Bypass overdrive solenoid?

My 1990 Volvo 740 Turbo with AW71 automatic transmission keeps taking itself
out of fourth gear.
I have traced the problem to a faulty overdrive solenoid.
After nearly suffing a heart attack when I discovered how much the local
Volvo wants to replace the soleniod, I began looking for other options.

Is there a way to bypass the overdrive solenoid so that the car will remain
in fourth gear on the highway? If so, will doing this cause any damage to
the transmission itelf?
I do mostly highway driving and I don't tow anything, therefore I have no
need to ever take the car out of overdrive gear.

Any advice is greatly appreciated.
J.Copeland

 

Have you checked the relay if so & it is good you can do the following
action
Remove the overdrive solenoid from the transmission
clean solenoid of any atf & grease
Purchase the larger of the 2 O-Rings
very carefully make a small grove between the inner flange
Reinstall you should now have overdrive
I have never personally tried this repair so I do not know if this works
It was posted here in this group a couple of months ago
I wish I could give credit to the original poster but I am unable to find
the post now
Glenn

--
"*-344-*Never Forgotten"
Is for the New York City Firemen who lost their lives on September 11,2001.
The official count is 343, but there was also a volunteer who lost his life
aiding in the initial rescue efforts. And I will never forget them as long
as I live,
nor should any American.
"Mow Green"

 

Does the groove in the new O-ring mentioned above actually bypass the
solenoid valve, or repair it?
It looks to me like the larger O-ring contains the hyraulic pressure being
fed to the valve and stops fluid from leaking all over the floor under the
car.

The only reason I ask is that from my experience of messing with the
overdrive on a manual volvo gearbox (the auto is probably different),
strange results happen when overdrive is engaged in any gear but the one
it's intended for, such as horrible crunching or screaming noises when in
reverse, and having overdrive 1st, 2nd, 3rd; instead of 1st, 2nd, 3rd,
overdrive 3rd (4th).

Sorry if I've misunderstood something here, but good transmissions cost a
lot more than a bit of TLC on what amounts to a simple electromagnetic
plunger valve.

A question for the original poster; have you tried activating the solenoid
by directly applying voltage (12v) to it's wire? The coil in the solenoid
should have a resistance of about 13 ohms if checked with a multimeter
connected between its body and the supply wire. Does it click solidly when
energised? If yes, then the valve is working, the only things that could
then give problems are, is the valve clogged up and restricting the fluid
flow (they are usually cleanable with care), or is the fluid pressure
actually high enough to activate the overdrive unit.
As an experiment, you could rig up the direct power feed to the solenoid,
drive the car, then have a passenger connect the wires to activate the
solenoid when you're in top gear, if it works and stays in fourth, then the
solenoid and fluid pressure is ok, the wiring or control system is not.

Good luck, Ken

Does the groove in the new O-ring mentioned above actually bypass the
solenoid valve, or repair it?
It looks to me like the larger O-ring contains the hyraulic pressure being
fed to the valve and stops fluid from leaking all over the floor under the
car.

The only reason I ask is that from my experience of messing with the
overdrive on a manual volvo gearbox (the auto is probably different),
strange results happen when overdrive is engaged in any gear but the one
it's intended for, such as horrible crunching or screaming noises when in
reverse, and having overdrive 1st, 2nd, 3rd; instead of 1st, 2nd, 3rd,
overdrive 3rd (4th).

Sorry if I've misunderstood something here, but good transmissions cost a
lot more than a bit of TLC on what amounts to a simple electromagnetic
plunger valve.

A question for the original poster; have you tried activating the solenoid
by directly applying voltage (12v) to it's wire? The coil in the solenoid
should have a resistance of about 13 ohms if checked with a multimeter
connected between its body and the supply wire. Does it click solidly when
energised? If yes, then the valve is working, the only things that could
then give problems are, is the valve clogged up and restricting the fluid
flow (they are usually cleanable with care), or is the fluid pressure
actually high enough to activate the overdrive unit.
As an experiment, you could rig up the direct power feed to the solenoid,
drive the car, then have a passenger connect the wires to activate the
solenoid when you're in top gear, if it works and stays in fourth, then the
solenoid and fluid pressure is ok, the wiring or control system is not.

