Vibration at higher speed, when not accelerating

[TomsResto]

So I made half of this years Hot Rod Power Tour and overall was a great trip, met some great people, watched the late night hotel parking lot tattooing sessions, etc.

One thing that is bothering me though is that on a couple spirited runs on the connecting interstate detours I experienced a substantial vibration/hum that would occur when getting out of the throttle at higher speed (75+)

At 55/60mph everything feels nice and smooth (90-95% of the 900miles I rolled in 4 days), if I drop the fun pedal down everything is good and pulls hard (and with that low end gearing behind the overdrive like final gear in the 700R4 it certainly wants to find triple digits) but when I let out of the throttle I get a substantial vibration (rear view mirror shaking) and low frequency "hum" ... get back in the throttle heavy and it goes away, get the speed back down to ~60mph and it goes away.

My ride is a '69 camaro with Detroit Speed front end, art morrison "weld in" 4 link on GM 10 bolt rear with 3.42 gears, pulled down the road by Ramjet 350 (350hp) and 700R4 on 4 new HRBB wheels (19" in the rear, 18's up front) wrapped in Michelin Pilot Super Sports.

To troubleshoot this I assume I'm best to confirm balance on all four wheels, have pinion angle re-checked, but if those check out then am I looking next at torque converter, tranny, u-joints, something else in the rear end?

Let me know your thoughts and in what order (or if the conditions described above suggest something specific to you)

Thanks in advance!

[icemanrd19]

whats the rear pinion angle? if on acceration the pinion would climb then you would need slighly more neg pinion. If its on deceleration the pinion is going lower so the pinion needs raised slighly. This is if its a driveline vibration.

Im experiencing vibration at 75mph as well which i think i need a custom CV driveshaft.

[TomsResto]

whats the rear pinion angle? if on acceration the pinion would climb then you would need slighly more neg pinion. If its on deceleration the pinion is going lower so the pinion needs raised slighly. This is if its a driveline vibration.

Im experiencing vibration at 75mph as well which i think i need a custom CV driveshaft.

I don't remember the pinion angle measurements, but I had a local shop check it for me while it was on a platform (wheel, not frame) lift and given how low it sits I'll probably have to take it back to them to get re-measured (sits to low to the ground to check on the pavement)

Out of curiosity what's causing you to think you need a custom driveshaft to resolve your issue?

[hifi875]

make sure driveshaft is balanced and rear tires are balanced and tires are good. I fought this for a few years only to find out driveshaft wasn't even close. Fixed that and it got 85 percent better, I was ecstatic. Put new rear tires on prior to power tour this year and it got even better. Id say 95 percent. perfection is unobtainable.

[TomsResto]

make sure driveshaft is balanced and rear tires are balanced and tires are good. I fought this for a few years only to find out driveshaft wasn't even close. Fixed that and it got 85 percent better, I was ecstatic. Put new rear tires on prior to power tour this year and it got even better. Id say 95 percent. perfection is unobtainable.

Thanks hifi875 ...

Based on the feedback here I think I'll take the wheels/tires somewhere to spin for balance check and make sure I didn't lose a weight or something, from there get a measure on pinion angle "as is" and check u-joints, from there pull drive shaft to get balanced and hopefully that will get things better.

[gator68428]

I'm having a similar issue. I've been meaning to take my driveshaft out and double check everything and maybe have it balanced again. But the driveshaft is brand new and freshly balanced last year. New tranny as well. Driveshaft angles fine.

I recently upgraded to a full cage and 315s all around and competed in several AutoX and some track days. Could the abuse have bent an axle? I suppose i could check that by watching the wheel spin with car on jack stands? My right axle is pretty new (replaced a slightly bent one from long time ago) and left axle was fine at the time I replaced the right one.

As an example of the forces involved, shortly after I first put the 315s on the front, i was out scrubbing in new front tires on a back road at <30 mph, slaloming back and forth and I cracked a hub (the area around the outer bearing). I had already done one AutoX event on concrete with 315s up front a few weeks prior, with the same hubs, but the difference was the addition of the roll cage since the AutoX. See pics below. These were CPP hubs that failed. Replaced with Kore3 hubs (black hubs in pic). Luckily the hub failed prior to optima NOLA back in April and it didn't happen at speed on the track--and it was lucky I had enough time to get the Kore3 hubs in time. Competed in the optima NOLA and FM3 cars and cones Road trip the week after, with the new setup. Maybe this is when the racing abuse caused the vibration? I noticed the vibration while on highway driving on the FM3 road trip. Very similar symptoms as Tomsresto is describing.

The broken hub up front may be an indicator of amount of force being transferred to the suspension components. Maybe my stock GM 8.5" 10 bolt (a commonality both tomresto and I share) setup is prone to bent axles after this type of abuse?

[rjselky]

sounds like a U joint is about to fail.

[TomsResto]

Thanks for the input guys, I'll update once I get it up on the rack and start checking things off the list

[TomsResto]

make sure driveshaft is balanced and rear tires are balanced and tires are good. I fought this for a few years only to find out driveshaft wasn't even close. Fixed that and it got 85 percent better, I was ecstatic. Put new rear tires on prior to power tour this year and it got even better. Id say 95 percent. perfection is unobtainable.

Did you run the full HRPT this year? ... I can't tell from your avatar, but I wonder if I saw you on the interstate between Champaign and Madison IL on Wednesday morning? (I was in the right lane to pull off on one of the two lanes to follow the "official route" and you were motoring on in the left hand lane and I gave you a thumbs up)

You running tour again next year? ... I'd like to try to catch up with some other PT forum guys running Gen1's and see/chat about mods folks have done

[icemanrd19]

Ordering a 3.5" aluminum driveshaft from the driveshaft shop tomorrow. They also have the option of a vibration/harmonic reducer that they install inside the shaft as well. Common upgrade on the new G
Hellcats to quite the driveshaft harmonics.

My vibration was 70mph and above. I even had the car up on jack stands with the wheels removed and had the same vibration. It's either my driveshaft or rear end. Will update whenever I receive it

[1985olds]

So I made half of this years Hot Rod Power Tour and overall was a great trip, met some great people, watched the late night hotel parking lot tattooing sessions, etc.

One thing that is bothering me though is that on a couple spirited runs on the connecting interstate detours I experienced a substantial vibration/hum that would occur when getting out of the throttle at higher speed (75+)



At 55/60mph everything feels nice and smooth (90-95% of the 900miles I rolled in 4 days), if I drop the fun pedal down everything is good and pulls hard (and with that low end gearing behind the overdrive like final gear in the 700R4 it certainly wants to find triple digits) but when I let out of the throttle I get a substantial vibration (rear view mirror shaking) and low frequency "hum" ... get back in the throttle heavy and it goes away, get the speed back down to ~60mph and it goes away.

My ride is a '69 camaro with Detroit Speed front end, art morrison "weld in" 4 link on GM 10 bolt rear with 3.42 gears, pulled down the road by Ramjet 350 (350hp) and 700R4 on 4 new HRBB wheels (19" in the rear, 18's up front) wrapped in Michelin Pilot Super Sports.

To troubleshoot this I assume I'm best to confirm balance on all four wheels, have pinion angle re-checked, but if those check out then am I looking next at torque converter, tranny, u-joints, something else in the rear end?

Let me know your thoughts and in what order (or if the conditions described above suggest something specific to you)

Thanks in advance!

Did you ever figure out your vibration, in going through pretty much the same thing? Been fighting it awhile.