General Motors (Muncie) SM-420 4-Speed
When you start thinking about gear ratios you need to look at the whole picture, not just transmission
gearing, but rear axle gearing & tire size play a lot into the equation too. There is a formula or
two for this, This is the one found in the 1965 GMC Dealer data book;
RPM x 60 divided by Final Ratio x tire revolutions pre mile = Miles pre hour.
3500 x 60 (210000) / 3.54 x 745 (2637.3) = 79.63
To get "tire revolutions pre mile" paint a spot on the tire & ground, then roll the truck forward
tell the paint spot on the tire meets the ground again, then paint the ground there. Move truck out
of the way & measure the distance between paint spots in inches, then divide that number into how
many inches in a mile (63360"). That will give you "tire revolutions pre mile".
So lets look at a GMC 1/2 ton truck with rear axle ratio of 3.54:1. We also know this info; 4 speed SM420
transmission, 1st = 7.06:1, 2nd = 3.58:1, 3rd = 1.71:1, 4th = 1.00:1. With this set up, that will give
you a final drive gear ratios of; 1st = 24.99:1, 2nd = 12.67:1, 3rd = 6.05:1, 4th = 3.54:1. Engine max
RPM of 3500, 15 inch tire will have a revolutions pre mile of around 745. So our first number will be
3500 x 60 = 210000, the 2nd number in 4th gear 3.54 x 745 = 2637.3, so now take 210000 / 2637.3 = 79.63 mph.
Top speed in low gear would be 210000 / 18617.55 = 11.28 mph. Just for the record, 16" tires = 705 rpm.
GMC used the The SM-318 as the standard 3-speed tranmission in GMC series 1000 & 1500 trucks. In 1963 they
also offered the New Process 746G as a Heavy Duty option for 1000, 1500, K1000 & K1500 Series trucks.
In 1964 the Warner T-89B was offered as an option for P/PB1000, P/PB1500 & P/PB2500 series chassis.
The SM-420 4-speed transmission was produced by General Motors between the years of 1947 & 1967.
It was the standard transmission for GMC 2500, 3000, 3500 & 4000 series Trucks, & an option for 1000 &
1500 series trucks. There was no option for any other transmission in GMC 2500 & 3000 Series Trucks.
Starting in 1966 General Motors offered the NP-435GA for its light truck applications as an option.
The NP-435-GA became the standard 4-speed some time in the late 1960s. The cast iron case with large
bulge on the passenger side makes the SM-420 easy to identify. Ribbing was added to the bulge on
later cases, my 1965 GMC 2500 has this feature. The ribbed SM-420 case should not be confused with
the later SM-465 transmission. How can you tell which 4-speed your 1966 has, if reverse is to the
driver & down, it's the SM-420, if to the passenger & down, it's the NP-435-GA. The SM-465 Replced the
SM-420 in GMC truck in 1967. The General Motors Transmissions are also called Muncie by many folks.
SM = Synchro-Mesh, NP = New Process.
General Motors (Muncie) SM-420 4-Speed
General Motors (Muncie) SM-420 4-Speed
Advantages of the SM-420 is it's length is the shortest of all the heavy duty 4 speeds. When you add
the fact that the SM-420 has the lowest low gear of any light truck transmission, it makes this a
very sought after Transmission with 4-Wheeler's. The SM-420 only had a backup light switch in 1967.
The SM-420 used from 1960-1966 did not have this feature which many would take for granted today.
All SM-420's have a casting number on the drivers side. The numbers seem to vary from transmission to
transmission, All seen has "GM", The screw heads are what holds the tag on when making the casting.
So now you ask, "How can I install one of these into my GMC?", well Buckie, just check out this page:
*~~> Upgrading a SM-318 3-speed to a SM-420 4-speed <~~*
New Process NP-435-GA 4-Speed
New Process NP-435-GA 4-Speed
Even thou the SM-465 was not used in the 1960-66 trucks, I have some info here on those as well, as
it was used behind the GMC V6 in the later 1967-69 (74) GMC Trucks. This would be a bolt on if you
found a SM-465 from a 1967 GMC truck, otherwise you would need to change a few more item as The 1968
& Up SM-465 has a bigger input shaft. The SM-465 offers newer needle bearings, & a somewhat higher
1st gear then the SM-420. The one seen below is from a 1967 GMC 4-wheel drive.
