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Old 08-06-2018, 12:37 PM   #1  
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Speedometer cable

Hey all! I'm in the process of working on fixing my speedometer, as it wasn't working when I bought it. I have found that the cable going into the driven gear has eroded and there's nothing left. My question is, I have a 2 piece speedometer cable that splits right below the brake booster, would you replace just the bottom half of the cable or both? I have done some searching and there aren't many threads about this. I have found that the stock GM part number that was listed at some point was 25033662 but I have not been able to find a pic of this cable yet. My lower cable has 1 end (at the trans) has a female threaded nut as usual. The end under the brake booster is male threaded. I can't find any cables that would replace that for sure since I can't even find the stock part. I have not taken the speedometer cable off the back of the speedometer as of yet because I was thinking that I would just do the lower cable. What are your thoughts? Part numbers would be appreciated!! TIA!
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Old 08-06-2018, 02:21 PM   #2  
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Re: Speedometer cable

Get a 1pc replacement cable and be done with it? Fairly certain the two piece cables are leftovers from a bygone era, that really don't serve any purpose in 2018. ATP offers a 1pc replacement. A lot of thirdgens came with 1pc cables. Easiest to replace it with a 1pc.
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Old 08-06-2018, 02:23 PM   #3  
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Re: Speedometer cable

Drew,

Do you have any part numbers? Someone in another thread said CA3001 or Dorman 03159 would work, but I believe those were for earlier models. Not that any of the third gens are all that different. Just curious if someone has a part number from this decade and not from like 04. lol
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Old 08-06-2018, 05:48 PM   #4  
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Re: Speedometer cable

Sure. I'd imagine most will interchange, but here's whats listed for 1988.

https://www.rockauto.com/en/moreinfo...5672&jsn=10741

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Old 08-07-2018, 12:46 PM   #5  
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Re: Speedometer cable

Thanks Drew! I have to see if my fat bear paw hands can actually fit up under the dash to get that smaller/upper speedometer cable out. I can reach and grab part of it, but not really the end of it at the back of the speedometer. I know there's a clip/ring that holds it in as well that has to be moved to release the cable. That was part of the reason why I was thinking of just doing the lower/transmission side cable since it's already out and waiting to be replaced.
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Old 08-08-2018, 07:14 AM   #6  
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Re: Speedometer cable

IIRC, it is easier to pull the cluster partly out, The spring clip needs to be pushed toward the rear of the car to release the cable. To install is easy, just push it into the speedometer head.

The reason for the two piece cable was for ease of assembly at the factory.

RBob.
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Old 08-08-2018, 07:29 AM   #7  
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Re: Speedometer cable

RBob,

Thanks for that tip! I was able to get the upper cable that attaches to the speedometer cable out last night. You have to push the clip in towards the speedometer. I think the bigger issue will be hoping that the cable will go in nicely and will line up without me taking the cluster out, but that kind of worries me since I don't want to damage the speedometer itself. Guess i'll wait until I replace all of the cluster lights to put the cable in.
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Old 08-08-2018, 12:48 PM   #8  
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Re: Speedometer cable

The really fun part is getting the new cable snaked behind the power brake booster, and through the rubber grommet in the firewall. I finally pulled mine out, libricated the grommet with silicon grease, pushed the new cable throughout the grommet, then reinstalled the grommet.
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Old 08-08-2018, 12:52 PM   #9  
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Re: Speedometer cable

Galaxie, you're just trying to cheer me up now! lol. When I took the upper half out, the grommet came out with it. I'll put some dielectric grease on it to get the cable through it and then wipe it off once it's in. I have a bunch of that grease sitting around. Thanks for the tip. I have a feeling finding the hole blindly will be another fun part to getting the cable in.
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Old 08-08-2018, 01:04 PM   #10  
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Re: Speedometer cable

The sad irony is that was only 7 months ago, and the T56 I’m swapping into the car now isn’t going to need the cable..
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Old 08-08-2018, 02:09 PM   #11  
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Re: Speedometer cable

Getting the cable back in the car really isn't too bad, worst part is making sure it clears everything around the firewall (steering, brake lines, fuel lines, exhaust). It's stiff enough that once it's approx lined up with the cluster, you can just grab it in the engine bay and push until you hear it click.

Two piece cables are a throwback to when GM used a transducer to generate a speed signal for cruise control. One cable in, one cable out, two cables. At least that's the way I view it.
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Old 08-08-2018, 02:37 PM   #12  
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Re: Speedometer cable

Drew,

I'll look closer at the end of the cable, I was just worried about the cable being turned 1 direction and the gear that it goes in being a different direction. Like if the end of the cable is rectangular and it's horizontal and the gear that it goes in has the slot vertical. I don't want to break the gear is my main concern. I need to take the cluster out to replace a bunch of bulbs regardless, so I may just get it mostly installed and wait to get the bulbs to finish the install.
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Old 08-08-2018, 02:46 PM   #13  
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Re: Speedometer cable

It's harder to get enough slack in the cable to reach behind the cluster and snap it in, then to do it with the cluster installed... At least that's been my experience. The cable core should just be square. Go slow and it should just guide itself into alignment, the drive on the speedometer will turn easily enough for it to line up.
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Old 08-08-2018, 03:23 PM   #14  
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Re: Speedometer cable

I got one at the local auto parts a month or so ago, just tell them make and model O'Reileys I think.
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Old 08-08-2018, 10:19 PM   #15  
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Re: Speedometer cable

I got the Pioneer CA3100 speedometer cable today and was able to put it in with the cluster in place. It is longer than needed so I had to kind of push some of the excess length up over the top of the trans while being careful not to link it. I took the car for a drive and it works well. Thank you everyone for your help and suggestions! On to figure out why my new coolant temp sensor goes from cold to off the charts and nothing in between now. I swear there’s always going to be a problem with this car. Lol.
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Old 08-09-2018, 06:58 AM   #16  
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Re: Speedometer cable

I thought the 2-piece cable was for the cruise control...
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Old 08-09-2018, 07:40 AM   #17  
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Re: Speedometer cable

I don't know but there's nothing that was hooked up/connected between the 2 pieces to say that it was a 2 piece cable for any reason. If it was there for the cruise control I'll never know as I don't like cruise control and never use it. I guess the next time that I take it out and can drive it over 40 MPH I can test it and report back. It won't be this weekend though.
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Old 08-09-2018, 01:36 PM   #18  
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Re: Speedometer cable

Up until 1984, the cruise control system needed a way to determine how fast the car was traveling. They used a box called a 'transducer' to convert the spinning speedometer cable signal to an electronic signal. The box was mounted to the frame rail on the driver's side, one speedometer cable from the trans to the box, another from the box to the cluster. Then in 1984 GM went to using the VSS on the back of the speedometer to tell the cruise control the vehicle speed, and the transducer went back to the place of nightmares and evil that it came from, and peaceful happiness rolled over the lands like a warm fuzzy sweater.

My best guess is that someone at GM probably decided they had a few million short speedometer cables leftover from the old system, so they burned them up on later cars.

The trans-doucher...
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