I have a knock from the back at take off.

[ld50]

I`m trying to track down this noise I got, looking through the threads kind of tells me I`m on my own, but I thought I`d try.

Last time out in the bush, I kind of heard this metallic groan which sounded like it came from the passenger side, or the rear of the truck. Eventually it turned into a chattering knock that happens most often when the truck is cold, starting off in first gear. On the road, it tends to do it when I`m starting off uphill. It doesn`t do it once I past 1st gear.
I think it even knocks once when I start it, but that doesn`t make sense, unless the noise is rebounding around and misleading me about it`s location.

I had my friend stand outside, and listen and it sounds like it`s from the back, I`m going out now to lay underneath for a while. I just can`t figure it out.

Any ideas?

 

[Bashman]

Possibly U-joint, loose driveshaft bolts or loose part in rear suspension maybe?

 

[ld50]

I have some U-joints I was planning to put in the rear shaft, but they don`t show any play right now, like they don`t appear to be messed up. Just visually and grabbing things under there isn`t giving me any leads.

I wonder if a bearing wearing out in the rear end would do this?

Anyway, I might as well put the joints in tomorrow and go over all the bolts and such to make sure everythings tight.

 

[ld50]

Well It sounds like the back, but on further inspection, it sounds like it`s from the engine or tranny. Crap, that`s bad news.

:frustrate

 

[Bashman]

That sucks Jim, I was really hoping it was just worn u-joint bearings. Keep us informed as you continue to investigate.

 

[Crankcase]

Check the engine mounts.....A bad one can knock/rattle when the engine first torques up in first gear.....

Get somebody to watch the engine as you apply power to it...watch to see if it moves side to side much, or back to front.

 

[BIG HVM]

heavy cars like this make a noise when you apply power, a slight vibrating, if you have a knock that is loud please check your wheels are on tight and then your oil levels in the diff and trans box, hope this helps.

 

[ld50]

Both engine mounts are only a couple months old, as with the tranny mount. It definitely wasn`t the U-joints. I`m wondering if it is this Carbon knock I`ve heard of, or if it had something to do with my recent switch to high mileage oil. I might just do the carbon knock remedy, and switch back to normal oil. Be a lot better if I could pinpoint the exact location of the noise!

The manual talks about worn crank bearings and things I don`t want to think about.

I got almost 200,000 kms on her, I want 200,000 more!

we`ll see I guess..

 

[ld50]

Well after work, I looked around the engine, I was worried that the mount bolts had backed off one side or something but they`re tight. It is knocking just as it starts up now too!

I`m gunna let it cool off and get the Wife to start it while I`m underneath, so I can track this down...

 

[Crankcase]

Well after work, I looked around the engine, I was worried that the mount bolts had backed off one side or something but they`re tight. It is knocking just as it starts up now too!

I`m gunna let it cool off and get the Wife to start it while I`m underneath, so I can track this down...

Don't pull a Doug though...make sure she has it in neutral first..LOL!

 

[ld50]

Well I didn`t (wouldn`t) do a Doug!

But of course, just like these things always seem to go, it refused to make the noise for start after start.



Gotta find it eventually!

 

[ld50]

Well....

-Knocks a couple times at start up
-Knocks at low Rpm with load on engine, starting off in first gear.
-Seems to happen less when the engine is warmed up

I was talking with a mechanic buddy who works in a dealership, and he kind of parallels my theories on it.

Since there is a knock at start up, it kind of rules out a problem with the tranny. It makes the sound most probably be from the engine.

This makes it either:

-a piston problem
-a crankshaft problem

The one last hope is that it could be carbon knock, but my buddy says that is a wee bit of a long shot, judging by my observations. He suggests trying the remedy anyway, it`s worth a try I guess.

Funny thing happened yesterday, I`m driving home from work, listening intently to my engine, I go around a corner and she chugs like crazy. I mumble to my self "WTF NOW?" only to realize that in my preoccupation with this damn noise I have inadvertently almost run the gas tank completely dry!
Luckily there was a station right there, so I got me some gas. LOL, gotta laugh, I have never run out of gas in my life, almost broke that record!

 

[mrboyle]

From the descriptions it definatley sounds like somehing in the bottom end of the engine. My first recomendation would be to switch back to standard motor oil. The "extended life" oils aren't much more than standard oil with additives that help swell oil seals. You might also consider running a heavier weight oil (during the warmer months).

 

[ld50]

Hmmm.

I`m excited, I finally got to hear it from outside while it was happenning and it sounded like it was from the back again. I shook the muffler around by grabbing right by the muffler and yarding on it, and nothing..

I grabbed the tailpipe and yarded on it, and found that I could make it hit the frame right near the rear tire. I pushed all the rubber deals to the side that would bring everything away from the frame more, and went for a drive And it hasn`t made the sound yet, so maybe it was that after all.

I can`t believe how much it sounded like the engine though, so I`m not gunna get too excited yet!

-oh yeah, this is what made me double check the muffler
http://www.explorerforum.com/forums/showthread.php?t=52606