Beemon

Hard shaking 60-70 mph: is this the end?

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I cam up the Lewiston grade the other day (max 7% grade) and there was a strong shudder/vibration between 2500 and 3000 RPM (62-71~ MPH). I can't replicate it in Low, so its not the driveline. Its not the ignition because after 70+ MPH it smooths out. It does it when going around a corner, so its not the drag link. I also haven't lost any balancing weights on the wheels so its not that either. I'm thinking bearing clearances or ring clearances? It's only under load, the vibration or shudder diminishes when cruising. Any ideas?

Edited by Beemon (see edit history)

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I'd look at the transmission before any engine issues, as long as you have eliminated fuel or spark.  Engine bearings or ring issues present themselves differently than what you are describing.

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How are all the engine/transmission mounts?  Can you replicate the shudder in neutral as the engine revs?

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29 minutes ago, Beemon said:

Its not the ignition because after 70+ MPH it smooths out.

I wouldn't be too quick to rule out the ignition system. Usually a weak ignition system, especially bad plug wires, will show up when the engine is under a load at lower RPMs. The miss/shudder disappears when the transmission is shifted to a lower gear because RPMs go up and the load on the engine is reduced.

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1 minute ago, Ronnie said:

I wouldn't be too quick to rule out the ignition system. Usually a weak ignition system, especially bad plug wires, will show up when the engine is under a load at lower RPMs. The miss/shudder disappears when the transmission is shifted to a lower gear because RPMs go up and the load on the engine is reduced.

 

But if its tested at the same RPM, surely the issue would also exist in Low?

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21 minutes ago, Beemon said:

 

But if its tested at the same RPM, surely the issue would also exist in Low?

Not necessarily different load on it 

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33 minutes ago, Beemon said:

 

But if its tested at the same RPM, surely the issue would also exist in Low?

You would think so but that's not always the case if the ignition is the problem.  As 1956322 said, it is the load that causes the problem. Not the RPM.

 

Assuming you have an automatic Try this... drive around to get the engine up to normal operating temperature.  Then, in a safe location, apply the brakes really hard and press the accelerator down to put a heavy load on the engine. See if the engine starts missing/shuddering as you described earlier.

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23 hours ago, Ronnie said:

You would think so but that's not always the case if the ignition is the problem.  As 1956322 said, it is the load that causes the problem. Not the RPM.

 

Assuming you have an automatic Try this... drive around to get the engine up to normal operating temperature.  Then, in a safe location, apply the brakes really hard and press the accelerator down to put a heavy load on the engine. See if the engine starts missing/shuddering as you described earlier.

 

I did the test, nothing to note when stationary. There was a small whine from the torque converter.

 

6 hours ago, old-tank said:

Uphill and around corners?  check transmission fluid level.

 

I should have checked it today but I'll definitely check the dipstick tomorrow. That's another issue. When I pull the transmission this summer to replace hopefully just the rear main seal, I also need to pull the transmission and replace the front seal as well. Although I had documentation that the front seal has been leaking, the transmission shop would not fix it because the engine was also leaking and that it was "just engine oil".

 

Quote

Intake valve leaking...sticking or burned.

 

I would surely hope not after paying money to have the heads rebuilt, but I would not put it past my luck.

Edited by Beemon (see edit history)

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@Beemon  Was this a one time event? Or could you repeat it under the same conditions?  And thinking about the conditions it did happen under,  was it a steep incline?

 

I ask because it sounds like a bad gas event to me.  Either some water or something else. 

 

Here's an off the wall thought.  I can't remember, but did you install one of those glass bowl fuel filters?  If so, I wonder:  if you were on a steep incline could the angle of the bowl and the rate of fuel usage, have caused contaminants in the bowl to be sucked into the fuel stream? 

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9 hours ago, JohnD1956 said:

@Beemon  Was this a one time event? Or could you repeat it under the same conditions?  And thinking about the conditions it did happen under,  was it a steep incline?

 

I ask because it sounds like a bad gas event to me.  Either some water or something else. 

 

Here's an off the wall thought.  I can't remember, but did you install one of those glass bowl fuel filters?  If so, I wonder:  if you were on a steep incline could the angle of the bowl and the rate of fuel usage, have caused contaminants in the bowl to be sucked into the fuel stream? 

 

John, I've had a glass bowl fuel filter on my car since 2015 with zero issues. I might try changing the filter and see if the condition goes away. I'll also check the inlet filter on the WCFB to make sure nothing has it stopped up. 

 

The transmission was 2 quarts low, but the shuddering and shaking is still present. The issue is repeatable and is on flat and slightly inclined roadways. I might do some more short distance highway driving to confirm the shaking/shuddering is still there after filling back up, but it still felt present around town on the hills.

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Broken valve spring................Bob

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1 hour ago, Bhigdog said:

Broken valve spring................Bob

 

I don't want to hear that either, but... I guess I'll pull a valve cover tonight..

