Updated: Bang or thump from passenger side rear end

[jacklndn]

My '86 2.1 has developed a new noise. As I am a 'Nervous Nellie' (my mechanics words, I won't argue) I thought I would run it by the Samba Brain Trust and see if anyone has any ideas besides what's come up.

Engine is a factory crate new a few years ago and has about 15,000 miles on it.
I've driven it from Northern CA to Southern NV once (~1500 miles round trip) and it was smooth running.

Here's the backstory, apologies if it's too much. No one's ever accused me of being concise:

A week or two ago the engine developed a power drop in first gear coming off a stop.
I read Samba! I found a loose vacuum hose and reconnected it. Problem solved.

At that same time, I replaced the air filter. The old one was dirty. I didn't get the topmost far right clip in place and the air filter was slightly loose; not secured to the body.

Problem surfaces: After driving at speed, and coming to an idle at a signal, the car stuttered, maybe twice, with a loud bang. Another mile, idling at a signal, stuttered once, again a loud bang.

I opened the engine compartment, wiggled the air cleaner and got it attached to the body.

Now I'm getting a 'regular - intermittent' (it doesn't happen every at idle, but often) single stutter with a thump. Always from the passenger rear side of the car.

I took it in to my mechanic, he drove it, said something feels the slightest bit rough, but nothing dramatic. He looked under the car and commented that the exhaust pipe is very close to the bumper (it's less than 1/2 an inch away) and that anything causing the engine to shudder severely enough would make the exhaust hit the bumper and make the thump sound.

He said it could be a number of different things, from spark plugs to a loose motor mount, but we won't know until it's up in the air and he's had a chance to look at it.

The van is going in to him tomorrow. This mechanic is good, real good, and I trust him completely. I just wanted to run this by the Group Mind and see if anyone has any other ideas of possible causes to look for.

I will be driving about 1500 miles round trip at the end of next week to be with my Father for his 87th birthday, and I want the van to run smoothly.

Thanks, all!
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1986 Westy GL 4 spd

[insyncro]

Worn motor mounts allowing the idleing engine to shack and the tail pipe is making contant with the rear vallance.

Have the wrench check the timing too.

[Wildthings]

The only way I can see that having the air cleaner attaching clamp loose would make any difference was if the S boot was either cracked or its clamps not tightened down. Either could cause a bad air leak that might be worse on decel and/or if the engine mounts were bad.

[jacklndn]

Turned out to be a crack in the exhaust pipe just before the muffler. The muffler was aftermarket, and combined with extra flex from the crack and a close tolerance installation, a rough running engine let the tailpipe resonate until it built up enough movement to hit the valence.

Needed a complete tune up. I've not tuned the car since I got it in August, about 4000 miles I've put on it. The points and cap were burned, and the plug wires were corroded.

It's running much better now. The muffler/ pipe fix should be less than $50 at a nearby shop I know.

Thanks for the input.
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1986 Westy GL 4 spd

[jacklndn]

Well, I thought it had something to do with the engine, or exhaust, but three times now the clunk has happened after the engine has been off for 10 to 20 seconds.

Any ideas? Anyone, anyone?
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1986 Westy GL 4 spd

[IdahoDoug]

OK, that last post bears explaining. Vehicle and engine at dead stop, parking brake on and then......clunk? Same clunk?

DougM
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Two fully locked 80 Series LandCruisers. 2013 Subaru Impreza boxer. 1990 Audi 90 Quattro 20V

[jacklndn]

[danfromsyr]

check your rear trailing arm lower spring perch for rusting right the #$%^ off..

unbolt the bottom shock bolt (make sure it's not loose 1st)
then jack up the van till the wheel is at full droop and remove the spring..
it's fairly easy and safe todo.. just don't drop van on yourself. use a stand/solid blocking for safety.
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VW Club of Central New York SPRING VW GTG
Upstate NY 2013 VWCCNY events
NY State VW Camping 2013 season events

[IdahoDoug]

So, parking brake on? Could you also say if it was in gear, or in neutral? The spring perch is an interesting lead, but if it's cracking off you would be able to see with a good flashlight vs dealing with rusted shock bolts, jacking, etc.

How would you describe the sound - heavy deep clunk, or lighter metallic clang? Does it happen if you reverse into a parking spot also, or only when you stop the van while rolling forward? Does the van move even the faintest bit when it happens?

DougM
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Two fully locked 80 Series LandCruisers. 2013 Subaru Impreza boxer. 1990 Audi 90 Quattro 20V

[jacklndn]

[jordauto]

Last year my 88 westy was making a loud squeak/clunk noise from the rr corner after shutting it off with a warmed up engine.It took a while to find but it was the wire clip that holds the plastic coolant pipes up at the rear.The pipe was expanding and contracting and sliding on the clip.I applied a bit of silicone grease and the noise has been gone ever since.

[IdahoDoug]

One fast way to know would be to shut it down as normal, then get out and jog to the gas cap and open it. Big woosh = possible candidate. Or do it when it's running, I guess. At idle, there is maximum vacuum being produced, at full throttle, less or zero. So that may explain the timing of sitting at a stop light at idle. And when shutting down you likely idle a bit as you're parking. So, possible candidate right there.

DougM
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Two fully locked 80 Series LandCruisers. 2013 Subaru Impreza boxer. 1990 Audi 90 Quattro 20V

[bigsteve141]

Doug, Just saw your post. I'm a little confused. I played around with the line coming from the filter valve on the recovery tank (i'm assuming thats the charcoal filter housing??--correct me if im wrong!)

At idle there was no draw on the end of the fitting, at anything above idle, there was vacuum on the tube. I didn't feel this first hand since I was running the throttle, but this is what I was told.

Are we talking about the same thing?

[Luckyphil]

Check your charcoal canister, they can make a bang when clogged. Take it off and blow some air through. It is located on the passenger side rear just above the wheel. It looks like a black cylinder about 8 inches high.