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Longer speedo cable for doubler setup needed

Desert Rat

Desert Rat

Fetch the comfy chair
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I've got a 700R4 swapped into my 76 Blazer with an ORD NP203/NP205 doubler setup. The stock speedo cable is about 8"-10" short. I've got a 20" extension but that is just too long. Anybody out there do the doubler and find a cable that is just right without ordering a custom one? My stock cable is 80" with a push on top and a 7/7 nut bottom.
 
ORD's website tells you that the later trucks with the 700R4 trans has the cable you need. My 89 blazer for instance has a cable that will work when i finally install my doubler.

Right from ORD's website.
[FONT=Arial, Helvetica, sans-serif]Speedometer Cable[/FONT]
[FONT=Arial, Helvetica, sans-serif]You may need a new speedometer cable to reach the t-case in the new position. They are available from the dealership or a parts store. Ours is from an '82 blazer with the 700R4 and 208 t-case. It reaches with no difficulty. [/FONT]
​
Click to expand...
 
I bought a stock replacement cable from autozone for my truck (77 jimmy, th350, np203)... the listing was the same for about 8 million different trucks. When I got it, it's 1-1.5 feet longer than the stock one. Made it a lot easier to mate it to my aftermarket speedo which isn't quite in the stock location.
 
I'll try the later model Blazer. An extra foot or so would be perfect. Once I get the cable in, I have to take it out and have somebody drive 40, 50, and 60 mph so I can write down my speeds. Then I will have to find a ratio adapter to bring the speedometer in line. I was going to take it to a speedo shop but they were quoting me $300-$400 to make it accurate. One of the websites I went to (http://www.transmissioncenter.net/speedometer_calibration_______va.htm#Speedometer_Cables ) only lists the 80" cable for 69 through 82 trucks. I think I'll have to hit up the local shops and just have them pull out a late model cable and compare it.
 
You can take your truck to Speedometer Electric Service in Hayward and they can calibrate the speedo for you for about $100.00. If they need an adapter then they can sell you one at an additional cost or you can scrounge the wrecking yards for an adapter and have it on hand in case it is needed. There are two different types of adapters and one is riveted togethere and can't be used but the other is screwed together and that's the one you want.

Speedometer Electric Service
21101 Mission Blvd.
Hayward, Ca. 94541
510-276-1522

EDIT: I've had them do about 3 or 4 calibrations for me over the years and i've yet to pay more than $100.00 or so.
 
The Hayward shop is the one that was quoting me the $250- $400 for the fix. I jumped onto partsamerica.com today and looked up an 82 Blazer. I went to Kragen and picked up a Pioneer cable (part # CA3003) which is 100". It is slightly longer than I wanted, but will probably do the trick. It has the push on top and 7/8 bottom bolt. I'll install it tomorrow and take it out for a few runs to log what my speedo reads compared to actual speeds.

Once I find out my exact speeds, the website I posted above sells a ratio adapter that will allow me to correct the speeds. The cable from Kragen was all of $15. The ratio adapter is only $62. All I will need is to find out what percentage I need to speed it up. I talked to a guy from the website on the phone. He says once I give him my actual vs. registered speeds, he will sell me the proper adapter to correct the speedo. I'm guessing it won't be exactly perfect, but close enough. If it is a couple of miles per hour off, I can live with that. Right now I'm way off. If I can fix this myself for under $100, I will be happy as a clam.
 
Here is a shot of my receipt so you can see what i had them do and what i paid for it. It has been 5 years ago but i can't beleive that it has went up that much in 5 years.

SpeedOmeter electric.jpg
 
I definitely had a bit of a shock when I heard what I was looking to pay. Maybe he ballparked it higher than it would've been, but still... I suppose if you want your speed completely accurate and certified, then you have to pay. Close is good enough for me. I have heard good things about that shop but it was pricey.
 
What size tire and gear are you running? There are enough people on here that i'm sure either have an accurate speedo and can tell you what speedo gear they have or find one of the calculators and do it yourself.
 
35's w/ 700 r4 and 4.56's. Once I get my actual speeds vs. my registered speed, I should be able to calculate how much of a percentage I need to increase. At least I can get pretty close.
 
Why do you need a ratio adapter? Can't you find the right speedo gears for that T-case to correct the speedo? I have adjusted mine twice and both times I paid like $5 for a used gear from a driveline shop after doing the math myself. Worst case is that you would have to remove the tailshaft housing to change the speedo drive gear. I got lucky both times and only had to change the driven gear, which is like a 10 minute job.
 
Desert Rat said:
35's w/ 700 r4 and 4.56's. Once I get my actual speeds vs. my registered speed, I should be able to calculate how much of a percentage I need to increase. At least I can get pretty close.
Click to expand...

Those are my exact specs so you should be able to change the same parts that were changed in mine and be all set.

Here is a good site i just found for you if you want to fix this yourself. http://chevelleengineer.home.comcast.net/speedo.htm
 
The ratios adapter simply goes onto the end of the speedo cable and looks to be a lot easier to install than swapping in a speedo gear. However, as usual nothing every goes right. I went to install the new cable today, which is 100" as opposed to the stock 80" but I figured I could route is in a way that it wouldn't kink or have too many sharp angles. So, first shot at it I route it the same as the stock setup using the brackets that attach it to the tranny case in a couple of spots. When I get back to the T-Case, I've got a ton of extra length. So, I kind of do an S curve to use up the extra and hook it up.

I take it for a test drive and it works but the needle is bouncing. I jump on a speedo website which tells me the cable is either kinked, or there is gunk up top at the back of the speedo. I re-route the cable in a totally different setup which lessens the sharp turns, make sure everying is as clean as possible up at the back of the speedo, and hook everything back up. I must've knocked something loose under the dash because now the friggin' thing won't start. It got dark and I ran out of time so I'll be back at it tomorrow. Once I rectify the no start issue, I'll see if the bouncing has gone. If not, I'm seriously tempted to just pay the money for a custom build cable that will route in the stock location with no big turns.
 
Buy a cable for an 89 blazer. I can clearly see that my cable will be long enough when i install my doubler and it is the factory cable.
 
I looked up the part for an 89 Blazer, it lists the cable at 100.5". I have a 100" cable on there now. I think I'm going to have a custom one made. I also wonder if the cable I got was just too cheap. It was a Pioneer from Kragen and the cable isn't very thick.
 
Well if it helps you any i could climb under my rig tonight and try and take some pics of how it is routed. I highly doubt my cable is 100.5" inches though.
 
Mine came out of the firewall, then ran down between the shifter lever over to the area where the tranny meets the engine. There was a bolt there with a small bracket that the cable went through. Then it ran back and attached to another bracket that was also on the tranny higher up about midway back. Then the cable went straight back and into the T-Case. With the new 100" one, I have oodles of extra.
 
Alright, the more I look into this, the more I think I need a 383 stroker crate motor to drop in. That will fix this whole thing...
 
Desert Rat said:
Alright, the more I look into this, the more I think I need a 383 stroker crate motor to drop in. That will fix this whole thing...
Click to expand...

What the Hell does a stroker engine have to do with a longer speedo cable. :confused:
 
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