Model A knocking rear end while driving

C

Chrisverling

Junior Member
I just was taking my 1929 Model A for a ride, when going uphill in 2nd gear I heard a strong knocking sound from the rear end. I stopped on the side of the road and the knocking stopped. Reversing into a parking lot, no knocking. I turned back downhill and the knocking started again at about 10 km/h. At home I tried to reverse a bit longer and no knocking. I have no clue what this could be.

Anyone any suggestions?

Chris
 
Maybe the U-joint?

Try lubing the u-joint and see if the noise stops or changes...

And also check the oil in the rear end :)
 
Hi Chris,

The most difficult problem, (as you are already aware), is to find exactly "where" the knock is originating after realizing that sound can be transmitted through connected steel assemblies.

Not long ago one gentleman heard a knock he thought coming from his transmission; but after disconnecting his [Drive shaft/U-joint/differential assembly], the knock stopped.

Through further investigation, he found the knock was in the differential.

Several clues you report thus far:

A. Knock apparently coming from the rear when in 2nd gear going "uphill".

B. Stopped on road side .... no knocks .... Hint (1): Model A "NOT" in gear.

C. When driving in Reverse ..... no knocks ... Hint (2): Model A "NOT" in "Forward" gear.

D. Knock heard going "downhill, while "in gear" .... Hint(s) (3):

(a) "NO" knocks when traveling in "Reverse" gear.

(b) "NO" knocks when engine running in "Neutral" on side of road.

(c) Knocks heard from rear when traveling "Uphill" or "Downhill" .... and "In a Forward Gear".

E. How about answering "if" knocks are heard from the rear when traveling both "Uphill" and Downhill", not only in 2nd gear; but also in 1st gear and 3rd gear.

Others will surely add to this most normal "Model A Forum Bingo Game" of guessing at possible Model A problems from far away where the knocks on your car cannot be heard from far away.

Please do not give up.
 
Thanks 1955cj5

I will look at lube/oil. However, it started knocking at once, all of a sudden. With load it seemed to knock more, with no load it seemed less but still very loud.

Chris
 
The two pinion gear lock nuts may have loosened, which allows the pinion gear teeth to "bounce around" against the ring gear, creating a banging or clunking sound. The usual cause of this is that funky-looking lock washer with bendable "ears" (tabs). Repo tabs are not long enough to be pounded over the two large nuts deep enough to hold in place. The constant pressure from the driveshaft turning and the torque eventually springs the tabs and allows the forward-most nut to back off first, followed by the second one. It's the loosening of this nut closer to the pinion gear that creates the knocking.
This happened to my friend's 1929 Cabriolet that I had restored for him 10 years earlier. Same symptoms as you describe. Upon disassembly, it was the repo lock washer that failed. An original one with longer tabs was installed, the nuts tightened up, and the torque tube replaced. That solved the problem. Check the previous good suggestions out, too, but if they don't pan out, don't eliminate loose pinion gear nuts from consideration. I am afraid the only way you can check that is to pull the torque tube forward at least a couple inches so you can visually inspect the nuts for tightness, which effectively means pulling the rear end or engine/transmission. Given that choice, take out the rear end. It's a heck of a lot easier and faster.
Marshall
 
Hi Chris,

Per reply #3 above:

Now "Knocks" are known to be heard from what appears to be from the rear only in when the drive train is engaged in:

1. All three (3) forward gears ..... whether going Uphill or Downhill; and,

2. "NOT" in Neutral; and,

3. "NOT" in Reverse.

4. As parochial as this question appears:

Do you hear .... or do you Not hear .... knocking when traveling in any or all gears, (1st, 2nd, 3rd, and Reverse), when "NOT" traveling Uphill or Downhill ...... but traveling in gear on LEVEL surfaces?

Next question after answering 4. above will involve no disassembly.
 
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Several years ago there was an interesting thread " knock in third gear" Very good reading!
The noise sounded like it was coming from the flywheel area! Turned out it was a loose pinon nut. You may get lucky and found it right away or you may be in for a long haul !
 
My truck did the same thing once, driving along slowly, and the knocking noise started. Ended up being the pinion nuts in the rear end had loosened up.
 
It is very difficult to determine where the noise in the drive train is coming from as the noise is telegraphed up and down the whole drive train. About the only thing you can do is start taking things apart and look for something that has come loose.

