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What's that buzzing/grinding noise at low RPMs?
Why won't my automatic tranny shift into overdrive at wide open
throttle?
Can I replace my 700R4 automatic tranny with a
later model?
What's the best way to install a Hurst
shifter?
What's that buzzing/grinding
noise at low RPMs?
It could be related to this technical service
bulletin:
Bulletin #: 277142
Publish Date: 10/92
Models: 1984-1993 Firebirds w/ Hydra-matric 4L60/700R4 Trannys
Condition: buzzing noise from tranny at idle (more so when in reverse)
Cause: pressure regulator valve oscillating due to oil pressure
instability at lower idle RPM
Correction: a new pressure reg. valve has been made to improve oil
pressure stability at lower RPM (part #8684048)
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Why won't my
automatic tranny shift into overdrive at wide open throttle?
It's designed not to shift into overdrive if your
foot is all the way to the floor. You must be at 2/3 throttle or less before
the tranny shifts into OD. So when you hit the top of 3rd gear, you'll have to
let off the gas to allow for the shift. But putting your foot back into it will
probably cause a downshift resulting in the same problem.
B and M makes a kit modified
kick down valve (part #
70237) which fixes this problem. It costs about $30 and can be ordered through
the Summit or Jegs. GM also makes a modified up shift
valve which it included in
police packages and that part # is 8673948 and sells for around $15. This will
allow the tranny to shift into OD at full throttle.
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Can I replace my
700R4 automatic tranny with a later model?
Yes. In fact, if your car was built prior to the 1987
model year, it's probably a good idea (if you have the cash). In 1987 (and even
on some of the very-late-1986 cars), a number of improvements were made to the
700R4, the most prominent of which was a change to the auxiliary valve body
with the main body and stronger components. This valve body is a section added
in conjunction with the full valve body that routes the fluid differently.
Earlier versions simply have a cover plate in place of this valve body where a
small amount of fluid reserve is kept for some operation. The newer model has
an accumulator to regulate the engagement of the forward clutch so that the
shift into "D" would be smoother. An abuse valve was added which, based on
throttle position, would short circuit the accumulator and cause the "D" shift
to occur faster (benefits apparent when rocking a car that's stuck in snow or
sand as it causes the clutch to engage faster to eliminate slippage and heat
built-up). These two items were also made applicable to the engagement of the
reverse clutch, thus smoothing its operation except during "abusive"
conditions.
The auxiliary valve body is on the drivers side, just
behind the trans valve body (opposite the accumulator housing). Four bolts hold
the a 6 x 2 inch block in place with a tube a tube connecting it to the
front-side of the main valve body. You can tell if you've got the auxiliary
valve body without pulling the pan. The later tranny has a slightly deeper pan
to accommodate the auxiliary valve body. To make certain identification, GM
changed the pattern of markings on the pan bottom where the magnet is located.
These markings are visible from the underside, near a rearward corner, forming
a square shape of size 1.75 inches or so. The later pans (accommodating the
auxiliary valve body) have unequal length lines (one set is longer than the
rest) unlike the earlier pans which have all lines equal length. Also, behind
the torque converter, look for a casting number on the front pump. If the last
three digits are "732", then you have the new, improved version of the
700-R4.
The newer trannies also have a 10-vane pump instead
of the old 7-vane pump (more pressure results in quicker, firmer shifts and
tranny longevity).
If do want to upgrade, you should check that the
input and output shafts will function with your existing converter and
driveshaft. One of the other upgrades for 1987 was the change of the input
shaft from a 27 spline to a 30 spline. But keep in mind that there have been
subsequent changes after 1987 as well. Your best bet is to use the most recent
model you can find.
But, also remember that if you want the shift points
to remain the same as before, you should try to get one from a similar auto and
engine since the valve body springs and the governor are sometimes different
for different auto and engine combinations. In some cases the differences are
subtle and others not. The valve bodies on the early 700R4s are not
interchangeable with the later models, so you do not have the option of simply
swapping valve bodies to get around this issue. Also, note that if the newer
tranny has an electronically controlled shift, it can be overridden.
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What's the best way
to install a Hurst shifter?
Your best bet is to follow the service manual. This
involves removing the radio and heater/AC controls and the entire console. But
you need to do this to get to the bolts to the lower rubber shifter boot. The
hardest part is putting back together the heater/AC control unit. Try to
remember how it comes apart. Also, there are actually six bolts that hold the
console on, but you need to take the top part of the console off first. This is
why you need to remove the radio and ventilation controls. The last two bolts
are hard to find as they are under the convenience box. Once all of the top
torx screws are removed, lift up the rear convenience box to get to the rear
two bolts. It's a worthwhile modification as the shifter is more positive and
accurate than the sloppy stock unit, and power shifting is much better.
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