trans code
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trans code
well..I figured out that the engine and trans in this 71 convert is from a 78 vette 220 hp...but...which trans...where is the trans code...stamped don these ?
Last edited by jack mac; Dec 8, 2017 at 02:19 PM. Reason: spelling
Race Director
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how do we tell from this information whether you are referring to a manual or automatic transmission and which transmission, 350, 400, Muncie, Borg Warner?
this link is for automatics and the different pan shapes http://transmissiontechnologies.com/...an-shapes.aspx
this link is fore muncies
https://www.hemmings.com/magazine/mu...s/1495624.html
this link is for automatics and the different pan shapes http://transmissiontechnologies.com/...an-shapes.aspx
this link is fore muncies
https://www.hemmings.com/magazine/mu...s/1495624.html
Last edited by MelWff; Dec 8, 2017 at 03:11 PM.
Thread Starter
Advanced
Joined: Sep 2017
Posts: 63
Likes: 1
how do we tell from this information whether you are referring to a manual or automatic transmission and which transmission, 350, 400, Muncie, Borg Warner?
this link is for automatics and the different pan shapes http://transmissiontechnologies.com/...an-shapes.aspx
this link is fore muncies
https://www.hemmings.com/magazine/mu...s/1495624.html
this link is for automatics and the different pan shapes http://transmissiontechnologies.com/...an-shapes.aspx
this link is fore muncies
https://www.hemmings.com/magazine/mu...s/1495624.html
Melting Slicks
Joined: Sep 2004
Posts: 3,228
Likes: 672
From: Northeast
Couple of sites for the BW since normally in 78 it is attached to a L82 not 4spd L48.
http://www.hunt4cleanair.net/Articles/fourspeeds.pdf
http://pontiacpower.org/BW.htm (input shaft groove)
and more help "Count the cross-grooves on the input shaft. The input shaft enters the engine at the front of the transmission. Since there are many gear-ratio variations of the T10, there are identifying grooves cut across the clutch spine of the input shaft. According to Drivetrain.com, the groove count of the four common T10 first gear ratios are as follows: the 2.43 first gear ratio has two grooves, the 2.64 first gear has three
http://www.hunt4cleanair.net/Articles/fourspeeds.pdf
http://pontiacpower.org/BW.htm (input shaft groove)
and more help "Count the cross-grooves on the input shaft. The input shaft enters the engine at the front of the transmission. Since there are many gear-ratio variations of the T10, there are identifying grooves cut across the clutch spine of the input shaft. According to Drivetrain.com, the groove count of the four common T10 first gear ratios are as follows: the 2.43 first gear ratio has two grooves, the 2.64 first gear has three
Racer
Joined: Nov 2017
Posts: 319
Likes: 125
From: Midwest
Yes, counting the cross-grooves on the input shaft of the transmission would reveal if it is close- or wide-ratio. But if the transmission is installed in the car, you’d have to go to the trouble to separate the 4-speed from the engine to see the input spline.
Based on my research, the only external indicator Chevrolet put on BW Super T-10 4-speeds, to signify close or wide-ratio (that can be seen after it was installed), was a stamped ink broadcast code. Such ink stamps would not have lasted for many years underneath most cars. And, practically speaking, they only needed to be legible until the gearbox was installed.
However, using a little math and driving the car, there are ways to distinguish the two gearboxes from each other. By noting RPM, you can derive, beyond a reasonable doubt, which 4-speed you have. To keep things fairly simple and keeping the OP’s circumstance in mind (which might be similar to others), the particular procedure below will work with the following assumptions.
> You have a Borg-Warner ST-10 4-speed transmission in or from a ‘74-’79 Corvette.
> Your tire diameter is about 27.1 inches. That’s close to a 255-60-15, 225-70-15 or 215-70-15.
> Your tachometer and speedometer are reasonably accurate.
> You know what your rear axle ratio is. (If you’re not sure, it’s easy to determine on a lift.)
If so, drive on an open highway and bring your speed up to 65mph and shift into 4th gear.
With a 3:70 rear axle, you should be near 2,985 RPM—give or take a couple hundred--due to accuracy issues.
If you’re nowhere near 3,000 RPM, then at least one assumption is incorrect.
