I am helping a friend of a friend who has a Model A. Car runs fine but recently started a vibration on deceleration. If the clutch is pressed in the vibration stops. Acceleration and constant cruise have no vibration, only on deceleration and pressing in the clutch stops it. I haven't seen the car as it's not near me, just looking for ideas for him. Thanks.
Check the universal joint. That the vibration lessens when the clutch pedal is pushed in is because the pressure has been taken off the U-joint. If left un-repaired, vibration will be felt through all ranges and eventually the yokes will break. Ensure that the bolts holding the U-joint housing are tight, too. When replacing the U-joint, be sure to use the special large washer beneath the center bolt. This washer has serrations in it to seat into the drive shaft front splines. It also acts as a spacer to make the bolt tight properly against the U-joint's center. If left out, the U-joint could work back and forth on the end of the shaft, eventually causing vibration.
Also be sure to check the fan blade for cracks or signs that a blade is about to let loose. This is VERY common among original fan blades, as has happened to me over the years with both two and four blade versions. If you're lucky, you'll feel vibration through the drive train before the fan lets go. That's its warning sign to those, who know what to look for when this happens.
My money is still on the universal joint, though.
he might also post on Fordbarn.com in the Model A section.
Thank You. We suspected the U-joint, but wanted other opinions too.
I had 13 Model A's in the past, and all of them had vibration when going downhill on compression. The vibration is in the engine. I don't know the cause, perhaps the engine needed balancing. But it seems to be the way Model A's run. They run very smooth, and the faster they go the smoother the engine runs except when the throttle is closed going downhill.
Model A's seem to viberate some and i wonder if the fact they are a[offseat engine]has anything to do with it? On the other hand they are a very good car and proably the number of survivers beats chebby and doooge by 100 to 1.Bud.
Kenneth, please explain [offseat engine] I have never heard that term.
Bad tranny mounts can cause that.
Norman,Me neither it's a product of my spelling.What i was trying to say was offset.I think the crankshaft in a model A is offset 5 deg from the bore? Bud.
In my experience, most Model As start vibrating around 48 mph, and it goes away about 52 mph. It is so frustrating to long-distance tour with folks who get to the vibration point and back off, so you're forced to "put" down the road, and create a traffic hazard!
Now in a Model T, I'm not going anywhere near that fast!