General Motors (Muncie) SM-465 4-Speed
More SM-420 Info here, & Parts too, Novak Conversions.
Looking for an Overdrive unit? Got Cash? Check this one this Gear Vendors Overdrive.
GMC used the Following Automatic Transmissions:
Hydra-Matic 177CA ~ 1960-62 GMC 1000
Hydra-Matic 300GH ~ 1960-62 GMC 1500
Hydra-Matic 210U ~ GMC P1500
Hydra-Matic 330GP ~ GMC V3500
AT-218 Pow-R-Flo (Chverolet Powerglide) ~ 1963-66 Option
Turbo Hydry-Matic 400 (Chevrolet) ~ 1966 Option
An Automatic Transmission WILL NOT Bolt on to the back of a GMC V6 with out speical parts that
can only be found on GMC trucks that came equiped with a V6 engine & Automatic transmission.
Below are two different Adapter set ups I have seen, so it may be that they use different ones
for different trans missions. I Don't know for sure. Still looking for more info.
Here are photos of one of the two Adapter set ups I have seen.
Here are photos of the other Adapter set ups I have seen.
The Auto Trans Flywheel & Flexplate.
See Bendtsen’s Transmission Adapters for the ALL NEW GMC V6
Custom Built Automatic Adapters, Now Available for the 305 & 351 V6s.
Here are photos of the "Bendtsen’s Transmission Adapters" GMC V6 Adapter parts.
They include the Hub to mount the flexplate to the crankshaft, Flexplate, Adapter,
& the starter. This Adapter will mount any of the Chevrolet Automatic Transmissions
to the back of the GMC Big Block V6 from the 1960s, like the 305 & 351 V6s
found in GMC Light trucks.
GMC Used New Process, Clark & Spicer 5-Speed Transmissions in the 4000 series & bigger
Trucks. The New Process NP-540 series of 5 speed transmissions came in a few different models.
The "GL" is Pictured below & the others will look the same. The "GO" was an overdrive model,
the other models just had some different gear sets in them for the lower gears, see charts below.
The NP-450-GL was mounted behind a 401M in a 1963 4000 model, not stock running gear
for that truck, you will note that the trans top cover has a back up light switch, which came
out in 1967. This trans will be used in my 1965 GMC 1 ton with the 401M for power.
New Process NP-540-GL 5-Speed
New Process NP-540-GL 5-Speed
New Process NP-540-GL 5-Speed
GMC Used the follwoing Four & Five Speed transmissions.
|
Manufacturer |
Transmission |
1st |
2nd |
3rd |
4th |
5th |
Rev |
Oil Capacity |
|
