home register FAQ memberlist calendar

Go Back   Turbobricks Forums > Mechanical > maintenance & nonperformance

Reply
 
Thread Tools Display Modes
Old 03-20-2018, 09:16 PM   #1
Grommit55
Newbie
 
Join Date: Mar 2018
Location: Edmonton, Alberta, Canada
Question Lazy tachometer.

I just bought an '84 240 Turbo (321,000 Kms) which has been fully restored. It runs great but I notice that the tachometer drops to the bottom of the gauge at idle but still increases with revs. I figure it is about -1000 rpm off accurate. Any ideas to fix?

Cheers.
Grommit55 is offline   Reply With Quote
Old 03-20-2018, 09:47 PM   #2
TestPoint
Board Member
 
TestPoint's Avatar
 
Join Date: Jul 2009
Location: Ellijay
Default

Probably the simplest solution is to replace it.

But . . . the tach operates off of a ground pulse from the spark coil. Make sure that you have good continuity.

If you perceive that it is off 1000 rpm at all times it could be that the needle just needs to moved a bit on its shaft like adjusting the hands on a clock.
__________________


1982 Volvo 245 with a Ford 302 V8

Ford V8 Conversion Manual -
http://forums.turbobricks.com/showthread.php?t=250257

Bertone Restoration - http://forums.turbobricks.com/showthread.php?t=256460
TestPoint is offline   Reply With Quote
Old 03-21-2018, 03:21 AM   #3
stiligFox
Part-time Tinkerer
 
stiligFox's Avatar
 
Join Date: Feb 2015
Location: Austin, TX
Default

Mine did this, it ended up being the cable going from the speedo sensor up into the cabin had a break in one of the two wires that was causing it to short out and act all wobbly.
stiligFox is offline   Reply With Quote
Old 03-21-2018, 04:30 AM   #4
John242Ti
manofewords
 
John242Ti's Avatar
 
Join Date: May 2003
Location: Duvall, WA
Default

^Tachometer, not speedo.

Anyway, if the needle is sitting at the bottom with the key off, you can take it out and readjust the position of the needle. You will likely find that it maxes out at 6500 when you rotate the needle. Just spin it on the shaft until it points to ~7500, then let it drop. Should be sitting at zero or just slightly above zero when you're done. I've fixed a few that have had the needle sitting way too low when the car's off.

-J
__________________

1982 242Ti - black, M46. 1985 245Ti - blue, M46. 1989 745Ti - red, Aw71.
Formerly Blue245Ti, 245GT-Turbo, and, originally 242GT-Ti.
John242Ti is offline   Reply With Quote
Old 03-21-2018, 08:05 PM   #5
stiligFox
Part-time Tinkerer
 
stiligFox's Avatar
 
Join Date: Feb 2015
Location: Austin, TX
Default

D'oh, my bad. It was late last night lol.

If you take your foot off the gas, does it just collapse down to 0, even at highway speed? Or does it hang steady, just at an RPM too low?

I've once or twice had the issue where the tachometer would just collapse quickly to 0, and spike up when I gave it gas, but it's working now.
stiligFox is offline   Reply With Quote
Old 03-22-2018, 10:29 AM   #6
Grommit55
Newbie
 
Join Date: Mar 2018
Location: Edmonton, Alberta, Canada
Default

Yes. The tach needle stays steady at higher rpm/speed but drops to the bottom while the car is at low idle or off. It is just like it is not positioned properly.
Grommit55 is offline   Reply With Quote
Old 03-22-2018, 08:30 PM   #7
RP80242GT+T
R-Sport Cluster Guy
 
RP80242GT+T's Avatar
 
Join Date: Apr 2003
Location: Cape Coral, FL
Default

Quote:
Originally Posted by John242Ti View Post
^Tachometer, not speedo.

Anyway, if the needle is sitting at the bottom with the key off, you can take it out and readjust the position of the needle. You will likely find that it maxes out at 6500 when you rotate the needle. Just spin it on the shaft until it points to ~7500, then let it drop. Should be sitting at zero or just slightly above zero when you're done. I've fixed a few that have had the needle sitting way too low when the car's off.

-J
^ This
__________________
RP R-Sport and OEM Stock Instrument Cluster Restorations, Sales, parts, service, and customizing. LED Conversion Services
Volvo GT Stripe Kits.
1980 242 GT Turbo
2006 Mini Cooper S GP number 1148
1989 240 Wagon " The Beast" Daily Driver
RP80242GT+T is offline   Reply With Quote
Old 03-23-2018, 12:58 AM   #8
John242Ti
manofewords
 
John242Ti's Avatar
 
Join Date: May 2003
Location: Duvall, WA
Default

Ok, so, now that we know what's going on, here's how to gain access to it...

