Mechanics

CLUTCH PEDAL STAYS DOWN

2003 Toyota Prado

Transmission problem
2003 Toyota Prado 6 cyl Four Wheel Drive Manual 133000 miles

Prado 5 dr - normal usage, no off road, town driving average less than 20,000Km a year.

With warning, after using the clutch pedal to disengage, change gear and release, the pedal stays down and must be manually pulled up ( against pressure) to the normal engaged position. Once there it may operate normally for some time or it may again fail as before.

No external leaks
Full reservoir
When pedal is on the floor, the clutch is engaged
Happens engine cold and hot

History
at 85,000 Km first occurence of problem. Dealer changed fluid and it worked fine until 109.000 Km when exactly the same symptoms occurred. The dealer changed the master cylinder and it worked fine until 133,000 Km when after a written compliant copied to Toyota they also looked at it and determined :

Changed Master Cylinder again (no problem since now at 135,000)

Said " the clutch mechanism ( mechanical) is causing vibrations in the master cylinder seals so that they fail : recommendation Change all the mechanical clutch system ! (NOTE NO clutch problems of any kind apart from the pedal sticking down have been evidenced)

I have a problem with that clutch changeout answer as it doesnt make much sense to me ( apart from having to buy a new hi $$ clutch system from the dealer )

I think the fluid in the master cylinder is bi-passing the seals for some reason and hydraulically locking the cylinder until it can be mechanically pulled back to the correct position and displacing the fluid back to the high pressure side.

If it were the slave cylinder sticking would it cause this symptom? ( Note no leaks and a recovery of normal operation after the pedal is pulled back)

Do you have any other suggestions as to what is happening and more particularly why the repeated frequency of the problem at about 25,000KM average.

Would fluid be required to be changed before 25,000 Km in normal circumstances? ( Dealer says good for 40,000KM)

Could fluid contamination cause this problem? (No-one touches the fluid between 25,000 km events )

Thanks
Andy
Avatar
Pradouserec
September 26, 2010.




I'm not buying something.
I've never seen a pushrod to a master cylinder be positively attached to the piston.
So pulling up on the pedal would simply pull the pushrod away from the piston in the master cylinder bore.

Check for something binding the pedal under the dash.

BUT you said the clutch is engaged when the pedal is on the floor.

Buddycraigg
Sep 28, 2010.
Nothing is binding on the floor of the vehicle

I cannot comment on whether this model has a mechanical connection pedal / piston or not -I have not taken everything apart. Can you determine this from a service manual exploded view?

Yes, the clutch is engaged when the pedal is on the floor - that causes the dangerous condition.

The pedal was not loose on the floor, it was held there. The ONLY way to get the pedal back into full travel with hydraulic pressure was to physically pull it up either with my foot or hand AGAINST PRESSURE which I assumed was hydraulic.

There is a spring attached to the pedal but it is to help pedal return ( not hold it down) and to stop pedal vibrations in normal operation (dealer comment)

Andy

Tiny
Pradouserec
Sep 28, 2010.
Ok let's start with the pedal on the floor, but the clutch is still engaged.
When you pull the pedal back up, does it start working normally and you can disengage the clutch by stepping on the pedal again?
AD

Buddycraigg
Sep 28, 2010.
Also, could you tell me what US model your truck would be comparable to?

Buddycraigg
Sep 28, 2010.
Yes - once you pull the pedal up the clutch is operable as normal until the same problem re-occurs

The present day model I have read is the Lexus GX460 ( Much more refined that the 2003 Prado)

. The model I have is built in Colombia

Tiny
Pradouserec
Sep 29, 2010.
Ok, let me roll this around in my head for a while.

Buddycraigg
Sep 29, 2010.
Do you know how to bleed your clutch system if needed?

Buddycraigg
Sep 30, 2010.
Yes - No problem.

Just to be sure : I am looking for suggestions why the repeated ocurance might have happened. At this time the vehicle is fully operational following change of master cylinder and fluid at 133,000.

My concern is that this was done before ( change of Master cylinder) and 25K Km later the same thing - sticking pedal - happened again.

Andy

Tiny
Pradouserec
Oct 1, 2010.
Missed that part.

I was thinking that the problem was currently on going.

I asked if you knew how to bleed the system because I was going to have you disconnect the hydraulic line at the master, and see if the pedal will come up any easier.
I was expecting it to still be stuck down verifying the problem is in the master.

But to answer your question as to why it's happening. I can only speculate that the master cylinder is a poor design. Possibly disassembling it after the problem happens again would allow you to find the cause and perhaps come up with a workaround.
Flushing the system so you know the fluid isn't contaminated my bring some piece of mind.

Buddycraigg
Oct 1, 2010.
This is an old thread, but just in case you are still watching. I have this problem ( not repetitive ) with my Prado. At first I was confused as to why the pedal had to be pulled up against resistance, but when I was bleeding the clutch I realised the the pedal return spring has an over-centre action so from about one third of the way to the floor it is actually assisting you to press the clutch. To clarify the spring is in compression not tension and reaches it maximum compression part way down the travel after which it is pushing the pedal toward the floor.

BTW I don't buy the mechanical force going back to the master cylinder theory because when the pedal is all the way up the fluid is open to the reservoir so there is no pressure in the system.

Tiny
Predatory Eel
Dec 24, 2011.

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