Jolt when driving from cold, Rear axle/Diff

[Kermitpwee]

Hello

I have a 17 Is300h with 70k miles on the clock. When I drive away from cold in 'Eco Mode' and accelerate smoothly after 400- 500 yards there is a sudden jolt from the rear of the car, it feels like windup in the rear axle.

It only happens when accelerating smoothly, give it more throttle and it never happens. It only happens on the first start of the day, car is driving otherwise perfectly and has FSH with all the rear diff oil changes done on times.

Any ideas what this might be? 

[Anthony B]

I have a similar experience with my IS300h when pulling away from standstill, but as I have to pull a hard left immediately after start I have always assumed it was a steering geometry issue, and therefore I have assumed the jolt originated from the front of the car.  The garage have checked the steering alignment and found no problem, and are as puzzled as me.  I'm going to check the car back into the garage, but any illumination from you experienced IS300h drivers would be helpful before I do so.

[royoftherovers]

4 hours ago, Kermitpwee said:

Hello

I have a 17 Is300h with 70k miles on the clock. When I drive away from cold in 'Eco Mode' and accelerate smoothly after 400- 500 yards there is a sudden jolt from the rear of the car, it feels like windup in the rear axle.

It only happens when accelerating smoothly, give it more throttle and it never happens. It only happens on the first start of the day, car is driving otherwise perfectly and has FSH with all the rear diff oil changes done on times.

Any ideas what this might be? 

Why are you starting off cold in  Eco mode?

You need to digest the Handbook Anthony.

[Kermitpwee]

35 minutes ago, Anthony B said:

I have a similar experience with my IS300h when pulling away from standstill, but as I have to pull a hard left immediately after start I have always assumed it was a steering geometry issue, and therefore I have assumed the jolt originated from the front of the car.  The garage have checked the steering alignment and found no problem, and are as puzzled as me.  I'm going to check the car back into the garage, but any illumination from you experienced IS300h drivers would be helpful before I do so.

My jolt is in a straight line and at 30-40mph. I presume yours is at low speed on at least half lock?

I also have that and its nothing to worry about, it happens on Mercedes as well. its from the width of the tyre and slight slippage of the tyres thread.

[Kermitpwee]

I

2 minutes ago, royoftherovers said:

Why are you starting off cold in  Eco mode?

I always drive in Eco mode, it doesn't happen in Normal or Sport or if I accelerate briskly in Eco. I don't drive in EV mode. 

Is there any reason I shouldn't drive in Eco from cold?

[Thackeray]

4 hours ago, Kermitpwee said:

When I drive away from cold in 'Eco Mode' and accelerate smoothly after 400- 500 yards there is a sudden jolt from the rear of the car,

If it only happens from cold, could it be power generation kicking in and applying a load to the transmission after the engine has warmed up, going through the various stages. Here's a Prius forum where the various engine warm-up stages are described. Scroll down to the post by Grumpy Cabbie about half way down that lists the engine stages.

You can watch the car's energy monitor screen to see when power generation begins - it's usually after about a minute. Or you could use the Hybrid Assistant app if you have an Android phone which shows the power generation begin in more detail and also specifies which engine stage the engine is running in. If power generation begins when you feel the jolt that may be the reason. Having said that, I wouldn't have thought it would be very noticeable, so maybe there is a problem of some sort.

[royoftherovers]

Just now, Kermitpwee said:

I

I always drive in Eco mode, it doesn't happen in Normal or Sport or if I accelerate briskly in Eco. I don't drive in EV mode. 

Is there any reason I shouldn't drive in Eco from cold?

I`m pretty sure that is the way to do it per the Handbook. Thy Hybrid system is set up so the the computer system determines when to go into each mode. Not the driver.

Generally speaking a cold start will not permit ecomode as the capacity of the Hybrid Battery is insufficient to power the car.

[Kermitpwee]

8 minutes ago, Thackeray said:

If it only happens from cold, could it be power generation kicking in and applying a load to the transmission after the engine has warmed up, going through the various stages. Here's a Prius forum where the various engine warm-up stages are described. Scroll down to the post by Grumpy Cabbie about half way down that lists the engine stages.

