Two and Four Speed Transmissions - Rebuild Your Jerico

Ctrp 1211 Two And Four Speed Transmissions Rebuild Your Jericho 01

Jerico Performance Products' Jerry Hemmingson may have first begun reworking Ford's Top Loader transmission into his own unique design in order reduce his timeslips on the dragstrip, but the quality of the transmission has made it a winner in many different types of racing.

Jerico's two- and four-speed Top Loader transmissions are extremely popular among road racers because of their light weight, extremely low rotating mass, and durability. But that has also made these transmissions highly prized among asphalt oval track racers with open transmission rules. Besides the already mentioned strengths, these transmissions also offer a wide variety of gearing options to help you find the right match for your track, and the simple design means repairs and rebuilds are surprisingly easy.

We recently stopped by the shop of Jim Cook Racing Transmissions while Cook was beginning the process of inspecting a Jerico two-speed transmission that an asphalt Super Late Model team had purchased used from another team. Wisely, the new owner of the transmission didn't want to risk a failure that kept them from finishing a race, so they had asked Cook to go through the unit and make sure everything was up to spec before bolting it into the race car.

It turned out to be a wise move by the race team. The transmission looked good at first glance, but Cook did find a few issues that he was able to correct quickly and easily before they could become big expensive problems on the racetrack. Cook also gave us some invaluable advice and things to look out for when rebuilding your own Jerico transmission.

1 For oval-track racers, the two-speed version is often preferable over the four-speed version because you only need the high and low gears anyway, and the two-speed cuts rotating weight. Cook says it’s easy to spot a two-speed Jerico because it uses a special case that only has two holes for shifter inputs. Jerico three- and four-speed transmissions all have three shifter inputs.

1 For oval-track racers, the two-speed version is often preferable over the four-speed ve
2 The tailhousing comes off with the removal of four bolts, and it quickly becomes apparent just how simply these transmissions are built. Unlike a T10, another popular circle track racing transmission, the Jerico keeps reverse inside the main housing. The only thing inside the tailhousing is the lengthy output shaft.

2 The tailhousing comes off with the removal of four bolts, and it quickly becomes appare
3 The team that sold the Jerico apparently used a mid-plate for mounting the engine and transmission, eliminating the transmission crossmember. To reduce weight they had cut off the crossmember mount (left). If you use a crossmember, make sure you find a tailhousing that still has the cast-in mounts (right, although this one has been modified as well).

3 The team that sold the Jerico apparently used a mid-plate for mounting the engine and t

4 A C-clip is used to lock in both the main bearings for the input and output shafts. But the bearings have a slight press fit so even after removing the clips they won’t just fall right out. Cook says you can use a chisel against the bearing’s inner race to punch it from the inside out.

4 A C-clip is used to lock in both the main bearings for the input and output shafts. But
5 The gears can’t be removed from the case until the shifter fork is out of the way, and before you can do that you have to remove the shifter rail. Start by removing the bolt that holds the inner spring and detent plug in place.

5 The gears can’t be removed from the case until the shifter fork is out of the way, and
6 There’s also a bolt on the exterior of the case that holds in another detent and spring set. Cook uses a pick to get the spring out.

6 There’s also a bolt on the exterior of the case that holds in another detent and spring

7 Now you can remove the main shifter rail. Make sure the rail is still smooth without any scars or wear grooves.

7 Now you can remove the main shifter rail. Make sure the rail is still smooth without an
8 Now you can rotate the shifter fork up until it’s off the selector and lift it straight out of the case.

8 Now you can rotate the shifter fork up until it’s off the selector and lift it straight
9 Finally, you can separate the input and output shafts—thought should pull right apart. Remove the output shaft like you see here.

9 Finally, you can separate the input and output shafts—thought should pull right apart.

10 Here’s a shot of the input shaft and the main gear after it has been pulled from the case. Note the groove cut into the face of the gear and the hole in the shaft that’s on the same spline the groove in the gear runs to. The purpose of this hole is to feed oil to the needle bearings the shaft spins on. (The needle bearings have been removed, but you can see the housing bore it spins in.) When reinstalling the gear onto the input shaft, you must make sure the groove in the gear and the hole in the shaft line up, otherwise, Cook says the needle bearings will be burnt up by your second or third night of racing.

10 Here’s a shot of the input shaft and the main gear after it has been pulled from the c
11 With the main gears removed, the cluster shaft, as well as the reverse idler are revealed. The reverse idler gear spins on its own shaft and has its own shifter fork.

11 With the main gears removed, the cluster shaft, as well as the reverse idler are revea
12 Next, you can knock out the cluster gearshaft, but the cluster gear itself won’t come out until you use a pick to remove the shim in the back side of the case. After that the cluster gear should lift right out.

