Doug Nash 4+3 markings

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Jul 11, 2013 | 06:13 PM

QCVette

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Le Mans Master

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From: South Dakota

Doug Nash 4+3 markings

There were two OD ratios (0.60 & 0.68) that were available.

Is there any external way to visually tell which ratio it has? Is there any marking or code stamped on it to tell? Or any other way?

I am aware that if you know the car it came out of, you can look on the SPID label for MH5 or MK2 (MK2 used on Z51 cars), but some of the transmissions that are out of the cars don't have information about what they came from.

Thanks

Jul 11, 2013 | 06:58 PM

WVZR-1

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Quote:

Originally Posted by QCVette

I believe the ratios are actually .59 and .68 but not to debate that I'd take your question directly to the people that are likely the only ones that could give you a "definitive" answer.

http://www.5speeds.com/nash.htm

These guys are the 4 + 3 folks period. There's very good information on their website and I'd suspect they would be the easiest source of information as to how to identify. I don't recall seeing any mention ever of the tooth counts on the planetary gears and I know of nothing else that distinguishes the two.

I believe they sold all their hard parts to these people and a quick glance at their website it seems they've purchased the rebuilding services also. Someone else to call:

http://www.skspeed.com/

Last edited by WVZR-1; Jul 11, 2013 at 07:06 PM.

Jul 11, 2013 | 07:08 PM

WVZR-1

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Is there any stampings on any of the external surfaces that appear to have been done after or during assembly. Not casting information but stamped information?

Jul 11, 2013 | 07:18 PM

c4cruiser

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From: Lacey WA RVN 68-69

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I think it was the Callaway twin turbo (RPO B2K) cars with the 4+3 that had the .060 ratio in the OD. I had also read that the OD may have been an .062 ratio in those cars.

Because the cars ordered with the B2K option were sent from the Bowling Green Assembly Plant to Connecticut for the necessary modifications, I would expect that the Assembly Plant used a separate batch of 4+3 trannys for the install as they would have known exactly what cars would be going there.

Jul 11, 2013 | 08:27 PM

QCVette

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Le Mans Master

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From: South Dakota

Thanks for the responses.

Quote:

Originally Posted by WVZR-1

You are probably right. I have read both the 0.59 and the 0.60 ratios. My '85 FSM references a 0.59 ratio. I have also read 0.67 and 0.68 for the other one. I don't know what the actual ratio is, but I suspect that it may be as simple as a rounding difference on both of them.

I will try checking with your references.

Quote:

Originally Posted by c4cruiser

I think it was the Callaway twin turbo (RPO B2K) cars with the 4+3 that had the .060 ratio in the OD. I had also read that the OD may have been an .062 ratio in those cars.....

I don't know what the Callaway cars used, but the 0.60 ratio was not limited to them. I had one in a base '87 coupe.

I had not heard of the 0.62 ratio before, but interesting that there might be another ratio.

Jul 12, 2013 | 02:47 PM

QCVette

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Le Mans Master

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From: South Dakota

I got a response from 5speeds.com that "The MK2 was .68 and the MH5 was .59 Some gearboxes had that stenciled on the top of the main case...."

Other than that they referred to the SPID label.

So I guess it is hit or miss if they happened to be stenciled on top.

Jul 13, 2013 | 09:52 AM

Chuck Tribolet

Burning Brakes

Joined: Dec 2008

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From: Morgan Hill and Marina California

You should be able to tell via the tach. Put on cruise control, OD on,
at 2000 rpm. Turn OD off, resume the cruise control if necessary, not
tach setting, do the math. OD ratio will be 2000/OD off RPM.

Chuck

Jul 13, 2013 | 11:10 AM

c4cruiser

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From: Lacey WA RVN 68-69

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Quote:

Originally Posted by QCVette

Thanks for the responses.

You are probably right. I have read both the 0.59 and the 0.60 ratios. My '85 FSM references a 0.59 ratio. I have also read 0.67 and 0.68 for the other one. I don't know what the actual ratio is, but I suspect that it may be as simple as a rounding difference on both of them.

I will try checking with your references.

I don't know what the Callaway cars used, but the 0.60 ratio was not limited to them. I had one in a base '87 coupe.

I had not heard of the 0.62 ratio before, but interesting that there might be another ratio.

If you look at the various forums that specialize in Corvettes, there will be a variety of 4+3 OD ratios mentioned. I have seen everything from the .59 to .62 for the higher gears to .67 or .68 for the lower ratio.

I would expect that Callaway would know what the specific OD ratio was for the '87 C4's that they built (the '88 used a 6-speed). I would also expect that Doug Nash Engineering only made two ratios for that OD unless there was some sort of custom application they could have made.

The build sheet for my '87 4+3 shows "MH5 Econ" for the trans but nothing that specifies a ratio.