Hello. 1986. Sedan. M46 tranny W/overdrive. A couple of years ago as the switch that only allows OD operation in 4th gear was defective I bypassed it. I realize that if by mistake you are in overdrive while in reverse gear that this is really bad for tranny/overdrive. However every so often(maybe once or twice a month)I by mistake have overdrive on while in 1st, 2nd, 3rd gears. Been like I said a couple of years and seems fine. However I was just wondering if being in overdrive while in #1, 2, or 3 gears is bad for tranny or overdrive. Its not like I do it regularly or for long. Soon as I catch it I disengage overdrive. Just curious about this. Thanks.
--
' 86 manual sedan nearly 210,000 and ' 87 auto sedan nearly 125,000

Bad??? for the overdrive in lower gears...Depends*...

Remember, OD is engaged and held by a continuous flow of fluid volume at pressure controlled by internal valving. Herinafter the term fluid refers to the later.

If OD switch ON in lower gears, nothing will be affected in 1st gear. Trans output shaft is not spinning fast enough for the OD pump to deliver enough fluid to engage the OD.

2nd gear. Probably not enough fluid to engage or even move the system at first, BUT...toward the top end of second gear there can be enough fluid to move the system but probably not hold it properly. Slip will most likely occur.

End result of slip is abnormal wear on the friction material that allows shock absorbtion as the system changes rotational state. See the following for more info. Under Basic Operation.

http://www.brickboard.com/FAQ/700-900/TransmissionManual.htm#ManualM46LaycockOverdriveUnitBasicOperation

3rd gear. At lower end there will probably be some slip due more to friction needing to overcome the higher mass of the Volvo vehicle. At the upper end of third there is usually nothing to worry about until the unit has higher milage and wear and the actuating piston O-rings start to fail.

FYI The British cars using the SAME J type OD are a lot lighter so in their third friction is not an issue. The JP and P Type ODs were not used in British car but were manufactured for trucks and Volvos until Laycock sold the rights to Gear Vendors and went out of business.

*This is where it becomes how bad. Since there is always some slippage occuring when rotational changes occur during engage/disengaement, wear is normal and controlled somewhat buy the flow control within the fluid system.

A method to minimize slip is to partially or fully disengage the clutch with requisite lifting of throttle to minimize the duration the lining actually slips during rotational speed change.

If the wear on the lining is excessive and becomes an issue, the least that will happen is the need to replace the part (sliding member/cone clutch) to which the friction material is bonded.

The worst is other internal parts are damaged as the sliding member is broken into little pieces and the damages other parts.

Cost of the sliding member: J type OD only, P type I have no source for this part. If I have one $120 but it is usually cheaper to get a whole used OD. New J type sliding member is $420, ( whole tranny/OD cheaper even if shipped from China :>)). Time vehicle is out of service becomes an issue.

J or P type OD. See dealer ($1400+ for rebuilt OD)only or obtained used. I cannot obtain rear end parts for the JP and P type through my source.

Given the above, the time to swap and cost ($35 max??) for the switch might be a good investment???

Duane

Wouldn't his '86 have a P type unit?
Some of the folks at Gear vendors have let it slip that their current unit is the same P type unit in the newer Volvos ( and that if you can manage to get ahold of some of their adapters , which they guard like gold so nobody can make their own units, you have to trade in an old adapter to buy a new one and it has to be a GV adapter, not a factory Volvo one, so ebay is it, but you can make your own gearvendors unit and the band clutch in the volvo units is actually better than the one they sell in their new units, but they had to change the material for some environmental regulation , but there is one guy on ebay wrangling adapters and tooling up to build his own, and rebuilding laycock J and P units for various applications)

I've been doing a serious amount of research lately while looking for some extra gears for my diesel pickup, and the P units on the later M46 are the same units used currently by gearvendors rated for, what 30k pounds? and there's plenty of the older units that GV used before the P units running around pulling 18k pounds, and all the GV units have been setup to be able to split each gear( although low speed in 1st is a no-no and reverse a big no-no)

