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  #1  
Old 10-06-2001, 03:11 PM
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Location: Tucson, Arizona
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Guide Rod Noise & Timing Chain Wear Limits

Greetings All,

Just a few quick questions relating to my '80 300TD
The first question relates to the clunking sound that occurs when braking at a slow speed, that I am told could be the guide rod or as others have called it a strut rod bushing that has failed and allows movement, hence the clunking sound during the end of the braking motion. Which end of this guide rod is causing the movement? Is it the firewall end or the wheel end? Has anyone replaced these bushings at home and if so what is the difficulty level and or special tools required to complete the job?.

The second question is quite simple. While adjusting the valves a few weeks back I checked the timing chain for stretch, visual alignment of timing marks only, not using a dial indicator. Rough guessing it appears about 4 degrees off. What is considered allowable stretch on the timing chain before it has a negative effect on performance. Also, would an offset woodruff key of 4 degrees show an appreciable difference in performance.

Thanks for any input or suggestions you can provide.

Charles
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  #2  
Old 10-07-2001, 10:00 PM
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Come on guys give me some help here

Don't make me beg!
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  #3  
Old 10-08-2001, 08:22 AM
LarryBible
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Can-do,

Glad to see you still keeping those MB diesels on the road.

Have you raised the front of the car with the wheels suspended and started shaking and prying on everything to find the loose part. I have never had a track bar mount fail, which is kind of a mystery given the force it must deal with. If it is the track rod, you should be able to tell by shaking the wheel fore and aft. If it must be replaced, you'll want to check everything and replace whatever is needed while it is apart. To replace the track rod, you have to remove the spring, so you are far enough into it, it would be the time to replace ball joints or whatever might be loose.

I do understand aligning the marks to check the chain stretch. Even though it is not totally scientific, it does give an idea about stretch. If you see what appears to be four degrees, I would think that it is time to roll in a new chain. The chains are expensive, but it's not too big a job to roll one in, and it is much less expensive and less work than the consequences. I would think that you could take time to prepare and not rush into doing it though.

Best of luck,
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  #4  
Old 10-09-2001, 02:42 AM
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What is the clunking sound during braking?

Greetings Larry,

All the posts I have read show the strut rod bushing or the guide rod bushing to be the culprit if there is a clunk in the braking force toward the end of the cycle, isn't this true? The other item concerning the timing chain. Is 4 degrees really considered considerable stretch to roll in a new chain when the MB service manual shows offset keys for up to 16 degrees offset? I'd think unserviceable would be beyond that point. Is this not so?

Charles
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"Tell me and I will listen, Teach me and I will learn, Show me and I will accomplish, Involve me and I will succeed."
'84 300SD 256,000 Gold on Brown (Mileage Award)
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  #5  
Old 10-09-2001, 07:34 AM
LarryBible
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Charles,

Yes the offset keys are available, but; remember, the four degrees you are seeing is not a scientific, dial indicator type measurement, it could be more, or it could be less. Additionally, in my way of thinking the worst thing about a stretched chain is not the fact that the cam and pump timing are off, but rather the risk of chain breakage. As these pins and bushings wear, the risk of timing chain breakage increases. On the other hand, this is a double row chain which is quite strong. A broken chain would probably be the result of a broken guide or some other event jamming the chain.

Changing the chain is a personal decision. Although it PROBABLY will not break, the ease of changing it should be weighed against the catastrophic effects of a broken chain.

Best of luck,
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  #6  
Old 10-09-2001, 12:05 PM
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Take it from one who knows, you don't want your chain to break! I'm still working on that one. I've got about $900 in parts alone beacause of my chain break.

I think the replacement IWIS chain I got was less than $50. Cheap insurance.

Roll in a new one.
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