This is the Chevy/New Process A-833 four-speed OD, offered as optional equipment on '81-86
Call it old-fashioned, but there's just something satisfying about rowing your own in a vintage truck. Bench seat, vent windows, and a stick-shift transmission, it's almost the perfect package.
Most of our trucks came with manual gearboxes, most of them were three-speeds, and most were of the "bolt-action" column-shift variety, though a "Granny-Low" four-speed was also a favorite, with a long shifter coming through the floor operating the keg-like box. If you had need for a work truck (and your work was pulling down buildings with nothing more than a length of chain), the Granny four-speed with compound-low was your transmission of choice. For those times you weren't trying to crawl up a mountain or pull a freight train, you ignored First gear and just started out in Second, treating the gearbox as though it were a three-speed, the final drive being 1:1.
Times have changed. Today, everything we drive has an overdrive transmission in it, and we're used to honkin' down the road at 2,300 rpm, not 4,000 rpm, with engine life and fuel economy better than ever due in large part to overdrive gearing. We rolled with a Granny four-speed in our '62 Suburban for a couple years and more than once pushed in the clutch only to realize there wasn't a gear left.
Chevy offered this as a COPO option on 1/2-ton trucks from '81-87, known as MY-6. There are two versions of the Chevy case: the first has the regular GM mounting ears to the bellhousing, while the second retains the Chrysler mounting pattern and requires the specific factory aluminum bellhousing. We have one with a boss for a hydraulic clutch slave, and we've seen a picture of one with a Z-bar ball stud on the side. It looks to us like Chevrolet simply modified an existing mold for the bellhousing-silver plastic push-in plugs fill the unused Chevy mounting holes.
There are two versions of the main case available: one retains the Mopar trans mount. Thou
If you're a Chevy or Mopar owner, the New Process 833 four-speed OD is an easy and affordable way to get overdrive. Mopar guys have been hip to the trans since it came out in the early '70s, and found its way into passenger cars, vans and pickup trucks through the mid-'80s. Chevy enthusiasts, on the other hand, are barely aware of this option. Based on the Mopar 833 transmission, the overdrive version uses the same case as Mopar muscle cars, but with an aluminum main case rather than the muscle car-era cast-iron case. To get overdrive, they simply run Third gear straight thru as 1:1, employing what is traditionally the Fourth gear position for the shift arms and cluster. By inverting the lever on the shifter arm at the case, when the shift mechanism engages what is the Third gear gate, the transmission shifts into what is typically Fourth gear. For the final ratio, they run through what is typically the Third gear cluster, coming out the tailshaft as 0.73:1 overdrive, the gate on the shifter going into the traditional Fourth gear position.
The input shaft on these is GM-spec, with the tailshaft housing, driveshaft yoke, rear seal, and speedo gear being the same as a TH350. Internals are the same as Mopars. We read a single post on a website that this transmission was also available in diesel pickups, using an iron case. We haven't seen one in person, but we always check diesel trucks in the junkyards for the stronger iron case. If there's a weakness to these transmissions, it's that the countershaft registers directly in the aluminum case-behind engines with a lot of power, or after years of wear, the bore in the case can wallow out, causing the internals to bind. One fix in the Mopar camp is to have the case machined for a steel insert bushing.
For the Mopar-style mount, you must use the original Chevy bellhousing. This one has a bos
The other version of the trans has a retooled case with standard Chevy/GM mounting holes.
Both versions of the trans use a special Chevy-style tailshaft housing. It has a Mopar pat
The bearing retainer plate is Mopar-spec and is 1/4-inch larger than a passenger car and e
Because the MY-6 tailshaft is based off of GM dimensions, and the main case is the wider Mopar style, the only shifter that works is one of two factory GM units, both made by Hurst. They look very much like a Competition Plus shifter, and have a grease fitting, but they're unique to this transmission. Due to the narrower tailshaft, the shifter mount is closer to the centerline of the transmission, while the shift-fork levers are farther from the centerline. The fingers that come out the bottom of the shifter mechanisms have exaggerated bends in them, and the linkage rods also have big bends. Our two shifters have different offsets for the fingers, and the brackets that mount them to the tailshaft are correspondingly different. We also noticed that one of them is a decidedly beefier assembly than the other-bracket, shifter housing, rods, and all-leading us to think it was either superseded during the production run, or one was on a heavier truck. If you wanted to use any other shifter, you'd need to fabricate a mounting plate to move the shift mechanism out away from the transmission. We also checked them against the shifters out of Dodge junkyard trucks with the A-833 OD-they don't interchange, and generally appear like a lighter application than the Chevy units. We have both Hurst and Inland shifters from the Mopars.
