Is this the Stewart-Warner speedo adapter that was originally used for high-ratio combos? And if not, what was the make and what did they look like?
and here's another view w/numbers, etc:
and here's another view w/numbers, etc:
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Re: C3: Gear reduction adaptor for 411 and 456 pos
Dan-----
It's the same TYPE of adapter that was used on some Corvette applications. However, this one has a ratio of .9743:1. I don't know of any Corvette application that used a ratio like this. It would almost seem that such a ratio might be used for final calibration for "certified" police vehicle speedometers.In Appreciation of John Hinckley -
Re: C3: Gear reduction adaptor for 411 and 456 pos
I looks like the speedo adapter "some" car dealers used to cut the miles in half on the demos in the 70s .Comment
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Re: C3: Gear reduction adaptor for 411 and 456 pos
i've owned 3 71 z28's all with m22 trans and all 3 had that style of adapter and i think the same ratio joe mentioned as i checked one once and it seemed to be 1:1. i always wondered why gm put it in if it was 1:1.all 3 z's were 3.73 rear gearComment
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Re: C3: Gear reduction adaptor for 411 and 456 pos
I believe the 4.56 used a similar adapter, would have to check the parts book for ratio. As I recall, 4.11 did not need the adapter.Bill Clupper #618Comment
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Re: C3: Gear reduction adaptor for 411 and 456 pos
'69 Camaros used the adapter, but only with the 4.56 axle; not used on the 4.10 axle.Comment
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Re: C3: Gear reduction adaptor for 411 and 456 pos
Bill----
It depends on the year model. For 1971 and later, an adapter was required for all Corvettes with 3.70:1 or 4.11:1. There was no way to achieve accurate speedometer calibration without them since there is no driven gear with greater than 22 tooth count available for 1971 and later 4 speeds.In Appreciation of John HinckleyComment
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Re: C3: Gear reduction adaptor for 411 and 456 pos
John-----
Yes, for 1968 through 1970 4.10 (or, 4.11) ratios could be accommodated for most applications with a GM #3924097 DRIVE gear and a 25 tooth, GM #3860348 DRIVEN gear. There was no driven gear of greater than 25 tooth configuration available (or, any other DRIVEN/DRIVE gearset that would accomplish the same thing), so the only way to accommodate the 4.56 ratio was through an adapter.
For 1971 and later Muncies, the installed DRIVE gear could not accommodate any DRIVEN gear with a tooth count of greater than 22 (SILVER ONLY). So, the only way that most rear gear ratios numerically higher than 3.55:1 (and, in some cases, even 3.55:1) could be accommodated was through the use of an adapter.
I suppose that GM figured there was no reason to design a speedometer gearset for 1971+ Muncies with the capability to accommodate such ratios since there would not be that many such cars built. As expensive as adapters are, it was probably cheaper than such a design and the extra transmission part numbers that would be required.In Appreciation of John HinckleyComment
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Re: C3: Gear reduction adaptor for 411 and 456 pos
Any idea what one stamped 666 F R6 and .8974B was used on, and if used on any Corvette's? I think it is probably off a mid-1970's Chevy, but not positive. TIA. DaveComment
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Re: C3: Gear reduction adaptor for 411 and 456 pos
Dave-----
I can't find that ratio for any Corvette applications. However, there are a few adapters for which I can't determine a ratio. So, it could be one of those. I doubt it, though.In Appreciation of John HinckleyComment
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Re: C3: Gear reduction adaptor for 411 and 456 pos
Joe-
So what ratio adapter would be correct for a 456 posi unit w/a close ratio transmission? TIA.Comment
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Re: C3: Gear reduction adaptor for 411 and 456 pos
Dan------
It depends upon several factors. The first is the tire size of the car. The second is the installed speedometer DRIVEN gear.
For a C3 with F-70-15-equivalent size tires and a 19 tooth speedometer DRIVEN gear, the adapter ratio would be 0.7333:1. As the DRIVEN gear tooth count increases, the adapter ratio gets closer to 1:1, but never equals 1:1 as long as the standard DRIVEN gears (25 tooth count maximum) are utilized.
Once-upon-a-time, there were some special speedometer gearsets available which could achieve calibration for 4.56:1 rear ratios without an adapter. Primarily, these were used for pre-1968 applications. However, the could have been used for 68-70 and may or may not have been actually used. They could not be used for any 1971+ application.In Appreciation of John HinckleyComment
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Re: C3: Gear reduction adaptor for 411 and 456 pos
Thanks Joe. I really didn't think it was used on any Corvette's. I have since found it was actually removed from a 1976 Chevrolet Monza Coupe that originally had a 305 engine, Saginaw wide ratio 4 speed (2:85 or 3:11 1st gear?, not sure), 3:23 non-posi rear gear and 195 (?) x 13" tires. It was probably used to correct the speedometer reading with that drivetrain/tire size combination. FWIW. DaveComment
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Maybe not a Monza part
Unless it was your Monza, I think your info may be wrong as the 1976 Monza had the 4.3 liter engine, I do not think the 5.0 came out until 1977 (I owned an original 5.0 in 1980- my mom's car). The 1977 V8 had a stock 2.29 (yep, that's 2.29) ratio open diff, as far as I know, the V6 used a 2.6 ratio and the 4 cyl used the 2.9. Even the 2.9 ratio with the saginaw trans did NOT use an adapter setup (I ran the saginaw and 2.9 ratio posi in my 1976 with a destroked 400 SB when it was first assembled).
MarkComment
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Re: Maybe not a Monza part
Mark, You are correct. I forgot the 305 was swapped in, it was not original to the car, the original engine was a 262 V-8. The rest of the drivetrain, as far as I know, was original to car. Of course, that does not mean parts could not have been changed or added, some where along the line. The car was about 8-10 years old when it was acquired, so who knows. The car was sold about a year later, without the engine and 4 speed, to a guy that used it for parts. I just wanted to know if the adapter had any other applications, anyway. DaveComment
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