Breaking parts: Pressure regulator valve and bore blues - Transmission Digest

Breaking parts: Pressure regulator valve and bore blues

One of our ATSG members, Bob at Trans Tek, recently shared with us an experience he encountered with a 2011 GMC 3500 Mini School Bus with a Duramax diesel engine in front of a 6L90 transmission. It came in to the shop slipping, along with having no second or sixth gear. After the transmission was removed, during the initial teardown process, he noticed that the unit was exceptionally clean.

There was no evidence of converter clutch failure or pump damage. But once the center support assembly was removed (which houses the 2-6 clutch), the secondary cause to the complaint was identified. The lugs above the groove of the snap ring used to retain the 2-6 clutch assembly were blown off (see Figure 1, above).

To replace this support now required determining what caused these lugs to break the way they did in the first place. Bob’s diligent search discovered a severely worn pressure regulator valve and bore. It apparently had worn in such a way that caused enough of an uncontrolled pressure spike to snap these lugs off the housing. Changing the center support, reaming the bore and installing and oversized PR valve completed the repair.

But this was not the only incident he shared with us concerning reaming the pressure regulator valve and bore. The next was with a vehicle with a 6R80 transmission.

Reaming with a dull reamer, without enough lubricant, or at the wrong speed can easily compromise the ream. The result can be that the valve will get stuck in the fully stroked position, or not stroke completely, due to the incomplete ream. When the valve is stuck in the fully stroked position, low line pressure will occur, burning clutches. When it is not stroking completely, this can cause high enough pressure to crack pistons. Figures 2 through 4 show three different pistons cracked from the same transmission because of the PR valve not being able to fully stroke. The damage to the transmission was immediate.

Tech-Speak-April-Figure-2-1400
Figure 2.
Tech-Speak-April-Figure-3-1400
Figure 3.
Tech-Speak-April-Figure-4-1400
Figure 4.

Here’s a quick method in checking the PR valve after a ream, aside from doing a physical inspection. Once the valve assembly is installed into the valve body, use a pick to stroke the valve from the retainer end of the valve as seen in Figure 5.

Tech-Speak-April-Figure-5-1400
Figure 5.

You will quickly notice if the valve is incapable of stroking completely, which will cause this type of damage. If it does fully stroke and then stick, there will no longer be any spring tension on the valve and there will be a gap between the retainer and the valve’s end cap sleeve. There may not be any broken parts when this happens—just burned parts.

Read more stories from our Technically Speaking column series here.

You May Also Like

Back with force: ATSG is back in full swing to educate the transmission industry

“Everywhere you turned, there was something amazing. It’s probably the coolest man cave I’ve ever been in,” says Wayne Colonna who, as president, heads up the technical team at the Automatic Transmission Service Group (ATSG). Wayne is describing the host venue for his company’s inaugural 2024 seminar that was held at the John Force Racing

“Everywhere you turned, there was something amazing. It’s probably the coolest man cave I’ve ever been in,” says Wayne Colonna who, as president, heads up the technical team at the Automatic Transmission Service Group (ATSG). Wayne is describing the host venue for his company’s inaugural 2024 seminar that was held at the John Force Racing facility and museum in the Los Angeles suburb of Yorba Linda, California. Transtar’s Orange, CA branch served as the presenting host for the event.

Ford 8F35 maintenance tips: Planetary failure and no-pressure conditions

Our shop has had several vehicles come in with the Ford 8F35 transmission having planetary failure. Apparently, there was a run where the pinion needle bearings had a hardness problem (see Figure 1). Related Articles – Don’t fear customer complaints about CVTs – 2024 State of the Powertrain Industry – Powertrain industry directory and buyer’s guide

Figure 12.
Don’t fear customer complaints about CVTs

Continuously Variable Transmissions, or CVTs, are more common than you think. Audi, Subaru, Nissan, Ford, GM and many other automakers use CVT transmissions in cars and SUVs. There is no way to avoid them. Chances are there is one in your shop right now. Related Articles – Shift Pointers: A Chrysler 300 no-shift complaint –

CVT-Transmission-2
Shift Pointers: A Chrysler 300 no-shift complaint

The case study has to do with a 2009 Chrysler 300 C 5.7L Nag1 RWD with 71,923 miles on it (see Figure 1, above). Related Articles – Sometimes, a diagnostic code is all you need – 10L80 and 10R80 pump gear differences – Top 20 Tools and Products: The Winners It is based on a

A guide to common GM, Ford and Nissan programming issues

One of the most common complaints I hear from shops when trying to install a new GM TCM is, “The module will not communicate.” While that might be partially true, by design they won’t communicate until they are programmed. If programming fails, there will be an “E” code set which will help you get to

Other Posts

Schaeffler, ATSG partner to support technical education

Schaeffler announced that it has entered into a partnership with the Automotive Transmission Service Group (ATSG) to become its primary sponsor. Through this agreement, Schaeffler will provide ongoing technical education support to the members of ATSG, which has offered technical support and repair information for transmission technicians for nearly 40 years. Related Articles – ALI

Diagnosing Ford 10R60, 10R80 and 10R140 series speed sensor issues

Ford 10-speed 10R series transmissions utilize four two-wire, Hall-effect sensors — TSS, ISSA, ISSB and OSS — for providing speed signals to PCM or TCM. They are supplied nine volts by a PCM or TCM and assist in the control of clutch apply/release timing that is used in determining shift quality, including TCC. Related Articles

Jatco JF613E transmission quick reference material

For those working on the Jatco JR613E transmission, a widespread transmission with plenty of applications, the following should be a helpful guide. Related Articles – Hidden problems: Three tales of electrical issues – Easy TH400, 4L80-E reverse servo setup: Craft your own tool – Outgrowing the walls: The story of EVT Transmission Parts Domestic and

Complete the 2024 transmission shop survey for a chance to win a gift card

Every year, Transmission Digest conducts the Retail Shop Survey. This survey will take five minutes or less. The results of this survey will appear in the March edition of our Powertrain Bulletin email newsletter, and should serve as a valuable benchmark for your business. Your responses will be kept confidential and reported only in the