Overdrive troubleshooting checklist

[DerekJ]

Guys,

My overdrive ceased working about 100 miles into my return journey from our Sprint meeting in South Wales. The track was fast with tight bends, the best way round it for me with my 3.9 diff was using 3rd and 3rd overdrive a lot. The overdrive got a lot of heavy in and out use but I don't know if this has contributed to the problem or not.

Can someone suggest a good checklist to work my way through to troubleshoot the problem starting with the easiest things first.

BTW, the Sprint was at a track near Swansea called Pembrey where the outright track record is held by a bloke called Ayrton Senna.

 

[Healey 100]

Start by checking the oil level. Most Healey's leak tranny oil from various places and eventually the oil level falls enough so the OD will fail to engage or fall out of gear.

Most of the OD problems I've had are due to the solenoid. Those tiny contacts that must close to bring in the low resistance pull-in coil have a very difficult job to do. They have to break when carrying 50 amps or more and remake with very low resistance. Just a few ohms of contact resistance will keep your solenoid from having enough oomph to engage the OD. I have tried cleaning or filing these little beauties. It usually fixes the problem, but not for long.

I don't think there is a way to replace the bloody contacts. I have found installing a new solenoid or a proven used one will keep the OD going for a few years anyway. Fortunately, the repro solenoids are not too outrageous in cost.

 

[DerekJ]

My overdrive and transmission has been leaking oil. However every time I check the level it still reads over the level not under. I have not changed the oil since i bought the car 2 years ago and therefore I don't know how much oil was originally put in it. Maybe as a first step I'll drain both and refill with the correct amount per the manual.

 

[roscoe]

Do you hear the clicking of the solenoid if you are parked, motor off, ignition on, when you go in and out of either 3rd or 4th? If you do not then you have at least some sort of electrical issue, although it could be a broken 3rd/4th gear switch. If you do hear it you might need an adjustment to the bits that are after solenoid. A shop manual describes that best.

 

[DerekJ]

Jon, I checked and the solenoid is clicking. I drained the oil and only got about 5 pints. I'll get some non detergent oil tomorrow and refill and then see where that appears on the dipstick, which doesn't seem to be reading correctly.

 

[Keoke]

Well I wi8ll add check the pressure in the OVD it may be the pump has failed.

 

[germanmichel]

Hello,
i know that it is important additional to the right oil level , to use the right oil specification. Also I has made on my TR6 OD positive experience with cleaning the pump filter and adjustment the operating lever. Good descriptions of all this difficult valve functionallity are very good descriped in a Haynes owners workshop Manual. The Healey has unfortunately additional an overdrive throttle Switch who can influence the OD function. Good luck Michael

 

[Patrick67BJ8]

Jon, I checked and the solenoid is clicking. I drained the oil and only got about 5 pints. I'll get some non detergent oil tomorrow and refill and then see where that appears on the dipstick, which doesn't seem to be reading correctly.

The solenoid can click but that doesn't mean it has the strength to operate correctly. A large current draw is needed to initially operate the solenoid and then after it has engaged a smaller amount of current is all that's needed to hold it in the engaged mode.

 

[Healey 100]

I certainly agree with Patrick, "clicking" proves little -- the solenoid will "click" without energizing the pull-in coil. But the pull-in coil is essential to engaging the OD, the solenoid simply does not have the strength to lift that little ball under operating pressure without it.

High contact resistance (by high, I mean 2 or 3 ohms) in the OD relays or at other connections between the battery and the solenoid can also weaken the pull in force. I found that my solenoid had a poor ground to the tranny due to oil and debris and that really degraded it.

 

[DerekJ]

I filled the box with 6 pints imperial as per the manual. My box is a centre shift. The dipstick is 15.5 cms long from tip to flange.

The markings on the stick are I LOW I HIGH MOWOG (The I's indicate the level marks)

The LOW I is 0.5 cm from the tip and the HIGH I is 2.2 cmd from the tip. The 6 pints register on the stick at between the word HIGH and the word MOWOG where there is no mark. Clearly what I thought was the HIGH mark is not correct on my dipstick. No idea why. Can anybody provide details of theirs for comparison.

 

[DerekJ]

Success! The o/d is working again. Seems like the problem was insufficient oil due to the misreading on the dipstick. Effort not wasted as I now have clean oil, clean o/d filter and now know the correct oil level mark.