RX400h Brakes & Sunroof

[Rutlandlex]

I went for a test drive in a 400h today and I noticed that the brakes seemed quite spongy and not very responsive to begin with so you apply a bit more pressure then they bite hard.  If you hit the pedal hard to begin with then the spongy period is reduced before they bite hard but there is still that disconcerting delay.  Is this normal behaviour on these cars or is it a sign that the callipers might be sticking?  They were quite rusty I noticed.  I currently drive a Fiat Bravo and the brakes are super responsive so maybe I've been a bit spoiled.

With the sunroof I saw the 2 switches, one marked Tilt and the other with 2 arrows pointing front and back.  What I found was that both switches did the tilt and slide function and they also didn't stop when the sunroof was in the closed position, instead it just carried on past so it made it difficult to close properly.  Is this normal too?  I have had other cars with a sunroof before and they all stopped in the closed position so this behaviour just seems a bit weird.

[Britprius]

You must remember with a hybrid vehicle that the initial braking is done through regeneration. That is the motors that are in the transmission act as generators to produce electricity to charge the traction Battery thus saving energy for later use to accelerate. As you brake harder the normal braking system comes into effect slowing the car by producing heat, and wasting energy. This is probably the effect you are feeling.

The more you can use regeneration the better the MPG.

John.

[Stupot]

I test drove an RX300 with similar sunroof issues to the ones you describe, I thought it must have just been that particular car and it is one of the issues that made me decide not to buy it along with the cruise control not responding properly (electrical gremlins are a no no for me) so I'd be interested to hear if that is normal sunroof behaviour. My LS400 sunroof did not work that way and did stop when closed.

[Jaystar77]

Morning Neil, my RX had the same sunroof issue when I bought it.  Just needed the set-up procedure done on it (took 60 secs) and it's been fine ever since.  I think they sometimes lose their calibration.

 

 

[Jaystar77]

BTW I found the reset sequence here:  http://us.lexusownersclub.com/forums/topic/58458-one-touch-open-or-close-for-moonroof/

Worth a punt before you buy it I reckon.

[Stupot]

Useful info... thanks Jay

[ColinBarber]

6 hours ago, Jaystar77 said:

 I think they sometimes lose their calibration.

Cars up for sale often end up with flat batteries which is the cause for a re-calibration

[Rutlandlex]

23 hours ago, Britprius said:

You must remember with a hybrid vehicle that the initial braking is done through regeneration. That is the motors that are in the transmission act as generators to produce electricity to charge the traction battery thus saving energy for later use to accelerate. As you brake harder the normal braking system comes into effect slowing the car by producing heat, and wasting energy. This is probably the effect you are feeling.

The more you can use regeneration the better the MPG.

John.

Thanks for your explanation John although I do find it slightly worrying on 2 counts.  Firstly, if a child runs out in front of the car then suddenly my MPG becomes unimportant!  Secondly, wouldn't hybrids then become a great target for crash for cash scammers?  That slight delay translates into metres travelled before the brakes kick in depending on speed.

Does your GS behave in this way too?

[ColinBarber]

All Toyota hybrids operate that way. There should be no delay. If you apply high pressure the mechanical brakes operate straightaway.

[ColinBarber]

[Rutlandlex]

Thanks for the diagram Colin.  So from what I understand then the brake force should be proportionate to the pressure on the brake pedal just like any normal car then the THS-II system manages the proportion of braking power supplied by the regenerative braking and the hydraulic brakes.  Maybe I should test drive one that is in daily use rather than stood on a forecourt for a couple of months.

[ColinBarber]

Correct. When you lightly press the brakes you will see the power meter needle go down indicating regenerative braking (grey area on diagram). If you apply more pressure the needle will max out and all extra effort is provided by the mechanical brakes - it doesn't switch from one to the other, it will provide more force with the addition of mechanical brakes, and it can apply those and modulate the force in a fraction of a second.

As the generation of electricity from the motor/generator is related to speed, the amount of braking force felt is less a higher speed, hence the curve. The motor itself can generate more power than the batteries can cope with being charged so the drop off curve is quite steep. If you have a full Battery, or the batteries are too hot, the regen braking force is much less than the graph.

Some people do complain about the brake feel, and that if you gradually apply more pressure you can feel when the mechanical brakes take on most of the work. On the 400h I find it very subtle though. It is more pronounced if the mechanical brakes haven't been bled correctly, or non-standard discs/pads are used as their initial grab may be different to OEM.

At the very left of the graph you will see all white. At speeds around 5 mph or lower, all braking is mechanical - this is something you can sometimes feel, as you slow to a stop, where is does switch from one method to the other. 

As you say, it is better to drive two or three so you understand what is normal and what isn't.

[Rutlandlex]

A quick update on this.  I test drove another one on Saturday and the brakes felt much more reassuring so I think that there was a problem with the first one I drove.  Also the sunroof stopped in the closed position.  The car was in excellent condition for its age (early 2007) and I agreed to buy it on condition that the strange vibration at motorway speeds was addressed.

Buying from a private seller and he diagnosed sticking front brake caliper so he offered to replace it for free and also asked if I would like the other front caliper replacing for the cost of the caliper alone after discounts.  He has now replaced them both and taken it out for a good long run and says the difference is amazing.  Going to pick the car up next weekend 

[ColinBarber]

Excellent news. Sounds like you have found a good car from a genuine seller.