Loud clanking noise in top gear

[1930-AA]

Hi all,

I'm working on my AA (1930) that's been partly restored by a previous owner, and I'm in the process of finishing off a few jobs to get it road-usable.

On test runs down the road, I notice that when I drive along in 4th gear, there's a loud clanking/banging noise from somewhere down in the transmission. It's most noticeable under load, however slight, but when I back off the throttle pedal it quietens down. If I depress the clutch pedal while driving along in 4th, the sound goes away, lift the pedal to take up drive again and the noise returns. It's not a constant noise, like a slightly worn bearing, there's no pattern to the noise but it is quite loud.

The noise isn't apparent in gears 1,2,3.

Does anyone have any clue as to what might be going on? I think it's in the gearbox but it could be somewhere in the forward end of the torque tube/bearing area too. As gears 1,2,3 seem ok, my guess is gearbox.

Thanks for your help

Richard (UK)

[Stakebed]

Hmm ive had modern U joints only make noise in top gear under a load.

Im assuming youve checked all the fluid levels in everything drive-line related?

Could be a chipped tooth on gear#4...

when its making noise is it just a sound or is it a vibration also? can you feel it in the seat or is it mostly felt in the shifter?

[1930-AA]

Fluid levels are ok, I don't feel a vibration through the seat, but you can "feel" the clanking noise (if you see what I mean) through the gear/shift lever. It's not a regular noise, it's fairly random and sounds like something's about to make a bid for freedom.

RJ

[Stakebed]

Hmm

do you have the floorboards in? if so remove them and go for a drive and see if you can pinpoint it better.

If you hold the shift lever in 4th gear - like shift to 4th and hold it in there does the noise get better or worse or no change?

[1930-AA]

Hi, the main floorboard was loosely in so that I could drive it. From what I recall, holding the lever in 4th didn't make any noticeable difference.

When I had a crawl underneath earlier today, I noticed a small amount of up and down movement in the shaft nearest to the back end of the gearbox. Whereas everything else is painted, this shaft has surface rust, which makes me wonder if the previous owner (who had a large collection of different trucks), swapped over the shaft from my truck to another one, maybe installing the poor one from another vehicle onto this one. Just a theory.

First thing I'll do is remove the top cover on the gearbox and see if anything is obviously wrong.

Can the box be removed without touching the engine? say by moving the axle and torque tube assembly back?

thanks for your help, RJ

[captain marty]

It sounds like a broken gear.
I've had the same noise only in 1st gear.
Good luck with it.
Marty

[Stakebed]

yea not hard to remove the gearbox cover, crack it open and slowly rotate the gears and see if you can see any issues. (rememebr to block the truck so it doesnt roll on you and turn your fingers into pasta noodles...

[1crosscut]

yea not hard to remove the gearbox cover, crack it open and slowly rotate the gears and see if you can see any issues. (rememebr to block the truck so it doesnt roll on you and turn your fingers into pasta noodles...

You painted quite a mental picture Tom. Eating at an Italian restaurant will never be the same.

[Stakebed]

I'm just sayin! I had it happen with an old riding mower we had with a 3 speed gearbox. Took the top off - straight cut gears, found an icecube in it as thats why it wouldn't move forward in the winter. Was laying on the seat and had my fingers inside fishing out ice chunks when it started to roll forward. the mass of a riding mower on level ground is much less than of an AA truck... my fingers were ok but did smart pretty good...

[1930-AA]

Mmmm sounds like it could be a lengthy fix, I'll report back once I've had a peer inside!

thanks again for your help, RJ

[tiredtruckrestorer]

My guess would be a badly worn couple shaft gear on the back of the trans output shaft and/or the front of the coupling shaft itself. Since, on the 4 speed, you are directly coupling the input and output shafts together in 4th gear and not using any other gears in the transmission I really doubt if you will find something wrong in there. Take the six bolts out that hold the front of the coupling shaft cover to the back of the transmission. Sometimes you can slide the bell shaped cover back over the tube to check how much play is in that coupling. I've seen the teeth in this area worn as sharp as cats teeth.

Keith

[1930-AA]

My guess would be a badly worn couple shaft gear on the back of the trans output shaft and/or the front of the coupling shaft itself. Since, on the 4 speed, you are directly coupling the input and output shafts together in 4th gear and not using any other gears in the transmission I really doubt if you will find something wrong in there. Take the six bolts out that hold the front of the coupling shaft cover to the back of the transmission. Sometimes you can slide the bell shaped cover back over the tube to check how much play is in that coupling. I've seen the teeth in this area worn as sharp as cats teeth.

Keith

Hi Keith, that's interesting, thanks for posting that. Like I said before, the rest of the transmission and torque tube is all painted up nicely, apart from the section immediately behind the gearbox itself, which makes me think that it could have been swapped out to another truck by a previous owner. I'll report back once I've had a look underneath

thanks, RJ