Speedo working intermitantly

[timshap]

My speedo seems to come on and off..I think the sensor is fitted somwhere near the diff. Having waxoyled the surrounding area do you think I could have blocked the sensor?
The dials are 1994 black rimmed and are either stewart warner or etb
Does any one know have to find the unit or check its working? Its a borg warner box with a GKN diff.
From cold it appears to sit at around 10mph and later springs into life for a few minutes then back to 10 etc..
If I need to renew I am not sure which one it is...I think I can get one from clever trevor though..

Thanks

[spend]

Sensor is up in the transmission tunnel above the toothed wheel on the front of the diff / rear prop shaft flange. The wiring to the sensor is easily damaged, it goes from the sensor forward to a connector, then up into the car, and is located under the transmission tunnel cover.

Since you have the T5 box you probably also have the added complication of the splitter that sends the signal to the ECU as well as the speedo.

Dave

[timshap]

Thanks Dave

Can I physically get my hand round to the sensor to check its condition?
Are the sensors the same?
Its off to offords in the next couple of weeks..should I let them look at it?

Tim

[spend]

I think you have to at least drop the exhaust, and possibly prop shaft to get at it. Would all be a lot easier on a lift obviously..

My wires/connectors were just stuck into the sensor with sealant!, tried to find a proper connector - but only managed to get as far as tracking down the manufacturer in Hungary. There is also the connector block, both are possible sources of problems.

Not sure but if the signal is a fault you may be able to get some indication out of the idle behaviour of the ECU? ie if teh signal from the sensor is barfed it should affect ecu & speedo, alternately if it is the splitter thingy then only either the speedo or ecu might be affected?

Dave

[BryanWilton]

Had a similar problem, it turned out to be the speedo sensor unit near the diff
I replaced the sensor & all is well (think it was about £60)

I'm not sure it actually needed replacing, I now suspect the gap just needed adjusting to the toothed wheel thingy
I only realised how critical the gap is when I fitted the new one

If you ve been using Waxoyl around that area you may have got Waxoyl on the pick up & it might just need cleaning

Either way you re probably going to have to take the sensor out to clean it, if its clean try adjusting the gap (I used the thinnest feeler gauge in the set)
You don't have to take the exhaust off or get the car on a ramp. I did mine on Axle stands without removing any other parts
Just unplug the wiring connector, cut the cable ties holding the wiring, undo the locknut, then unscrew the sensor & same in reverse to put back

It is a bit fiddly though, took me about 1 hour once the car was on the Axle stands

If you ve got the TVR Bible it shows you what the sensor looks like & where it is...

[timshap]

Thanks

I've only got the first bible not series 2..
Am I right in thinking its towards the off side, but need to access from directly underneath rather than through the wheel arch?

Tim

[spend]

Noooo... that sounds like the description of the later BTR diff. Yours will be at the front of the diff, where the propshaft from the gearbox joins to the diff.

Dave

[timshap]

Dave

Mines a GKN as you know...I thought that was the later one not the BTR?

[BryanWilton]

Access is directly below on mine (1997 car with silver trim dials)

Its a bit of a pig to get a spanner (& your hand) up on to the Sensor & you can only turn it a little bit at a time as everythings in the way
Think mine needed a 20mm or 22mm spanner from memory...

I believe there are two different types of sensor, different depending on early or late Chim

Personally i'd try & clean it & the adjust gap before buying a new one
I found the gap adjustment to be really critical to work correctly
Too close & it will rub on the toothed wheel when you put the car back on the ground (& nasty grinding sound when driving, not recommended)
Too far away & Speedo doesn't start working until you reach 10-20MPH

[spend]

No Tim. GKN were used on early cars, BTR introduced c95/96 IIRC.

Bryan, I think you are talking about the later BTR diff, which would not be relevant in this case...

Generally, later BTR uses an ABS ring on the diff output flange (facing n/s rear wheel) and the earlier GKN has a 'crown' on the diff input flange (facing gearbox). But as always you can do any weird & wonderful thing that takes your fancy with a TVR

Dave

[timshap]

I have seen the crown on the input side of the diff albeit from the wheel arch. Need to get back end well up and have a good look from underneath.

Thanks Tim