Both close and wide-ratio gearboxes will yield identical RPM in 4th gear at any speed.
The next step is to downshift into 3rd gear, while still maintaining 65mph.
If your tach jumps about 1,000 RPM (to ~ 4,000), then you have the wide-ratio version.
If your tach jumps only about 670 RPM (to ~ 3,670), then you have the close-ratio/M21.
With a 3:55 axle, check that you’re about 2,860 RPM in 4th gear @ 65mph. Shift to 3rd gear, maintaining your speed.
The wide-ratio would cause an increase of about 975 RPM—to about 3,835 RPM.
The M21 would only cause a rise of about 660 RPM—to about 3,521 RPM.
For a 3:36, confirm you’re about 2,710 RPM (4th gear @ 65mph). Downshift to 3rd.
The wide-ratio will cause an increase of about 920 RPM—to about 3,630 rpm.
The M21 would increase RPM by about 620, putting you at just under 3,330 RPM.
This procedure works because we know that the 4th gear ratio is the same for both -> 1:1. And we also know that 3rd gear is 1.23 in the close-ratio and 1.34 in the wide-ratio. The three axle ratios I calculated above are the three most popular ratios for C3s that had an M21 installed.
The Muncie 4-speeds, installed in C3s up to mid-'74, have different gearing in the lower three gears than the later Borg-Warner gearboxes. So their calculated numbers would be a bit different than those above. But the idea would be the same. And the M21 was gone altogether after '79.
Based on my research, the only external indicator Chevrolet put on BW Super T-10 4-speeds, to signify close or wide-ratio (that can be seen after it was installed), was a stamped ink broadcast code. Such ink stamps would not have lasted for many years underneath most cars. And, practically speaking, they only needed to be legible until the gearbox was installed.
However, using a little math and driving the car, there are ways to distinguish the two gearboxes from each other. By noting RPM, you can derive, beyond a reasonable doubt, which 4-speed you have. To keep things fairly simple and keeping the OP’s circumstance in mind (which might be similar to others), the particular procedure below will work with the following assumptions.
> You have a Borg-Warner ST-10 4-speed transmission in or from a ‘74-’79 Corvette.
> Your tire diameter is about 27.1 inches. That’s close to a 255-60-15, 225-70-15 or 215-70-15.
> Your tachometer and speedometer are reasonably accurate.
> You know what your rear axle ratio is. (If you’re not sure, it’s easy to determine on a lift.)
If so, drive on an open highway and bring your speed up to 65mph and shift into 4th gear.
With a 3:70 rear axle, you should be near 2,985 RPM—give or take a couple hundred--due to accuracy issues.
If you’re nowhere near 3,000 RPM, then at least one assumption is incorrect.
Both close and wide-ratio gearboxes will yield identical RPM in 4th gear at any speed.
The next step is to downshift into 3rd gear, while still maintaining 65mph.
If your tach jumps about 1,000 RPM (to ~ 4,000), then you have the wide-ratio version.
If your tach jumps only about 670 RPM (to ~ 3,670), then you have the close-ratio/M21.
With a 3:55 axle, check that you’re about 2,860 RPM in 4th gear @ 65mph. Shift to 3rd gear, maintaining your speed.
The wide-ratio would cause an increase of about 975 RPM—to about 3,835 RPM.
The M21 would only cause a rise of about 660 RPM—to about 3,521 RPM.
For a 3:36, confirm you’re about 2,710 RPM (4th gear @ 65mph). Downshift to 3rd.
The wide-ratio will cause an increase of about 920 RPM—to about 3,630 rpm.
The M21 would increase RPM by about 620, putting you at just under 3,330 RPM.
This procedure works because we know that the 4th gear ratio is the same for both -> 1:1. And we also know that 3rd gear is 1.23 in the close-ratio and 1.34 in the wide-ratio. The three axle ratios I calculated above are the three most popular ratios for C3s that had an M21 installed.
The Muncie 4-speeds, installed in C3s up to mid-'74, have different gearing in the lower three gears than the later Borg-Warner gearboxes. So their calculated numbers would be a bit different than those above. But the idea would be the same. And the M21 was gone altogether after '79.
Last edited by C3Highway; Dec 10, 2017 at 10:02 AM.
