You get a Ram 4500 in the bay with two complaints on the ticket: the 2-3 shift hangs and flares like the clutch is slipping, and Reverse takes two or three seconds to load up when the driver backs off a dock. Maybe there is a pressure switch code stored, maybe not. The owner already paid somebody for a solenoid. The flare came back.
On the Aisin Seiki AS68RC, that pair of symptoms - a 2-3 flare plus a delayed Reverse - is close to a fingerprint. It points at one worn valve bore, not at burnt clutches and not at a bad solenoid.
What the two symptoms together are telling you
A flare is a loss of hydraulic control during a shift: engine speed runs up because the oncoming clutch is not filling and holding fast enough to take the load. A delayed Reverse is the same story at a standstill - the apply circuit is leaking down, so it takes extra time to build enough pressure to lock the element.
Separately, either complaint could be a dozen things. Together, on an AS68RC, they are the giveaway, because the 2-3 upshift and the Reverse apply share a single piece of hardware.
The AS68RC clutch layout, in plain terms
The AS68RC is a six-speed rear-wheel-drive automatic Chrysler used behind the 6.7L Cummins in cab and chassis trucks only. Per Next Gen Drivetrain's AS68RC teardown notes, if the truck is not a factory cab and chassis configuration it does not have this transmission - the standard-bed 2500 and 3500 trucks got the 68RFE. It ran model year 2007.5 through 2012 before the AS69RC replaced it for 2013. The same basic unit shows up under Isuzu and Mitsubishi Fuso box trucks, and Next Gen notes those valve bodies use a different hydromechanical calibration than the Dodge version, identified by the numbers cast into the valve body. That matters when you order parts.
Internally, K1 is the underdrive clutch and applies in first through fourth. K2 is the overdrive clutch, and K1 applying on top of K2 is what creates the 1:1 ratio - there is no dedicated direct-drive pack in this unit. K3 and B1 select which planetary gearset is doing the work, which is how the unit gets two underdriven and two overdriven ranges instead of one of each. Per published specs at Transmission Repair Cost Guide, the unit is rated to roughly 730 lb-ft and 26,000 lbs GCVWR and calls for Mopar ASRC ATF / Mobil 3309.
The root cause: one valve doing two jobs
Here is the part most people miss. Per Sonnax, vehicles equipped with the AS68RC use a dual-functioning K3/B2 valve - a single valve that controls the application of both the K3 clutch and the B2 brake. Sonnax states the innermost bore of that valve has shown to be prone to wear, and that the resulting low pressure in the K3 and B2 circuits causes "2-3 flare shifts, delayed Reverse and pressure switch codes."
That is the whole mechanism. Aluminum bore wears, the valve no longer seals, pressure bleeds off in both circuits that valve feeds, and you get a soft 2-3 shift and a lazy Reverse from the same defect. The clutches are usually still serviceable when you catch it early. If you let it run, the flaring will cook the friction material and then you own a rebuild instead of a valve body job.
Worth knowing: this is a different wear location than the damper bores that set P0746 and P0776 on this unit. If your complaint is intermittent pressure switch and linear solenoid performance codes rather than a flare, read our writeup on why replacing the AS68RC solenoid does not fix P0746 and P0776 - different bore, different kit, same lesson about not condemning solenoids.
How to diagnose it before you condemn anything
Do this in order. It is cheap and it keeps you from pulling a unit you did not need to pull.
- Pull codes and read the full definition. Sonnax makes the point that scan tools commonly truncate these definitions - you may only see the first four or five words, and "pressure switch" often never appears on the scanner even though the code covers a pressure switch mechanical fault.
- Check the fluid. Dark, burnt-smelling fluid with friction material in it means the flare has already been eating clutches. That changes the job from a valve body service into a teardown.
- Verify line pressure. Confirm base pressure and pressure rise are in spec first. If line pressure itself is low, you are solving the wrong problem.
- Drop the pan and vacuum test the valve body. This is the step that proves it. Sonnax's method: apply vacuum at the specified port and watch the reading while working the valve side to side. If the reading drops as you move the valve, the bore is worn. For scale, Sonnax reports that on the AS68RC damper pistons a new piston and casting will test 20-plus inches of mercury while worn bores can read as low as 4 in-Hg.
Test the whole casting while it is on the bench. Sonnax notes the AS68RC also has relief pistons in the upper valve body - a cooler relief and a solenoid feed relief - and both vacuum test the same way at the spring-side exhaust port on the back of the casting. Finding a second worn bore after the truck is back together is a bad afternoon.