General Motors/Muncie |
SM-318 |
2.94:1 |
1.68:1 |
1.00:1 |
|
|
2.94:1 |
2 pints |
|
Warner |
T-89B |
3.17:1 |
1.75:1 |
1.00:1 |
|
|
3.76:1 |
2.75 pints |
|
New Process |
746G |
3.02:1 |
1.76:1 |
1.00:1 |
|
|
3.95 |
?? pints |
|
General Motors/Muncie |
SM-420 |
7.06:1 |
3.58:1 |
1.71:1 |
1.00:1 |
|
6.78:1 |
6 pints |
|
General Motors/Muncie |
SM-465 |
6.54:1 |
3.57:1 |
1.70:1 |
1.00:1 |
|
6.54:1 |
6 pints |
|
New Process |
435GA |
4.56:1 |
2.28:1 |
1.31:1 |
1.00:1 |
|
5.64:1 |
6.75 pints |
|
New Process |
435GD |
4.90:1 |
2.27:1 |
1.19:1 |
1.00:1 |
|
8.26:1 |
6.75 pints |
|
New Process |
435GL |
6.68:1 |
3.34:1 |
1.66:1 |
1.00:1 |
|
8.26:1 |
6.75 pints |
|
New Process |
433G21 |
6.47:1 |
3.35:1 |
1.86:1 |
1.00:1 |
|
6.86:1 |
10 pints |
|
New Process |
433G22 |
6.47:1 |
3.35:1 |
1.86:1 |
1.00:1 |
|
6.86:1 |
10 pints |
|
New Process |
434G22 |
6.68:1 |
3.35:1 |
1.86:1 |
1.00:1 |
|
6.86:1 |
10 pints |
|
New Process |
540GD |
6.05:1 |
3.31:1 |
1.84:1 |
1.17:1 |
1.00:1 |
6.86:1 |
10 pints |
|
New Process |
540GL |
7.41:1 |
4.05:1 |
2.40:1 |
1.48:1 |
1.00:1 |
7.85:1 |
10 pints |
|
New Process |
540GO14 |
6.05:1 |
3.31:1 |
1.84:1 |
1.00:1 |
0.82:1 |
6.86:1 |
10 pints |
|
New Process |
541GD |
6.15:1 |
3.30:1 |
1.86:1 |
1.17:1 |
1.00:1 |
6.13:1 |
10 pints |
|
New Process |
541GL |
7.25:1 |
3.88:1 |
2.19:1 |
1.37:1 |
1.00:1 |
7.22:1 |
10 pints |
|
Clark |
261F |
6.32:1 |
3.41:1 |
1.77:1 |
1.00:1 |
|
6.26:1 |
12 pints |
|
Clark |
264VO |
6.06:1 |
3.50:1 |
1.80:1 |
1.00:1 |
0.80:1 |
6.00:1 |
12 pints |
|
Clark |
267V |
6.06:1 |
3.50:1 |
1.80:1 |
1.18:1 |
1.00:1 |
6.00:1 |
12 pints |
|
Clark |
269V |
6.06:1 |
3.50:1 |
1.91:1 |
1.18:1 |
1.00:1 |
6.00:1 |
12 pints |
|
Clark |
305V |
7.00:1 |
3.92:1 |
2.34:1 |
1.42:1 |
1.00:1 |
7.00:1 |
15 pints |
|
Clark |
307V |
6.27:1 |
3.51:1 |
1.89:1 |
1.18:1 |
1.00:1 |
6.27:1 |
15 pints |
|
Clark |
385V |
7.01:1 |
3.971:1 |
2.34:1 |
1.42:1 |
1.00:1 |
5.71:1 |
16 pints |
|
Clark |
387V |
6.27:1 |
3.55:1 |
1.89:1 |
1.18:1 |
1.00:1 |
5.11:1 |
14 pints |
|
Clark |
401V |
7.07:1 |
4.33:1 |
2.68:1 |
1.64:1 |
1.00:1 |
6.90:1 |
20 pints |
|
Clark |
406V |
6.61:1 |
3.56:1 |
2.11:1 |
1.43:1 |
1.00:1 |
6.02:1 |
20 pints |
|
Clark |
407V |
6.61:1 |
3.56:1 |
2.11:1 |
1.43:1 |
1.00:1 |
6.02:1 |
20 pints |
|
Clark |
408V |
6.17:1 |
3.56:1 |
1.90:1 |
1.16:1 |
1.00:1 |
6.02:1 |
20 pints |
|
Clark |
