Overdrive has a mind of its own

[moremonkey]

Spring finally arrived in New England so I took the 100 out for its first real drive of the year.

This year the overdrive has a curious problem - even with the selector switch in Normal, the unit will shift into overdrive as soon as it is able. (The centrifugal switch on my car, like so many others, is not connected because it does not work.)

With the dash selector-switch in Overdrive the unit stays in overdrive as intended. It shifts crisply into overdrive when I flip the switch from Normal to Overdrive. But regardless of whether the dash switch is flipped or not, the unit will shift into overdrive as soon as the car is moving at a decent clip (enough pressure in the system?) and I'm off the gas a little bit. If I stay on the gas, the transmission stays out of overdrive.

If I am moving slowly, say 15 to 25 mph or so, I can hear the solenoid clicking as it tries to shift into overdrive. I think once there's enough pressure in the system, it shifts. The unit does not stay in overdrive if I employ the kick down option. And it drops out of overdrive when I am in neutral if I wiggle the gearshift to toggle the first gear switch that always kicks the solenoid off.

So, any thoughts about where to look first?

-Jonathan

 

[Novamonte]

Suggest you check oil level in transmission first.

 

[DerekJ]

Sounds like the dash switch may be the problem and is permanently engaging overdrive.

 

[RAC68]

Hi Jonathan,

I also see the switch as the potential culprit of your problem. As I understand on a BJ8 and think similar on your 100, power is sourced at the fuse box and passes through the activated switch to all additional OD control components, including the solenoid. Since the solenoid's circuit receives power and is locally grounded, the solenoid could not actuate without power passing through the switch.

I would use a multimeter to check if power is interrupted when the switch is turned off to see if the switch is performing properly. As an alternative, I would disconnect and separately tape both lines attached to the switch to eliminate operation and any power flowing to and through. A short ride validating the elimination of OD use could verify a switch issue.

Good luck,
Ray(64BJ8P1)

 

[Bob_Spidell]

The shop (Bentley) manual has a good diagnostic procedure for the OD electrics. I used it while on a road trip the fix an intermittent problem (it was the relay).

 

[Jack T]

The dash switch would be my first suspect, then the throttle switch if the system is the same as on a BT7.

 

[bob hughes]

Just to throw my pennyworth in, I recently had a similar problem ish It would not go into overdrive, so I switched to normal and the overdrive would kick in. I did all the tests but in reverse as I was hoping that it was the switch - it was not. in the end I had to resort to pulling the trans cover and found that the overdrive solenoid was goosed. £70 plus including the dreaded VAT obtained me a new one from Bill Rawles and solved the problem.

Looking through my receipts it would appear that I had changed the overdrive unit 10 years ago. - They are the weakest link in the system



Bob

 

[Bob_Spidell]

... Looking through my receipts it would appear that I had changed the overdrive unit 10 years ago. - They are the weakest link in the system



Bob

Ugh ... second or third time I've heard that. I just changed out an original solenoid--still working fine after 51 years and almost 200K miles--for a new repop. Is there a particular brand that's not showing much longevity?

 

[RAC68]

Hi All,

Bob makes a good point and presents a valid possibility for the cause of the issue. Nelson Riedel describes the operation of the OD Type A Solenoid as follows:

"The solenoid case contains two coils, a pull-in coil that draws 15 to 20 amperes and a holding coil that draws about one ampere. When the relay contacts close, current is supplied to both coils and the plunger moves up very rapidly, taking a tenth of a second or less. When the plunger reaches it's upper most position it operates a switch inside the top of the solenoid that opens the current path to the pull-in coil. Once operated, the holding coil supplies sufficient magnetic force to hold the plunger in the operated position. "

The OD relay was included within the Solenoid circuit to handle the greater amperage of the Solenoid's pull-in circuit as it was thought the switches would not reliably handle the power. As such, if excessive power starts to deteriorate the internal coil switching of the Solenoid, I could see how an intermittent condition could cause the OD to seem to have a mind of its own.