The fix: recondition the bore, install an oversized valve
You cannot fix a worn aluminum bore by putting a new stock-size valve in it. The stock valve was never the worn part - the casting is. The repair is to ream the bore true and oversized, then fit a valve sized to the reconditioned bore.
For this specific complaint, Sonnax's answer is oversized K3/B2 valve kit 99740-09K. Per Sonnax, reconditioning the bore and installing the kit "restores proper K3 clutch and B2 brake control." The valve is hardcoat anodized aluminum to resist repeat wear, and Transmission Digest's product announcement confirms the kit also includes an extra spacer for the K1/K2 valve.
While the valve body is apart, the other bore worth addressing on a high-mileage AS68RC is the clutch control plunger valve. Sonnax reports the sleeve there wears from constant plunger oscillation, which produces assorted shift complaints as the clutch control valves stroke to apply and release the elements. The AS68RC clutch control plunger valve kit (Sonnax 99740-01K) replaces the worn sleeve and restores valve control. Doing both bores in one teardown is the difference between a repair and a return visit.
Replace while you are in there
The pan is down and the fluid is out. These are cheap relative to the labor of getting back in:
- Filter and pan gasket. Raybestos Powertrain lists AS68RC filter 515617, with 515618 covering 2WD AS68RC and A465 applications. Confirm which one your unit takes.
- Inspect the K2 clutch pack. Next Gen Drivetrain identifies K2 as the most frequently damaged clutch pack in the entire unit. If the truck flared long enough to burn something, K2 is where to look first, and the AS68RC K2 clutch backing plate kit (Sonnax 99582-02K) addresses a known weak point in that stack.
- Friction and steel modules if you go deeper. Raybestos catalogs friction module RCP96-241 for the Dodge trucks and RCP96-242 for Mitsubishi Fuso and Isuzu, plus steel module STMAISIN16 and GPZ performance module RGPZ-012. Match the module to the make.
- The right fluid. Mopar ASRC ATF / Mobil 3309 per the published spec.
Browse the full transmission valve body parts selection to pull this job in one order, and keep the AS68RC ATSG A4600 / A465 rebuild manual on the bench for the factory procedures.
Cost and effort
The valve body on this unit is serviceable from underneath - pan down, valve body out, no need to pull the transmission for the bore work. That is why catching this complaint early matters so much.
What trips up first-timers is the reaming. Reconditioning a valve bore is not a parts swap; it takes the correct bore-reconditioning tooling and a steady setup, and a bore reamed off-center is worse than the one you started with. If your shop does not have the tooling, send it to a builder who does. Skill level is high, parts cost is modest, and the alternative - letting a flare burn the K2 pack - is a full teardown. One honest caveat: if the fluid came out dark with material in it, budget for the rebuild. A valve body kit will not restore clutches that are already cooked.
FAQ
Can a bad solenoid cause an AS68RC 2-3 flare and delayed Reverse?
It can cause shift complaints, but that specific combination points at the K3/B2 valve bore, because one valve controls both the K3 clutch and the B2 brake. Sonnax lists exactly those symptoms for wear in that bore. Vacuum test before you buy another solenoid.
Will a replacement valve body fix it?
A used valve body is a coin flip - this is a design-driven wear pattern, so a core off a truck with similar miles may have the same wear. Reconditioning the bore and fitting an oversized valve addresses the cause.
Is the Isuzu or Fuso AS68RC valve body the same as the Dodge one?
No. Per Next Gen Drivetrain, those units use a different hydromechanical calibration, identifiable by the numbers on the valve body casting. Raybestos splits its friction modules the same way - RCP96-241 for Dodge, RCP96-242 for Fuso and Isuzu. Identify the unit before ordering.
Sources
- Sonnax - Oversized K3/B2 Valve Kit 99740-09K (AS68RC)
- Sonnax - Diagnosing AS68RC Intermittent Pressure Switch / Linear Solenoid Performance Codes
- Transmission Digest - Aisin Seiki oversized K3/B2 valve kit now available from Sonnax
- Raybestos Powertrain - AS68RC Transmission Rebuild Kit Parts
- Next Gen Drivetrain - Aisin Seiki AS68RC Transmission: Problems, Solutions & Upgrades
- Transmission Repair Cost Guide - AS68RC Transmission Specs & Updates