• Hi Guest!
    If you appreciate British Car Forum and our 25 years of supporting British car enthusiasts with technical and anicdotal information, collected from our thousands of great members, please support us with a low-cost subscription. You can become a supporting member for less than the dues of most car clubs.
    There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Subscribers don't see this gawd-aweful banner
Tips
Tips

Stumbling overdrive

Share this page

Randy Harris

Randy Harris

Jedi Warrior
Offline
'66 BJ8 - Car runs very well but now a new issue: Cruising at freeway speed in 4th gear overdrive. Car stumbles, tach needle swings wildly and then settles down and car continues on. This has been happening more and more frequently. Yesterday afternoon, it happened several times in a 5 mile freeway ride (I thought at first I had bad fuel), culminating in the overdrive disengaging and not re-engaging even after flipping the switch several times. Now it's working again - but for how long?.
What's going on here and can anyone suggest where to begin? 3rd gear overdrive seems to work just fine - I think.
Thanks
Randy
 
This was happening to me before I had my generator rebuilt-wasn't keeping enough charge to power the overdrive. However, it has to be pretty bad (the generator) for this to happen.
 
I believe the generator would be a good place to start given the effect on the tach and relative ease of fix that might have to be done anyway However, I experienced similar problems as you have mentioned. There is a couple of things that had to be fixed on mine in order of severity...

1) is the dash board switch working properly and in possible need of cleaning or replacing. Run the car in 3rd overdrive that you say is stable. Wiggle the switch back and forth when its switched on... if it disengages then you know.

2) There is a limiter switch attached to the gear shift mechanism, with an anval that engages only in 3 or 4th. Examine the switch surfce for wear that is keeping it ative or inactive... a quick fix is to rotat the switches contact a 1/4 turn and reinstall.

3) The other problem is the hydraulic pressure insuffient to activate the overdrive and misadjustment of the solonoid linkage. I believe the the Jim Werner has this covered well on his healey page.
2) There is a
 
Can't be the dynamo as I run a negative-ground alternator.
The other suggestions are good ones. I'll begin right away.

What has me confused is that 3rd speed overdrive appears to operating as normal. If it was an electrical short or bad switch connection, wouldn't that present in both 3rd and 4th gear running?

Thanks.
Randy
 
No Randy, that anvil is slightly tapered the switch on the gearbox can be properly set for third gear but maginal in fourth.---Fwiw---Keoke
 
Randy,

I had this problem before and found that many things can cause it.

3/4th lock-out switch not adjusted (remove spacer washer)

Low OD oil (add some)

Plunger needs adjusting (adjust lever)

Wiring to OD relay got hot (find intermittent short)

I recommend you go back through all your adjustments. If all this fails then you might have leakey o-rings.
 
[ QUOTE ]
'66 BJ8 - Car runs very well but now a new issue: Cruising at freeway speed in 4th gear overdrive. Car stumbles, tach needle swings wildly and then settles down and car continues on.
Randy

[/ QUOTE ]
The tach needle & stumble is a good indication that power is being interrupted or short circuited somewhere upstream of the ignition & OD wire take off point. ie. terminal A3 at the fuse block, the ignition switch, or the feed from the alternator. (The old A or A1 connection where the voltage regulator previously connected.) Don't know how your alternator conversion is wired.

Don't know why it would happen in fourth & not third. Coincidence or mis-read.
D
 
Back
Top