The Ford Barn - View Single Post

ErnieF · 02-01-2024, 05:12 PM

Hi all,

My 31 slant window sedan has a strong vibration when holding back downhill. It does not do this at any rpm speed when on level nor when pulling uphill. It only does it when holding back going downhill, starting at about 1800 rpm and becoming quite bad by 2000 rpm. Transmission gear does not matter - it’s all about rpm speed. If I shift into neutral and coast or shift into overdrive to drop the rpm speed down to about 1500, the vibration goes away.

I expected (hoped maybe) that the problem was in the transmission. But I just installed a new Mitchell transmission and overdrive. I replaced the universal with a Bob Drake universal. I took my first test drive yesterday and the problem remains. I have talked with Steve Mitchell, and he is out of ideas.

Combined with this transmission is a new Burtz engine with a Burtz head and a Burtz cam shaft. Motor mounts are new. Fan is new. Clutch is upgraded to a new V8. New Burtz flywheel. I’ve had the engine up to 3000 rpm while it was unhooked from the transmission, and it just purrs. I have talked with Terry Burtz, and he is also out of ideas.

I have had this car completely apart and rebuilt it from bumper to bumper. There is nothing that I haven’t had fully apart, examined, and replaced as needed. In the end, almost all parts are new.

The only thing I can say, is that this is all still new. I’m up to about 130 miles on the engine, and 20 or so on the transmission. But I don’t think break-in alone would account for the vibration.

I do not feel that videos pick up the vibration very well, but I did take some. My low post count won't let me include the links in this post. I can message them to anyone interested, or I was able to post them in my similar thread over on the VFF.

I have talked to Terry Burtz, I have talked to Steve Mitchell, I have talked to Sam at Arizona Model A. I posted on the Model A Restorers Club on Facebook, as well as the Burtz Engine Facebook group. I've gotten lots of ideas, but so far nothing that has turned out to be a solution.

I have checked the universal joint (no change with the original, nor the new bob drake), rechecked the bearing preload on the pinion bearings, checked the flywheel housing for cracks, the kingpins are new and tight, brakes are all new with cast iron drums. I tried a different carburetor with no change.

I am 18 months into the restoration of this car, and have countless hours invested. I am at my wits’ end over this. Everything has been gone over. Everything is new. What could I possibly be missing that is causing this vibration??

02-01-2024, 05:12 PM	#1
ErnieF Junior Member Join Date: Aug 2022 Posts: 7	Downhill, Deceleration Vibration Hi all, My 31 slant window sedan has a strong vibration when holding back downhill. It does not do this at any rpm speed when on level nor when pulling uphill. It only does it when holding back going downhill, starting at about 1800 rpm and becoming quite bad by 2000 rpm. Transmission gear does not matter - it’s all about rpm speed. If I shift into neutral and coast or shift into overdrive to drop the rpm speed down to about 1500, the vibration goes away. I expected (hoped maybe) that the problem was in the transmission. But I just installed a new Mitchell transmission and overdrive. I replaced the universal with a Bob Drake universal. I took my first test drive yesterday and the problem remains. I have talked with Steve Mitchell, and he is out of ideas. Combined with this transmission is a new Burtz engine with a Burtz head and a Burtz cam shaft. Motor mounts are new. Fan is new. Clutch is upgraded to a new V8. New Burtz flywheel. I’ve had the engine up to 3000 rpm while it was unhooked from the transmission, and it just purrs. I have talked with Terry Burtz, and he is also out of ideas. I have had this car completely apart and rebuilt it from bumper to bumper. There is nothing that I haven’t had fully apart, examined, and replaced as needed. In the end, almost all parts are new. The only thing I can say, is that this is all still new. I’m up to about 130 miles on the engine, and 20 or so on the transmission. But I don’t think break-in alone would account for the vibration. I do not feel that videos pick up the vibration very well, but I did take some. My low post count won't let me include the links in this post. I can message them to anyone interested, or I was able to post them in my similar thread over on the VFF. I have talked to Terry Burtz, I have talked to Steve Mitchell, I have talked to Sam at Arizona Model A. I posted on the Model A Restorers Club on Facebook, as well as the Burtz Engine Facebook group. I've gotten lots of ideas, but so far nothing that has turned out to be a solution. I have checked the universal joint (no change with the original, nor the new bob drake), rechecked the bearing preload on the pinion bearings, checked the flywheel housing for cracks, the kingpins are new and tight, brakes are all new with cast iron drums. I tried a different carburetor with no change. I am 18 months into the restoration of this car, and have countless hours invested. I am at my wits’ end over this. Everything has been gone over. Everything is new. What could I possibly be missing that is causing this vibration??