Since I got my daily driver deuce pickup last year I've done nothing to the engine except new plugs and change the oil and filter. I've driven it about 12K. Lately I have noticed it's developed a slight harmonic vibration at low speeds around town. I was at the machine shop today ordering an engine for another project and asked the owner to take it for a spin. He definitely felt the tremble but didn't have a clue what is causing it. We experimented with the idle settings which made no difference. Suggestions?
If you can induce this in neutral with the truck stopped it's powerplant related. If it only happens when moving it's more likely drivetrain or ch***is. In either case look for something that's loosened up and might vibrate at a particular frequency.
My thought also, U-joints? Any chance a tire is separating? That should get worse as speeds increase though.
Vibration is at very low speeds but goes away at over 10 MPH or when you put it in neutral. Just put on $1700 worth of new Excelsiors, drives smooth as silk down the road. U joints are tight. It's a 56 Chevy 265 with biscuits mounts in front and the middle plus a trans mount, mounts look good. No vibration above 10mpg thru 80mph. I fear the trans is beginning to take a **** due to my problems about 3000 miles ago with the modulator ****ling the trans dry. Even though the pan and filter were clean and the fluid looked like the day we put in with no smell, and the trans has been working perfect, I can't help but think there may have been some transmission damage which is causing the vibration? Planning on taking it to the ROC. I guess I'll just drive it until I have to call the rollback!
Have you pulled the driveshaft and checked the yoke for unusual wear since you mentioned the transmission giving you problems? A couple years back, a friend of mine was having the same issues with his OT Chevelle. He brought it to me and when I pulled the driveshaft, the yoke was egg shaped where the tail shaft bushing had wore it out. He had run the transmission low on gear oil (muncie 4 speed car) and had caused the issue.
If it's under 10 mph I'd also check the front wheel bearings. And rear axle bearings as well. I had an axle start to come apart where the bearing rode on it and it would rumble. Another thing you can do is jack up the rear end and let it idle in gear, if you hear or feel the noise it's in the driveline and not the front.
Front wheels bearings just checked and serviced. Fairly sure it isn't the U joints or rear axle bearings since it does it when the car is sitting still in gear?
Ok... Didn't know it was doing it while sitting still. The only thing that comes to mind would be the torque converter bolts ( already mentioned) or the flex plate? Usually they make a noise like a rod knock if they are loose or broken.
No knocking just this slight tremble at idle when in gear sitting still and just when you start moving. Smooth above 10mph. I ***ume it'll eventually expose itself?
Have the rubber biscuits collapsed? Those early Ford style rubber biscuit motor mounts tend to collapse unless they have a steal ring around the base. My 39 Ford had collapsed biscuits and the oil pan was just touching the front spring u bolts.
Auto or stick ? I had a slimmer issue, started after maybe 200-300 miles (new combo) the vibration Only @ idle & under 25 mph , put in neutral at 20 no vibration, @ first I thought solid front mounts , trains is was polyurethane mount , changed front mounts to polyurethane , vibration went away ,, Then 900 miles later , The engine makes 575-650 torque .32 full boxed frame with double tube K member. I know yours way less but Maybe same issue? From pics I have seen crack starts on p***enger side around starter pocket / hump on bell of case ,
Could be an engine miss at idle and low RPM. It has to be engine torque converter, or something hitting something else if it does it sitting still.
Still chasing the problem. Changed the idle several times, nothing. Drop it in drive it trembles, back to neutral it stops. Put it in gear and as I said by 8-10 mph it goes away. Took it on another several 100 mile trip and it goes down the road just fine. Can't see a problem with the balancer. I'm wondering if I don't have an undetectable to the naked ear ignition problem? As I said above the mtr mounts look good. If it's not ignition related I'm afraid it may be transmission related because of the previous problem explained above. I'm thinking just keep driving it until the problem finally surfaces and manifests itself and I call the rollback? If I take it I'm trailering it to the ROC both because I don't want to subject my wife to the trip and because if it shots ****s I can get it home.
Krylon32 .... Since you changed spark plugs, and then this began, I'd inspect them real-close, maybe go ahead and replace them (I'm going to ***ume you did NOT install Platinum or Uridiam plugs ... Only old-style copper resistor plugs) and also look really close at the plug wires and boots for any cracking or small burn marks from possibly touching the exhaust. We find these issues on engines all the time that come through our Hot Rod Shop.
When comes to this wired symptoms we have to think outside the box and there a lot outside the box!! We think Older is better and easier ,, they also can be a challenge which you already know this , On a ot old 90s Gm , I developed a slite vibration /miss only at idle and right off idle, it would come and go after diagnosing and doing many many things to figure out the problem ,I came to conclusion that one of the lifters at idle and a little off idle was bleeding down ( Hyd roller) and it would go away above 10 mph also. Another Years ago I also experienced miss /vibration at a certain RPM , was one spark plug, Also took a while to figure out.. One other time , slight Tick here & there ,about every 30-40 sec , it turned out to Be a , 1 Exhaust valve guide
Go out in the dark and start it up. Look for things that may be arcing. Even minor ones will be visible.
I’ve had a torque converter fail, and act similar to that. I was able to diagnose it by unbolting the three torque converter bolts, then sliding it back and running the engine with the converter unhooked.
Are you running an electric or a belt driven engine cooling fan? If belt driven, remove the belt temporarily and go for a short drive and see if the vibration stops. Stock fan blade or aftermarket flex fan? Either way inspect the fan for missing, cracked, loose or damaged blades. Check the fan hub on the water pump for cracks or rough pump bearings. Also check water pump and alternator pulleys for damage and misalignment. Make sure all the accessory mounting brackets on the front of the engine are properly tightened and not cracked or damaged.
When adjusting the idle are you adjusting the idle mixture or the speed? I chased a similar issue and could see it on a vacuum gauge happening. Eventually found my idle mix was quite a bit lean. Flattened it up and everything’s groovey
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