Sudden & Silent low speed disappearance — what happened?

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CJB
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Joined: Fri Jan 04, 2019 10:01 pm
First Name: Chris
Last Name: Bamford
Location: Edmonton AB Canada

Sudden & Silent low speed disappearance — what happened?

Post by CJB » Tue Jul 09, 2019 4:44 am

Went out for a spin this evening with Lady Michelle in our '26 Touring, the last drive before a big cleanup ahead of an event Wednesday.

Last drive indeed! I stepped on the low pedal to leave a stop sign and... nothing. Pedal went the usual distance but there was no sound, no motion, no drag on the engine. Nothing.

Brake and clutch pedals worked fine as before. High speed was fine as before and the hand lever behaved properly. The low speed pedal engaged neutral part-way down as usual. A visual of the linkages found no obvious problem.

With no bad noises, I chose to baby it the two miles home in high. Probably a gamble, but I got lucky.

Anyway, after my nap I went out to the garage and took off the inspection cover. Again nothing apparently amiss. The low pedal tightens up the band as one would expect, the ear is secure, the band adjuster is tight, the wood bands aren't visibly worn and the pedal and shaft are securely pinned together.

I engaged high with the lever forward and jacked up a rear wheel to rotate the low drum and don't really understand what I found...

Bit of grease on each drum to mark location

all drums grease.jpg

Turned the rear wheel a bit and the reverse and brake drums moved, but not the low speed!

low drum grease.jpg

So I just went back to the garage to check and yes, the low drum can be rotated separately from everything else, just by pushing the edge with a screwdriver. There was no obvious noise or roughness.

And for reference, this photo shows the low pedal engaged and the band ears clamped together

low pedal down.jpg

As near as I can tell, the drum and the gear teeth are no longer connected, That could only be what... all the rivets shearing off? A circumferential failure between the teeth and the drum? Both seem really unlikely, and inconsistent with a zero drama failure. I did re-rivet a low speed drum some years back, but don't remember if it was this car or the speedster.

Clearly the damned thing has to come apart no matter what, but it would be very interesting to hear others' speculation and/or experience about what's happened here. The only thing I know for sure is that the event Wednesday is going to need a different car!


Scott_Conger
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Re: Sudden & Silent low speed disappearance — what happened?

Post by Scott_Conger » Tue Jul 09, 2019 10:26 am

Chris

very sorry to hear of this development

If you're looking for speculation, you've come to the right place! :lol:
Scott Conger

Full Flow Float Valves - deliver fuel like Henry intended!

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twrenn
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Re: Sudden & Silent low speed disappearance — what happened?

Post by twrenn » Tue Jul 09, 2019 10:51 am

Well the one speculation that ISN'T...you're gonna be pulling the engine. Sorry about that.
Now get cracking! The season is already half over! Good luck pal!


Norman Kling
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Re: Sudden & Silent low speed disappearance — what happened?

Post by Norman Kling » Tue Jul 09, 2019 11:12 am

If the gear teeth had gone bad, you would have a problem with all the gears. The gears would make a bad noise and only work in high, not neutral or reverse. I think either the rivets holding the gear to the drum have sheared, or the webbing on the drum has cracked all the way around.
You will know more after you get things apart.
Norm


Hal
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Re: Sudden & Silent low speed disappearance — what happened?

Post by Hal » Tue Jul 09, 2019 12:47 pm

Well, while we're speculating....I'm with Norm.


Scott_Conger
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Re: Sudden & Silent low speed disappearance — what happened?

Post by Scott_Conger » Tue Jul 09, 2019 8:44 pm

I agree with Norm in that there is preggy good evidence the rivets have sheared. I doubt anything cracked on the drum, as the drum would both be off axis and would make a devil of a noise (and if it had made noise, I suspect you'd be directed ignore it, and to tear the rear end down...that's a joke).

With the rivets captured in place, the gear is spinning on a nice cushion of oil within the drum's round ID.

All speculation, of course. :?

Mike Bender offers a video that is very good on this subject and his method ensures good contact between gears and drum, ensuring no motion between the two parts can develop. I suspect if it is indeed sheared rivets, there will be some evidence of movement between the two parts that was going on for some time...let's hope nothing is Worn too far that one or both parts cannot be reused. If this is indeed the scenario, some rivets parted ways well prior to the final failure and you will likely have to dress up thrust faces on other drums if the rivets have scored them...let's hope they have not.
Scott Conger

Full Flow Float Valves - deliver fuel like Henry intended!

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Topic author
CJB
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Re: Sudden & Silent low speed disappearance — what happened?

Post by CJB » Wed Jul 10, 2019 1:12 am

Thanks all for your comments, especially yours Scott. I expect it will be sheared rivets. So this likely the low drum I re-riveted some years ago. Oops.

I may not get to it for a few weeks but will report back then.

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