speedo question

[TJC46]

Hi guys last year when doing my bodylift i managed to ever so slightly damage part of the electric cable on my speedo transducer. I thought i had managed to repair it. but my speedo does not work. Before i spend to buy a new one can someone tell me how close to the toothed wheel on the diff does the transducer have to be, Also i painted the diff and the toothed wheels would the paint affect it in anyway? Just want to be sure before splashing the cash, have you seen the price of one of these.

[BliarOut]

About thirty thou IIRC. The Steve Heath one will work with a greater clearance. It's easy enough to adjust the tangs of the rotor if you've bent them, don't ask how I know

[shpub]

It's about 10 thou or even less. Depending on what paint you used, the coating thickness may be greater than that and the sensor won't work. My intelligent speed sensor will work with a gap of over 1mm and doesn't care about paint.

[spend]

Maybe Robs is on the nose of the diff (tang?) and those big teeth seem to be happy with a much greater clearance than the ABS sensors type on most of the cars.

Mines the original (hungarian IIRC) sensor Steve, and its fine at @3mm, hardly surprising the teeth+separation must be 10x as big as the abs wheel type. It's so good I have to switch it off occasionally to keep it calibrated to TVR mileage

[Simon Says]

spend said:

Maybe Robs is on the nose of the diff (tang?) and those big teeth seem to be happy with a much greater clearance than the ABS sensors type on most of the cars.

Mines the original (hungarian IIRC) sensor Steve, and its fine at @3mm, hardly surprising the teeth+separation must be 10x as big as the abs wheel type. It's so good I have to switch it off occasionally to keep it calibrated to TVR mileage

Thats a heads up thought both types running clearance was vital was rqather hoping a quick adjust would fix mine(sometimes intermittent op)i have put up with it for over 2 years though

[spend]

The heads up on those types is make sure the wiring is OK (and if the OP has one - that he corrected them the right way around)

[BliarOut]

spend said:

Maybe Robs is on the nose of the diff (tang?) and those big teeth seem to be happy with a much greater clearance than the ABS sensors type on most of the cars.

Mines the original (hungarian IIRC) sensor Steve, and its fine at @3mm, hardly surprising the teeth+separation must be 10x as big as the abs wheel type. It's so good I have to switch it off occasionally to keep it calibrated to TVR mileage

Got it in one

[TVR Beaver]

Isn't there an input into the ECU from this thing?.. If it's not working (for what ever reason) dosen't it impact on the ECU and what it thinks the car is doing?..

[spend]

TVR Beaver said:

Isn't there an input into the ECU from this thing?.. If it's not working (for what ever reason) dosen't it impact on the ECU and what it thinks the car is doing?..

You mean the extra complexity required because the T5 box has no speed sensor Rarely mentioned when folks bleet on about T5's being better - just another tricky thing to go wrong really

TBH we can talk round all these differences til the cows come home, that's why its quite important that if posters want relevant responses they should actually put some details of their car on their profile!

[shpub]

spend said:

Maybe Robs is on the nose of the diff (tang?) and those big teeth seem to be happy with a much greater clearance than the ABS sensors type on most of the cars.

Mines the original (hungarian IIRC) sensor Steve, and its fine at @3mm, hardly surprising the teeth+separation must be 10x as big as the abs wheel type. It's so good I have to switch it off occasionally to keep it calibrated to TVR mileage

The original sensor is analogue and the output voltage is dependent on several factors such how much metal is being moved by the sensor, its speed and the gap between metal and sensor. One other factor is the mark space ratio. If this is too short... the sensor won't register it. For the diff drive shaft trigger wheels, the gap has to be around the 10 thou otherwise the sensor cannot differentiate the gaps etc. I can believe that with the bigger propshaft system, the gap can be more but 3mm is really pushing it for a small high frequency sensor which is what you need for the ABS wheel types. I suspect that it is a big diameter sensor such as a M16 or M18 type.

As for the callibration aspect, I am working on a calibration unit that allows you to recallibrate the speedo at any time without having to send it away. So if the speedo is out or you want to run different tyre/wheel combinations, the speedo can be corrected at the press of a button (or several presses in some cases).

[spend]

2 completely different designs really Steve (you used to have a 4.3 once upon a time didn't you - or was it pre-cat?).

The way the 'tangs' / 'teeth' are bent over on the 'crowned' wheel would make it very difficult to have the tolerances that you could get simply turning down an ABS toothed wheel. So I would guess they are designed to have a relatively large clearance, and yes from what I remember the sensor is quite large - none of those pin sized inductive ends IYSWIM. From experience I did close the gap when I rebuilt that area, and the speedo worked but was very jerky & seemed to 'ponder' at certain times, opening the gap back up made everything hunky dory again. (I only tried opening the gap - because like a numpty I rewired the sensor the wrong way round and got nothing! - so I was trying anything..) All the time I spent trying to make sure all the teeth were 'set' perfectly was just character building

I have no doubt that the clearances / muck / alignment of the ABS type arrangements is much more critical (but in its favour it is a lot easier to access).

[shpub]

Actually it's the same design but different implementations.

I spent a lot of time playing round with different sensors for the speedo unit and traction control and the sensor design is one big compromise. Big sensors support big sense gaps at the expence of resolution and switching frequency. Small sensors trade sense gap for resolution and switching speed. And then there are additional restrictions depending on the switching speed which is probably why moving the sensor out helped give a better resolution of the mark space ratio. If you look in detail at some of the sensor specs there are so pretty mind numbing factors to be taken into account.

PS never had a precat... went to a couple of 500s

Edited by shpub on Wednesday 10th March 13:44

[spend]

shpub said:

Actually it's the same design but different implementations.

I spent a lot of time playing round with different sensors for the speedo unit and traction control and the sensor design is one big compromise. Big sensors support big sense gaps at the expense of resolution and switching frequency. Small sensors trade sense gap for resolution and switching speed.

PS never had a precat... went to a couple of 500s

I've always assumed that the speedos electrics were customized to see a particular waveform ie early ETB a nice wavy line & later CAI a choppy square form. That's what I was referring to 'by design' - from the gauge providers, who will have tested paired triggers+sensors, with just TVR implementing them to the providers specs?

The ABS sensor scenario has always made me curious - it seems the need the best granularity as the wheel approaches locking - ie calibrated to most sensitive as the signal tends to 0!

Sorry I had it in my mind you had had a 4.3 - but senility is approaching fast

[TVR Beaver]

spend said:

TVR Beaver said:

Isn't there an input into the ECU from this thing?.. If it's not working (for what ever reason) dosen't it impact on the ECU and what it thinks the car is doing?..

You mean the extra complexity required because the T5 box has no speed sensor Rarely mentioned when folks bleet on about T5's being better - just another tricky thing to go wrong really

TBH we can talk round all these differences til the cows come home, that's why its quite important that if posters want relevant responses they should actually put some details of their car on their profile!

So if you have the T5.. what happens to the ECU and it's performance if the sensor fails or may be a wire is broken?... Anyone know the end result?.. under / over fueling may be??

[TJC46]

Managed to get the car up on the axle stands tonight, and although i have not measured the gap exactly, it looks to be about 2 to 3 mm. Will set it correctly this weekend and see if that sorts it. Thanks for the replies. Managed to reset the gap friday afternoon to slightly less than 10 thou, speedo now working perfectly.

Edited by TJC46 on Friday 12th March 18:04