36 GEARSMay/June2007

Working on the ATRA Technical HotLine can be really interesting at times.

Not only do we get to assist members with technical questions, we also spend a lot of time researching the problems that ATRA members run into every day.

With this year’s seminars and the upcoming 2007 EXPO in Las Vegas, your ATRA Technical Department invests a lot of time researching and preparing some of the most comprehen-sive seminars and presentations avail-able in the automotive industry.

While preparing for the upcom-ing seminar and EXPO season, I was asked to present a seminar entitled Understanding Today’s Domestic Four Wheel Drive Systems. As I started pre-paring, I had the opportunity to pick up a couple transfer cases to build my presentation around.

One of the transfer cases I selected — due to the number of calls we get on this unit — was the Borg Warner 4405 semi-automatic transfer case, used mainly in Ford Explorers from 1996 thru the present day. While I was disas-sembling the transfer case, I discovered a problem we hear about all the time on the HotLine, but have been unable to document. The call almost always starts out the same: “I’ve overhauled the transfer case and it still has a ratcheting or grinding noise during deceleration; the noise goes away during tip-in or acceleration.”

By the time we get the call, the transfer case is usually back apart on the bench and the technician swears everything looks great. No problems found. There’s nothing worse than get-

ting a transmission or transfer case disassembled on the bench, and not be able to find anything wrong with it.

So if there’s nothing wrong, what’s causing the ratcheting or grinding noise?

During disassembly of my 4405 transfer case, I noticed the shift fork

pads were missing from the shift fork; they were broken into little pieces, sitting on the bottom of the case. The purpose of the shift fork pads is to insulate the shift fork from the high-low shift collar and center the shift collar in the shift fork. With the shift fork pads missing, the shift collar would be able

W h at’s T h at G r i n d i n g N o i s e C o m i n g f ro m M y Tr a n s fe r C a s e?

KEEP THOSE TRANNYS ROLLING

by Pete Huscher

Figure 1

Figure 2

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38 GEARS May/June 2007

to move around, and wouldn’t remain centered in the shift fork.

As I disassembled the transfer case further, the cause for the ratcheting or grinding noise became more apparent. I removed the output shaft assembly from the case and then the high-low shift collar. The shift collar inner gears were partially stripped, and the input shaft gears were damaged (figure 1). This usually indicates the shift collar was moving out of position, allowing the shift collar gears to interfere with the input shaft gear. This is what was causing the grinding or ratcheting noise on deceleration.

During disassembly, I noticed the shift fork rail was worn on each end (figure 2). After checking the transfer case halves, I discovered both case half bosses were worn where they hold the shift rail in position, allowing the shift rail and fork to move out of position (figures 3, 4 and 5). This let the shift collar move out of position, where it could interfere with the input shaft gear, damaging both the shift collar and input shaft gears.

The FixWith both case halves worn at the

shift rail bosses, both case halves would normally have to be replaced, at cost of about $600. Some of our members have chosen to send their transfer case halves to a local machine shop and have the shift rail bosses drilled out and a bush-ing installed. This type of repair usually runs between $70-$100 (about an hour labor plus bushings), depending on the machine shop’s labor rate.

Once you have the transfer case

halves replaced or repaired, the next step is to replace the damaged parts, such as the input shaft, high-low shift collar, shift rail, and shift fork pads. You’ll also need to replace any other worn parts, such as bearings, gears, chain and seals. With the new parts in hand and the shift rail bosses repaired, reassembling the trans-fer case should go pretty quickly. And that should take care of the “grinding noise coming from the transfer case on deceleration.”

A Personal InvitationI’d like to invite each and every

ATRA member to join us for the 2007 Powertrain EXPO in Las Vegas this year. Your ATRA Technical Department has worked long and hard to bring you the most up-to-date, cutting-edge information available to the automotive industry.

I’ll be hosting an interactive dis-

cussion entitled Understanding Today’s Domestic Four Wheel Drive Systems. The discussion will include basic iden-tification, operation, overhaul and diag-nosis of today’s domestic, four wheel drive systems. We will also be discuss-ing the KISS process for diagnosing today’s vehicles. Attendee participa-tion will be encouraged, so bring your thinking caps.

Now that you have the fix for the grinding noise on deceleration on the Borg Warner 4405 transfer case, it should be no problem for you to keep those tranny’s rolling!

What’s That Grinding Noise Coming from My Transfer Case?

Figure 3

Figure 4

Figure 3: Close up view

Figure 5

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