The Ultimate Mopar A-833 4-Speed Fix: Get Overdrive & Strength!
Mopar muscle car owners have been dealing with the same dilemma for decades: solving the gear ratio paradox. If you actually drive your Mopar muscle you know exactly what we are referring to. Let`s face it, these cars are about acceleration, and for that you need deep rear gears. How deep? Back in the day, Three.23 gears were considered a highway ratio. Three.54/Trio.55 ratios were spectacle gears, and anyone truly serious would consider nothing less than something like Trio.91/Four.Ten/Four.11 ratios. For the dragstrip, this muscle car gearing was perfection–four on the floor with a four-series rear gear, and you`re through the traps at redline in top gear.
All of that is well and good, until you take things into the context of street driving in the present era. Sure, those low gears will help a classic Mopar accelerate like a Navy jet off a catapult, but at speed it`s like dragging the anchor. Go with the flow of interstate traffic at a high-speed cruise, say at eighty mph, even a set of «highway» gears like the old Trio.23 has your tach suspending around the Trio,500 rpm range. Determine to be a street hero and switch that to a «Super Track Pack» ratio of Four.11, and the needle will go to Four,500 rpm. You`ll soon find yourself in the slow lane at sixty mph, still revving well over three grand, getting passed by every soccer mom in a minivan. It is truly kind of abasing.
What`s switched is gear ratio. It doesn`t take six hundred hp from a jerked big-block to run the quick lane on the interstate; relaxed cruising is all about the gearing. That minivan might have a fraction of the power of your classic Mopar, but it also has overdrive via a four-, five-, six-, or even eight-speed transmission. You truly don`t need eight gears when you have V-8 torque, but what matters is the trans gearing from low to top. Having the extra ratio of overdrive to bring the revs down makes all the difference on the open road.
When considering manual transmission vehicles, there are many options available to Mopar enthusiasts seeking overdrive gearing, each with their pros and cons. Very first on the list is the factory A-833 overdrive. This unit provides a healthy overdrive ratio and bolts in as a direct replacement, but it has some real drawbacks. With the factory overdrive, you`ll give up a good chunk of the A-833`s legendary strength due to its floating countershaft, undercut mainshaft, and 23-spline input arrangement. In terms of gear ratio, the low Three.09:1 very first, borrowed from the slant-six transmissions, creates too broad of a ratio leap from Very first to the 1.67:1 2nd gear. That leap is a deal breaker for real spectacle as a 6,500-rpm shift will drop you back well below peak torque to Trio,350 rpm. That shift almost cuts engine rpm in half.
Other options include add-on overdrives or conversions to non-original five- or six-speed transmissions. These conversions are good when pulled off correctly, but involve considerable modifications, are conspicuously non-original appearing, and are fairly costly, making this route less than practical for many Mopar fans.
Jamie Passon of Passon Spectacle is a recognized accomplished in sales, service, and manufacturing of Mopar A-833 transmissions and components. Of the many fresh parts these guys manufacture is a unique overdrive gearset for the A-833. With four gears available from the A-833, Passon could see that Mopar missed the mark on the overdrive A-833`s ratios. The deep six-cylinder–spec, Very first gear ratio, and fairly high overdrive ratio necessarily results in big, awkward ratio leaps inbetween gears. The solution here was ordinary: take the four speeds but slice the salami up a little differently as far as ratio spreads, even up the gear splits, and tighten up the ratio range considerably inbetween very first and overdrive.
The very first thing that needed to go here was the Three.09:1 Very first gear ratio, in favor of a Two.66:1 ratio. This is basically what you would have with a factory non-overdrive muscle car version of the A-833. In Very first gear it is exactly like having a stock Hemi four-speed. Next, the ratio of the overdrive gear was backed off just a little, from 0.73:1 to 0.80:1. Of course the «Third» gear ratio is motionless at direct 1:1, so all that was left was to improve the 2nd gear split with a ratio of 1.59:1. The result here is a very nice street overdrive gearset for the stock Mopar four-speed, with gear switches that feel natural and progressive, all contained in the factory stock transmission.
The Passon gearset fits in any A-833 transmission case as a retrofit, and gets you an overdrive transmission with no modifications other than a switch in the three – four gearshift linkage rod, which is also provided by Passon. Unlike the factory overdrive transmission, which was never designed as a high-performance chunk, Passon`s internals retain all of the beef of the stoutest A-833. In fact, this gearset improves on the power-handling capacity of the A-833 transmission considerably, with better materials, broader and heavier-duty gears, and a high-strength 18-spine Hemi-style input pinion shaft.
Building the Passon Spectacle retrofit Hemi Overdrive transmission is indeed not different than building any factory A-833. Since the retrofit gearset will usually be installed into a used core, now is the time to freshen the remaining parts of the transmission with the needed rebuild parts. Usually, the rebuild will include a gasket and seal kit, a petite parts kit, the synchronizer stop rings, rear bushing, and bearings. Other typical wear parts include the shift forks, synchronizer clutch gears and sleeves, detent ball-sac, and it is always a good idea to substitute the countershaft if any wear is demonstrating. What needs replacement here will depend upon your individual unit, and fortunately Passon can supply anything you may need for the A-833.
