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BobMurphy · Posted: Thu Feb 16, 2012 22:47 Post subject:

werminghausen · * Joined: 05 Feb 2012 Posts: 27 Location: Muscat Oman

Bob: That is what I thought. No access to the clutch bearing and anyhow there is not much that can really go wrong.
Thanks for the pics and diagram. This really helps me understand

Well, as you said, the banging was there before the clutch was changed. I just hope that the shop has done the job right and exchanged all parts that were worn. But there is no guarantee.
In this country many things don't go according common sense in a western sense. So at this point anything is possible even if the shop was the best place in town.
If the shop did a good job and the banging was there before and after in pretty much the same way then the cause might not be the clutch.
if it is not the prop shaft and differentials... then only place left is the gearbox....uhhhh..bad question. I fear I won't go that deep down.

Is there anything that could wear inside the gearbox that might cause the banging?
Do you think if I did testing in HL and LL positions there is a way to narrow things down? I'll try if shifting in HL and LL makes any difference.
Thanks so much for your help
Martin

BobMurphy · Posted: Fri Feb 17, 2012 11:32 Post subject:

werminghausen · * Joined: 05 Feb 2012 Posts: 27 Location: Muscat Oman

Bob,

With the car stationary: (and gear in H, not in HL / LL)

Do you get a 'bang' when engaging first gear ?? NO! I don't think so.

Do you get a 'bang' when the clutch starts to bite on take-up ?? NO! No bang from start to first gear. It bangs when clutch bites shifting 1/2, 2/3, 3/4, less at 4/5 shift,
bang is harder if speed difference of engine rev and output is higher ... bang is less when I coast a second with clutch pressed to match the engine revs and road speed (waiting for engine speed to go down, then shifting slowly and releasing clutch slowly...that is what bus drivers do when shifting gears in an ancient manual bus.. I see this here in Oman).
Another detail on down shift: There is no bang when when car is on speed and I shift down to slow down the car no matter how fast I release the clutch, I believe.
So the speed difference comes into play only one way.

Do you get a 'bang' when the car starts to move ?? again NO in first gear. Maybe this is because the clutch is engaged slowly typically at start up.

"My '95' has about the same mileage as yours. I get a 'clonk' from the transmission when shifting 3rd to 4th and 4th to 5th on the road, unless I'm careful to match the engine revs and road speed. I think that's normal given all the components in the transmission. It certainly isn't a 'bang' and I don't get noises associated with the clutch action. "
Why is there no clunk from 1/2 and 2/3? What is your explanation of this clunk?

I'd love to send you a video/sound. Would be much easier than words. But I am not a video gig. Don't know how to do this properly.

I'll do test shifts in HL and LL gear.

Martin

BobMurphy · Posted: Fri Feb 17, 2012 20:24 Post subject:

BobMurphy · Posted: Sat Feb 18, 2012 1:19 Post subject:

Martin,

Wonderful things hot baths . . No wonder Archimedes had his 'Eureka' moment in one Laughing

.

There I was, up to my neck in hot water, thinking about gearboxes (well, what else Shocked

) when it dawned on me that I once had a similar knock in a car almost 20 years ago.

I used to tow my daughters' horses with a Volvo 240 Estate. One day we went to a local show that entailed driving up a steep, rutted farm track. It was quite a haul for the Volvo and half way up I suddenly heard a bang, followed by a knocking.

Looking at the car / motor I couldn't see anything wrong but, when changing up or even causing it to pull hard there was a knock.

To cut a long story short, the nearside engine mounting had sheared - the rubber block had become un-bonded from one of the metal mounting plates. The result was that when under load, torque reaction caused the motor to tilt and the cam box was hitting the brake master cylinder.

On the over-run it simply compressed the broken bits together and everything was normal.

New engine mounts cured it.

Does this sound familiar Question

You are getting a 'bang' when changing up, but not when changing down.

The 'bang' can be heard/felt through the dashboard.

I think at very least your L/H engine mounting should be looked at. It may not be broken but I guess its hot where you are and that can affect the rubber.

There isn't much room between the clutch bell housing and the transmission tunnel in the bulkhead. I suspect there is enough movement in the motor for something to touch under load.

That would explain why changing the clutch didn't fix the problem and why there are no other symptoms pointing to transmission problems.