You can watch the car's energy monitor screen to see when power generation begins - it's usually after about a minute. Or you could use the Hybrid Assistant app if you have an Android phone which shows the power generation begin in more detail and also specifies which engine stage the engine is running in. If power generation begins when you feel the jolt that may be the reason. Having said that, I wouldn't have thought it would be very noticeable, so maybe there is a problem of some sort.

Yes that could be it, thanks for taking the time to post and help me.

[Thackeray]

3 minutes ago, royoftherovers said:

the capacity of the Hybrid Battery is insufficient to power the car

I'm not sure that's right. It's the petrol engine which isn't sufficient to power the car until it's gone through the first warm up stages. During this time, as I understand it, it's mostly the Battery that gets the car moving. If that's wrong I hope someone will correct it.

[Kermitpwee]

6 minutes ago, royoftherovers said:

I`m pretty sure that is the way to do it per the Handbook. Thy Hybrid system is set up so the the computer system determines when to go into each mode. Not the driver.

Generally speaking a cold start will not permit ecomode as the capacity of the Hybrid Battery is insufficient to power the car.

Thanks for getting back to me, just to be clear I am not driving on Battery, I have the car in Eco mode not EV, perhaps I misunderstand what happens in Eco mode but I can hear the engine running in Eco mode.

[Kermitpwee]

2 minutes ago, Thackeray said:

I'm not sure that's right. It's the petrol engine which isn't sufficient to power the car until it's gone through the first warm up stages. During this time, as I understand it, it's mostly the battery that gets the car moving. If that's wrong I hope someone will correct it.

This would make perfect sense to my problem, hopefully thats it as its a cracking car and I dont want to have to fix a read diff!

[royoftherovers]

Just now, Kermitpwee said:

Thanks for getting back to me, just to be clear I am not driving on battery, I have the car in Eco mode not EV, perhaps I misunderstand what happens in Eco mode but I can hear the engine running in Eco mode.

OK Peter, if your happy, then so am  I !  Enjoy your car and stay safe and well.

[Kermitpwee]

Just now, royoftherovers said:

OK Peter, if your happy, then so am  I !  Enjoy your car and stay safe and well.

Having read Thackeray's point I now understand your point better, I will start it in Normal mode in future, thanks again

[Thackeray]

1 minute ago, Kermitpwee said:

This would make perfect sense to my problem, hopefully thats it

You could try letting the engine warm up for a minute before setting off. You can check power generation has started on the energy monitor screen. Then set off exactly as you normally would and see if you still feel the jolt. Of course, you might still feel the jolt while you're stationary - it's certainly possible to hear the generator increase power when the engine warm-up stage is right.

[Kermitpwee]

Just now, Thackeray said:

You could try letting the engine warm up for a minute before setting off. You can check power generation has started on the energy monitor screen. Then set off exactly as you normally would and see if you still feel the jolt. Of course, you might still feel the jolt while you're stationary - it's certainly possible to hear the generator increase power when the engine warm-up stage is right.

I will try that tomorrow morning, thanks

[Anthony B]

2 hours ago, Kermitpwee said:

My jolt is in a straight line and at 30-40mph. I presume yours is at low speed on at least half lock?

I'm nowhere near 30 - more like 5mph - if that - and on half- to full lock to get out of my parking area at the side of the house.  Plus if I've reversed out, another full lock shortly thereafter.  But nothing after warm-up.  I'm pretty sure it's a tyre situation, rather than down to engine or drive mode, as it's more pronounced if the surface is wet or icy.

[Kermitpwee]

7 minutes ago, Anthony B said:

I'm nowhere near 30 - more like 5mph - if that - and on half- to full lock to get out of my parking area at the side of the house.  Plus if I've reversed out, another full lock shortly thereafter.  But nothing after warm-up.  I'm pretty sure it's a tyre situation, rather than down to engine or drive mode, as it's more pronounced if the surface is wet or icy.

Yes i also have experienced your problem when pulling out of the drive, i must turn sharply, it is the tyre and nothing to worry about according to my research, it is however very unsettling and it does make me feel like it couldn't be good for my steering. apparently it does no damage, its the tyre blocks been compressed.

 

[Adge]

Interesting.  GS300h I have  a jolt in eco mode as the car starts to reverse out of the garage.  i thought it might be binding brakes part frozen on.  I’ll try normal mode tomorrow to see if it’s still there.  Thanks for all the comments.

