Knock/hit and Play when fast releasing and pushing back the GAS pedal

[pradolover90]

Hi Prado Lovers,

When fast releasing and pushing back the gas pedal I can hear Knock/hit sound and feeling big play, this happens on any speed, when driving 10km/hr, or 30, or 80km/hr, (feels like something has big play - maybe transmission, maybe engine, maybe front suspension - not sure exactly), if I am Selecting Central differential lock then this sounds and play go away... (I am not driving with CD locked on roads, I locked it just for testing purpose)

What Can be the issue?

By the way this play and hit becomes very big when selecting L (Low gear). (when fast releasing and pushing back the gas pedal)

Prado 90, 3.0 Turbodiesel Automatic Gearbox.

As I mentioned when CD is locked I have no issues - can we say that this is not gearbox chain related issues for sure? or this still might be the stretched chain issue?

Thank you.

 

[Shayne]

I'm reminded of the many transfer box threads on here but i cannot remember the issue presenting in an auto before ?

 

[AdventureWagon]

Sounds like the trans is slipping (common failure mode on most autos) but doesn't correlate with locking the centre diff.

 

[pradolover90]

@BobMurphy can you please read this thread and provide feedback please?

 

[BobMurphy]

Looking at your other posting, the rotational play in the Transfer Box companion flange doesn't look unusual at all.

So, some questions:-

1. Has this just started or is it the result of gradual wear ?

2. What's the mileage ?

3. Do you off-road it at all, has it seen any extreme hill climbing/ rock crawling etc. ?

4. Do you tow - and if so, what weight ?

5. Is it regularly serviced, if so, what was the Transfer Box oil like when drained?

A slack chain COULD be caused by worn bearings on the Transfer box front output shaft. That results in an oil leak, a worn oil seal and then the water & muck get in and the box fills with mud ! I have pictures if you're interested . Looking at the oil will tell you.

Locking the centre differential removes play between the front and rear propshaft drives and tightens-up the Hi-Vo chain so that points to the issue being with the Transfer box. These trucks are getting old and play in the transmission is to be expected. If the drive isn't 'skipping' I'd live with it as fixing it (i.e. a Transfer Box overhaul) can be expensive. If it's your 'baby' though, you may want to take that route.

Answers to the above will help us narrow-down the problem.

Bob.

 

[BobMurphy]

And another thing . . . .

What are the Hardy-Spicer joints in the propshafts like, once play starts it can develop rapidly (I've seen them with no needle rollers left )?

Bob.

 

[pradolover90]

1. Has this just started or is it the result of gradual wear ?

Gradual Wear, first time I have noticed it 1 year ago.

2. What's the mileage ?

280 000KM

3. Do you off-road it at all, has it seen any extreme hill climbing/ rock crawling etc. ?

Yes, few extreme hill climbs and off-roading sometimes, especially last 8 months...

4. Do you tow - and if so, what weight ?

Never

5. Is it regularly serviced, if so, what was the Transfer Box oil like when drained?

All (engine, auto gearbox, transfer box, front and rear differential) oils were changed regularly as it was recommended in manual, Transfer box oil was in normal condition, normal color.

have pictures if you're interested

Yep interested

Experiment1:

I have removed front Drive shaft, locked Central differential, drive few KM and car was driving like new, no Knock/hit or Play

Experiment2:

I have removed rear Drive shaft, locked Central differential, drive few KM and all old symptoms came back - Knock/hit or Play

What you think about this? @BobMurphy

 

[Shayne]

Take a look at your lower wishbone arms . Took me ages to work out that worn bushes allowed them to shunt back and forth not half an inch against the frame .

Could see it but couldn't replicate the knock while parked jacked up whatever , i could move them only a little with a crowbar but i don't weigh a ton and couldn't whack it with 100 odd horsepower .

 

[BobMurphy]

Well, driving with the front prop removed (& diff locked) proves that the centre differential is OK. I was thinking that this could have been damaged by 'extreme off-roading' as I have seen them burst.

Driving with the rear prop removed puts all the drive through the Hi-Vo chain. Clean oil in the Transfer Box rules out extreme wear in the output shaft bearings so the finger of suspicion points at the chain.

It sounds as though a Transfer Box rebuild is on the cards but don't just replace the chain, change the bearings as well as small amounts of wear can add up.

Will you be doing this yourself ?


The pictures I mentioned were of the inside of a Transfer Box which had filled with water & dirt thanks to a failed front oil seal. Thankfully you won't be faced with this . . . .

It should, of course, look like this .

Good luck with it.

Bob.

 

[pradolover90]

@Shayne My lower and upper wishbone arms rubbers both have play - I will fix them as well. Do you have experienced same Knock/hit sounds before you fix them?

@BobMurphy thanks for image, thanks god my is in good condition.

Will you be doing this yourself ?

Nope I will fix it in service.

Thank you all for you help, If I will have any progress I will let you know.

