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Ive been asking a lot of questions here about saginaw into hk. So firstly thanks everyone whos helped. The car will have a mild 307 and 3.36 10 bolt factory lsd. Does it really matter which saginaw i buy. Cant afford an original part numbered one. Apparently the grooves or lack of grooves on the input shaft tell the ratios? How important is this? Also do muncies use the same system for checking ratios. The sag im looking at has no grooves and the muncie im looking at has 1 groove. I know the muncie will need the reverse shift rod shortened if i go that route. Hard to find a reasonably priced one so saginaw or muncie will work for me. Just wanna use period parts. Thanks
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Muncie is far stronger. There are a few ratio sets, but M21 Muncie is too tall in 1st - 2.20:1. You would want an M20, 2.52:1 1st.
Saginaws come in 4 x ratio sets, just google it and you'll find them.
You'll find an original HT-HG 253 Saginaw cheaply, these are the same as a HK one. |
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What about the saginaw no groove input. Would 2.84 first gear be to high? Would i loose first gear so to speak?
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The 2.54 box was known as the M21 here, and was standard on everything except 6 cylinder commercials, which used the 2.85 box, known as M22. The M21 was described as close ratio, has a single input shaft groove, and the M22 described as wide ratio.
The speeds in gears, assuming something like 205/70 14 tyres, your 3.36 differential and 5500RPM max would be:
M21:
1st 46mph
2nd 64.9mph
3rd 81.1 mph
4th 116.7mph
M22
1st 41mph
2nd 57.8mph
3rd 86.5mph
4th 116.7mph.
As you can see, 1st in an M22/2.85 box would not be "lost", but your 307 will easily deal with the taller 1st gear of an M21. I guess it depends on what you want to do with the car. The main difference between the two boxes is the gap from 2nd to 3rd.
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...the taller 1st gear was an attribute to anything with decent horsepower....anything else was just thrashing the engine and changing gears madly...otherwise all the while your potential nemesis is pulling away... ...these long 1st gearboxes are the "close ratio" 4 speeds that make a performance car come alive.... Edited by user Friday, 2 October 2015 8:31:29 PM(UTC)
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So i guess my best bet is to look for a saginaw or muncie with approx 2.5 first gear?
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2.52:1 Muncie, 2.54:1 Saginaw. The standard HK 2.54:1 1st gear Saginaw was the standard V8 M20 Saginaw in the USA used for most lighter duty applications so will be fine, I think the highest torque application in a similar size car to a HK a Saginaw ever got put in was a 1967-8 L30 (275hp) 327, other than that our own HT-HG GTS350. Both of these applications saw the Saginaw beefed up though with heavier duty bearings. However a Saginaw can still easily be chewed up by a 307 - they aren't all that much more durable than an Aussie 4spd relatively speaking (sit somewhere on a sliding scale between an Aussie and a Muncie maybe less than halfway). With the 3.36:1 rear axle, as long as the tyres are close to original diameter you'd probably be able to live with an M21 Muncie (2.20:1 1st) rather than M20 Muncie (2.52:1 - we called this MC7 in HQ). A HT-HG 253 4spd is the 2.54:1 Saginaw with a 3.08:1 rear axle which is overall still lower than 2.20:1 with 3.36 but the 307 will have a lot more torque. 2.20:1 M21 Muncie with 3.55:1 rear axle is the same overall 1st gearing as 2.54:1 with 3.08. As long as you aren't reversing up steep driveways or regularly taking off on steep hills you'd probably be OK. I have an M21 Muncie for my HK 5litre GTS, but it'll probably have 3.70:1 gears (9") but also 15" rally rims with taller than original 15" tyres. Edited by user Sunday, 4 October 2015 2:24:21 PM(UTC)
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Originally Posted by: HK1837  A HT-HG 253 4spd is the 3.54:1 Saginaw Should be 2.54?
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