I was at a national years ago when a car came into the maintenance tent with the symptom being a loud banging noise coming from the transmission every time they let up on the gas. The tent gurus convinced the owner his trans needed overhauling. They pulled the rear end and the trans and the owner spent many bucks on trans parts. I looked at the trans parts they removed and they looked fine to me. When all was back together the noise was still there. The rear was pulled a second time. When they removed the torque tube they found the two large nuts that secure the pinion gear had come loose and were clear up at the front of the toque tube.

What was making all the noise was the pinion gear banging against the ring gear. The noise was clear back at the rear end yet it sounded as if it was coming from the trans.

Tom Endy
 
Hi Chris,

Humble opinion after reading typical Model A Forum "Bingo" type problem responses after over 20 years:

Appears there is a very slight difference between a "Neurosurgeon's Advice" and a "Model A Forum Mechanic's Advice", for example:

A. JOE goes to a "Neurosurgeon" with a headache. After a few test, JOE's head is cut open to remove his brain tumor. Next day JOE's brother JACK goes to the same "Neurosurgeon" and after a few simple tests, and taking two (2) recommended aspirins, JACK's headache is gone.

B. JACK's brother JIM goes to "Model A Forum Member Mechanic Advisor" with a headache. The "Model A Forum Member Mechanic Advisor" conducts NO tests and receives a call from JOE about his having no headaches after his brain tumor was removed. JIM's head gets cut open, and .......... NO tumor is found.

C. JIM is rushed to the "Neurosurgeon's Office"; it onlycost $75,000.00 to patch his head; a few simple test are performed, where afterwards, JIM is given two (2) recommended aspirins, and his headache is gone.

At the very least Chris, nobody recommended the most often Model A recommendation from years ago ....... i.e., to try changing your condenser.
 
Hi Chris,

Had to go to work; but, I'm back and even with no response to above #4. in above Reply #8; I would at the very least try this very simple test prior to beginning massive disassembly of anything:

1. Jack up both rear axles, (L & R, w/ tires still on), and place L & R axles on sturdy jack stands after providing blocks in fronts of both L & R front tires.

2. Remove key after making sure ignition switch is OFF; and open hood and remove all (4) spark plugs.

3. Ask someone to get inside car, (maybe with a watch or clock with a second hand), and inform them when you give the signal, to hit the starter button for approximately (7) seconds, then remove his/her foot off of the starter switch, and wait for your next command.

5. You lay down on the outside perimeter of the car, (preferably with a mechanic's stethoscope, or an approximately one inch square wood stick where one end is placed on your ear and the other end can be placed on different metal parts of the drive train) to test and listen for knocks that may originate from different parts of the drive train, or other areas.

6. Not that adamant, single Model A Forum past experiences of Model A owners are not helpful; but, after possibly 80+ years of Model A maintenance on this car, and sometimes with later difficult to find Model A parts a few years back, there could always be several causes for strange knocks that we on this Forum cannot hear.

7. After rudimentary and very quick, simple testing, you may at the very least find a clue and maybe avoid lots of wasted time, money, and efforts in chasing a Model A unicorn ...... all headaches are not brain tumors ..... some have been known to even be caused by hangovers.
 
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Hello H.L. Chauvin

Your story with the Neuroscientist is sooo funny and really fits. Thanks for your tip about locating the knocks. I will do just that and report back.

Many thanks to all who have contributed with advice. It all helps.

Regards
Chris
 
Check the clearance between the rear crossmember and the body. There should be some sort of padding between the two. Sounds bad easy fix.
 
Kind of had the same thing thought the noise was coming from the transmission area
needed to pull the car apart anyway so upon inspection there were lots of teeth missing on almost all trans gears,but i also found the center main pounded out really bad
i would take the shiftier top cover off and have a look see
i kind of new to these A's but i'm thinking that the teeth in the trans are not real strong
and i sure wish i would have started playing with these 40+ years ago
thanks to all i have read on hear i have gained a hole lot of knowledge
so keep reading and learning you will find the answer to your problem>
 
I had quite some work cut out for me. When we started to look for the noise, the mechanics stethoscope pointed towards the wheel bearings first. So we took off the wheels and found that indeed, the bearings had a lot of play. But nothing really wrong with them and definitely not the source of the knocking noises.

So we continued with the recommendation list. We let out the transmission oil and sure enough, there was metal in it. By reaching with a magnet into the differential, we pulled out the pieces in the pics below. So now its off to take out the rear axle and differential. Will keep you posted.
 

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