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strange noise/vibration when downshifting

azrider84
Explorer
Explorer
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.
16 REPLIES 16

Geocritter
Explorer
Explorer
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
Explorer II
Explorer II
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
2008 Newmar Mountain Aire
450 HP CUMMINS ISM
ALLISON 4000 MH TRANSMISSION
TOWING 2014 HONDA CRV With Blue Ox tow bar
A man who carries a cat by the tail learns something he can learn in no other way.
-Mark Twain

azrider84
Explorer
Explorer
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
Explorer
Explorer
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.
Noel and Betty Johnson (and Harry)

2005 GulfStream Ultra Supreme, 1 Old grouch, 1 wonderful wife, and two silly poodles.

Gjac
Explorer III
Explorer III
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
Explorer
Explorer
Ever see a car do a pole Vault?? It ain't pretty.
Noel and Betty Johnson (and Harry)

2005 GulfStream Ultra Supreme, 1 Old grouch, 1 wonderful wife, and two silly poodles.

RoyB
Explorer II
Explorer II
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...
My Posts are IMHO based on my experiences - Words in CAPS does not mean I am shouting
Roy - Carolyn
RETIRED DOAF/DON/DOD/CONTR RADIO TECH (42yrs)
K9PHT (Since 1957) 146.52M
2010 F150, 5.4,3:73 Gears,SCab
2008 Starcraft 14RT EU2000i GEN
2005 Flagstaff 8528RESS

azrider84
Explorer
Explorer
Thanks all for the inputs. All good ideas to look at.

Ductape
Explorer
Explorer
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.
49 States, 6 Provinces, 2 Territories...

Johno02
Explorer
Explorer
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.
Noel and Betty Johnson (and Harry)

2005 GulfStream Ultra Supreme, 1 Old grouch, 1 wonderful wife, and two silly poodles.

azrider84
Explorer
Explorer
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
Explorer
Explorer
Torque converter chatter?
Amateur Radio WA4GIY
2015 Montana High Country 305RL
2013 RAM 3500 4x4, crew cab, long bed, 6.7 CTD, Aisin trans.
CGVW 20460 Lbs.

PastorCharlie
Explorer
Explorer
I suspect a U-joint or driveshaft support.

Johno02
Explorer
Explorer
Check U-joints on the drive shaft.
Noel and Betty Johnson (and Harry)

2005 GulfStream Ultra Supreme, 1 Old grouch, 1 wonderful wife, and two silly poodles.