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  1. #1
    Join Date
    Sep 2007
    Location
    Peak District
    Posts
    363

    Speedo Sensor - IVA problem

    So.
    Not the result i wanted from the IVA retest today.
    The outstanding item that needed resolving was a speedo that didn't work previously. I thought i had fixed it and had tested it on some quiet / private roads. All seemed OK.

    The IVA retest went OK and with a few re-calibrations the speedo worked upto 40mph.
    This is where it gets problematic. When the tester took the car upto 60mph the speeedo dropped back to zero. We tried again, and it worked fine. He then went up to 70mph and it dropped back to zero again.
    Obviously this was a fail. Very frustrating to say the least. The tester (who also had Kit Cars so had a bit of knowledge) thought it could be the high number of pulses that was causing the problem. No idea if this theory holds water or not.
    The setup I've got is as follows

    Engine SBC350
    Gearbox Getrag 265
    Diff - XJ40
    I'm using a Smiths non-mangetic sensor reading the propshaft. I found that it was counting the edges of the flanges of the propshaft U/J so i had to calibrate it for 8 pulses for 1 revolution.

    The only other approach i can think of would be to swap the non-magnetic sensor for a magnetic sensor and glue some magnets to the propshaft. Has anyone had a similar experience or got any thoughts?

    Plan C would be to change the Gearbox for a Tremec but that's a very drastic plan I'm not very keen on.

    Does anyone have any thoughts / tips?

    Cheers,
    Mark

  2. #2
    Join Date
    Feb 2007
    Location
    West Sussex
    Posts
    9,113
    Sorry to read this.
    I dont think you should swap gearboxes - that seems crazy.
    There is probably a simple solution that others can comment on - I have always gone 'old tech'.

    But in the absence of other simple solutions have you considered an old tech solution of simply fitting a speedo cable and using a cable drive speedometer.
    It'll cost you£50 to get it calibrated by Richfield Speedograph, but its easy to do, its just a bit of faff, but would involve spending about £300 all in with a new speedo - a lot cheaper than a gearbox tho'. And just works
    Crendon Chassis No.49
    Huddart FE428 + toploader

    Not listed in the Shelby Register.

  3. #3
    Join Date
    Dec 2013
    Location
    Newark, Notts
    Age
    70
    Posts
    1,585
    I would suggest that it is not picking up correctly on the propshaft. I have found that you need to have the probe as close to the nut head as possible. Beware that you need to make sure all the nuts on the propshaft are at the same angle (point of pickup) and when setting, be very careful the nuts do not move round or else you will take off the tip of the sensor. I had a similar issue with mine
    Charlie

    Quote Originally Posted by Mark_Robinson View Post
    So.
    Not the result i wanted from the IVA retest today.
    The outstanding item that needed resolving was a speedo that didn't work previously. I thought i had fixed it and had tested it on some quiet / private roads. All seemed OK.

    The IVA retest went OK and with a few re-calibrations the speedo worked upto 40mph.
    This is where it gets problematic. When the tester took the car upto 60mph the speeedo dropped back to zero. We tried again, and it worked fine. He then went up to 70mph and it dropped back to zero again.
    Obviously this was a fail. Very frustrating to say the least. The tester (who also had Kit Cars so had a bit of knowledge) thought it could be the high number of pulses that was causing the problem. No idea if this theory holds water or not.
    The setup I've got is as follows

    Engine SBC350
    Gearbox Getrag 265
    Diff - XJ40
    I'm using a Smiths non-mangetic sensor reading the propshaft. I found that it was counting the edges of the flanges of the propshaft U/J so i had to calibrate it for 8 pulses for 1 revolution.

    The only other approach i can think of would be to swap the non-magnetic sensor for a magnetic sensor and glue some magnets to the propshaft. Has anyone had a similar experience or got any thoughts?

    Plan C would be to change the Gearbox for a Tremec but that's a very drastic plan I'm not very keen on.

