does not experience any discomfort by shift shock, the pulley controls shift change to minimize gear ratio variance before and after shifting. This high level of control technologies for carrying out smooth two-step shift change is one of the important advancements CVT with an auxiliary gearbox. JATCO’s high level of control technologies and knowhow cultivated over many years makes this new product possible."

 

So if the pulley is slow to adujst after a hard braking, that might be the reason why there is a loss of power, because the pulley cannot "tell" the gearbox to engage in first gear? I don't know if I understood that right :P

 

Jatco CVT7 - JF015E.pdf

Edited by Alexandre Dubé
Minor text changes

Share this post


Link to post
Share on other sites

That's some nice tech info in your post and I think the product sheet pdf will give some readers a better understanding of their CVT. Looks like nice on the tech info, but the reality with the Spark is a whole different story. The same tranny seems to work well on at least some cars..and the new 1.4 engine in the '16 Spark seems to meet all the requirements for this tranny as far as torque is required...so, not sure what the heck is going on.

 

     If I was in the market for another car I would not consider a CVT until the bugs are ironed out rather than the only current fix that works for the Spark being a complete tranny replacement. Seems like there are so many of these units being replaced that the factory where they are made, in Thailand can't make them fast enough...

Edited by Retired old Gearhead

Share this post


Link to post
Share on other sites

Well, it looks like there's a TSB related to the Powertrain released for the 2016 Spark.

I found it on the NHTSA website: Source linked here

 

Manufacturer Communication No.: PIP5328 
Component(s): POWER TRAIN

NHTSA ID Number: 10075742

SUMMARY TO BE PROVIDED ON A FUTURE DATE.

 

In fact, there are 3 other TSB that have been released related to that car this week (I've check last week and it wasn't there).

For the 2 TSBs related to the MyLink radio, I've experience some of those errors.

 

Manufacturer Communication No.: SB-16-NA-109 
Component(s): STEERING

NHTSA ID Number: 1007843

"THIS TECHNICAL BULLETIN PROVIDES A PROCEDURE TO INSPECT THE STEERING GEAR FOR A NORMAL CONDITION OF GREASE OR SEALANT ON EXTERIOR CASE OF GEAR DUE TO THE MANUFACTURING PROCESS."

 

Manufacturer Communication No.: SB-16-NA-108 
Component(s): ELECTRICAL SYSTEM , EQUIPMENT

NHTSA ID Number: 10078427

THIS TECHNICAL BULLETIN PROVIDES A PROCEDURE TO REPROGRAM THE RADIO TO CORRECT A CUSTOMER CONCERN OF BUZZ OR STATIC NOISE FROM RADIO AUDIO SPEAKERS, ANDROID AUTO CONNECTION ISSUES, INTERMITTENT BLACK SCREEN OR SIRIUS XM REVERTS TO XM1 CHANNEL INTERMITTENTLY.

 

Manufacturer Communication No.: SB-16-NA-107 
Component(s): ELECTRICAL SYSTEM

NHTSA ID Number: 10078420

THIS TECHNICAL BULLETIN PROVIDES A PROCEDURE TO REPROGRAM THE RADIO TO CORRECT A CUSTOMER CONCERN OF RADIO INOPERATIVE, BLUE SCREEN, AM CLIPPING NOISE, HD ON/OFF STATUS NOT RETAINED IN STATIONS, TIME LAG ON TRANSITIONS, NO AUDIO WITH INTERNAL AMP, PARK ASSIST SYMBOL POSITION WRONG IN REAR VIEW CAMERA.

Edited by Alexandre Dubé
Added source link

Share this post


Link to post
Share on other sites

After a bit of researching, I've found the complete TSBs from GM (linked to this post).

 

@Retired old Gearhead

Also, I've found a lot of technical information about the Jatco CVT7 if you're interested (including the inner workings/ gear ratios and etc).

I've zipped (Transmission.zip) it and linked it to this post also.

Maybe someone more knowledgeable than me can make use of it!

16-NA-107_Document ID_ 4481927.pdf

16-NA-108_Document ID_ 4454099.pdf

16­NA­109_Document ID_ 4484722.pdf

PIP5328A_Document ID_ 4360226.pdf

Transmission.zip

Edited by Alexandre Dubé

Share this post


Link to post
Share on other sites

Nice work Alexandre! I'm sure some '15 & '16 Spark owners will find this interesting and useful. Quite some complex issues to fix on those models.