My last thought on this reflects the fact that we are talking about coils and their effect on inducing high voltages as in the points-based SU Fuel Pump. Keeping in mind that Power(Watts) = Amps X Voltage, it is possible that, as with the fuel pump where an induced voltage of as much as a few hundred volts could cause premature points burn, this induced voltage within the Solenoid could cause switch contact deterioration and premature OD failure. Since it is likely, with coil-induced voltage, that at the high amperage state (<20 amp) of the Solenoid Voltage could also exceed hundreds over the normal Healey circuit level of 12+/-3 volts, I am wondering if it would be a good idea to install a Trans-Voltage Suppression diode somewhere into the circuit of the Solenoid to maintain an Operating Voltage and Power closer to around 12 volts and 240 watts possibly expected ? This TVS would gate the excessive hundreds of induced voltage to ground and maintain a constant operating voltage/power level more conducive to the extended longevity of the Switch/Solenoid.

Comments?

Just my thoughts,
Ray(64BJ8P1)

 

[Bob_Spidell]

re: "... I am wondering if it would be a good idea to install a Trans-Voltage Suppression diode somewhere into the circuit of the Solenoid to maintain an Operating Voltage and Power closer to around 12 volts and 240 watts possibly expected ? ..."

Should work, theoretically (I think). However, points wear in the OD solenoid should be trivial compared to a fuel pump, which operates a couple orders of magnitude more often than an OD switch (and even without any protection pump points probably operate in the tens of thousands of times before failing). Are we convinced points wear is causing the problem? Could it be failure of internal windings or something else? I have on good sources--myself and David DuBois--that aftermarket points for the pumps are crap. It appears the manufacturers are cheaping out by not using tungsten on them; wonder if the same, er, 'efficiency' is being employed in the solenoid? Most electronics now are solid state; as the market for 'hard' switching gets smaller the makers are bound to try to cut costs.

Side note: The OD dash switch is very fragile. I had to pull the terminals off mine to install the shift lever switch in parallel with the dash switch and just trying to pull the terminals caused the switch to destruct into several pieces. I had a spare on hand because I've had them fail before.

 

[RAC68]

Hi Bob,

Yes, the fuel pump points are getting a much greater workout then the contacts within the solenoid switch when going from Pull to Maintain. And Yes, the quality of components is getting close to crap and why I was thinking that any increase in Power going across the contacts from the induced voltage increase could accelerate the crap contacts in these units. Yes the induced voltage, as a result of coil magnetic activity, would be greater in the fuel pump (Hundreds of volts) and may be quite a bit less from the OD solenoid. However, I would also expect the switch contacts in the solenoid would be much less robust as well and, on a proportional basis, would be as vulnerable to over power failure.

Bob, I still have a points pump and with a TVS diode installed and it runs without worry. Prior to installing the TVS and with the rash of transistorized SU failures, I and 2 MG owners from Oregon, designed an Optically triggered head for the SU pimp and, although the unit proved reliable and without the necessity for any maintenance, we ended the project in favor of a much cheaper TVS diode implementation. I still have the Optically triggered head in the boot as a backup but I will probably not be around when my points/TVS causes the backup to be needed.

Last, although I would install a very inexpensive TVS on my solenoid if I ever to gain access for another reason, I expect I would apply the diode to the switch input within the solenoid... if room permits.

All the best,
Ray(64BJ8P1)

 

[bob hughes]

When I pulled my old overdrive solenoid to pieces, the points are the only thing that you can get at and they looked good, I guess that the windings burn out with time. I think that it is important to get the setting right on the operating arm otherwise you would burn the unit out quicker.



Bob

 

[RAC68]

Hi Bob,

If the points are easily accessible, even though yours were good, I would expect it would still be worth installing a $1.00 component to better control power into and through an expensive (with questionable quality) Solenoid.

I also agree that proper adjustment and the rubber button under the piston are very important for longevity of the unit. Without the button or even if the button is flattened, the potential for the piston to fall below the effective and efficient distance of the Pull cycle and would cause excessive power to be drawn by the coil in its effort to retrieve the piston. You will know if it doesn't succeed but even if it does pull the piston, the excessive power draw could cause a total coil burnout over a rather short period of time.