Our transmission was a pretty nice, used E-Body unit, so it only required the gearset and basic rebuild parts. This small-block transmission originally came with the smaller No. Three hundred seven front bearing and petite Three.454-inch bellhousing register on the bearing retainer. We intend to use this transmission in a big-block application with the large Four.805-inch register. Fortunately, Passon can supply bearing retainers for virtually any combination of bearing and pilot. For our trans they supplied an 18-spine No. Three hundred seven bearing retainer with the Four.805 register, a combination never suggested as OEM. As veterans of the A-833, we found the retrofit kit came together just like a stock rebuild. The Passon Hemi Overdrive kit comes with detailed step-by-step instructions that guide you through the process.
1. Taking an A-833 manual transmission apart to this stage is nothing but wrenches and bolts. Liquidate the side cover very first to clear the shift forks, then the extension and upper gear train comes out as an assembly; the front bearing retainer just unbolts. Factory overdrive transmissions require ripping off the cluster gear in the case by removing the countershaft to permit the extension housing to be eliminated.
Two. The three – four synchro assembly and Third speed gear can slide right off the mainshaft once the front snap ring is eliminated. The mainshaft and one – two geartrain can be eliminated from the extension by expanding the bearing retaining ring at the front of the extension housing (308 bearing; compress retaining ring with three hundred seven bearing).
Trio. Once the mainshaft bearing is pressed off, the remaining Very first and 2nd speed gears and synchronizer assembly can be eliminated from the mainshaft.
Four. To eliminate the cluster gear, drive the countershaft rearward and out of the case using a long arbor or drift.
Five. On a trans with the No. Three hundred seven front bearing, the countershaft must be eliminated and the cluster gear dropped to the bottom of the case to permit the drive pinion assembly to be eliminated through the case. On No. Three hundred eight front bearing transmissions, the pinion can come out the front of the case.
6. Here we have our conversion and rebuild parts from Passon. Included is the gearset, 18-spine input pinion, bearing retainer, bearings, bushing, stop rings, thrust washers, gaskets, seals, O-rings, and a fresh Third/Fourth gear operating rod for our Hurst Pistol Grip shifter
7. This is the fresh overdrive gearset laid out. The Passon gears are made in the USA from improved materials, and feature broader gear faces for even more strength than OEM. Below is the cluster gear, with above from left to right, the Very first and 2nd speed gears, the overdrive gear, and the 18-spline pinion.
8. Here we see a typical 1-inch, 23-spline input pinion (left) compared to bulky one Trio/16-inch, 18-spline «Hemi» spec Passon unit.
9. We blasted the rust from the exterior surfaces of the fully disassembled metal castings, then cleaned the parts spotless in a caustic bath, and finished the detailing with a metal resto finish from a splatter can.
Ten. All of the components we were re-using from the core transmission were accurately cleaned and investigated. In prep for assembly, we pre-assembled the synchronizers, loaded the pinion roller bearing in the rear bore, pressed on the front bearing, and loaded the cluster gear with its roller bearings, spacers, and an arbor implement to hold it all in place for installation. The arbor implement should fit the countershaft bore with a slight clearance, be long enough to string up the thrust washers at both completes, and fit inbetween the thrust surfaces inwards the case without interference. Ours was made of appropriately sized 0.125-inch wall tubing.
11. Assembly of the main case began with re-installing the Switch sides gear train, and then cautiously lowering the cluster gear assembly to the bottom of the case (make sure the thrust washer tangs engage the slots in the case). Next the input pinion is inserted, however, the bearing retainer is left off for now.
12. The extension was reassembled beginning with a fresh rear bushing and seal. The Very first and 2nd speed gears and synchronizer assembly were installed on the mainshaft, along with a fresh bearing, and then the loaded shaft was dropped into the extension housing and secured with the retaining ring. This is most lightly accomplished with the extension held in a vertical working position. Once the shaft is in the housing, the overdrive gear and OD/direct synchronizer assembly can be installed at the front of the mainshaft.
13. The front stop ring should be secured to the synchro assembly with grease to hold it in position while the extension is mated to the case. To build up clearance for installation, slide the pinion and front (Trio – Four) synchro forward, and set switch sides gear to mid-position. With the gasket affixed to the extension, angle-in the extension housing assembly, engaging the roller bearings in the pinion bore. Stir the front synchro back to neutral. With the extension loosely in place, clock it to expose the rear countershaft bore. Invert the trans case cautiously to permit the cluster gear to mesh with the upper geartrain. Drive in the countershaft, making sure to clock it so that the woodruff key will align with the ease in the bore. Rotate the extension to its correct orientation, and bolt it down. My preference is to use grease as a sealer on both sides of the extension housing gasket.
14. Once the extension is bolted up, the pinion can be secured with the bearing retainer. For protection against seepage, apply thread sealer to the bearing retainer bolts, and the front of the countershaft bore can be cleaned and knifed flush with silicone.
15. The side cover and shift assembly finish the transmission. The forks must be loaded into the synchro clutch sleeves, and then the cover is lowered into place to engage them. With the brutal strength of a Hemi four-speed, unspoiled stock looks and factory fit, and the extra-long gams of the overdrive ratio, the Passon Hemi overdrive has everything we want for our street-bound Mopar muscle car.