Knocking While Accelerating, Loose U-Joint?

S

sandbug

Member
I have been getting this loud knocking noise for over two years now. Replacing the Weber with a Stromberg has not gotten rid of it, but it sure byppasses it faster.

Some facts:
It happens on the top of 2nd and 3rd while fully accelerating. Letting off the gas while it is happening removes the knock immediately.
The differential, rear axles, and driveshaft is recently rebuilt by Tom Endy. Bearings have been repacked.
It doesn't sound like it is in the engine (32B), and it sounds like almost the sound of pre-detonation knocking, but it is not.

Someone said watching the video that I may have a loose U-Joint or something in the drivetrain that pulls apart during the acceleration and slaps.
Ideas?
https://youtu.be/-iehc7PbtqY?si=T11z5uE5o7eQEZ2M
 
U-joints constantly vibrate under load if there’s a balance issue. They knock and try to tear the car apart when decelerating if they are failing.

Pushing in, engaging the clutch quickly helps you isolate the issue. The gas pedal quickly helps too.
 
If I push in and engage the clutch, the car stops acceleration and the sound stops. If I'm at an idle, and I punch the gas and rev, there are none of the knocks. Only under load of accelerating and only in second and third gears (as first is likely short lived, so the knock/clap sound never comes in).
 
This slide may help you. The original Model A u-joint may not behave like a modern Spicer type joint because of its design.
 

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It could be a number of things but most likely a loose main bearing, or bearings. You will need to drop the pan and check the clearance. However, the best and most accurate way is to remove the engine and mount it on an engine stand up side down.
 
You mention "The differential, rear axles, and driveshaft is recently rebuilt by Tom Endy. Bearings have been repacked." I'm pretty sure Tom would have checked your u-joint while he was in there. It would not have suddenly gone bad. I think I would concentrate elsewhere.
 
If it has been doing this for over two years, I would think that it was a bearing issue, something would have given up by now. I would drive it with the floor board out and see if you can isolate the sound direction better.
 
sandbug said:
If I push in and engage the clutch, the car stops acceleration and the sound stops. If I'm at an idle, and I punch the gas and rev, there are none of the knocks. Only under load of accelerating and only in second and third gears (as first is likely short lived, so the knock/clap sound never comes in).
Click to expand...

Based on what you described, I would place doubt on the u-joint. U-joint failures usually accompany a lot of vibrations as well, and change whether under load or decelerating.

I'd pull the trans top and check to make sure none of the gears are broken or chipped. Make sure there are no metal pieces in the bottom from gears or bearings.

Also, make sure your u-joint is properly greased. Usually takes an entire tube of grease.
 
Thanks all. When Tom repaired my rear axle, and renewed my differential; I took it to him (Driveshaft and backwards. He wouldn't have seen my U-joint. We've had the the floorboards out, and can't isolate the noise - although does not seem to be coming through the engine. We've had the cover off the trans, and no chipped gears or broken ones.

Seems that when the car is accelerating, the drivetrain is stretching, and something starts slapping around. Soon as you let off the gas, the stretching stops and the part stops slapping.
 
nkaminar said:
It could be a number of things but most likely a loose main bearing, or bearings. You will need to drop the pan and check the clearance. However, the best and most accurate way is to remove the engine and mount it on an engine stand up side down.
Click to expand...

I agree!
 
Engine pans? can make noises if bolt is loose or ear cracked.
You said “B” engine— what timing cover- what distributor?
Where are you setting the timing?
Have you tried with the belt off?

Does the hood have the bumpers at the latches and the corner covers?

How long since the rear was rebuilt— has the oil been checked or changed,the ujoint lubricated and the transmission checked/ changed (and inspected for metal debris?

I had a splash pan loose and lost some hood bumpers that caused some strange noise sometimes similar to yours.
A generator can make noises too — when was that last lubricated?— this is where taking the belt off can help
 
'32 B Motor, High-compression head, FSI ignition and distributor (I worked with them to dial in the degree), Smithy exhaust, Red's Headers, Stromberg 97, push button starter, F-100 steering, 12 V Neg with alternator from Randy/Mel Gross, Seatbelts, LED lights. Rear was recently rebuilt. Trans has been inspected and no chips or flakes. Splash pans are attached well.

Again: Seems that when the car is accelerating, the drivetrain is stretching, and something starts slapping around. Soon as you let off the gas, the stretching stops and the part stops slapping.
 
Bob Bidonde said:
This slide may help you. The original Model A u-joint may not behave like a modern Spicer type joint because of its design.
Click to expand...

FWIW, the only place recently I’ve been able to find that stocked the U-joint rebuild kit was Brattons. That, sadly, is no longer, although I was able to get one right near the end. If anyone else has a source, please enlighten us.
 
I’ve listened to the video several times , it sure sounds like pre-ignition/ spark knocking , I can get the same thing sometimes . Most of the times that I get it’s climbing up a hill at speed , sometimes at highway speeds when I try accelerating . When this happens to my A I back off the throttle and it goes away , retarding the hand timing lever also the noise goes away , then back to accelerating its not there . Many things can effect pre-ignition/ spark knocking, #1 advanced timing it would be easy for you to retard your timing 2-4 degrees, #2 a hot spot in the combustion chamber due to carbon , a dose of MMO could help , get the engine throughly warm and slug the carburetor with water steam cleaning the combustion chamber . #3 try a cooler set of spark plugs . When I haven’t been running MMO for awhile is when I can get the knocking, of course when it happens to me I just retard the timing with my hand lever . Reading the ground electrode on your spark plugs will tell if your running to much advanced timing , look online on how to read spark plugs , basically you don’t want the change in color to go past the bend on the ground electrode .
 
That's the most reasonable, and when I have either upped the octane or put MMO in the gas it helps. I can't retard by hand since I have an FSI and have nothing connected to the rod. I'll try all these things, and I can easily change the timing. I have many spark plugs to try too. Thanks!
 
If you have the FSI automatic ignition, that’s your problem because of all your modes. IMO, and from other sources. I’d pull it and just run a normal electronic ignition with the spark lever. Probably around 22° max advance to start.
 
Run it on jack stands. You should be able to find the noise location easily that way. Even though the load will be less the loose parts should still rattle.
 
With the high compression head and FSI distributor, it could be ignition knocking, as others have said. Consult with FSI or just retard it a little.
 
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