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03-11-2012, 04:27 PM | #1 |
Roadtrip!
Join Date: Feb 2003
Location: Grand Rapids MN
Posts: 13,787
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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.
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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 |
78K & 79C Jimmys
Join Date: Nov 2009
Location: Ottawa Ont CANADA
Posts: 7,901
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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?
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John 1978 GMCJimmy4X4-350/203 1979 GMCJimmy4X2-305/350 |
03-12-2012, 02:38 PM | #3 |
Moderator
Join Date: Oct 2008
Location: Wentworth, NH
Posts: 4,977
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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.
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03-12-2012, 03:51 PM | #4 |
Roadtrip!
Join Date: Feb 2003
Location: Grand Rapids MN
Posts: 13,787
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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 |
Moderator
Join Date: Oct 2008
Location: Wentworth, NH
Posts: 4,977
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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.
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