Valve-Body ‘Kibbles
& Bits’
In all the years of building transmissions,
I think the worst thing that could happen is having the R&R
guy, manager or owner come back after a road test and tell you,
“It’s not working.” All of a sudden you get
this knot-in-your-stomach feeling that makes you wish this were
not really happening.
So you take the vehicle for a ride to see
what it’s doing; maybe it needs a minor adjustment or
more fluid, or it’s an engine problem – anything
but MY transmission.
Once you admit to yourself that it
doesn’t work right, you come to the determination that
it’s a valve-body problem – not so bad; at least
the unit doesn’t have to come out, which makes the
R&R guys happy even though they’re not thrilled about
handling a hot valve body.
Of course, depending on what it takes to
get the valve body out, it could be another story. In some
instances, I’m sure the R&R guys would rather pull
the unit out.
All this brings us to some valve-body
problems that have been coming across the ATSG tech line
lately. Some problems are man made, but others just happen.
The first problem is found on Honda Accords
with the BAXA/MAXA transaxle hooked to the four-cylinder engine
or with the B7XA behind the V-6 engine.
TCC slip or cycling with the possibility of
storing code P0740 in a BAXA/MAXA/B7XA may be caused by leaving
out the lockup-control-valve sleeve. Figures 1 and 2 show the
sleeve and valve lineup.
The steel sleeve can roll away while the
valve body is on the bench, disassembled, for cleaning
purposes. Since the lockup-control valve is one of the valves
responsible for controlling the rate of lockup-release oil,
leaving this sleeve out can reduce converter-clutch
backpressure, resulting in the complaints mentioned.
While we’re on the subject of code
P0740 – this is one of the most-common calls we get
– one of the more-common causes is leakage of the
lockup-control-valve bore plug (see Figure 3).
The best way to fix a leaking bore plug is
to machine a groove in the plug and install an O-ring in that
groove. If this method is not available, you can always use
your tubing cutter to cut a ridge in the bore plug, as shown in
Figure 4, so the plug fits tighter in the bore. However, this
may not last as long as the O-ring fix would.
Be aware that the BAXA/MAXA also has a
sleeve on the 3-4 orifice control valve, in the secondary
valve-body section. Leaving this sleeve out can cause a poor or
flared 3-4 shift.
The B7XA has one of these sleeves on the
reverse CPC valve, in the main valve-body section. Leaving this
sleeve out would certainly cause slipping or a shudder in
reverse.
Our next valve-body kibble concerns the
Ford 4/5R55E family of transmissions. The bore plug for the 2-3
shift valve is held in place by the solenoid retaining bracket
that holds the EPC, SS2 and coast-clutch solenoids by means of
a hook at the end of the bracket that hooks around a knob on
the bore plug as shown in Figure 5 on the next page.
What sometimes happens is, while struggling
with the positioning of the bracket, you may not pay attention
to the hook position. It then ends up on top of the bore plug
instead of around the knob, pushing the 2-3 shift valve in too
far (see Figure 6).
When the valve body is installed this way,
the 2-3 shift valve will block oil to the reverse servo by
positioning the spool of the valve in the way of the oil, which
normally travels between the spools on its way to the servo,
resulting in a no-reverse condition.
Our next valve-body bit comes under the
heading of #@&* happens. In this particular example, the
transmission is the 5R55W. The fluid was severely burnt, lockup
did not work and a P0741 code was stored. Once the unit was
rebuilt and installed with a reman converter, code P0741
returned during the road test.
To make a long story short, because code
P0741 is never a short story, the cause of the problem was the
thermo-bypass valve, shown in Figure 7. The valve is supposed
to open when the ATF warms and allow oil flow through the
cooler. When the fluid is cold the thermo valve bypasses the
cooler and directs flow to the lube circuit. This is necessary
for two reasons: One is to allow oil flow to lube the gear
train in the event the fluid in the cooler has jelled. Those
who live in places that get colder than a brass monkey know
what I mean. The other reason is that should the cooler become
blocked, fluid will still circulate through the transmission,
thereby saving the hard parts.
In a 5R55W the thermo valve is in a sleeve.
It flops around in this sleeve, which is normal; it
doesn’t fit snugly as other valves do. It also affects
lockup operation because it is in the same bore as the
lockup-control valve (see Figure 8).
Other Ford transmissions, such as the
5R55N, 4R/5R55E and 5R110W (it’s in the pump), also have
this valve. A cooler-flow check should reveal a problem if the
thermo valve does not open. 
©2006 Transmission Digest