 

Share this post


Link to post
Share on other sites

It can vary i think car to car.  For example:

2014 car, Was bought brand-new when I got it.  No crashes, no hard-breaking, regular driving at 27,000 miles so far to date.  98% of the time it will accelerate from a stop, pretty quickly. 2% of the time it will be sluggish and have a mindset like "Uhhhhh....oh...you want me to go? ummmmmm.. okay!!!" and rpms go from low to like 3000-4000rpms  suddenly, after moving like 10ft at slow speed. MOST of the time, it'll just take off nice and quick when commanded to.  I also notice with my car, around 30-35MPH, when im on a road going from 0-55 leaving my foot at a constant level, the car climbs in RPMs at a constant rate. Right at 35MPH, that constant-speedup stalls for about 5 seconds, then the CVT goes into its "second gear" i guess and suddenly we're back to speeding up at a constant rate again, and it'll do this to 55...60..70..whatever speed I'm trying to go to. but it will always, have that short-stall, around 35mph.  I just naturally assumed this was some 2nd-shift/set in the CVT system.

NOW! Where this gets weird, my dad owns the same car, but in 2015 model. His car, drives a lot different than mine. Doesnt accelerate near as fast, takes him quiet awhile of traveling up the road, until it finally kicks into the higher speed. Put our sparks side by side and mine out-beats his by a LONG shot.  Yet, we both have the same series spark. Just a 2015 for him. He feels mine is a lot more peppy and has a lot more get-up-and-go.  I dont 'race' my spark but its got me habbits to be peppy and take advantage of that.  Friends with full-size cars and much more HP, tend to have to really step on the gas and spin RPMS way up to take off as quick as my car does, from a stop..and im just like "Oh..didnt even relize I took off that fast? Wasnt even giving her any gas..hardly touched 2000rpm.." But its a light car. I'd expect that. Always way ahead of everyone when the light turns green, and its not at all intentional, im just normally accelerating.

Also, as mentioned above, I to notice the lower 25-20s theres like this odd 'breaking' feel. Like automatic engine breaking. I always wondered what the F that was. Sometimes I hate it, as i expect to coast not slow down.  Othertimes I dont mind it, because when im on the highway or a main road, i dont use my breaks that much to slow down 10-20MPH, i just let off the gas and watch the speed gauge drop after a second. I just assumed its because light car. wind dynamics.. But especially when going 20-25, you really notice this weird breaking.

But. To the dealer ( different dealers as I got my car elsewhere ) Both cars...are said to be fine, and running within expectations.

Share this post


Link to post
Share on other sites

Nicely detailed post KillaX!..."2nd-shift/set in the CVT system" ya, that's controlled by the attached aux tranny that engages first, second and reverse..Still by your description..CVT not working as it should..I have driven CVT's in bigger engines and smooth all the way up and down....same as my '13 Spark auto 4sp tranny. Only thing is the 4 speed auto tranny runs higher rpms which is what this engine is designed for. I have almost 90Kmiles on it and still burns no noticeable oil and gas mileage is better than it was at 50K miles. Yup..I'm surprised at this stage in what I thought would be a 50Kmi burner car we bought for $12K cash as a tiny solution to handling in the tight Miami beach roads...

Share this post


Link to post
Share on other sites

Today I drove a lot of miles on I-95 & I-295 on my Spark 2017 LS with CVT. The transmission performed great going from 0 to 70+MPH. It felt like the car understood exactly my speed demands, and responded positively & smoothly. I don't think I will ever want the geared auto tranny. I am sold on the CVT concept. I do realize the CVT is governed by a computer program and there are many variables the program has to tackle. Such as:

 

Current vehicle speed

Current engine RPM

Change in position of gas pedal (acceleration demands by driver)

How much is the total load on the CVT (passengers+cargo+wind+upgrade/downgrade)

Current temperature inside the transmission

Is the car brake being applied and how strongly

Engine power output based on current condition of engine (well tuned or not)

 

Anyone who has developed complex computer programs, will immediately understand how difficult it is for the CVT computer program to perform ideally under all these conditions. If the CVT performance matches driver's instantaneous demands 97.5% of the time, it is a top rated program. I gladly accept the 2.5% mis-behavior because of the wonderful MPG, smoothness, lack of gear shift jerks, and compact size of the CVT transmission. 

 

 

Share this post


Link to post
Share on other sites

I agree , I love the CVT transmissions . I have had them for many years in my Hondas  . When I bought my 13 Spark it came with the conventional automatic . It's a good proven transmission but is annoying the way it shifts compared to a CVTs smooth power delivery . 

Share this post


Link to post
Share on other sites

My 2014 slipped into Neutral on its own twice after hard breaks. I told dealer service department, because I had to go there for my tail light and 2 recalls. They noted it(before 36,000 miles), but could not give me an explanation

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now