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Daimler CB22


PITT24423

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Good evening gentlemen involved in trucks with worm drive diff's,

I am a regular reader of all of these great build's and have a similar interest,   the great photo's of the diff build got me thinking about it's design,   I would like to ask you guy's who drive vehicles with these diff's,    do you get any feeling of "braking" when lifting off the throttle due to it's design ?

 

 

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Andy

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All marks of Antar have worm rear axles (combined with an epicyclic gear train).  When you down hill, the load will push you faster and the revs will increase just the same as any other axle, as Andy Pugh says.  In some situations, if you are not careful, you can serious over rev the engine.  The revs can go through the roof very quickly because of the 14:1 reduction.

The ratio of the worm drive in an axle is always arranged so that the vehicle can speed up when going down hill on the over-run.  If this was not the case either the axle and the wheels would lock up and cause a terrible skid or something would break.

 

John

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Leyland recommended not to bump start their worm drive models, however my mate starts his 3 tonner that way all the time.

In Australia because of the long distances, little traffic etc it was usual to use 'angel gear' on down hill sections thus increasing speed from the usual maximum of 30mph. Not a safe practice but they did it. With heavy worm drive diffs over-speeding in this way means that eventually the worm can't keep up and the top literally blows off.

As said, effect of engine braking is down to the ratio.

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9 hours ago, Scrunt & Farthing said:

Does a worm drive prevent you from "bump starting", due to the irreversibility (or inability to back drive) of a worm drive?

They are typically low enough ratio to be reversible. 

We have an old worm-drive chain hoist. That is irreversible, but only because it has a friction brake on the end of the worm shaft. With good bearings and adequate lubrication worm drives are fully reversible up to fairly high ratios. 

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16 hours ago, attleej said:

All marks of Antar have worm rear axles (combined with an epicyclic gear train).  When you down hill, the load will push you faster and the revs will increase just the same as any other axle, as Andy Pugh says.  In some situations, if you are not careful, you can serious over rev the engine.  The revs can go through the roof very quickly because of the 14:1 reduction.

The ratio of the worm drive in an axle is always arranged so that the vehicle can speed up when going down hill on the over-run.  If this was not the case either the axle and the wheels would lock up and cause a terrible skid or something would break.

 

John

I would expect the mass of the epicyclic rotating will act as as an extra  flywheel.

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On 3/14/2021 at 10:42 PM, PITT24423 said:

Started to seriously think about the diff as this proved quite painful for the lorry. I was lucky in that I was able to get a second axle which had a top casting. Over the years I’ve picked up the remains of worm drive diffs on the off chance and today it paid off in a monumental manor. I need a ratio of 7.25 to 1 = 29 teeth on the crown wheel and a 4 lead worm . I cleaned up the top casing a while back and had measured one of the spare diffs with a hunch that looks close but with 26 teeth. Undid the four clamp nuts and low and behold it dropped straight in as if it was made for it without even requiring new bearings.Our suspicion is that this diff is American possibly Peerless  . The plan is to use the diff centre and get a new crown and worm machined  .I’ve been recommended a gear cutting firm that can cut from a copy so we have stripped the diff out of a Daimler CC we finally got home this week to use as the pattern inc the worm. 

Making gears is a lot of fun! I have spent a few days figuring out the maths before attempting to make these on my contemporary milling machine. They were missing from a 1912 gas engine that I am restoring. Looking forward to seeing the new gears, it would be nice if you could make some pictures of the machining.

Marcel

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Diff hub split and cleaned this evening. Some rust pitting on the thrust faces far from being ideal we will call them oil reservoirs as they are immersed in the thickest of oils so will run with what we have.

The Holley carburettor came back today looking very shiny after being sorted by John who in normal circumstances forms part of Wednesday night team . 
I won’t be cutting the gears as I don’t possess the necessary patience for being a machinest probably because you have to stand still 😁 even though a couple of us have been known to turn out the odd shaft. 

Dave the chippy has been in and started machining up some Opepe I had for the stair which were off cuts from London Underground sleepers .They have machined up far better than we expected and are incredibly dence with a high silicate content so the blades on the planer came in for hard time.

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Managed to bunk off most of today so between Dave and myself managed to get the stairs nailed ,still have the inner stringer to fit plus the landing.
Diff bearings unfortunately are pitted and are unusual in that they are metric Id and od with a imperial width . Fearing the worse due to their size our bearing supplier had a pair old stock which have now finally found a home. 
The windows and front vent now have their new retainer springs fitted managed to reuse all but 7 of the ally brackets as they were beyond salvage.

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Spent the spare hours I had over the weekend measuring and going through the diff to harden up my plan . The CC crown wheel and worm are the same part number as the CB22 so  and will be used to reverse engineer the new gears for the bus . The new crown wheel will have the gear profile as per original shown on the left in the pic with the internal detail to match the grafted in hub shown on the right in the pic.The Daimler diff has two planet wheels where as the replacement has four so this is an improvement for a start to smooth out the action .

The shaft centres measured up to within 25 thou between the three Daimler castings I have . One casting being the correct one for the bus being plum average which helps deciding how much clearance to give the new gears.

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Inner stringer fitted which has made the stair quite rigid . Rear platform fitted with steel brackets and modified bottom step which I have made so it folds up. The reason for this is I was forewarned that the step is  a problem grounding when loading onto a lowloader.

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Posted (edited)

This is one of the buses we have used as a guide.All-though it’s a AEC the dimensions are almost identical and has been perfect for our project.The kick plates are visible in these photos.

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Edited by PITT24423
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Not sure what this box was originally for but guessing it was a safe box for collecting the used tickets we have copied it from Barry s AEC B type . The flip over seat is best described as a perch and a few one liners were flying about ref who’s backside would actually fit in the gap 

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Collecting used bus tickets on exit in the way the railways did wasn't a practical proposition with a bus full of people getting on and off in the rush hour. The tickets had serial numbers and the office would record which conductor had which numbers for each value ticket and the conductor would have to complete waybills at each terminus, which the office would check against unused tickets returned and money handed in [and the conductor would have to make up any shortfall]. Tickets would be manually clipped or punched on issue [no machines in the early days], and the conductor  shown a ticket issued earlier would know it wasn't from his batch, so both office and conductor had checks against fraud.

What neither wanted was unused tickets going absent. Given its location on the platform the only potential user, officially at least, was the conductor, so I would suggest that each conductor had a padlock and key issued to him, and kept his stock of spare tickets locked in the box.

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Thanks.Couple of things which made us question it’s use was the cut out in the flip section of the seat but no slot in the top “if” it had been used for returned tickets . Barry had told us that this was all original as he had salvaged this item along with his handrail in the early seventies . Your probably correct in that it was for spare tickets . Thanks for your comments. 

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  • 3 weeks later...
Posted (edited)

I`m no expert on trams so please correct me if i`m wrong, but purley going on gut instinct  it appears to be a double decker tram due to the detail / style and heavier build than a bus of the same period ..

Edited by PITT24423
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This body is consistent with that of a 1900 Nottingham Corporation Tramways double decker, according to the illustration in Wikipedia.

Edited by Noel7
deletion of one word
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