Hello just bought an 1977 GMC Frontier 18ft Motorhome

[Baron Bruce]

I was driving it and when I go like 25 or more MPH this vibration on the right side, thinking it something to do with the suspension, any ideas, would help, Surrey, BC

One thing he said was it needs a wheel alignment, so would that be it? He put new tires on it was not balanced!

 

[RF_Burns]

FYI, This forum supports the 23 &26 Ft motorhomes made by GMC in the '70s with a VIN that starts with TZE. Your motorhome appears to be a van chassis class C motorhome. You can find out more about our GMC motorhomes at:
GMCers.org

 

[Mike_H]

I was driving it and when I go like 25 or more MPH this vibration on the right side, thinking it something to do with the suspension, any ideas, would help, Surrey, BC

One thing he said was it needs a wheel alignment, so would that be it? He put new tires on it was not balanced!

Like Bruce said, This forum is specific to the GMC produced, Class A motorhome. You appear to have a GMC van chassis that was upfitted by an RV company.

However, to help out, first thing I would do, before throwing a bunch of money at suspension would be to get the tires balanced and checked for a bent wheel. You might also have a bad tire...sometimes the belts inside can break and throw an imbalance issue. IF everything checks out with the tires, then you can start looking into suspension, but in my experience, vibrations are almost always caused by something to do with the tire/wheel combo.

 

[Bill Bryant]

I was driving it and when I go like 25 or more MPH this vibration on the right side, thinking it something to do with the suspension, any ideas, would help, Surrey, BC

One thing he said was it needs a wheel alignment, so would that be it? He put new tires on it was not balanced!

Hi,
A voice of "trial and experience", 200+K miles & 34 years.

This started about 40 years ago, no reason NOT to expect the same results NOW with similar conditions.
Test vehicle:
1976 Palm Beach GMC MotorHome
8.75x15.5 radials (various brands over the years)
original steel wheels w/GMC hubcaps
starting mileage ~40K
new Delco shock absorbers (on rear, replaced with KYB later))

A wonderful coach, loved everything about it except a vibration from the rear suspension!

Methods tried to fix the vibrations.
Balance using lead weights with both static & spin methods.
Result: At best, changing the speed where the vibration occurred or minimally reduced it.

At the time there were Dynamic balancers (an accessory using a tubing ring with steel balance balls inside clipped to the inside of the wheel. The balls were distributed centrifugally where needed for balance.
Result: Somewhat better over lead weights, but still a "patch" not a real FIX.

Finally, new 16" alloy wheels w/tires.
Result: The fix is in! Excellent ride with little to no vibration. Add glass beads and you have perfection.

Pretty much unknown to the public was that in 1973 MH steel wheels were sorted from the best truck inventory for the motorhome use. Obviously GM knew the rear MH suspension was subject to imbalance, I'm sure the bias tires didn't help.

Other ways to balance tires is to grind the tread??, your mileage may vary.
Balance beads (inside the tire) work very well and are a good fix.

 

[tmsnyder]

Hi,
A voice of "trial and experience", 200+K miles & 34 years.

This started about 40 years ago, no reason NOT to expect the same results NOW with similar conditions.
Test vehicle:
1976 Palm Beach GMC MotorHome
8.75x15.5 radials (various brands over the years)
original steel wheels w/GMC hubcaps
starting mileage ~40K
new Delco shock absorbers (on rear, replaced with KYB later))

A wonderful coach, loved everything about it except a vibration from the rear suspension!

Methods tried to fix the vibrations.
Balance using lead weights with both static & spin methods.
Result: At best, changing the speed where the vibration occurred or minimally reduced it.

At the time there were Dynamic balancers (an accessory using a tubing ring with steel balance balls inside clipped to the inside of the wheel. The balls were distributed centrifugally where needed for balance.
Result: Somewhat better over lead weights, but still a "patch" not a real FIX.

Finally, new 16" alloy wheels w/tires.
Result: The fix is in! Excellent ride with little to no vibration. Add glass beads and you have perfection.

Pretty much unknown to the public was that in 1973 MH steel wheels were sorted from the best truck inventory for the motorhome use. Obviously GM knew the rear MH suspension was subject to imbalance, I'm sure the bias tires didn't help.

Other ways to balance tires is to grind the tread??, your mileage may vary.
Balance beads (inside the tire) work very well and are a good fix.

Can confirm, new alloy wheels got rid of all those pesky vibrations!

I measured the 'out of round'ness of my old steel wheels. I 'farm boy' checked for roundness by jacking up the coach at each corner and using a steel pointer set up next to the wheel. Initially set the pointer to just touch the largest outside diameter, rotated by hand and measured the largest gap. None were round, most were 1/8" and one or two 3/16" out of round!

I suspect what happened was after 50 years of bumping into curbs, the steel bead was bent inward at some points. This caused the tire to stand taller at that point. That's my theory anyway.

Bill it's interesting that they picked out the best rims for the motorhomes!

 

[Bill Bryant]

Picking out rims was only 1973, that was over 50 years ago, suggesting you find some beads for your set of tires. They may be sufficient to work with your tire set but only if you tires are in reasonable balance

 

[tmsnyder]

Picking out rims was only 1973, that was over 50 years ago, suggesting you find some beads for your set of tires. They may be sufficient to work with your tire set but only if you tires are in reasonable balance

I tried beads , they made it slightly better.

New alloys completely solved the vibration.