I'll await your response with great interest.

Hopefully this isn't just another 'wrong tree' to be barking up Rolling Eyes

.

Cheers.

Bob.

werminghausen · * Joined: 05 Feb 2012 Posts: 27 Location: Muscat Oman

Excellent idea Bob! under hot water.

I'll be very eager to find out about the engine mounts and maybe transmission mount? I hope I'll find and get access to these parts.
Best, Martin

BobMurphy · Posted: Sat Feb 18, 2012 20:14 Post subject:

werminghausen · * Joined: 05 Feb 2012 Posts: 27 Location: Muscat Oman

Hi Bob,

I tried to check the engine mounts. They seem to be okay from what I can see. I could not move the engine with rocking the thing with bare hands. I'll try rocking again when engine is cold. Engine was a bit hot when I tried.
to move it. Didn't pop corks...yet. Not sure what to do if it is not the mounts? Would you replace them anyway?
Martin

BobMurphy · Posted: Wed Feb 22, 2012 19:33 Post subject:

werminghausen · * Joined: 05 Feb 2012 Posts: 27 Location: Muscat Oman

Hi Bob

I am also running out of steam. Your observation is sharp. The bang is torque related and only at upshift.
When the shift is done there is never a bang....uphill...full torque...nothing. Does this tell you that it is not the rotating engine causing the hit?
I am getting paranoid somehow because it is probably something very obvious before our eyes and we can't see it. You are absolutely right here too.
I was thinking today if there could be a fault in the clutch engagement hydraulics?
I got the Haynes manual yesterday. Saw that there is a clutch slave cylinder. Could there be a fault in this part?

Question: If you shift and release the clutch very sudden (fast) in your Prado...so that it snaps...is there a bang?
Martin

BobMurphy · Posted: Fri Feb 24, 2012 0:35 Post subject:

Martin,

It doesn't sound as if there is a fault with the clutch slave cylinder. You say that the clutch action is normal and a cylinder problem wouldn't happen only on upshifts. Its a simple hydraulic system (with a tortuous pipe run Rolling Eyes

).

I am not aware of a 'bang' if I release the clutch too sharply. A bit of a clunk from the transmission and a lurch but that is all.

Another possibility is worn bushes in the upper and lower rear control arms. If they are slack the axle can twist under load (and un-load) and the slack in the rod eyes can produce a knock. I don't think it would cause a rattle in the dashboard though.

Have you had a look at them while you were underneath ??

The upper ones can be seen here (with new orange bushes fitted).

While you are underneath, check the steel 'towers' that the upper bushes attach to. They have been known to rust and become detached from the axle. I doubt that this has happened where you are but check them just the same.

Here is a highlighted diagram, the Control Arms are parts 48710 and 48720, but also check the bushes and mountings in the Panhard Rod (lateral stabiliser) Part No. 48740.

I really don't think its those items, but I'm clutching at straws now Rolling Eyes

.

Bob.

werminghausen · * Joined: 05 Feb 2012 Posts: 27 Location: Muscat Oman

Thanks Bob,

I'll check the bushings of the upper and lower CAs at rear axle. However I think I would be able to identify a clunk from worn bushings in the rear.
The bangs are clearly located in the front so that not only I can hear the banging sound but the entire dash is shaking.
The slave cylinder is a no go you are saying. Is there a way to adjust the speed of clutch release and travel of the clutch pedal?
Martin

BobMurphy · Posted: Sat Feb 25, 2012 12:15 Post subject:

Martin,

There is no adjustment on the clutch action, though it might be possible to adjust the 'throw' of the pedal. Its not power assisted as it is on the '80 Series'.

You could try bleeding the hydraulics in case you have air in the system. It should be smooth and easily controlled on release.

This is all very puzzling . . .

Has any other work been done on the car recently (before you acquired it) ?? I'm wondering if something is loose somewhere under the dash.

One would hope that with the clutch being replaced all gearbox mountings and clutch fittings would be good. As the 'bang' was there before and after the clutch change it rather points to it being caused by something else.

We'll just have to eliminate one thing at a time.

Are there any other Landcruiser owners nearby who could listen to it and help pin it down ?? Diagnosis by proxy is notoriously unreliable Laughing

Bob.