[Anthony B]

I've been doing some careful testing and I'm now sure what the problem has been - for me at least.  I had wondered why the problem had only begun to show itself these last few months, after a year of driving since I bought the car in June 2019.  What has changed is that last Spring, needing new tyres for my MOT, I fitted a pair of  run-flats on the rear wheels.  Plus I always like to run my tyres pressurised at the top end, as I prefer a hard ride.  I now realise that when cold and pulling a sharp curve the diff has trouble adjusting both wheels.  I realise too that the jerk is at the rear, as Kermitpwee recognised in his first post.  After warm-up during a good trial run the issue has gone away.  How does that sound as a theory?

[royoftherovers]

27 minutes ago, Anthony B said:

I've been doing some careful testing and I'm now sure what the problem has been - for me at least.  I had wondered why the problem had only begun to show itself these last few months, after a year of driving since I bought the car in June 2019.  What has changed is that last Spring, needing new tyres for my MOT, I fitted a pair of  run-flats on the rear wheels.  Plus I always like to run my tyres pressurised at the top end, as I prefer a hard ride.  I now realise that when cold and pulling a sharp curve the diff has trouble adjusting both wheels.  I realise too that the jerk is at the rear, as Kermitpwee recognised in his first post.  After warm-up during a good trial run the issue has gone away.  How does that sound as a theory?

Is the theory Anthony emanating from the jerk behind the wheel?   :):):)

Not heard from you much since you acquired the Hybrid ?

[Anthony B]

It is but a theory but it seems too fit the facts.  If I'm a jerk it's not for want of deep thought!!

I love the IS300h, which nicely fits my needs, my budget and my sense of excitement which has not atrophied entirely, even at 78.  And I'm relieved to have sold my LS430, which was becoming expensive at 17 years old.  This hybrid will see me through my motoring career, unless the government comes up with more pointless proscriptions.  

[royoftherovers]

1 minute ago, Anthony B said:

It is but a theory but it seems too fit the facts.  If I'm a jerk it's not for want of deep thought!!

I love the IS300h, which nicely fits my needs, my budget and my sense of excitement which has not atrophied entirely, even at 78.  And I'm relieved to have sold my LS430, which was becoming expensive at 17 years old.  This hybrid will see me through my motoring career, unless the government comes up with more pointless proscriptions.  

Thanks Anthony, I glad you took that in Jest. I remember communicating with you when you were apprehensive about which car to move to, but have not noticed you posting for a while. Take care and stay safe.

[NemesisUK]

50 minutes ago, Anthony B said:

I now realise that when cold and pulling a sharp curve the diff has trouble adjusting both wheels.

Not sure I follow the reasoning here. How does the diff "adjust" both wheels? Surely (unless it's a LSD) it's simply relative rotation through the crown and pinion gears? If there really is a 'jerk' from the rear there must be play in the diff gears, adjustment of the thrust bearing but I can't imagine it's the problem.

I get a pronounce 'jerk' when exiting my driveway on full lock but only in the colder months and when it first happened (in my first RC back in 2016) I thought I'd actually run over a brick! I now know it's just the effect of tyre flex and extreme steering angles. More and more common on many marques as wheels get bigger/wider and tyre walls shorter shod with summer (warmer temp) optimised tyres.

[Anthony B]

I admit I don't fully understand wha's going on but the idea  seems to fit the observed phenomenon better than other ideas.  But I've learned much from the posts in this series since the topic was first raised.

[ColinBarber]

On 2/2/2021 at 9:35 AM, Kermitpwee said:

Hello

I have a 17 Is300h with 70k miles on the clock. When I drive away from cold in 'Eco Mode' and accelerate smoothly after 400- 500 yards there is a sudden jolt from the rear of the car, it feels like windup in the rear axle.

It only happens when accelerating smoothly, give it more throttle and it never happens. It only happens on the first start of the day, car is driving otherwise perfectly and has FSH with all the rear diff oil changes done on times.

Any ideas what this might be? 

It can only really be diff/brakes/suspension at the rear. Are your rear brakes freeing correctly, especially the parking brake?

Being in Eco mode should have nothing to do with it, and it is a mode that is perfectly acceptable to be using from startup if you so wish.