Remove clock bezel and bezel below clock
Remove rheostat knob and headlamp switch knob (you might have to use a slotted screwdriver inserted between the bezel and the knobs to pop them loose)
Remove headlamp switch bezel
Remove the four screws holding the cluster in place
Remove the two screws holding the top of the steering column trim in place and lift trim out - set on top of dash and leave screws in their holes, so you'll find them
Next, remove the three plastic clips that hold the front edge of the dash insulation piece in place and, also, remove the rubber donut around the floor vent
Drop insulation panel
Crawl under dash and reach up behind the speedometer, turn collar on speedometer cable counter-clockwise until it disengages the speedometer
Crawl out from under the dash, then pull cluster toward you and up onto the steering wheel trim piece
Remove the tach wire, clock wiring harness, the round plug, the half-moon plug, and, if your car has either cruise and/or an autotragic, remove the wires for the speed sensor and/or the overdrive wire from their terminals - If you do have working cruise, make note of which terminal the blue and gray wires attach to, so you don't get them backward and fry the speed sensor when you reattach it
Now, remove the cluster
Place it on a flat surface and remove the four screws that hold the tachometer to the circuit board
Use a slotted screwdriver to pop the tachometer out

Next, do what I mentioned in my previous post.

Reassemble cluster, and reinstall it. Fire up the car and take it for a test drive to see if everything works normally.

-J
John242Ti is offline   Reply With Quote
Old 03-24-2018, 10:11 PM   #9
Grommit55
Newbie
 
Join Date: Mar 2018
Location: Edmonton, Alberta, Canada
Default

That sounds like fun but a good plan. Hopefully we'll have some warm weather next week so I can tackle the job. It's a new car so I'm still sorting out the quirks. Like if the ignition key sits too far clockwise when running the stereo and w/w wipers don't work. Thought I had an electrical problem until I discovered moving the key back a degree. All well now.

Cheers.
Grommit55 is offline   Reply With Quote
Old 05-12-2018, 02:47 PM   #10
Alvito
Newbie
 
Alvito's Avatar
 
Join Date: Sep 2017
Location: Scarborough
Default

Quote:
Originally Posted by John242Ti View Post
Ok, so, now that we know what's going on, here's how to gain access to it...

Remove clock bezel and bezel below clock
Remove rheostat knob and headlamp switch knob (you might have to use a slotted screwdriver inserted between the bezel and the knobs to pop them loose)
Remove headlamp switch bezel
Remove the four screws holding the cluster in place
Remove the two screws holding the top of the steering column trim in place and lift trim out - set on top of dash and leave screws in their holes, so you'll find them
Next, remove the three plastic clips that hold the front edge of the dash insulation piece in place and, also, remove the rubber donut around the floor vent
Drop insulation panel
Crawl under dash and reach up behind the speedometer, turn collar on speedometer cable counter-clockwise until it disengages the speedometer
Crawl out from under the dash, then pull cluster toward you and up onto the steering wheel trim piece
Remove the tach wire, clock wiring harness, the round plug, the half-moon plug, and, if your car has either cruise and/or an autotragic, remove the wires for the speed sensor and/or the overdrive wire from their terminals - If you do have working cruise, make note of which terminal the blue and gray wires attach to, so you don't get them backward and fry the speed sensor when you reattach it
Now, remove the cluster
Place it on a flat surface and remove the four screws that hold the tachometer to the circuit board
Use a slotted screwdriver to pop the tachometer out

Next, do what I mentioned in my previous post.

Reassemble cluster, and reinstall it. Fire up the car and take it for a test drive to see if everything works normally.

-J
My speedometer cable has a plastic shield around it that prevents me from moving the cable. Whats the best way to break it?
Alvito is offline   Reply With Quote
Old 05-12-2018, 04:44 PM   #11
John242Ti
manofewords
 
John242Ti's Avatar
 
Join Date: May 2003
Location: Duvall, WA
Default

^Use a slotted screwdriver to break the anti-tamper seal. Then, it should come out.
John242Ti is offline   Reply With Quote
Old 05-12-2018, 05:09 PM   #12
Alvito
Newbie
 
Alvito's Avatar
 
Join Date: Sep 2017
Location: Scarborough
Default

Quote:
Originally Posted by John242Ti View Post
^Use a slotted screwdriver to break the anti-tamper seal. Then, it should come out.
Do I use the slotted driver and pry it off? Or do I use it like a chisel to weaken it??
Alvito is offline   Reply With Quote
Old 05-12-2018, 06:44 PM   #13
TestPoint
Board Member
 
TestPoint's Avatar
 
Join Date: Jul 2009
Location: Ellijay
Default

I have not experienced the anti tamper seal but there is a fragile plastic 90 degree twist lock connector holding the cable onto the back of the tach. Break that and you will have to create a way to hold the cable onto the tach.