One of the better-kept secrets in the automotive hobby is that Hurst has a shifter rebuild service. Our shifters had very sloppy gates-it was like stirring a pot of stew to get a gear. We sent one out over a year ago, the rebuild cost was $100, and it came back looking and working like an absolutely brand-new unit. We plan on using our own shifter handle, so we didn't use Hurst's handle rechroming service, but it's available. We've taken advantage of this service a couple times with other projects, and are always amazed when they come back. Since then the prices have gone up a bit, but it's still a screaming deal. The Chevy and Mopar shifters use any bayonet-style shift handle, and we've seen several different handles on Mopars; black-painted rod, chrome flat bar, chrome round rod ... any bayonet-style handle will fit. We found a black-painted handle from a Dodge van clears our bench seat nicely, and goes well with the spartan look of our interior.
Once the bearing retainer plate was turned down, we found the original hex bolts hit the I
One failing of this transmission, besides the weaker aluminum case, is that it will weep fluid out between the countershaft and the register in the case. We're not sure how GM handled this when they were new, but on a Mopar, the bellhousing mounting surface fully covers the front of the transmission so you can spackle a thin layer of RTV where the countershaft comes through the case and then sandwich it between the case and the bellhousing. On our GM truck bellhousing, this area is open-no spackle, so it leaks. We solved the problem by fabricating our own steel shim gasket to go between the case and the bellhousing.
Finally, the bearing retainer plate also needs to be given some attention. They retained the Mopar-spec bearing retainer cover, which is about 1/4-inch larger in diameter than most other GM transmissions, specifically the passenger car and early truck transmission. The register hole in the later truck bellhousings compensates for this, but you'll need to turn down its outer diameter to fit other GM bellhousings, such as our original '62. Once the diameter is turned down, socket-head Allen bolts and lock washers replace the hex-head bolts, as hex heads will hit the sides of the hole. We used lock washers, and after touching the edge of the washers with a grinder, it fits perfectly. Note that the bolts holding the bearing retainer are not blind-they go right into the case, and need thread sealant, otherwise they leak.
The easy fix for the hex bolts hitting the pilot hole is Allen bolts. These bolt holes go
On the side cover, only one of the bolts goes all the way through into the case, the other
To solve our leak at the countershaft's bore in the case, we made our own metal shim gaske
We broke out the black RTV and wiped it across the front of the countershaft, filled the b
We have several observations from our personal experience with the Chevy version of the New Process 833 OD. We're happy with its performance in our daily driven '62 Chevy Suburban-mileage and driveability over the original Granny four-speed are both way up, and it'd be an improvement over a three-speed, and probably even a regular four-speed by virtue of the overdriven final gear. The truck lopes down the Atlanta freeways in the left lane with the best of them, engine rpm nice and low (3.42 gears, with the enhancement of tall tires). They don't grow on trees though. We've only seen two Chevy units, and bought them both, but others have told us they have no problem coming across them. One of ours had a busted tailshaft housing due to a previous owner not removing the snap ring that retains the housing. The piece can't be repaired, so we were glad we had another for parts.
If you find a complete setup, we'd say go for it-you'll be happy. The one is a direct bolt-in after modifying the bearing retainer, while changing the bellhousing makes the other an easy swap. You'll have less money invested and an easier installation than "the good" T-5 swap (F-body main case, S-10 tailshaft and shifter, hydraulic clutch), but only if you start with a complete unit. Gear splits are the same as a three-speed manual or automatic transmission-some people prefer the splits of a traditional four-speed, though we don't mind. And with the final drive of 0.73:1, you'll drop your engine rpm by more than 25 percent, but still have deep enough gears to tow a trailer.
There are two OE shifters for the Chevy A-833, and another for the Mopar version, all made by Hurst. The Mopar unit is on the far right: note the difference in the fingers. We ran the shifter in the middle for a long time, and sent the one on the left back to Hurst for a total rebuild after it got too sloppy to find Second gear. Note the differences between the fingers and mounting brackets on the two Chevy units; the one on the right seems to be a little beefier. The bracket is certainly stamped from much thicker material, the offset on the bracket compensates for the different offset of the fingers between the two Chevy units. The Mopar unit, while plentiful in junk yards, won't work on the hybrid Chevy A-833. We couldn't find any applications in the Hurst catalog that would work with the Chevy A-833, so the OE shifters are the only option, unless you make your own mounting bracket.
|These are the gear ratios for the |
|MY-6 / New Process 833 four-speed transmission. |
|First Gear: ||3.09 |
|Second Gear: ||1.76 |
|Third Gear: ||1.00 |
|Fourth Gear: ||0.73 |
Hurst offers a shifter rebuild service. When we sent this shifter to Hurst for the rebuild
The best tip in the book when it comes to ensuring manual transmission longevity whether i