BN1 Overdrive discovery

[moremonkey]

Hello everyone,

This is my first post (although I have been lurking for a while.)

My car is a 1955 BN1. This winter I am trying to figure out an intermittent overdrive failure. (I am also trying to convince myself a coolant leak that manifests itself on the right side of the engine at the head gasket is actually merely a leaking water pump gasket.)

Anyway, the overdrive works intermittently. When it does work, it works perfectly. No slip, engages crisply, disengages perfectly. But sometimes it won't kick in for many minutes and miles, other times it just doesn't work. For weeks at a time.

And last summer I realized I can hear the solenoid clicking when I am stopped and move the shifter in and out of 2nd or 3rd gear. (I figured out today that someone bypassed the centrifugal switch many years ago. Since it hasn't been an issue in the last 20+ years, I figure I will leave that bit alone.)

So in the garage, on stands, I can get the solenoid to activate the lever when the dash switch is on and the transmission is in 2 or 3. Works like a charm. Next step was to take apart the operating valve. The plug, plunger, spring, and ball were all fine and moved as expected with the cap off when I moved the lever by hand. But the operating valve (long thin tube with rings cut into it and a pinhole part way down the side) was bent in the valve body and would only come up about 1/4" easily. I had to use needle nose pliers to get it out.

Curiously, the shaft of the valve had the number "13" engraved into it. Lucky 13 deep in the guts of a Laycock de Normanville, just what every Healey needs.

Anybody have any idea why and how that piece could get bent? No obvious signs of trauma.

-Jonathan

 

[Healey 100]

Johathan:

Not sure why the pushrod is bent, but it only needs to come up a small amount to activate the OD. A quarter inch sounds fine to me, I think that's about the amount of lift you need to open the hydraulic circuit.

I have tracked down intermittent OD failure to engage on my car for years. I have concluded this is almost always caused by those tiny electrical contacts inside the solenoid that bring the low resistance pull-in coils into the circuit. If there is just a few ohms resistance in these contacts, the pull in force is reduced dramatically at the OD and the unit will not engage. If you keep trying, the contact resistance falls slightly due to vibration, heat, or ??, and suddenly it all works perfectly. You also need to have a very good ground for the solenoid.

Suggest you try to clean and file those little contacts, it may help for a while anyway. But long term what is needed is a new solenoid. Fortunately, there are reasonably priced repro units available now.

 

[busybrit]

I agree with Bill, check the contacts and solenoid out. Whenever I get a A type o/d unit to work on for a customer I drive the with the cover off and my son activates the lever by hand on the passenger side, by passing the whole electric system, it works more often than not. That sends me back home to find the failing electric thingy.

 

[bighealeysource]

Hey Busy Brit,
Fellow South Carolina Healey owner here. Have started up a new chapter for Austin Healey Club of America- AHCA Lowcountry Chapter. We're based out of Beaufort, SC but have members from Columbia to Charleston to Savannah. If you're interested PM me and I'll get you the info.

As to the overdrive issue, that is always a scary feeling reaching over to engage the OD as you're driving down the road at 50 mph and reaching over the spinning U joint to hit that lever on right side ! You're right, if it works by doing that than usually electric but could be the operating lever adjustment on left side of the case.

Regards,
Mike

 

[moremonkey]

Mike,

I'll tell you what's about as scary as reaching over the spinning driveshaft at 50mph...it's hitting 40mph while the car is inside on jackstands. It turns out my tires like to be on the ground if they are even going to pretend to be balanced. When I ran the car in the garage to test overdrive oil pressure (it's fine) and electrical functioning (also fine now that it has new parts and tidier wiring) when I got up to overdrive speeds the rear of the car started hopping and I thought I was going to bounce off the stands and careen through the garage door and out into the black and frigid night. So I think the car shifted into overdrive, but the my heart was pounding pretty loud and the exhaust was roaring so I didn't really want to give it another shot. To know for sure it will have to wait a month or two until the salt is off the roads and I can take the car out for a drive.

Jonathan

 

[moremonkey]

.

 

[bighealeysource]

Know exactly what you mean Jonathon ! Nothing like getting it up to 40 or 50 sitting on jack stands and praying it doesn't come off and send you careening into your own garage wall ! Think I actually preferred taking it out on the road to test. Of course does mean you have to be paying attention to where you are driving as opposed to reaching for that lever to push on !

 

[Keoke]

When testing OD hook a wire to the lever and lay the end in your lap.

 

[bob hughes]

I have a BJ7 so I am not familiar with the 100 gear box and overdrive layout, but I had an intermittent problem and found it to be the overdrive switch.

Have a look at the little button on the over drive switch ( the one that stops you going into overdrive in reverse) mine was worn flat and needed replacing.

If the overdrive switch on the dash is engaged you will hear the solenoid click as you move into gear when stopped.

Also there is a method of checking the setting on the valve operating lever, but not sure if this is the cause of your problem.



Bob

 

[moremonkey]

Here's a belated update to my overdrive issues. After checking and doing a little rewiring of the many Rube Goldberg switches (have any of you investigated the awesomeness that lives inside the centrifugal switch? Very cool and very nutty), replacing the bent push rod, adjusting the solenoid lever, and testing the OD oil pressure, I put it all back together and waited for warm weather so I could road test.

Once I got the car on the road I found it ran beautifully but wouldn't go into overdrive at all. I despaired, did google-searches for Toyota transmission conversions, then finally got down to business and pulled the transmission cover off again to see what was going on. It was a loose wire. That's it. My winter fixes were good, but one lead hadn't stayed snugged down properly. Five minute fix. The car has run perfectly all summer. Not one problem. Fantastic.

So I am adding my voice to the collective wisdom that the vast majority of OD problems are electrical.

And now, with nothing left to fix (for the time being), I will go for a late summer New England drive in the Healey.

-Jonathan

 

[John Turney]

It was a loose wire.

Same thing happened to me.

 

[roscoe]

It's the craziest thing. For some reason it always seems to be the last thing you check that fixes it.......

 

[glemon]

It's the craziest thing. For some reason it always seems to be the last thing you check that fixes it.......

Strange but true...I had the same sort of thing happen to me, took off the tranny tunnel, checked everything, drove around with the cover off, checked all circuits. Turned out to be a loose wire connection to the dash switch. Tested fine with car sitting, but intermittent with the car bouncing down the road as they do.

Love electrical problems, often a long frustrating diagnosis followed by a quick easy fix.