Speedo cable 90º adapter
Thread Starter
Pro
Joined: Jan 2009
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From: Havelock North Carolina
Speedo cable 90º adapter
I'm in the process of restoring a 78 Pace Car and I've swapped out the TH350 for a 200 4R. The issue I'm having is the bend that needs to happen to enable the speedometer cable to attach to the tranny. I purchased a 90º adapter but it doesn't fit on the tranny. The cable fits fine. A friend of mine says that the adapter is probably for an early model C3 that the speedo cable is attached to the distributor and not for the tranny itself. Did anyone who made this swap to a 200 4R have similar issues and/or does anyone know where I can get the correct adapter to fit the 200 4R?
Team Owner
Joined: Jun 2001
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From: Virginia USA
Early C3's Tach is driven by the distributor. Speedo's still driven by the trans. I have a '71 SBC 4 speed so I can't help with the automatic trans car. I know my cable has the 90 ° adaptor.
Le Mans Master
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From: Central Texas
Race Director
Joined: Sep 1999
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From: Plano TX
The adapter was originally designed for the tach cable, but the tach uses the same fittings as the speedo.
Both ends of the adapter should have the same fitting, just male/female. If the speedo cable fitting fits the transmission hookup, then the adapter should fit as well.
Only downside to the adapter is that as it was designed for the distributor driven tach, it is not sealed. The transmission will pump some fluid into it and it will leak. I wrapped my adapter with the self vulcanizing tape they sell at parts stores for emergency hose repair.
Both ends of the adapter should have the same fitting, just male/female. If the speedo cable fitting fits the transmission hookup, then the adapter should fit as well.
Only downside to the adapter is that as it was designed for the distributor driven tach, it is not sealed. The transmission will pump some fluid into it and it will leak. I wrapped my adapter with the self vulcanizing tape they sell at parts stores for emergency hose repair.
Team Owner
Joined: Jun 2001
Posts: 23,375
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From: Virginia USA
This is what I'm talking about and the "bracket" is shown in this picture and is located at the trans end of the cable.
Le Mans Master
Joined: Aug 2010
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From: Central Texas
Originally Posted by theandies
If that is what he's talking about that is not stock.
This is what I'm talking about and the "bracket" is shown in this picture and is located at the trans end of the cable.
This is what I'm talking about and the "bracket" is shown in this picture and is located at the trans end of the cable.
Thread Starter
Pro
Joined: Jan 2009
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From: Havelock North Carolina
Thread Starter
Pro
Joined: Jan 2009
Posts: 605
Likes: 28
From: Havelock North Carolina
No. This is a pic sent by a forum member showing the stock cable that he has on his car. 
I was hoping that someone out there put a 200 4R in their 78 and had the same issue and they could tell me how they resolved it. I can put the cable directly onto the tranny but there is limited space in the tunnel and the cable has to be bent 90º in order to follow the tunnel and not be burned by the exhaust. With the design of the stock TH350, and the location the cable screwed into the fit was much better and the cable did not have to be bent so severely.
I was hoping that someone out there put a 200 4R in their 78 and had the same issue and they could tell me how they resolved it. I can put the cable directly onto the tranny but there is limited space in the tunnel and the cable has to be bent 90º in order to follow the tunnel and not be burned by the exhaust. With the design of the stock TH350, and the location the cable screwed into the fit was much better and the cable did not have to be bent so severely.
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Race Director
Joined: Sep 1999
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From: Plano TX
Can you post a pic of what you have? And a link to where you got it from.
Le Mans Master
Joined: Aug 2010
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From: Central Texas
The 200 transmission must have different threads on the driven gear adapter?
The threads are the same on the one you purchased as the ones that I see listed on the net.
I'd call a transmission parts outlet for more detailed parts ID.
The threads are the same on the one you purchased as the ones that I see listed on the net.
I'd call a transmission parts outlet for more detailed parts ID.
Former Vendor
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From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
I'd use this adapter because its 1:1 ratio, where as the original adapters were ratio'd
https://willcoxcorvette.com/corvette...-adapter-62-74
https://willcoxcorvette.com/corvette...-adapter-62-74
Thread Starter
Pro
Joined: Jan 2009
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From: Havelock North Carolina
Purchased from Corvette Central
[QUOTE=Street Rat;1593570406]The 200 transmission must have different threads on the driven gear adapter?
I don't think so. The cable fits fine on the tranny as well as the treaded end of the adapter shown here. I think the problem is that both ends of the adapter should have the same thread pattern but they don't. The nut end on the adapter does not fit the tranny. I could just screw the speedo cable onto the tranny, make the bend and hope it will last but wanted to avoid doing that.
Melting Slicks
Joined: Oct 2006
Posts: 2,417
Likes: 336
From: Texas
i used a BM lockup controller, it had a short piece of speedometer cable and a signal generator and the stock speedometer cable fit on the signal generator. i did have to change out the speedometer bullet adapter in the trans. because i changed the plastic driven gear too. its a tight fit under there but it has worked fine for several years now.
i thought those 90 deg. adapters were for tach drive on the distributor.
i thought those 90 deg. adapters were for tach drive on the distributor.
Last edited by speedreed8; Dec 1, 2016 at 09:02 AM.
Le Mans Master
Joined: Jan 2001
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I used a 10"-12" tach extender cable from mid-america
actually about 9 inches......when I was running a VSS from my tranny to my 730 ECM.
I don't see it on their website anymore, but perhaps you can call and ask them. here is the old part number:
609465-Tach Cable adapter from Mid America Corvette for VSS.
I'm not running the 730 ECM anymore, but that VSS and that tach extender cable is still under there.
Anyway, something to consider.
I don't see it on their website anymore, but perhaps you can call and ask them. here is the old part number:
609465-Tach Cable adapter from Mid America Corvette for VSS.
I'm not running the 730 ECM anymore, but that VSS and that tach extender cable is still under there.
Anyway, something to consider.
i used a BM lockup controller, it had a short piece of speedometer cable and a signal generator and the stock speedometer cable fit on the signal generator. i did have to change out the speedometer bullet adapter in the trans. because i changed the plastic driven gear too. its a tight fit under there but it has worked fine for several years now.
i thought those 90 deg. adapters were for tach drive on the distributor.
i thought those 90 deg. adapters were for tach drive on the distributor.
Last edited by carriljc; Dec 1, 2016 at 05:58 PM.