strange noise/vibration when downshifting

[azrider84]

I just purchased a 1999 Itasca 32T class A from a private party. It has about 55000 miles.
Just made a 700 mile trip and while traveling, noticed a terrible vibration (like a bumping) when going up a hill and the speed drops to around 55 and the tranny downshifts to a lower gear and it revs to around 3000 rpm. But if I mash the gas and it goes to 4000 rpm, it screams but no vibration. Also, when I'm going 60 - 65 on a slight grade and giving it gas, the same thing but only slightly happens. When I let off the gas, it goes away.

This is my first motorhome of this size so any help identifying this problem would be greatly appreciated.

[Geocritter]

If it's carbureted and missing on one cylinder you may have gotten a bunch of gasoline in your oil. It happened to me on a 60 mile trip I took in a classic twin engine boat. By the time I reached my destination my crankcase oil level had increased by a quart. Pull your dipstick, check your oil level and see if smells like gasoline.

Steve

[WILDEBILL308]

azrider84 wrote:
Got the vibration problem fixed. Turned out to be a spark plug wire was not pushed all the way on to the plug, there was about a quarter inch gap. So the engine was probably only running on 7 cylinders when under load. Sh runs just fine now. Hope that didn't cause any damage to the plug or cylinder...

You should be good to go. If it didn't run smooth pulling and cleaning the plug of carbon would have fixed it.
Bill

[azrider84]

Got the vibration problem fixed. Turned out to be a spark plug wire was not pushed all the way on to the plug, there was about a quarter inch gap. So the engine was probably only running on 7 cylinders when under load. Sh runs just fine now. Hope that didn't cause any damage to the plug or cylinder...

[Johno02]

the big engines in the 57-59 fords did have a tendency to pop u-joints if pushed too hard. Most times it happened from a slow or stopped, when you hit the pedal hard. You could hear that big 4-barrel suck, then BANG! If you were lucky, the drive shaft just rolled out from under.

[Gjac]

Johno02 wrote:
Ever see a car do a pole Vault?? It ain't pretty.

This happened to me when I was in HS. I had a 59 Ford convertible and was racing someone else on the thruway when the front drive shaft broke free and the rear end came up until the rear drive shaft let go. The convertible had large cross members which stop the drive shaft from coming through the floor. It was not fun. The drive shaft will brake free before it pole vaults a 20,000 lb MH but it won't be fun.

[Johno02]

Ever see a car do a pole Vault?? It ain't pretty.

[RoyB]

X2 on checking the U-JOINTS. If the one at the transmisson drops to the ground it will tear up a bunch of under belly items...

[azrider84]

Thanks all for the inputs. All good ideas to look at.

[Ductape]

TC should unlock any time brakes are applied. So test by applying brake very gently with left foot while maintaining throttle with right under the problematic conditions. Just enough to light up the brake lights.

If it smoothes out TCC or controls of TC need attention.

[Johno02]

Yes, if I u-joint fails, or horrors, breaks, you could be in big trouble. Especially if you are driving at the time. Best case is if driveshaft falls free and drops out of the way. Worst case, I don't want to ever see it again.

[azrider84]

Torque Converter chatter, now I was thinking the same thing. But how can I verify that's the problem? And, if I don't get it checked before I make the 700 mile trip back home, can it break something?

[Hiking_Hunter]

Torque converter chatter?

[PastorCharlie]

I suspect a U-joint or driveshaft support.

[Johno02]

Check U-joints on the drive shaft.