toothed wheel - what is it for?

[John Vine]

Is the number of teeth actually that critical? I would suggest that it is not.

I'd agree.  I'd surmise that our reluctor rings started life as ABS ones (but I still haven't identified a source).  To be ultra sensitive to fluctuations in wheel speed, ABS rings need lots of teeth, but that doesn't necessarily apply to our speedo application.  I guess we could easily get away with fewer teeth, although I don't know what effect going to, say, 20 teeth, would have on speedo performance -- in particular, the steadiness of the needle over a wide speed range. 

I feel like there are frequent posts about problems with speedo readings, either due to flex of the bracket, failed or out of adjustment sensors, or damaged wiring.  I would suggest that a redesign could massively reduce these issues.

Again, I'd agree.   

The problem might be whether the speedo code has the range with only a few signals. 

That's an interesting point.  To take an example, CC's recommended 6-digit code for the 195/50-15 ZZS of 038812 (pulses/mile) equates to 902/tooth, so a 20-tooth ring would need a code of 018052.  And we know that, when the leading zero is inadvertently overridden by a 1, the displayed speed slows right down to a crawl.  There seems to be plenty of scope in the range of possible of values.

Anyway, I don't personally need any reluctor rings, but there must be scope here for a Bulk Buy of either the usual 43-tooth ring or some other design?

JV

 

 

[timb2117]

Hi all - sorry I have neglected this thread since "lighting the touch paper" - possibly to do with arranging the purchase of a lovely Europa s - (anyone know a Mr Mooby who bought it originally from Pete Smith Sportscars in Hatton?)

Anyway I measured with my calipers the bottom of the castellation measures 3.71mm and the top of the castellation 2.81mm.

(As usual) cannot fault Johns logic borne out by the fact that in spite of very gentle and accurate and repeated wheel on test drive, wheel off reset, (X a lot!) the reluctor ring set up didn't work for my speedo application - essentially I believe too many pulses.

So (with apoligies to Mr Chapman) I ended up running it off front wheel hub with custom made bracket reading off the wheel bolts inboard side. - A1 readings tested against GPS and at last happy. The rear reluctor ring is in place and does nothing now.

[Tuck2020]

Here's today's effort JV.

Total outside diameter 93.3 (I know, I know, slightly different to my last reading...)

Trough to trough - 88mm. As close to correct diameter as I can get between the teeth with these calipers I think.

 

[John Vine]

Re #52:

... the bottom of the castellation measures 3.71mm and the top of the castellation 2.81mm.

I don't quite follow that.  Is that the width of the gap or the tooth? And if it's the gap, should the 2.81 read 3.81?

Re #53:

Thanks for that.   So the tooth depth is 2.65mm.  A outer diameter of 93.3mm gives a circumference of 293.11mm and (with 43 teeth) a tooth+gap dimension of just under 6.82mm.  Can anyone verify that?  (I would if I were closer to the car, but I'm 600+ miles away.)

Are we getting closer to the figures a CAD modeller would require?

JV

[timb2117]

The gap is 3.71 and the tooth 2.81 sorry John a picture would tell a thousand words :) Hope that clarifies

 

[John Vine]

Re #55:

Hmmm.... pictures.  You mean that B = 2.81mm and D = 3.71mm?

From #53 we have the trough-to-trough diameter as 88mm, which gives a tooth+gap (B+D) value of 6.43mm  That accords pretty well with your 6.52mm.

So, to summarize, we now have:

Thickness of ring 8.8mm
O/D of ring (at top of teeth) = 93.3mm
I/D of ring = 71.8mm or 72.6mm (needs clarifying?)
Height of tooth = 2.65mm
Width of tooth (at base) = 2.81mm
Width of gap (at base) = 3.71mm

Is that enough for a CAD drawing?

JV
 

[Richard Price]

Is that enough for a CAD drawing?

Yes. Plenty.

I did a 2d drawing a couple of days ago, which only took a few minutes to do.

Once you have a CAD file, what do you want to do with it?

I'm happy to share it (but anyone that can read a .dwg file, is also likely to be able to create he file as quickly as I did.)

I think the profile of the teeth is really not that critical to a few tenths of a mm.

As I've said before, if replacing one of these rings, I'd really go with a smaller number of larger teeth, and use a sensor with a greater sensing range and tolerance to adjustment.

[Richard Price]

[Jonathan Kay]

Please could I have a copy of the CAD file in case anyone needs it in the future?

Thanks

Jonathan

[aerobod - near CYYC]

The most important dimension to be absolutely accurate is the ID. It needs to be close to 0.1mm smaller than the OD of the driveshaft, if the correct interference fit is to be used. With a 0.1mm interference, heating it to 250C in the oven should allow it to be dropped on to a clean and polished driveshaft that is at room temperature.