 

[Shayne]

In truth i can't much remember , there was an occasional knock and i was convinced something was hitting the frame . Lower wishbone bushes were still tight and i'm sure i could have ignored the problem for a long time to come but i had to know . New lower bushes and i ever heard the knock again .

It should be noted that this was my 1kz-te 90 series and not to be mixed up with the transfer box knock suffered by my 1kd 90 series .

 

[pradolover90]

Hi again Guys, You want believe...

I have change the chain (it was starched) and installed brand new Toyota chain and guess wat... Now this Knock / Hit sound increased twice....

This drives me crazy...

Only 2x things left now - front Differential and front drive shafts, one of this two might be the issue I think..

Both front drive shafts have some play - especially the right one, it has more play then left one.
OR it might be front differential satellites....

What you think guys? @Shayne @BobMurphy

Thank you

 

[BobMurphy]

I've been having a think about this and nothing obvious comes to mind, so a few questions:

Did you compare the old and new chain before the new one was installed, I noticed the last time I bought one that the part number had changed (it still worked) but was the new one definitely smaller than the old one?

Were the bearings changed in the Transfer Box?

If you remove the front propshaft is it still quiet and smooth on the road?

If (with both propshafts in play) you go on and off the gas - can you detect where the noise is coming from and does the gear lever and/or Transfer lever move as you go on and off the gas?

The knock you hear (we call it 'shunting') can come from the suspension as Shayne has already mentioned, most likely from the rear axle trailing link bushes allowing the axle nose to rise and fall - but driving on the rear axle alone seems to disprove this.

This points to the front suspension - upper & lower wishbone bushes, upper and lower steering ball joints, shock absorber mounts, steering rack mounts, anti-roll bar mounts and drop links.

Play in the transmission can build up in a number of places - front CV joints, front tripod bearings, propshaft UJs, propshaft slip joints, splines between front driveshafts and wheel hubs (I have known one strip) and, of course, the differentials

Don't forget the body mounts and engine and transfer box mounts - they can fail but look normal when at rest.

The problem with all this is that the forces required to cause the knock are greater than we can manage with a pry bar. Tracing this is not going to be easy.

I'm afraid I can't point to a probable cause and therefore it will be a matter of elimination - checking each probable cause in turn and eliminating it as the cause.

That's the best I can do at the moment but I'll give it some more thought.

Good hunting.

Bob.

 

[pradolover90]

Hi again @BobMurphy and thank you one more time. Sorry for the big delay I was out of the country.

Did you compare the old and new chain before the new one was installed, I noticed the last time I bought one that the part number had changed (it still worked) but was the new one definitely smaller than the old one?

No new one has exact same size.

Were the bearings changed in the Transfer Box?

Nope - the mechanic says they are in good condition.

If you remove the front propshaft is it still quiet and smooth on the road?

Drives Like a New car, no issues...

If (with both propshafts in play) you go on and off the gas - can you detect where the noise is coming from and does the gear lever and/or Transfer lever move as you go on and off the gas?

Nope, they do not move. Feels like Noise coming from the front bottom part of the car. The dashboard vibrates a little - but if you put a hand on the dash during this you can feel a much more strong and more powerful HIT - feels like something big moving, like an engine (but it is not engine 100% )

Play in the transmission can build up in a number of places - front CV joints, front tripod bearings, propshaft UJs, propshaft slip joints, splines between front driveshafts and wheel hubs (I have known one strip) and, of course, the differentials

Everything was checked except the differential and they have no issues.

Don't forget the body mounts and engine and transfer box mounts - they can fail but look normal when at rest.

I have replaced them a few months ago - they are new.

On these days I will remove and open the front differential and will check if everything is ok inside of it and let you know. This is the only part I have not checked yet...

One Strange thing I have noticed - If I rise tire pressure to 60psi then this knock/hit 90% goes off - it is almost impossible to feel it. On the normal pressure 30 Psi it returns back. - What do you think about this?

I am also planning to mount a GoPro camera under the car and maybe this will helps me to find the issue.

Thank you.

 

[BobMurphy]

A strange one that. Very high tyre pressures reduce the rolling resistance so there will be less drag on the transmission and chassis/suspension mounts, you will probably find the same phenomena if you drive on ice.

Its all pointing to play in the suspension mounts to my mind, probably nothing to do with the differentials.

I'm afraid you will have to keep replacing bits until you find it.

Let us know how you get on.

Bob.

 

[Shayne]

The front wheels get more power so it takes a fraction of a second for the rear wheels to catch up is how i imagine it .

The tiny discrepancy is soaked up by rubber bushes when all is new but 20 years of wear stretches that discrepancy so it becomes noticeable .

That i can still feel it in a truck that has had in my ownership all new bushes and suspension etc etc etc leads me to believe the transfer box chain has stretched .

However without trying to the mrs and i have subconsciously learned to drive without making the noise , best i can explain because no conscious effort goes into it is we release the clutch a tiny fraction slower at the bite point while changing up a gear , slipping the clutch i suppose .

In your case though I think i would start at the rear by replacing the panhard and trailing arm bushes . Simple things first is the golden rule .