TestPoint is offline   Reply With Quote
Old 05-12-2018, 08:13 PM   #14
John242Ti
manofewords
 
John242Ti's Avatar
 
Join Date: May 2003
Location: Duvall, WA
Default

Quote:
Originally Posted by Alvito View Post
Do I use the slotted driver and pry it off? Or do I use it like a chisel to weaken it??
Insert it from behind, then twist the screwdriver slightly, and it'll snap into two or more pieces.

-J
John242Ti is offline   Reply With Quote
Old 05-12-2018, 08:14 PM   #15
John242Ti
manofewords
 
John242Ti's Avatar
 
Join Date: May 2003
Location: Duvall, WA
Default

If the collar on the cable breaks, the cable will usually stay in place, since it's a press-fit into the back of the speedometer.

-J
John242Ti is offline   Reply With Quote
Old 05-13-2018, 05:19 PM   #16
Alvito
Newbie
 
Alvito's Avatar
 
Join Date: Sep 2017
Location: Scarborough
Default

Quote:
Originally Posted by John242Ti View Post
Insert it from behind, then twist the screwdriver slightly, and it'll snap into two or more pieces.

-J
I cant get it to come off. I tried using plyers as well. No luck.

Can I disconnect it from the transmission and with the extra slack just pull out the cluster so it's easier to work on?
Alvito is offline   Reply With Quote
Old 05-13-2018, 05:25 PM   #17
Alvito
Newbie
 
Alvito's Avatar
 
Join Date: Sep 2017
Location: Scarborough
Default

Here's what I got.

Alvito is offline   Reply With Quote
Old 05-13-2018, 05:55 PM   #18
TestPoint
Board Member
 
TestPoint's Avatar
 
Join Date: Jul 2009
Location: Ellijay
Default

I know it is a 90 degree twist release. You might have to push in a bit to get it to turn.

Like you suggested, pulling a bit of slack by removing it from the transmission will make it a lot easier, coming out and going back in.
TestPoint is offline   Reply With Quote
Old 05-13-2018, 06:15 PM   #19
Alvito
Newbie
 
Alvito's Avatar
 
Join Date: Sep 2017
Location: Scarborough
Default

Sorry, does it connect to the tranny? Or the differential?
Alvito is offline   Reply With Quote
Old 05-13-2018, 06:29 PM   #20
TestPoint
Board Member
 
TestPoint's Avatar
 
Join Date: Jul 2009
Location: Ellijay
Default

Transmission tail shaft area on the left side.
TestPoint is offline   Reply With Quote
Old 05-13-2018, 07:39 PM   #21
John242Ti
manofewords
 
John242Ti's Avatar
 
Join Date: May 2003
Location: Duvall, WA
Default

Looks like the anti-tamper seal is gone already. Rotate collar toward the center dash area, and it'll disengage. Speedo cable attaches to transmission on the passenger side, if you do have to disconnect it.
John242Ti is offline   Reply With Quote
Old 05-13-2018, 08:22 PM   #22
Alvito
Newbie
 
Alvito's Avatar
 
Join Date: Sep 2017
Location: Scarborough
Default

Quote:
Originally Posted by John242Ti View Post
Looks like the anti-tamper seal is gone already. Rotate collar toward the center dash area, and it'll disengage. Speedo cable attaches to transmission on the passenger side, if you do have to disconnect it.
I used some pliers and just clamped down on the plastic bit. It released and the cable popped out. I was able to reuse the same piece when putting it all back together.

Sad news though, I cannot locate the red/white wire needed to go into the tach...
Alvito is offline   Reply With Quote
Old 05-13-2018, 08:59 PM   #23
Alvito
Newbie
 
Alvito's Avatar
 
Join Date: Sep 2017
Location: Scarborough
Default

I have an '83 DL. I didn't see the red and white wire in the cluster with all the other ones...

Alvito is offline   Reply With Quote
Old 05-13-2018, 09:37 PM   #24
TestPoint
Board Member
 
TestPoint's Avatar
 
Join Date: Jul 2009
Location: Ellijay
Default

The tach red/white wire is loose and is just hanging back there. It is not in a harness as such when it gets to the instrument cluster with a single female connector on it.
TestPoint is offline   Reply With Quote
Old 05-13-2018, 09:53 PM   #25
Alvito
Newbie
 
Alvito's Avatar
 
Join Date: Sep 2017
Location: Scarborough
Default

I'll have to go back in there and take a look next weekend.

Any tips on where it would come in from?
Alvito is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On

Forum Jump


All times are GMT -4. The time now is 09:54 AM.

Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2018, vBulletin Solutions Inc.