2653 |
7.08:1 |
4.08:1 |
2.23:1 |
1.46:1 |
1.00:1 |
6.73:1 |
12 pints |
|
Spicer |
3152A |
6.00:1 |
3.31:1 |
1.94:1 |
1.16:1 |
1.00:1 |
5.90:1 |
10 pints |
|
Spicer |
3153C |
6.00:1 |
3.31:1 |
1.94:1 |
1.00:1 |
0.79:1 |
5.90:1 |
10 pints |
|
Spicer |
5652 |
7.08:1 |
3.83:1 |
2.36:1 |
1.45:1 |
1.00:1 |
7.50:1 |
13 pints |
|
Spicer |
5752C |
6.10:1 |
3.30:1 |
1.81:1 |
1.17:1 |
1.00:1 |
6.46:1 |
13 pints |
|
Spicer |
6852G |
6.70:1 |
3.52:1 |
1.97:1 |
1.17:1 |
1.00:1 |
6.72:1 |
17 pints |
|
Spicer |
6852K |
6.72:1 |
4.02:1 |
2.49:1 |
1.57:1 |
1.00:1 |
6.72:1 |
17 pints |
|
Spicer |
6852S |
5.71:1 |
3.21:1 |
1.89:1 |
1.15:1 |
1.00:1 |
5.73:1 |
17 pints |
|
Spicer |
6853C |
5.71:1 |
3.02:1 |
1.78:1 |
1.00:1 |
0.86:1 |
5.73:1 |
17 pints |
|
Spicer |
8052, 8045* |
7.30 |
4.54:1 |
2.75:1 |
1.65:1 |
1.00:1 |
7.00:1 |
24 pints |
|
Spicer |
8052B |
7.30 |
4.54:1 |
2.75:1 |
1.56:1 |
1.00:1 |
7.00:1 |
24 pints |
|
Spicer |
8052D |
7.30 |
4.17:1 |
2.52:1 |
1.56:1 |
1.00:1 |
7.00:1 |
24 pints |
* 8054 Same as 8052 except aluminum case
GMC Used the follwoing Transfer cases.
Timken became Rockwell.
Coleman transfer cases used in the KV4000.
Model 22 is Declutcher type & model 42 is Differential type.
|
Manufacturer |
Transmission |
Low |
High |
Oil Capacity |
|
Timken |
T-221 |
1.94:1 |
1.00:1 |
4 pints |
|
Rockwell |
T-221 |
1.94:1 |
1.00:1 |
4 pints |
|
Coleman |
22 |
2.11:1 |
1.00:1 |
5.75 pints |
|
Coleman |
42 |
2.11:1 |
1.00:1 |
6.24 pints |
GMC Used the follwoing Auxiliary transmissions.
Spicer 5831-B Transmission Information Page
|
Manufacturer |
Transmission |
1st |
2nd |
3rd |
4th |
Oil Capacity |
|
Fuller |
2A-92 |
2.30:1 |
1.00:1 |
|
|
12 pints |
|
Spicer |
2.35:1 |
1.00:1 |
0.85:1 |
|
4 pints |
|
|
Spicer |
7231-A |
2.14:1 |
1.00:1 |
0.74:1 |
|
8 pints |
|
Spicer |
7231-D |
2.14:1 |
1.00:1 |
0.86:1 |
|
8 pints |
|
Spicer |
8031-C |
2.59:1 |
1.00:1 |
0.75:1 |
|
12 pints |
|
Spicer |
8031-P |
1.19:1 |
1.00:1 |
0.84:1 |
|
12 pints |
|
Spicer |
6041 |
2.14:1 |
1.24:1 |
1.00:1 |
0.86:1 |
8 pints |
|
Spicer |
7041 |
2.31:1 |
1.21:1 |
1.00:1 |
0.83:1 |
11 pints |
|
Spicer |
8341-A |
2.40:1 |
1.29:1 |
1.00:1 |
0.84:1 |
12 pints |
|
Spicer |
8341-C |
2.40:1 |
1.19:1 |
1.00:1 |
0.84:1 |
12 pints |
|
Spicer |
8341-F |
1.60:1 |
1.19:1 |
1.00:1 |
0.84:1 |
12 pints |
GMC Used the follwoing 8, 10 & 12 Speed transmissions.
