Heavy Metal! - May - 2021

The 4R70W Getting the Shaft

When they work properly, the 4R70W and 4R75W is a reliable transmission. Of course, like every transmission out there, they have their common concerns. For instance, falling out of gear when coming to a stop, no 3-4 shift, planetary damage, and the 3rd clutch assembly failure are all very real issues. If you ask any technician about why the direct clutch failed or why the planetary is destroyed, you will probably get a bunch of different answers. It could be EPC or MAF sensor failure to a leak to the 3rd clutch. It could also be a misfire. The bottom line is, it’s important to know how the system works.

Recently, I did some research at my friend Rodger’s shop in Miami, FL. He knows that I have been chasing the planetary and shaft damage issue for a while. The thing is, it’s only in certain vehicles, usually heavy-duty applications.

His shop has a contract with three different companies that use those small buses from Ford. The vehicle in question was a 2014 Ford Econoline E-250 bus. When we dropped the pan it was full of metal, as expected. The RDI was ordered and taken to the bench for disassembly. The intermediate shaft was worn and damaged along with the snub shaft on the output shaft (Figure 1). The direct drum was burnt, as well.

The direct clutch assembly was incinerated (we expected that). The pressure regulator valve bore in the valve body was worn out. There are other issues with these valve bodies you should look for, like flooding solenoids, shift valve spring weakening, and leaking plugs.

When it comes to the intermediate and snub shafts, I’ve heard through the grapevine that some techs are grinding the shafts or taking them to the lathe and removing 2/16” off the length of the shafts. While this might not be a bad idea, it could lead to a clearance issue.

Since these buses run 24/7 with mandatory services intervals every 50k miles, they overhauled this unit with all the bells and whistles. We went on the road test, and the unit worked great. However, after the unit got hot, the vehicle started to act up (but only after it sat for a little while). Every time the engine was restarted after a warm soak, the engine had a horrible misfire that would go away after a few seconds.

Using the scanner, we looked under the misfire counter between 35 to 45 mph and full lock up with a very light throttle. Bingo! There it was a misfire. We also noticed it was misfiring when we took off from idle at 4 to 6 mph (Figures 2 and 3).

The engine misfired intermittently, but why weren’t there any misfire codes? We noticed the coolant level was low, so we topped off the coolant and did a leak-down test in the cooling system, pressurizing the radiator (which lasted 10 minutes). During this time, the coolant pressure went from 17 psi to 0. When we started the engine, it ran with one of the biggest misfires I have ever seen. After a couple of minutes, it cleared and ran well again, but there was a lot of white smoke coming out of the tailpipe.

Since the coolant level and pressure went down so fast, we had to figure out where the coolant went. It was not on the floor, so we figured the head gaskets were to blame. But when we checked the coolant for exhaust gases, there wasn’t any. Next, we suspected the intake manifold. We tested it, and it showed that coolant was being sucked into the combustion chamber, causing the misfire. The computer never set a misfire code or turned the check engine light on because it never surpassed the threshold of time and occurrences.

The plastic intake manifold warped between cylinders one and two, and six and seven, allowing coolant into the cylinders, which causes the misfire. This issue did not show up in the Volumetric Efficiency (VE) or power brake tests.

The fix was to replace the intake manifold. Also, keep an eye out for the A/C drain hose. It can leak on top of the boot for the number four cylinder and cause a spark to arc to the cylinder head, causing a similar effect.

PS. Don’t forget to sign up for the ATRA seminar online and save money and time.