AHExp

The 100 Forum

Overdrive jumping while engaged

Moss Motors
AutoShrine Sponsor
AutoShrine Sponsor
AutoShrine Sponsor
AutoShrine Sponsor

AustinOz Wayne Smith
Canberra, ACT, Australia   AUS
My 1954 BN1 has started to jump out of overdrive while on the highway. Everything is standard with the G/B and O/D except I have removed the Centrifugal switch from the circuit. The oil level is correct and I use Penlight GB 30 oil. Has anybody had any failures with either the Gear Box Switch or the Throttle Switch? The symptoms are:- while driving in O/D with the throttle open suddenly the O/D reverts to Direct Drive then back to O/D then Direct Drive and so on except I switch O/D off when it happens. All connections have been checked. Any ideas please.

. Hide banner ads & support this website by becoming a > Gold Supporting Member <
Vintage n Classic Avatar
Vintage n Classic Silver Member Geoff Golding
Nelson, Tasman, New Zealand   NZL
Hi Wayne,

Suggest the solenoid on the outside of the gearbox is not holding the O/D "in" and this may require a new solenoid unit. Maybe its a wire that has become disconnected or broken powering the solonoid down near the gearbox may be the easy solution

Cheers
Geoff

AustinOz Wayne Smith
Canberra, ACT, Australia   AUS
Hi Geoff

The solenoid certainly clicks “in” when the O/D switch is turned on and the gear lever is in the 2/3 position. What you are saying is that the solenoid may be jumping “in” and “out”? Is there any way I can test the solenoid itself? Does heat effect the solenoid? I will test the wires to the solenoid.

Cheers Wayne

. Hide banner ads & support this website by becoming a > Gold Supporting Member <
San Jose, CA, USA   USA
I've had random 'dropping out of OD' problems twice with my BJ8 (since you've disconnected the centrifugal switch the electrics are similar). The first time, it was a failing switch on the dashboard. The second time it was burnt points in the relay, which I fixed--in a motel room in Canada--by carefully opening the relay and filing the points (I replaced the switch when I got home). I recommend trying these easy fixes first--the relay is a bit on the pricey side, though--before pulling the transmission cover. FWIW, the solenoid was going strong at 200K miles, but I just replaced it 'on principle' because I rebuilt the OD and had bought a new one years ago.

Another possibility is a weak hydraulic pump. The best (only?) way to test this is with a pressure gauge.

PAN Avatar
PAN Alwyn Keepence
Ipswich, Queensland, Australia   AUS
G'day Wayne, I reckon your problem is the "top-gear" switch. On the BN1 this switch is exposed to the gearbox oil and they can get contaminated.

Vintage n Classic Avatar
Vintage n Classic Silver Member Geoff Golding
Nelson, Tasman, New Zealand   NZL
Hi Wayne,

I concur with a previous post with respect to the oil pressure In the overdrive as a possibility but in my limited experience with the overdrive "misbehaving" in our 100/4, the oil level is critical and we no run our car with the level up beyond the "Full mark". The manual indicates the pressure should be 450-500 PSI.........if your cars unit is not in this range I suggest the pump may be worn and not delivering the correct pressure. I'm not familiar with the oil you are using but 20/50 GTX is what we run in our car

If you go to YouTube and key in "Matthew Randle Austin Healey 100/6 restoration part 59 There are a series of videos based on the restoration of Matthew's car.................Part 50 is about the Solenoid and in his case it was burning out but a few episodes before this (great viewing to go back through all the previous episodes on a wet or very hot day) Matthew gives a demonstration of the operation and of the solenoid and the parts.

Cheers
Geoff

PAN Avatar
PAN Alwyn Keepence
Ipswich, Queensland, Australia   AUS
Wayne,
I still think it is the gearbox switch. Next time the fault occurs, push the shift lever over to the left. If the overdrive re-engages that proves it. You can also check this with car stationary. Switch on the ignition (no need to start the motor) and put the o/d switch in the 'overdrive' position. Now move the shift lever hard over to the left. You should hear the solenoid click.
I'm afraid I disagree with Geoff on his suggestion that it is a pressure problem. I have experienced low o/d oil pressure and once the pressure drops it does not come back until the oil has cooled right down, overnight. In my case the accumulator needed replacement.
If the solenoid was faulty, I doubt it would drop out and then back in again, unless it is simply a loose electrical connection.
I use Penrite Gearbox oil 40 and recommend it.
And Geoff, how do you overfill the gearbox on a BN1? I just fill to the level of the filler plug as the manual says.
Cheers,
Alwyn

. Hide banner ads & support this website by becoming a > Gold Supporting Member <
Vintage n Classic Avatar
Vintage n Classic Silver Member Geoff Golding
Nelson, Tasman, New Zealand   NZL
Hi Alwyn,

Our car has a BN 2 Gearbox.

Cheers
Geoff

AustinOz Wayne Smith
Canberra, ACT, Australia   AUS
Hi Alwyn and Geoff

Thanks to you both. I have purchased a new gearbox switch ($11 from The Healey Factory). The old one appeared to have oil inside it, when I pressed the ball plunger oil came out from the switch. I intend to dismantle the switch to see how it is constructed and see if oil can get into the body of the switch. As the car is up on stands I intend to do some other work on it and I probably won't get to test it for a couple of weeks but will report back when it is back on the road.

Cheers Wayne

. Hide banner ads & support this website by becoming a > Gold Supporting Member <
PAN Avatar
PAN Alwyn Keepence
Ipswich, Queensland, Australia   AUS
Wayne,
When you fit the switch, use as thin a gasket as possible to ensure that the plunger depresses to the correct extent.
Cheers,
Alwyn

Trevor Parker Avatar
Trevor Parker Silver Member Trevor Parker W
Sidney, BC, Canada   CAN
1954 Austin-Healey 100 "Healey Beep Beep"
1955 Austin-Healey 100
I had the same problem with my BN 1. In my case it turned out to be the throttle switch on the firewall. I want to retain the original switch so all I did was wire in an switch to override the throttle switch. I have found with the throttle switch override engaged I haven't experienced any more problems. Cheers Trevor

. Hide banner ads & support this website by becoming a > Gold Supporting Member <

To add your reply, or post your own questions




Registration is FREE and takes less than a minute!


Having trouble posting or changing forum settings?
Read the Forum Help (FAQ) or contact the webmaster





Join The Club

Sign in to ask questions, share photos, and access all website features

Your Cars

1963 Austin Healey Sprite

Text Size

Larger Smaller
Reset Save

Sponsor Links