Mechanical Speedo Correction Box - Install with Pics
#1
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Thread Starter
Mechanical Speedo Correction Box - Install with Pics
Not much of an install.
But, I have never seen pictures of these things before on YotaTech, so, since I bought one, I took some pics.
The box is pretty simple, it is a small gear box that you put in line between the transfer case and the speedo cable. I have 5.29's in my rig with 33" tires. This puts my speedo off by about 13%. The gear in my transfer case is the 18 tooth, so, no chance of changing that out, as they only make a small number of gears for it, and 18 is the biggest.
The box that I bought is a .879 reduction unit. Overdrive for the speedo cable. That is as close to .87 (13% reduction) as the gears available for the reduction box allowed.
I bought it from Commercial Speedometer in Sacramento, CA. Chuck at Commercial Speedo was very helpful and he turned it around in a day. I ordered it yesterday, on my doorstep today. Total cost was $95 with shipping and sales tax.
Picture of the reduction box:
Picture of the reduction box and the stock speedo gear module that I removed from the transfer case:
Picture of the two screwed together:
Picture of the unit installed:
I took it for a drive on the freeway, works great. There is a construction zone near my house that has a speed check radar sign at the start of the construction zone. I was going 60, it said 59. Good to go.
But, I have never seen pictures of these things before on YotaTech, so, since I bought one, I took some pics.
The box is pretty simple, it is a small gear box that you put in line between the transfer case and the speedo cable. I have 5.29's in my rig with 33" tires. This puts my speedo off by about 13%. The gear in my transfer case is the 18 tooth, so, no chance of changing that out, as they only make a small number of gears for it, and 18 is the biggest.
The box that I bought is a .879 reduction unit. Overdrive for the speedo cable. That is as close to .87 (13% reduction) as the gears available for the reduction box allowed.
I bought it from Commercial Speedometer in Sacramento, CA. Chuck at Commercial Speedo was very helpful and he turned it around in a day. I ordered it yesterday, on my doorstep today. Total cost was $95 with shipping and sales tax.
Picture of the reduction box:
Picture of the reduction box and the stock speedo gear module that I removed from the transfer case:
Picture of the two screwed together:
Picture of the unit installed:
I took it for a drive on the freeway, works great. There is a construction zone near my house that has a speed check radar sign at the start of the construction zone. I was going 60, it said 59. Good to go.
Last edited by OutlawMike; 11-05-2009 at 08:16 AM.
#2
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Location: Winnipeg, Manitoba, Canada
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Wow, that's pretty impressive actually. I thought I'd just have to live with my speedometer being off by over 26% for the rest of my life. I'll have to look into this product.
#5
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Stupid work computers, I can't see the pics.
I remember calling a speed shop once and asked them about getting a new gear for mine. It was gonna cost me some coin to get it fixed. In the end though, my tires/gears make my speedo dead on anyways.
I did not know that there was a mechanical reduction box(as opposed to the electical once like the Superlift Truespeed) for speedos, very cool.
I remember calling a speed shop once and asked them about getting a new gear for mine. It was gonna cost me some coin to get it fixed. In the end though, my tires/gears make my speedo dead on anyways.
I did not know that there was a mechanical reduction box(as opposed to the electical once like the Superlift Truespeed) for speedos, very cool.
#6
Registered User
Thread Starter
To determine the reduction needed, you need to time your car over a known distance course at a constant speed. Or, pace another car that you are pretty sure has an accurate speedo and then do the math.
In my case, over a known 1 mile distance, driving at 75 mph on the speedo took 55 seconds. Converting my 1mi/55 seconds to mi/hr: 1mi / 55 sec *3600 sec/1 hr = 65.45 mi /hr. Since my speedo read 75 mph, this is a difference of 9.55 mi/hr. 9.55 mi/hr is 12.7% of 75 mph, which is the reduction percentage I needed.
It is adjustable, if you have him swap different gears in. I should have asked him for a table of what ratios he could hit.
A neat little solution, but not my idea in the least. The thanks goes to: Roger at 4Crawler. Of course Roger has already done this in the past and has recommended it in many posts on this and other websites. I just got off my ass and called around to find out where I could get one.
Thanks again Roger,
Mike
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#13
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Location: Rigby, ID
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Speedo Adapt to compensate for Mods
I contacted Commercial Speedometer today for a gear reduction because with oversized tires, speedo was incorrect. The man there knew exactly what was needed. $80.00 + shipping. This should keep the cops off of me. Thanks for the posting here. 916-371-5873. Literally a 5 minute call.
#15
Speedo correction for Toyota pickup. I’m running 5.29 gears and 35” tires. I called Chuck and he set me up with a .865 reduction module. It works like a champ, speedo is dead on at 60mph now. $110 shipped to SC.
Last edited by Dark Knight; 11-22-2019 at 04:05 PM.
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