Although the application of a TSV could possibly retard the burnout of a miss-positioned piston by limiting total power drawn through the coil, I don't think it will stop its burnout if not addressed quickly. Since its benefit may only be marginal, I would not go through all the trouble of accessing the Solenoid to just install the TSV onto the Solenoid. However, also adding a slow blow Fuse (I would use a 20 amp or maybe a 15 amp) to the Solenoid line at the same time may also help justify the effort and would also add additional protection to the unit. However, not accessing the Solenoid, I have installed a 10 amp standard fuse to the input C1 terminal of the OD Relay to protect OD wiring in case of harness grounding due to switch failure or broken wiring.

Ray(64BJ8P1)

 

[bob hughes]

Ray

Could you please elucidate, what is the rubber button and where does it go? when I bought my unit all I had was the solenoid part, the piston had to be used from the old unit. I do not recall a rubber button. Arrgghh




Bob

 

[Bob_Spidell]

FWIW, my BJ8 has never had the 'rubber button,' just a small bolt IIRC (Moss catalog shows them only for 6-cyl cars up to BN6). The 'rubber boot' that came with the new one wasn't gonna fit no matter what; if anything, they'd add some resistance to plunger movement. David Nock says they throw them away.

 

[bob hughes]

Ahhhh

That is a sigh of relief



Bob

 

[RAC68]

Bob,

Below the solenoid is a rubber button that is mounted to the platform. When the piston falls (at rest), the button provides a soft landing and also helps raise the piston to a height for proper Pull-in by the solenoid. Without this button, the piston lands hard and resides too far for the solenoid coil to easily Pull-in the piston. The lack of this button could cause the solenoid coil to burn out.

The part is #41 Stop Rubber in the Moss Motors BN2 - BJ8 Overdrive Parts Diagram.

Ray(64BJ8P1)

 

[Bob_Spidell]

Hmmm ... the more I look at the catalog the more confused I get. I (initially) misread the 'Application' column. AFAIK, my BJ8's OD has never had one (and I looked closely when I rebuilt it recently). I didn't see any place where a rubber plug could go, either (and I looked). IIRC, I did have #39 and #40--adjusting screw and locknut--on the same Moss page. The pictures aren't definitive, but there appears to be a hole in the stop for the BN4-6 OD--the one without the enclosure--but the adjusting screw and nut have no such hole on my OD. If you look at the 'Application' for the adjusting screw and lock nut, it says '22/3087/10260, BJ7, BJ8.' I'd guess the '22' is for 22% OD (sun and planetary gears) but the other numbers must be model nos. (see part# 37, which goes to 22/3087/10259). I'm gonna SWAG that model no. 22/3087/10260 were used in BJ7s and 8s, while earlier cars used the other. Part# 37--'bracket N/A'--appears to differ between earlier and later models of OD. I think the catalog is ambiguous if not plain unclear/wrong, but I'm reasonably confident the latest ODs did not employ the rubber stop. There was no place for one in my OD, and David Nock looked mine over closely and didn't mention it.

Anybody know what '3087' stands for?

 

[RAC68]

Bob,

I have heard the importance of this stop rubber (button) #41 for ages in placing the piston in proper position for Pull-in retrieval by the Solenoid. I personally know of at least 4 different models of Healeys that have both closed and open mounts with the button installed. Also, the Moss listing indicates it is for Healeys from BN2 through BJ8. It also indicates that this simple part is unavailable from them (it is so simple a part it is confusing why they can's find a replacement source).

I can see not needing it with the replacement solenoids but if you are using the original piston I wonder. However, you indicated your BJ8 closed mounting doesn't even have the mounting hole. Was the mount replaced or changed for some reason? Now I am confused.

Ray(64BJ8P1)

 

[Bob_Spidell]

Ray,

My OD is all original. I bought the car @ 64K miles and, except for paint and some interior work I haven't found anything that wasn't original (at least, until I got ahold of it). I'm all but convinced the BJ7/8 used the adjusting screw and locknut to prevent the solenoid plunger from traveling too far down; I think earlier cars ('10259') used the rubber bumper. The screw and locknut arrangement would be an improvement because it's adjustable and should last just about forever, whereas rubber stuff tends to degrade and might compress over time allowing more plunger travel. I think the Moss catalog just fails to note that the later ODs used the screw instead of the bumper, as they appear to be mutually exclusive. I was aware of the rubber bumper when I rebuilt mine, and looked closely for any way to install one and could not find a way.

Bob