Tach dash questions. - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**too much stuff** · 03-11-2012, 04:27 PM

I made a harness to hook up tach dashes to test. The test rig is a 71 with hei. I hooked up a 73 dash and the tach went to zero and stayed there. I also hooked up an 87 dash and it seemed like it was 2,ooo rpms high but it was working. I tried some mid-late 70s ones and all worked fine. Does that mean i have 2 bad tach heads? or is there something different about certain years using the same tach harness? Any insight? Thanks.

motornut · 03-11-2012, 10:31 PM

i was reading about this repair
http://67-72chevytrucks.com/vboard/s...=503733&page=2
maybe some are for 6 cyl?

**hatzie** · 03-12-2012, 02:38 PM

A 6 cylinder tach should read 25% high on an 8. It may be a I6 tach or it may have a bad resistor in the DIP resistor pack.

**too much stuff** · 03-12-2012, 03:51 PM

Thanks for the info. I was wondering if the 73 dashes were better off a coil rather than hei.

**hatzie** · 03-13-2012, 10:28 AM

They both run off the coil - lead. I've looked at the tach signal from HEI and Points with a scope. They were similar. Points make more noise but are the same otherwise.

03-11-2012, 04:27 PM	#1
too much stuff Roadtrip! Join Date: Feb 2003 Location: Grand Rapids MN Posts: 13,789	Tach dash questions. I made a harness to hook up tach dashes to test. The test rig is a 71 with hei. I hooked up a 73 dash and the tach went to zero and stayed there. I also hooked up an 87 dash and it seemed like it was 2,ooo rpms high but it was working. I tried some mid-late 70s ones and all worked fine. Does that mean i have 2 bad tach heads? or is there something different about certain years using the same tach harness? Any insight? Thanks. __________________ 67 gmc custom lwb dakota truck. Sold...And bought back 69 swb 4x4 project (in progress) 70 c-10 lwb texas truck 70 4x4/BB/bkts/posi/tach(retired) 70 swb (wifes) 70 jimmy camper 71 K-5 factory 2wd 71 cheyenne 4x4/tach/posi/ plow rig 71 Cheyenne20 BB, buckets, tach, tilt, 4 speed 72 jimmy CST wyoming rig 72 jimmy Colorado rig 72 lifted texas 4x4 3/4 ton burb 65 fury conv. 383/auto 65 chrysler 300 "L" 413 auto

03-11-2012, 10:31 PM	#2
motornut 78K & 79C Jimmys Join Date: Nov 2009 Location: Ottawa Ont CANADA Posts: 7,901	Re: Tach dash questions. i was reading about this repair http://67-72chevytrucks.com/vboard/s...=503733&page=2 maybe some are for 6 cyl? __________________ John 1978 GMCJimmy4X4-350/203 1979 GMCJimmy4X2-305/350

03-12-2012, 02:38 PM	#3
hatzie Moderator Join Date: Oct 2008 Location: Wentworth, NH Posts: 4,977	Re: Tach dash questions. A 6 cylinder tach should read 25% high on an 8. It may be a I6 tach or it may have a bad resistor in the DIP resistor pack.

03-12-2012, 03:51 PM	#4
too much stuff Roadtrip! Join Date: Feb 2003 Location: Grand Rapids MN Posts: 13,789	Re: Tach dash questions. Thanks for the info. I was wondering if the 73 dashes were better off a coil rather than hei. __________________ 67 gmc custom lwb dakota truck. Sold...And bought back 69 swb 4x4 project (in progress) 70 c-10 lwb texas truck 70 4x4/BB/bkts/posi/tach(retired) 70 swb (wifes) 70 jimmy camper 71 K-5 factory 2wd 71 cheyenne 4x4/tach/posi/ plow rig 71 Cheyenne20 BB, buckets, tach, tilt, 4 speed 72 jimmy CST wyoming rig 72 jimmy Colorado rig 72 lifted texas 4x4 3/4 ton burb 65 fury conv. 383/auto 65 chrysler 300 "L" 413 auto

03-13-2012, 10:28 AM	#5
hatzie Moderator Join Date: Oct 2008 Location: Wentworth, NH Posts: 4,977	Re: Tach dash questions. They both run off the coil - lead. I've looked at the tach signal from HEI and Points with a scope. They were similar. Points make more noise but are the same otherwise.

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode



Register or Log In To remove these advertisements.

Register or Log In To remove these advertisements.