Good luck, Ken

 

The groove opens up a new passage through the solenoid, bypasses the
passage that the solenoid is supposed to open. This just means that the
overdrive gear is enabled (not engaged) as it would be during normal
driving, i.e. it allows the control system to engage the overdrive gear
as necessary.

This is completely different than the way the overdrive on a manual
works. On the manual, energizing the solenoid engages overdrive gear,
assuming there's hydraulic pressure. Since the pump is turned by the
shaft going through the unit, there's no pressure at a stop. If the
overdrive is switched on, it will engage as the pressure rises with
speed. Also manual transmission overdrive is not designed for use in
reverse.

--
Mike F.
Thornhill (near Toronto), Ont.

NOTE: new address!!
Replace tt with t (twice!) and remove parentheses to email me directly.
(But I check the newsgroup more often than this email address.)

 

Mike,

Cheers, thanks for the info, it is obviously very different, and much more
similar to the setup on my current 740, which has a 4 speed auto box
(retrofitted by myself, was a 5 speed manual car), no overdrive, but does
automatically lock the torque convertor into direct drive (like having a
normal clutch again) at 58mph, am I correct in assuming that the AW71
selects overdrive based on gear selected and road speed/torque when enabled
by the solenoid? I'd often wondered where all the external wires and
switches that I'd expected were!

TTFN, Ken

 

Yes, your assumption is correct. It seems stupid (and more expensive)
to have an electric method of disabling top gear instead of having a "3"
position on the gear selector. The hydraulic control is there already.
Since the 4 speed AW70/71 are a modification of the 3 speed AW55, the
only reason I can think of is that it would have required a major
redesign to stick that extra position in there.

--
Mike F.
Thornhill (near Toronto), Ont.

NOTE: new address!!
Replace tt with t (twice!) and remove parentheses to email me directly.
(But I check the newsgroup more often than this email address.)

 

I have jumpped the relay on every automatic volvo I ever owned (except
one with a ZF 4HP 22 tranny). It doesn't hurt anything. My '84 242ti has
been hard wired for fourth gear for about 4 years. The relay was fine. I
took it out and sold it to a fella who was having trouble with his and
didn't want it jumpped. I got $50 from him.

Mike aka Terrible Ted

 

Jeez, you can buy a new one for less than that...

99% of the relay failures just need to be resoldered, other problem I've had
is chafed wiring under the car.

 

I have a 1990 240DL wagon, had issue with the 4th gear overdrive and
made the modifications to the soleniod as follows:

1. Removed 2 bolts holding item on, with 12mm wrench, drivers side of
tranny just under the shifting linkage. Remove the wires, if not
already cut or smashed by the linkage. DO not cut wires if they are
intact, you may want to replace solenoid someday in the future and if
you cut the wire, you have another project to work on.
2. Removed both large O ring and small O ring around center of
solenoid, making sure that no dirt got into the area that the soleniod
was removed from. Clean areaa with rag and spray with wd-40 to removed
any dirt that gets lodged into hole. I used a mirror to view the area,
and bent the spray tube to get the spray to area to make sure it was
clean.
3. Instead of making changes to the tranny, i used a rotozip and
hogged out (in a straight line) from the center of the soleniod to the
hole outside of the small O ring. Do not go as far as the large 0
ring. Do not replace small o ring as it will prevent the fluid from
passing in the groove you just made.
It is imperative to be sure you flush the soleniod with cleaner such as
wd-40 to make sure that no metal frags get into the tranny.
once mod is made, replace the solenoid.

Car will have to heat up and it will shift into all gears as required.
If you are in 4th and need to pass, just step on the pedal and it will
do it automatically. You may notice a harder downshift when coming to
a stop, but this will have no effect on the tranny life.

works like a charm..good luck