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I need some technical help, I am using a 700R4 tranny in my 56 Chevy PU. The speedometer I have is gear driven. The tranny is electric. How do I convert the tranny drive to the older gear drive for the speedo cable? One shop said the gear drive from certain 350 turbo's will fit in place of the stock speed sensor ?? Any transmission guys around ?
LRW
 

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Revolution Calling
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Very simple actually, all you need is a mechanical 'speedo bullet', drive gear and clip (on output shaft), and driven gear. (fits in bullet) There were mechanical speedos in some older TH700R4's from the factory.

The hard part is removing the old reluctor from the output shaft.

You'll need all the 'numbers' to calculate the speedo drive and driven gears. There are numerous 'gear calcs' to get it right.
 

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C-10 said:
Very simple actually, all you need is a mechanical 'speedo bullet', drive gear and clip (on output shaft), and driven gear. (fits in bullet) There were mechanical speedos in some older TH700R4's from the factory.

The hard part is removing the old reluctor from the output shaft.

You'll need all the 'numbers' to calculate the speedo drive and driven gears. There are numerous 'gear calcs' to get it right.
I have found your answer with the search function, I have the same issue, but I have to say I cannot make anything of your answer: what is a "speedo bullet"? Where can I find more details on this issue/solutions?
Are these parts from an older trans (cable speedo trans)?
Is it possible and easy to swap the tailshaft housing?
Thanks
 

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Don't want to steal this thread but I'm not doing anything at the moment.

The tailshaft housing just unbolts. The "bullet" is the piece that holds the driven gear, speedo cable screws on to, fits into the side of the trans.

85-early nineties vans, trucks have the correct parts.
 

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So, it seems the easy way would be to swap the tailshaft housing, right? Or is there a reason to swap the small parts instead?
Does swapping the housing involve anything else I do not know? It seems every easy plan has a couple of tricks hidden somewhere!...
 

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wave1957 said:
So, it seems the easy way would be to swap the tailshaft housing, right? Or is there a reason to swap the small parts instead?
Does swapping the housing involve anything else I do not know? It seems every easy plan has a couple of tricks hidden somewhere!...
No reason to replace tail housing with another identical tail housing. Just swap the speedo parts.
 

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So, 3 months later, I am on the garage floor trying to swap the tail shaft housing from my '88 700r4 (electronic speedo drive) with a housing from an '86, with cable drive.
The output shaft on the '88 trans has a metal wheel with straight gears on it, I guess where the magnets for the electronic speedo drive got their signal: is this what you call the reluctor?
How do I remove this in order to install a plastic gear instead, that would work with the driven gear in my '86 housing?
I had looked around a fair bit online before I started the actual mod, I saw it is easy to swap gears, but never did I see anything about removing this reluctor wheel! And you say it is the hardest part! Help! Please!
I guess this is the hidden trick that always appears in every easy plan...
Thanks.
 

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Revolution Calling
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Get yourself a speedo gear set to accommodate your final drive ratio, (gets the speedo to tell you the correct speed) then a CLIP that holds that drive gear in place on the output.

You could fab up one of these quickly like I did to pull the reluctor:
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Thanks for the tool picture! Is it very hard to remove the reluctor? Since I do not weld, I will have to improvise, but I get the idea!
Next to the reluctor on the output shaft (between the reluctor and the rear end of the shaft), there is a thicker part, metal, about 3 inches long, pretty much the same diameter as the reluctor wheel, that would obviously have to go too: what is it, how do I get rid of it?
Then, how do I know where exactly to mount the drive gear on the shaft, is there some marking...?
 

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wave1957 said:
Thanks for the tool picture! Is it very hard to remove the reluctor? Since I do not weld, I will have to improvise, but I get the idea!
Next to the reluctor on the output shaft (between the reluctor and the rear end of the shaft), there is a thicker part, metal, about 3 inches long, pretty much the same diameter as the reluctor wheel, that would obviously have to go too: what is it, how do I get rid of it?
Then, how do I know where exactly to mount the drive gear on the shaft, is there some marking...?

there should be two holes in the out put shaft for the clip for the plastic gear...... install the clip into the front hole for proper position in a non corvette tail tail housing


:cool:
 

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C10, thanks for the tool picture! I made a tool inspired by yours with threaded pieces and 2 pieces of wood (2X4) and it worked very well, the reluctor came easily, uncovering the 2 holes for the new clip! Thank you, it took me less than 1/2 an hour to make the tool and remove the reluctor, without even getting dirty!
 

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Hi guys, it is me again! I am learning as I go...
So now, I was trying to install the drive gear on the output shaft of my trans... It was really difficult, I was using the same "tool" I had used to remove the reluctor gear to try and gently hammer the plastic gear in place: the gear barely moved until it broke!... Is there a trick there? Should I put some oil on the shaft, should I lightly sand the inside of the gear to make it fit?
Thanks!
 

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Well, I was using the gear the trans shop sold me! And apparently, heating the gear in boiling hot water makes it a bit bigger and mostly, less brittle; I am afraid I was not driving it perfectly straight...
And my new problem is that it is a discontinued gear, not available anymore... That shop had one, by chance and now, well...
It is a brown 20 teeth drive gear for a th700r4: any body knows where I can find one? Or any body has an extra one?
Thanks!
 
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