Pulling handbrake up affecting tachometer???

I have a really odd issue with my GQ.

I’ve just had bigger wheels/tyres fitted (285/75/16) so booked the car into a gauge place to have the speedometer recalibrated.
After picking up the Patrol I noticed the tachometer needle jump when i released the handbrake to drive off.

Anyway, further down the road i pulled over to go to the shops and when i pulled the handbrake lever up the tachometer was reading 0 RPM with the engine still running. So i then lowered the handbrake lever back down. With the lever halfway down the tachometer was reading 650RPM (which is what it idles at). Once fully down the tachometer was now reading just under 1000RPM. At no time during this happening did the engines ACTUAL RPMs change, just the tachometer.

I rang he gauge place and explained the above with his reply being “was it doing it before you dropped the Patrol in”. I said no and if the tachometer was doing that then I’d have got him to recalibrate the speedo AND fix that since i knew he would have removed the dash cluster anyway. He said he just took the cluster out and removed/attached “about 3 wires”.

Does anyone here know why the handbrake lever is affecting the tachometer reading when the only apparent thing is the dash cluster being removed??? I’m stumped 🤔

I believe the PCB on some of the GQ dash's would break or lose contact or something when disturbed. Could be this? Not sure...

I thought the recalibration for the speedo was done via exchange of the little gear at the end of the speedo cable at the gearbox? Saying that i do recall brunswick Diesels blowing up 2 dash cluster trying to get mine sorted out - now have an RB30 dash cluster, so maybe there is something back there to fiddle with?

Follow the loom to see if the cable rubs on any wires. Other than that, the only thing I can think of is the handbrake light circuit has somehow been compromised during the repair.

GQ instrument clusters are notorious for earthing issues, poor solder joints and also cracking the PCB tracks.

Thats why everyone (incl Mr Nissan) usually calibrates the Speedo by changing out the placcy drive gear in the box, much easier and cheaper than adjusting the trim resistors in the Cluster or adding a speed sensor signal dongle such as Marks Adapters.

If old mate only adjusted the cluster I would suggest that is 95% chance where the problem lies... but... if they did fart around with the box it is possible that they moved the loom and the cable from the handbrake lever to the drive shaft shoes is fouling the loom I spose.

Thanks all for the replies. Gives me something to work off.

I thought that the recalibration was also just done of the gearbox but he said he had to remove the dash cluster 🤷🏼*♂️

I’ll take all your advice. I’ll ring and ask him if he did adjust the calibration on the gearbox. If he did then I’ll check the handbrake electrical connection there. If he didn’t then it’s something with the dash cluster.

Which is f*cking annoying as it was repaired a few years ago when the speedometer was faulty (reading 180km/hr or 0 km/hr when driving - $300 repair. The recalibration was $240. I could have built a custom dash with aftermarket gauges for a few hundred more hahaha. Hindsight hey 🙄 Cheers lads 👌🏼

There is a small potentiometer (pot) situated near the top of a GQ cluster, that can be used to adjust the speedo reading.

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Originally Posted by mudnut

There is a small potentiometer (pot) situated near the top of a GQ cluster, that can be used to adjust the speedo reading.

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Yeah sure someone had done that years ago to adjust it but couldn't find post again or remember exactly how to do. . Might have a go with mine one day, sused out different cog for speedo drive but ended up not as straight forward as i hoped. If you can just adjust a potentiometer cheap as!

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I am not sure how much adjustment is there. Because I was researching the GQ cluster, I drilled a hole that fits the old style 240v GPO mounting hole caps to keep out any dust. Sorry about the blurry pic.

Was thinking about how much adjustment there is. .? Hmm maybe have a go one day if i get time lol, at east GQ cluster is pretty quick to get out. . . (Yeah pretty fuzzy pic lol) [emoji6] . .

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So just to update everyone. Turned out that the voltage drop across the dash cluster and tacho needle moving when applying the handbrake and power button (auto) was......DIRTY PLUG CONTACTS on the PCB 🤦🏼*♂️ Quick gentle scrape of every fucking plug contact. Plugged back in. Works perfectly. Just thought I’d let you know as i totally looked past the simple fix first 😂🤷🏼*♂️

That is good info. Thanks posting it as it might help someone else.