Gearbox/Engine Rumble

[Adrianjvr]

I know I have posted a similar post previously, but I am still no closer to a solution. So I'm apealing to all the experts out there for some assistance.

I have an annoying rumbling noise on the patrol when I depress the clutch to change gear and also when I depress the clutch and rev the engine while stationary (Noise generally occurs around 2000 to 3000rpm). There is no noise with the vehicle in neutral and the clutch engaged even if I put some load on the release bearing. I recently changed the clutch, pressure plate and release bearing and this did not solve the problem. Since changing the clutch I have had the gearbox out again to check the clutch, release bearing and pilot bearing and also changed the input shaft bearing. None of this has done anything to solve the problem. From my understanding this points to the pilot bearing, but I have had it checked and I would have thought it would make more of a squeeling noise at all speeds rather than a rumble between 2000rpm and 3000rpm. I must add that I don't hear the noise when the vehicle is cold so it would appear that the higher viscosity of the lubricant when cold has some or other influence. Could it possibly be the end float on the engine crank that is making this noise? All suggestions are welcome. I have spent hours on the internet browings forums to establish the cause of the noise but have come up with nothing.

[tour de frans]

Good day
The input shaft has no bearing,it is a oil-bush.
Any noise when driving in gear(load)?If so ,does the noise change with the gears?
Rdgs

[Adrianjvr]

Hi Tour de frans,

The guy who did my clutch apparently changed the gearbox input shaft bearing and said he checked the pilot bearing and said there was nothing wrong. The release bearing was changed with the clutch. I basically get a noise when I depress the clutch to change gears (all gears) and when I hold the clutch in and rev the engine (higher the revs the worse the noise). Only seems to make a noise above 2000rpm. When in gear the gearbox is quiet. If I hold the clutch in and rev the engine I can feel a vibration through the clutch pedal. Are you based in JHB? Cheers

[Peter Connan]

Hi Adrian

Frans is in the cape.

To me it sounds possible that it might be the crank thrust bearing. I would recommend getting the car on a hoist with somebody in the driver's seat. Start it and get it to make the noise, then use a long screwdriver as a doctor uses a stethoscope, by holding the handle almost against your ear while touching various possible sources of the noise. If the cause is worn engine thrust bearings, the noise should be eminating from somewhere around the middle of the block, but in this way you should at least be able to figure out whether it is engine or gearbox.

[Herrie]

It sounds like it is the thrust bearing that is making the noise. If you press the clutch in the gearbox is not turning so it can not be a gearbox problem.

Sometimes on my Patrol if I press in the clutch I hear a noise and when I take my foot of the clutch and press it again the noise is gone.

What happens when you put the gearbox in neutral? Then the gearbox input is turning but not the output.

[Peter Connan]

Hi Adrian

Looking at the pictures in the workshop manual, the thrust bearings are on the 6th (or second last) crank journal.

It also looks like it should be possible to replace them by just removing that main bearing cap, and not the whole crank. So if your oil pressure etc. are all stil OK, it might be worth just trying that.

[Adrianjvr]

Thanks for the suggestions. My gut feel is that it either the pilot bush or the thrust bearing on the motor. I tried doing a search on the internet but found no real references for either. I guess the next step is to establish if the noise is coming from the clutch or the engine.

[tour de frans]

Hi Adrian,ek het jou ge-PM
Cheers

[Adrianjvr]

I took the patrol to two gearbox specialists today to get their opinions on the noise. The first guy said it was either the release bearing or the pressure plate making the noise. The second guy said it is the hydraulic system making the noise and nothing to worry about. He mentioned that the hydraulic systems on isuzu bakkies make an even louder noise. I did search on hydraulic clutch noise and came accoss the following description of the noise of hydraulic clutch noise.

"Specifically, imbalances in the crankshaft of the vehicle engine or engine firing impulses are transmitted to the flywheel which undergoes a swashing movement, the flywheel swashing movement in turn leads to vibrations of the spring fingers of the clutch release mechanism, the vibrations of the spring fingers are transferred to the release bearing of the clutch, and the vibrations propagate backwardly through the hydraulic fluid in the slave cylinder, through the hydraulic fluid in the conduit interconnecting the slave cylinder and the master cylinder, through the hydraulic fluid in the master cylinder, and thence through the master cylinder push rod to the clutch pedal where they are experienced by the operator as vibrations of the clutch pedal. The propagated vibrations also generate fire wall buzz and pedal growl which is audible to the operator as well as a clutch roar which may also be audible to the operator."

[Adrianjvr]

I have just been reading a thread by Fiat 500 diesel owners complaining about the same noise I am experiencing. Seems their solution was to replace the hydraulic damper on the clutch circuit. Does the patrol have a damper that could have failed?