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09-06-2017, 02:23 PM | #1 |
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Join Date: Nov 2014
Location: between AZ & NV
Posts: 67
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speedometer reading slower than actual speed
i swapped a '95 GMT gauge cluster into my squarebody. Everything is working great minus the speedo. i have the VSSB I yanked from the same truck and wired it without an ECM. My 33 inch tires (295/75/16) and 3.21's out back equal an input ratio of 0.605xxx. I calibrated the VSSB to that nearest jumper settings (0.604492) found on the chart at http://tbichips.com/?page_id=504. BUT the speedo reads 5 mph slower than actual speed.
i.e. If im going 40 on the GPS, the cluster speedo reads 35.
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*UNDER CONSTRUCTION* '80 Suburban C20 (C6P) (Silverado) - '68 472 (Edelbrock 1813, PH8026 LT's, H pipe) / '91 4L80 (manual shift,vac modulator, 350 converter) / 14B FF 3.21 G80 34' s/ '96 GMT400 interior |
09-11-2017, 08:37 PM | #2 |
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Join Date: Nov 2014
Location: between AZ & NV
Posts: 67
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Re: speedometer reading slower than actual speed
UPDATE!! i got it working with the 0.632 input ratio ont he chart. Its dead on all the way thru, matching my GPS speedo. KEEP IN MIND for those who are doing taller gear swaps and keeping bigger than factory tires, that the calibration calculator is not always accurate. Try different ones on the chart whether its a lower than your input OR higher.
In my case: 0.591xxxx - 7-8 mph slower 0.598xxxx - 5 mph slower *0.604xxx - closest to my calculated input (3.21s and 33.42 inch tires--> 0.605) read 5 mph slower than GPS 0.611xxx - 0-20 dead on, at 25 mph went 5 mph slower 0.618xxx - read 7 mph too fast 0.625xxx - read 5 mph slower *0.632xxx - correct reading, dead on with GPS and school zone speed sensor. Now at 0.632xxx, the CALCULATOR specs are off on either rear gear or tire size. 32.24 in. tires/3.21's ***OR*** 33.42 in. tires/3.35s. I know damn well I have the factory 3.21's out back, so just a warning for those who get the calculator giving ratios that are off compared to your trucks specs. Keep trying them and mark em down 'till you get it right. Good luck eveyone.
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*UNDER CONSTRUCTION* '80 Suburban C20 (C6P) (Silverado) - '68 472 (Edelbrock 1813, PH8026 LT's, H pipe) / '91 4L80 (manual shift,vac modulator, 350 converter) / 14B FF 3.21 G80 34' s/ '96 GMT400 interior Last edited by 85raiderburban; 09-12-2017 at 02:19 AM. |
09-12-2017, 04:47 PM | #3 |
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Join Date: Jan 2006
Location: Big Pine Key, FL
Posts: 745
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Re: speedometer reading slower than actual speed
Yeah I've found that chart isn't completely accurate too. You can install the jumpers instead of having to resolder that way you can swap tires and just flip the switches.
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Mike |
08-18-2018, 09:39 AM | #4 |
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Join Date: Jan 2013
Location: Nacogdoches, Texas
Posts: 895
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Re: speedometer reading slower than actual speed
How hard was it to make that cluster work? Are there any write ups on it anywhere? Thanks
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Current Build 89 s10 ecsb 2wd 4.3/700r4 50k OG Miles Instagram- shaggin_s10 '86 Chevrolet C10 Custom Deluxe - Gen V 454 - 4l80e - welded 12 bolt (Build thread: http://67-72chevytrucks.com/vboard/s...d.php?t=611611 ) SOLD |
08-18-2018, 11:09 PM | #5 | |
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Join Date: Nov 2014
Location: between AZ & NV
Posts: 67
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Re: speedometer reading slower than actual speed
Quote:
My modified schematic thats been working flawlessly for the past year Also, just a heads up , this will NOT work for: - '98 1/2 and 3/4 ton pickups - '98-'99 suburban - - '99-'00 escalade - '98-'00 3500 dually. Those years mentioned have the speedo controlled by the PCM, so if your planning on converting to carb on any of those, you will need a 95-97 cluster with speedo wired like my schematic.
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*UNDER CONSTRUCTION* '80 Suburban C20 (C6P) (Silverado) - '68 472 (Edelbrock 1813, PH8026 LT's, H pipe) / '91 4L80 (manual shift,vac modulator, 350 converter) / 14B FF 3.21 G80 34' s/ '96 GMT400 interior Last edited by 85raiderburban; 08-19-2018 at 09:10 PM. |
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