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Exhaust Vibration


fhubler

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Question for the group.  Under certain circumstances while at a stop with the clutch out & the fluid drive engaged, we get a vibration toward the center of the exhaust system strait pipe about midway between the muffler & the kick up over the rear axle.  It is like the kind of vibration you get in the middle of a recurve bow string after releasing an arrow.  The previous owner had the exhaust recently replaced.  If I put it up on jack stands, leave it idle with the parking brake on & the clutch engaged, it will stop if I put some pressure sideways on the strait part of the exhaust with my foot.  Any ideas?  Would a short flex pipe right after the down pipe like a modern car often has be a possible solution?  Could it be the new style hanger they put on?  It will do it maybe one time out of ten when coming to a stop on the road...

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I think that your exhaust pipe is hitting something as it vibrates with the car is in gear, the clutch out and the brakes on.  

Your muffler pipe hangers incorporate a flexible strap to isolate vibrations.  Maybe the hangers are not installed correctly.  

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I have to agree with DonaldSmith. Mine does the same thing only under acceleration from a stop sign. On my "to do" list!

Maybe when they replaced the exhaust system they put one of the hangers in a bind?? Might try loosing then one at a time and see if it relieves any tension on the hanger or pipe. That's my next try.

Best of luck.

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It's not hitting anything - I jacked it up & crawled under there to have a look.  It vibrates so much, you can see it - like when Bugs Bunny runs into a closed door...

Forum Bugs Bunny.jpg

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I'll tell ya, though - after driving a Model A for 3.5 yrs., the Dodge is like sitting in the library.  When you start hearing a noise in the Dodge, you think, "something must be wrong...", when you stop hearing noises in the Ford, you think, "something must be wrong..."

Forum A Driver View.jpg

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I know that fluid drive cars have specified idle speed range , but have you tried changing your idle rpm to see it it changes anything?  I guess the bigger question is what is causing the vibration.  Have you checked the condition of your motor mounts?  A perished mount could cause a angle stress on the exhaust plumbing.  Put a piece of 2x4 or similar and jack each side of the bell housing up a quarter inch and see if that changes the equation.  Then do the front and lift a bit on the oil pan using the wood to spread the load.  Do you have an engine misfire at idle?

Edited by greg g
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Hello Greg G.

  No misfire. Had not thought about the motor mounts. Good idea.

We really haven't had the opportunity to spend much quality time with our new girl. Have several projects going at the same time and trying to get caught up as we speak. I am going to try to get into my Buddy's service station and put it up on a rack so we can do a full under side inspection. (maybe get a few pictures of her bottom?) :wub: Anyway, all good suggestions and I will follow up on all of them.  

  Still trying to sell a couple of items. Right before the holidays is a bad time for selling used cars and boats but we need the room in the shop!!!

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12 hours ago, fhubler said:

when you stop hearing noises in the Ford, you think, "something must be wrong..."

Kinda like a Harley.. One night a bunch of us were riding across Oklahoma, temps in the low 30s, I'm trying to keep my eyes open after 10 hours riding and thinking my old shovelhead sure has a lot of pep, must be the cold night air.....but what's that whine?? DUH!! I've run the last 25 miles in third gear!! :D

Edited by MackTheFinger
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20 hours ago, greg g said:

I know that fluid drive cars have specified idle speed range , but have you tried changing your idle rpm to see it it changes anything?  I guess the bigger question is what is causing the vibration.  Have you checked the condition of your motor mounts?  A perished mount could cause a angle stress on the exhaust plumbing.  Put a piece of 2x4 or similar and jack each side of the bell housing up a quarter inch and see if that changes the equation.  Then do the front and lift a bit on the oil pan using the wood to spread the load.  Do you have an engine misfire at idle?

Thanks, Greg.  I did not think of the mounts.  They are original, like most other parts of the car, and have dry rot cracks.  I do plan to replace them due to age.  We'll see if that changes anything.  I think checking the relationship between engine alignment & the vibration makes a lot of sense because the angle of the car when I come to a stop seems to make a difference.  I will wade into the things that need attention on the car after Christmas and see what I get done over the winter.  Motor mounts might make sense when I have everything apart to change the water distribution tube (if I have any sanity left after that job).

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Greg, here's why I think a new water distribution tube may be in order...  It's the original one in there, along with the original water pump.  The engine warms up at a normal rate & runs steady at 195-200 deg. in operation at any ambient temperature.  An IR temperature gun shows higher temperatures toward the rear of the water jacket (10-15 deg).  The dash gauge & the IR gun show the same temperature at the sending unit (measuring the same temperature from the same location).  The previous owner replaced all of the hoses, the belt & had the radiator professionally cleaned & pressure tested.  The radiator is providing about 20 deg. cooling at idle (195 at the inlet, 175 at the outlet).  I do not suspect any timing issues with the engine.  The heat riser is missing the counter weight & is being held open with a hose clamp.  That will also be rebuilt.  The engine fires right up under all conditions (still 6V + ground), idles smooth & produces smooth, even power through the rpm range.

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The true purpose of the tube is not general engine cooling.  It is designed to direct coolant upwards to assure proper flow to the valve seat area.  The slots in the top of the tube are shaped to provide that flow and the taper helps the rear slots provide the same volume as the fronts get.  Use your IR sensor to check the area of the block above the valve chamber covers and see what that tells you.  

If your tube isn't blocked with rust or scale and the top slots are intact, it likely doesn't need messing with. It is critically important for the exhausts valves as they only get cooled when closed and seated, the intake valves get cooled when opened by the incoming fuel air charge.  Exhaust valves work under much harsher conditions which is why Chrysler decided to provide hardened seats, and lesser brands did not.

Conspicuous through its absence is any semblance of a similar device in the Ford engine. They have a hole, but no tube.

6cg0001.jpg

Edited by greg g
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8 hours ago, greg g said:

The true purpose of the tube is not general engine cooling.

Really???  So, according to you, this quote (below) from the Tech Tips section of this forum is erroneous?

"Water Distribution Tube 
  
The water distribution tube provides a vital function in cooling your engine. It directs cooling water directly form the water pump to the upper block and valve area. Generally it is removed for inspection when an engineis overhauled, and replaced as required. However, in my experience, many production rebuilders do not perform this repair because the tube is rusted in place and difficult to remove. Failure to replace a rusted out water distribution tube will certainly lead to hot spots in the block and future problems. "

 

 

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