|
Manufacturer |
Transmission |
First |
Second |
Third |
Fourth |
Fifth |
Sixth |
Sevenst |
Eighth |
Ninth |
Tenth |
Eleventh |
Twelfth |
Reverse Low |
Reverse High |
Oil Capacity |
|
Fuller Roadranger |
R-46 |
9.78:1 |
6.98:1 |
4.99:1 |
3.68:1 |
2.66:1 |
1.90:1 |
1.36:1 |
1.00:1 |
|
|
|
|
11.01:1 |
2.99:1 |
19 |
|
Fuller Roadranger |
R-96T |
9.65:1 |
7.43:1 |
5.80:1 |
4.48:1 |
3.54:1 |
2.73:1 |
2.10:1 |
1.64:1 |
1.27:1 |
1.00:1 |
|
|
11.26:1 |
3.18:1 |
40 |
|
Fuller Roadranger |
RT-510 |
9.00:1 |
7.02:1 |
5.48:1 |
4.26:1 |
3.43:1 |
2.62:1 |
2.05:1 |
1.60:1 |
1.24:1 |
1.00:1 |
|
|
9.50:1 |
2.77:1 |
12 |
|
Fuller Roadranger |
RT-910 |
8.055:1 |
6.30:1 |
4.99:1 |
3.95:1 |
3.20:1 |
2.51:1 |
1.97:1 |
1.56:1 |
1.24:1 |
1.00:1 |
|
|
8.73:1 |
2.73:1 |
26 |
|
Fuller Roadranger |
RTO-915 |
6.51:1 |
5.10:1 |
4.04:1 |
3.20:1 |
2.59:1 |
2.04:1 |
1.59:1 |
1.26:1 |
1.00:1 |
0.81:1 |
|
|
7.06:1 |
2.21:1 |
26 |
|
Fuller Roadranger |
RTO-915 Deep Low |
9.73:1 |
7.62:1 |
6.03:1 |
4.78:1 |
3.87:1 |
|
|
|
|
|
|
|
10.55:1 |
|
26 |
|
Spicer |
8125U forward |
10.45:1 |
8.83:1 |
6.54:1 |
5.23:1 |
4.09:1 |
3.28:1 |
2.55:1 |
2.05:1 |
1.59:1 |
1.28:1 |
1.00:1 |
0.80:1 |
see |
below |
28 |
|
Spicer |
8125U Reverse |
10.45:1 |
8.38:1 |
6.52:1 |
5.23:1 |
4.09:1 |
3.28:1 |
|
|
|
|
|
|
|
|
28 |
GMC Used the follwoing Spicer compound 16-Speed transmissions.
Each is composed of a 4-speed main front section & a attched 4-speed auxiliary rear section.
Each unit is shifted by a separate shift lever.
|
Model |
Main Unit |
Low Low |
Under |
Direct |
Over |
|
SP7216-3B |
First |
8.59:1 |
6.50:1 |
5.37:1 |
4.45:1 |
|
|
Second |
4.83:1 |
3.65:1 |
3.02:1 |
2.50:1 |
|
|
Third |
2.77:1 |
2.09:1 |
1.73:1 |
1.43:1 |
|
|
Fourth |
1.60:1 |
1.21:1 |
1.00:1 |
0.83:1 |
|
|
Reveres |
8.60:1 |
6.51:1 |
5.38:1 |
4.45:1 |
|
|
Oil Capacity |
28 pints |
|
|
|
|
Model |
Main Unit |
Low Low |
Under |
Direct |
Over |
|
SP8016-3B |
First |
10.00:1 |
7.62:1 |
6.25:1 |
5.08:1 |
|
|
Second |
5.44:1 |
4.15:1 |
3.40:1 |
2.76:1 |
|
|
Third |
2.96:1 |
2.26:1 |
1.85:1 |
1.50:1 |
|
|
Fourth |
1.60:1 |
1.22:1 |
1.00:1 |
0.81:1 |
|
|
Reveres |
10.22:1 |
7.78:1 |
6.39:1 |
5.18:1 |
|
|
Oil Capacity |
32 pints |
|
|
|
|
Model |
Main Unit |
Low Low |
Under |
Direct |
Over |
|
SP8216-3B |
First |
8.30:1 |
6.18:1 |
5.19:1 |
4.36:1 |
|
|
Second |
4.72:1 |
3.51:1 |
2.95:1 |
2.48:1 |
|
|
Third |
2.75:1 |
2.05:1 |
1.72:1 |
1.45:1 |
|
|
Fourth |
1.60:1 |
1.19:1 |
1.00:1 |
0.84:1 |
|
|
Reveres |
8.50:1 |
6.32:1 |
5.31:1 |
4.46:1 |
|
|
Oil Capacity |
32 pints |
|
|
|
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