[John Vine]

Once you have a CAD file, what do you want to do with it?

That's a good question but, personally, nothing, as I don't need the ring.  However, there seem to be several members who have expressed an interest in obtaining one, so I was hoping one of them might pursue it and even set up a bulk buy.  I imagine it would be possible to send the CAD file to a steel fabricator?  You mentioned these people, and Mechanical Moz quoted these people as a possible source -- and maybe even free if this ring is the first one they've been asked for:

 

And CB mentioned these folks.

The most important dimension to be absolutely accurate is the ID.  It needs to be close to 0.1mm smaller than the OD of the driveshaft, if the correct interference fit is to be used.

That's a very good point, James, but it doesn't seem to be clear yet what the I/D actually is (or, for that matter, what the O/D of the tripode can is).  Richard Price quoted an I/D of 72.6mm for some bespoke rings, while Tuck2020 quoted 71.8mm.  CC themselves quoted 71.4mm to me.  That's quite a variation.

Anyway, I think I've gone about as far as I can with this.  If someone who actually needs a ring can take over from here, that would be great.

JV

 

 

 

[Tuck2020]

Absolutely JV.

If anyone here has access to accurate measuring equipment I could post them the ring, and they could confirm the measurements and send it back? I'd hate to allow my ineptitude and lack of decent kit to lead anyone down the wrong path.

[SLR No.77]

Picking up on this and not knowing where you're all up to, the slightly earlier electronic speedo fitted from around 2000 could not be calibrated, as far as I'm aware there are no dip switches in the back but it is pre-calibrated to work with the gearbox drive.

Is it feasible that the number of teeth could be matched to create the same pulse output as the original gearbox drive, meaning that by default it would work with all post-2000 speedos?

Stu. 

[John Vine]

Do you mean this type of sender?  I think it generates 8 pulses/rev, but I've no idea how that value translates to road speed. 

As I understand it, however, all Caerbont electronic speedos can be calibrated, either via dipswitches (for that sender), or via a 6-digit pulse code entered via the trip button.

JV

[SLR No.77]

Yes, the sender you have linked to John, and likewise I believe it is 8 pulses per revolution.

Stu.

[John Vine]

To work out how many teeth your reluctor ring would need, you'd also need to know (a) the ratio of the gearbox tailshaft worm/spindle combo, and (b) the final drive ratio.

From a bit of research, it seems that the worm could have 6, 7 or 8 teeth (aka "starts"), and the spindle 23, 24 or 25 teeth!  No doubt a call to Phil Stewart would clarify?

JV

[SLR No.77]

Or maybe look at it the other way round, work out the pulses/mph of the speedo and from there how many teeth would provide that for the distance travelled ...

Stu.

[John Vine]

...work out the pulses/mph of the speedo...

That's what the dipswitch setting should tell you.  Are you saying that your speedo is electronic but doesn't have dipswitches (that is, it can't be recalibrated)? 

I can well believe that the earlier cable-driven speedo couldn't be recalibrated.  In fact, I had one on my 1999 car, but I just lived with whatever speed it displayed.  I'd imagine that the only way to alter its readings would have been to change the gear ratio of the worm/spindle combo (short of getting it reset by Caerbont)?

JV

[Richard Price]

My 2002 car has just four dip switches, but there are actually only two settings.

When I originally swapped from 185/60-14 tyres to 185/60-13's, I found that the Speedo was over reading irrespective of how the dip switches were set :-(

I ended up swapping the speedo drive gear to get a reasonably accurate speedo reading. (But, that was around eighteen years ago, so I don't remember the detail.

[John Vine]

Re #69:

That's interesting.  I'd assumed (wrongly) the 4-switch version would be capable of greater precision (like the 10-switch version).  Did your car have the sender mentioned above (#64)?

JV

[Jonathan Kay]

"My 2002 car has just four dip switches, but there are actually only two settings."

...

"I'd assumed (wrongly) the 4-switch version would be capable of greater precision (like the 10-switch version)."

...

Is this the type described in the Guide as:

Jonathan

[John Vine]

Looks like it, Jonathan.  Tony Whitley was the author of that section.  If he's about, perhaps he could comment?

ETA: I wonder what that "potentiometer" does?  Would it allow a degree of fine tuning by adjusting the needle position?

To generate those pulse values (8380 and 8790), you would need a reluctor ring with around 8-10 teeth, depending on wheel/tyre size (which, of course, is what Stu was asking about back in #63).

I've often wondered what the effect would be (if any) of setting switches 2, 3 and 4 to the other possible values (000, 001, 010 etc).  Little or nothing, probably.

JV