12 Next, you can knock out the cluster gearshaft, but the cluster gear itself won’t come

13 Clean and inspect all of the needle bearings that ride inside the shafts. When reinstalling them, it’s helpful to use heavy grease to help stick them in place. Few things are as frustrating as hunting underneath your workbench for that needle bearing that fell out and rolled who-knows-where.

13 Clean and inspect all of the needle bearings that ride inside the shafts. When reinsta
14 Now you can get a clean look at the reverse idler gear and its shifter fork. To remove the gear, all you need to do is remove the idler shaft. Removing the shifter fork isn’t necessary unless it’s damaged or worn.

14 Now you can get a clean look at the reverse idler gear and its shifter fork. To remove
15 Here, the shaft is being slid out so that the reverse idler gear can be removed.

15 Here, the shaft is being slid out so that the reverse idler gear can be removed.

16 The individual gears can be removed from the main shaft by simply removing the C-clips.

16 The individual gears can be removed from the main shaft by simply removing the C-clips
17 Changing gear ratios on the Jerico transmissions is as simple as swapping out the gearsets. Numbers are stamped on each of the gears so it is easy to reference them to Jerico’s charts to determine the gear ratios. The key is to make sure you never mis-match the sets because they won’t mate properly.

17 Changing gear ratios on the Jerico transmissions is as simple as swapping out the gear
18 The reverse gears showed some pretty bad signs of wear. It’s likely a sign of a driver trying to move the transmission into reverse before fully engaging the clutch. Many other gear builders would have simply thrown out the reverse gear as well as the idler, but Cook always tries to work with his customers to save money wherever possible. With a little quality time with the grinder, Cook is able to recut the leading edges of the gear teeth. The three gear teeth in the foreground show how the teeth looked after Cook gave them back a bit of an edge. The teeth on either side are still untouched.

18 The reverse gears showed some pretty bad signs of wear. It’s likely a sign of a driver

19 These are the dog rings that engage the sliders. On the left (background) is a relatively new ring. On the right (foreground) is a dog ring that’s worn to the point of needing replacement. Otherwise, Cook says the transmission will continually pop out of gear.

19 These are the dog rings that engage the sliders. On the left (background) is a relativ
20 Reassembly is basically reversing the steps. The easiest method for getting the cluster gear is back in is to set the transmission on its end, slide the cluster gear into place and then slide the shim back on top. After that it should be a piece of cake to reinsert the cluster gearshaft.

20 Reassembly is basically reversing the steps. The easiest method for getting the cluste
21 It can be confusing to get all the detent slugs and springs back into place. Here’s how they lay out in relationship to the shift rails. When everything is properly installed, the detents will not allow the transmission to be in a forward gear and reverse at the same time.

21 It can be confusing to get all the detent slugs and springs back into place. Here’s ho

22 When putting everything back together, make sure the flat side of the dog rings are engaging the sliders. If the dogs are installed backward so that the angled sides are facing the slider to transmission won’t stay in gear.

22 When putting everything back together, make sure the flat side of the dog rings are en
23 Make sure to slide the input shaft into place first before installing the output shaft and gears. Then join the two halves together. Do it backwards and you won’t have room to slide the input shaft into the case.

23 Make sure to slide the input shaft into place first before installing the output shaft
24 With the main shaft in place, drop the high/low shifter fork in place and rotate it until the end is on the selector.

24 With the main shaft in place, drop the high/low shifter fork in place and rotate it un

25 Reinstall the main bearings and go ahead and lock them in place with the C-clips. This will hold the main shaft in the right attitude so that you can finish the shifter.

25 Reinstall the main bearings and go ahead and lock them in place with the C-clips. This
26 Getting the high/low slider shaft into place can be tricky. After installing the lower half of the detent spring set, use a pick to hold the shifter fork in the right spot until you can get the slider shaft through.

26 Getting the high/low slider shaft into place can be tricky. After installing the lower
27 Finish with the upper detent spring set and install the locking bolt. Be aware that you can’t use just any bolt here. The correct piece is a specific length and uses a tapered point so that the detent assembly will work correctly.

27 Finish with the upper detent spring set and install the locking bolt. Be aware that yo

28 Cook inspected the rear seal, which was still good so it wasn’t replaced. But he did apply some lubricant to protect it when the transmission is first used.

28 Cook inspected the rear seal, which was still good so it wasn’t replaced. But he did a
29 Instead of a gasket which can be finicky and leak-prone, Cook prefers a thin bead of silicone to seal the joint between the main case and tailhousing.

29 Instead of a gasket which can be finicky and leak-prone, Cook prefers a thin bead of s
30 After getting everything back together, Cook tests the transmission to make sure that all the gears can be engaged (also that either of the forward gears and reverse cannot be engaged at the same time) and everything spins smoothly.

30 After getting everything back together, Cook tests the transmission to make sure that

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