 

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Sounds like a stuck valve to me. Right after an expensive rebuild on my Chevy straight six, an exhaust valve, # 6 cyl. (the hot end) hung up.  She shook and shuddered like the hammers of hell,  real hard with huge power loss.

 

With the cover removed, the offending valve could easily be seen, frozen in place.  After the engine cooled off, the valve unstuck and all was fine , until the next drive. Evidently, the valve guides were assembled too tight by a few thousands.

 

Easy fix though. I removed the rockers and with the  valve stem exposed, I chucked it  into a portable drill and spun it in place for a while, adding MMO, re-spinning in both directions. Kind of a farmer fix, but it worked.

 

So it's not the "end" if you have a stubborn valve. 😄

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Wouldn’t it have a dead miss if it was a stuck valve?

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51 minutes ago, Beemon said:

 

I don't want to hear that either, but... I guess I'll pull a valve cover tonight..

 

If true its an easy fix. Use air pressure to keep valve in position.........bob

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1 hour ago, Kestrel said:

Sounds like a stuck valve to me. Right after an expensive rebuild on my Chevy straight six, an exhaust valve, # 6 cyl. (the hot end) hung up.  She shook and shuddered like the hammers of hell,  real hard with huge power loss.

 

With the cover removed, the offending valve could easily be seen, frozen in place.  After the engine cooled off, the valve unstuck and all was fine , until the next drive. Evidently, the valve guides were assembled too tight by a few thousands.

 

Easy fix though. I removed the rockers and with the  valve stem exposed, I chucked it  into a portable drill and spun it in place for a while, adding MMO, re-spinning in both directions. Kind of a farmer fix, but it worked.

 

So it's not the "end" if you have a stubborn valve. 😄

 

I do not think it's a stuck valve, otherwise my rockers and pushrods would be toast by now and that is a very noticeable sound.

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I had a similar experience once; it was caused by a worn transmission output shaft bushing.

The shuddering only occurred at a narrow range of vehicle speeds.

 

U-joints can also do this; only vibrating at a narrow speed range until they fail completely. 

 

 

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So I pulled the valve covers tonight, no broken springs and everything is okay and free to move (spun engine over by hand, no hard binding). The transmission was 2 quarts low, so I hit the highway tonight and the issue still persists. My next guess is that somehow the wheels have become unbalanced. There wasn't an issue until I came up the Lewiston grade (7%) at 70 mph. I double checked the filter screen on the WCFB, nothing is clogged.. I might try replacing the fuel filter next, since its a cheap fix and it has been a year since its some time since its been replaced, but I doubt that's the issue. I checked the oil in the air cleaner and its still below the fill line ridge, so I have no reason to believe the air cleaner is choking the engine at high RPM. Dwell is okay, timing hasn't changed.

 

I guess I shouldn't say loss of power, because I can power through the vibration from 60 to 70 with a lead foot and the vibration goes away above 70 mph. I have no plans to tear into the Dynaflow this summer, but the reality of the situation is, if it is the dynaflow, I guess it's going bye-bye. I really can't keep spending money fixing other people's mistakes.

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4 hours ago, 95Cardinal said:

U-joints can also do this; only vibrating at a narrow speed range until they fail completely. 

 

Concur.  I had a u-joint fail once.  Within a certain speed range it felt like you were sitting on a jackhammer.  Outside of that range, all was good. $10 fix.  Of course, I didn't have to mess with a torque tube. ;) 

 

Can you get that car to 70 mph in low?  If it's speed related rather than RPM related, it seems you'd have to do that to eliminate the driveline as a cause.  If you can get the rear end off the ground (jackstands under the frame and axle on each side), drop it in gear and run it up to 70.  See if the noise reveals itself.

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27 minutes ago, KongaMan said:

Can you get that car to 70 mph in low?  If it's speed related rather than RPM related, it seems you'd have to do that to eliminate the driveline as a cause.  If you can get the rear end off the ground (jackstands under the frame and axle on each side), drop it in gear and run it up to 70.  See if the noise reveals itself.

 

You don't need to go 70 MPH in Low.

 

CEuAF.png

 

Reading through this, it seems I may have been wrong in my previous assumptions of ruling out the driveline and had the procedure results backwards. I previously said I cannot replicate this condition in low, which is true, so therefor by the shop manual it indicates a driveline issue. Still, I can't imagine this issue just popping up out of no where if the drive shaft was unbalanced when I replaced the differential... so somehow the universal joint has worked itself, if that is the case. Universal joints are not available for the Dynaflow, that I know of.

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How often do these Dynaflow U-joints go bad? They are self lubricated, right? 

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As far as I know yes they are basically submerged in atf I don't think they go out very often that's probably why they're regularly on ebay  nos lol

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