    Does anyone have any thoughts / tips?

    Cheers,
    Mark
    Joint Area Rep - East Midlands Region
    AKCharlie - ''AKA SOOTY'' - AK GEN2 - LS3 - 6.2litre - 434bhp - A dream come true
    .

  4. #4
    Join Date
    Jan 2014
    Location
    Newark-on-Trent
    Age
    55
    Posts
    282
    As Charlie just said. Try to reposition the sensor so that it picks up on the diff flange bolts/nuts. Make sure all the flats on the nuts are at the same orientation so that it doesn't take the end of the sensor off when the flange rotates and get the sensor as close as you can without touching the nut/bolt head.

  5. #5
    Join Date
    Apr 2014
    Location
    Stourport on Severn
    Age
    62
    Posts
    277
    I’d agree with Charlie on this one. I use a similar product from ETB Gauges which is cheaper than the smiths sensor and has an led that illuminates when the sensor is in pick up range - very handy fo confirming the sensor is triggered on all pick up points on propshaft.
    Cheers
    Steve

    My missus asked me to build her a Cobra! – How good is that!

    AK Gen2 chassis arrived 12/2/15 IVA Passed 2/7/18 on road 29/7/18
    http://stevesakcobrabuild.blogspot.com

  6. #6
    Join Date
    May 2008
    Location
    Cambridge
    Posts
    140
    I've used these speed senders driven from the gearbox speedo cable drive:
    https://www.burtonpower.com/ford-ele...or-revfss.html
    Probably with the adaptor, depending on your gearbox
    https://www.burtonpower.com/revotec-...x-revt9-a.html

    This worked very well and is completely stable when gearbox mounted. You do have to have room for it though, and there isn't always room in the tunnel from the speedo cable drive. You can get right angle adapters which can help. This speed sender can also be driven by a speedo cable, though when tried I did find a bit of bounce to the needle caused by my old speedo cable which was over long and had poor routing.

    Not the cheapest solution, but I have found it reliable.

    Cheers, Richard
    --
    Richard
    GD Mk3 LS6

  7. #7
    Join Date
    Sep 2007
    Location
    Peak District
    Posts
    363
    thanks for tips guys. I'll try repositioning the sensor first and take it from there.

    It's a bit of a pain that the getrag gearbox doesn't have a sensor socket built in otherwise it would be the perfect answer.

  8. #8
    Join Date
    Dec 2009
    Location
    Barton Mills,Bury st Edmunds,Suffolk
    Age
    50
    Posts
    304
    Hi Mark I’ve had the same problem at least yours did work at IVA, so I found that you need cap head bolts if using a pick up from prop bolts I’ve got ETB set up the same as someone put in previous post, awkward to get a bracket that is stiff enough not to flex and give wrong reading. Flats from bolt heads are not consistent and I’ve also had the sensor rub on cap heads, I think although I’ve now passed the better way is to use a pick up from the abs ring on the outer driveshaft, I’m going to speak to ETB as I think they can supply this for about £40?
    Mark
    mark chambers
    Dax de Dion 350 Chevy

  9. #9
    Join Date
    Feb 2010
    Location
    Essex
    Posts
    237
    Hi,
    As previously mentioned i have the same sensor with LED light which picks up off of the propshaft bolts. I too had issues at IVA with the speedo dropping at about 50mph and it was because the sensor was still to far from the propshaft bolt heads so winding it in solved my issue. Also the bracket i made up to mount the sensor was pretty substantial so not to flex when in use
    Barry

  10. #10
    Join Date
    Jul 2007
    Location
    peterborough
    Posts
    240
    Hi,

    If you have the 3 bolt flange on the diff then make a new bracket so the sensor points at the flange casting ie the 3 curved ends of the flange and not the nut heads, you can get a much more accurate and even distance from these points , no more than 2mm. Your problem is it is loosing the signal so you either need to do as i described or move the sensor closer.

    Jon

    AK

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