After all the reading I've been doing, I've decided against a GV for my truck because of cost and problems people have had on the road trying to get parts from them ( basically once a new GV is out of warrenty, they don't even want to talk to you, they just want to get you to tow it to an authorized dealer and buy a new one and as far apart as their dealers are, you should see some of the tow bills people have racked up, even under warranty), and I'm going with either a 3 or 4 speed Spicer aux transmission.
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-------Robert, '93 940t, '90 240 wagon, '84 240 diesel (she's sick) , '80 245 diesel, '86 740 GLE turbo diesel, '92 Ford F350 diesel dually

As far as torque multiplication, etc it looks like it is pretty much a function
of rotational speed, which is roughly proportional to hydraulic pressure, which
is then proportional to engagement pressure of the cone clutch and hence its
torque-carrying ability. On my old 122 wagon it seemed to be nonfunctional at
about 20 mph and was very well engaged by 35, this with a 4.56 screw and
195-75/15 tires. The tranny was a 1975 240 box with J-type OD, so it was probably
about as "modren" as the M41 ever was.
On the basis of that I would think it would probably have been OK in 3rd or
maybe even 2nd if you were going fast enough, but there is not much to gain
as the tranny is fairly close-ratio. Careful engagement is always a plus.

Question: Are the Gear Vendors ODs close enough to have interchangeable parts
with Laycock-deNormanville?
--
George Downs, Bartlesville, Heart of the USA!

Having seen ONE GV unit many years ago, it was a J type verbatum with a trans case adapter with a tailshaft extension to drive the OD pump.

Newer GV units with integral pump, I have not a clue.

Duane

i cannot imagine that gear vendors units are anything like a volvo spec piece. those units can hold 500+ lb/ft of torque and are optional up to 1200lb/ft....there would be no reason to put such a robust unit in a volvo.

I think they make different models.
The pictures I saw look startlingly like the J-type.
--
George Downs, Bartlesville, Heart of the USA!

Too much torque multiplication in 1st and 2nd. 3rd might not be so much of a problem.

Many older British sports cars were in fact set up that way---so that you could engage OD in either 3rd or 4th.

As you are already aware, backing up with the OD on is a very bad idea, quickly leading to expensive noises.

Not OK.
The torque multiplication in the lower gears may be too much for the OD.

How tough is that overdrive??

In the old days (I had hair back then) my buddy's Healey 100-6 had o/d, as we used to use it as a splitter to keep near the power (215hp) peak in competition, and it never gave a moment's trouble. Whether the Volvo unit is good enough to handle it, I can't tell you...

Now you are bringing back memories! My dad had a (BN6) 100-6 in 58 new. Only problem with the car was that when it rained it wouldn't start and needed a few days in the sun with the hood open. Of course, as a result, I heard the term "Lucas... the prince of darkness!"

Great cars for their time though. A few folks have posted about slipping OD units after the OD got stuck on in lower gears on the M46, so it appears the Volvo selected OD can't deal with it.

jorrell
--
92 245 250K miles, IPD'd to the hilt, 06 XC70, 00 Eclipse custom Turbo setup...currently taking names and kicking reputations!

Mmmm, yeah... My buddy's 100-6 wasn't quite stock. He pulled the 2.6 and replaced it with a 3.0, then it got a cam, redone head, and three 2"SUs, bringing it up to 215hp. My job was to keep the SUs in tune, something I did to earn my beer money; 2 SUs were easy, three not so much! What a ride...

And Lucas was also known as the God of Intermittent Light. We ended up pulling out a lot of the connections and terminals and replacing them any way possible. We found that getting an actual twelve volts to the headlights really helped at 125mph.

The only connection I can make to this site is that the guy, like me, belonged to the local Volvo Club. (Oh, dear, that was 40 years ago!)