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BJ8 overdrive stops working after a while driving

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Airwave

Airwave

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Hello I'm new in the Forum. I already read out a lot of good hints, which I really appreciate a lot.Now, as something strange happens when driving, I'm just wondering if someone can help.

Since the mechanic replaced the clutch plate the O/D doesn't work properly anymore, right after starting the cold engine it works perfect (Switch in & out), but after a certain while when heated up the Switch is not responding anymore. Has anyone any idea what could cause this phenomenon ? It doesn't seem to be wobbled contact because driving the next day the O/D works again but sets out again, Groundhog Day. Before the O/D did work without any problems.
 
Hi
Drive the car to warm her up. Then if you turn the ignition on but don't start the engine, put the car in first or third and flick the switch, you should be able to hear the solenoid clicking on the gearbox. Don't get confused with the relay click which isn't as loud. If you don't hear it it means the problem is electrical.
That's a start.
Matthew
 
Hello, Airwave, and welcome to the Forum.
I do not believe there is a connection between your replaced clutch plate and the symptoms with the overdrive. Nor is the temperature of the engine directly related to those symptoms, but the temperature of the oil in the gearbox/overdrive could cause those symptoms if there are internal problems with the overdrive.
My first thought was that you are experiencing the same symptoms I did years ago. My O/D worked fine when its oil was cold, but once the oil heated up and I had to shift out of O/D it would not re-engage again until the oil cooled. In my case, the problem was a severely scored bore in the accumulator. That is a cylindrical aluminum part in the overdrive that has a piston with steel piston rings in its bore. Oil pressure from the O/D pump causes the piston to move back in the bore against a heavy spring until it exposes holes in the bore walls. These holes route the oil to the operating pistons to engage the overdrive. A scored accumulator bore causes too much leakage of the pressure (especially as the oil thins out at higher temperature) so the piston is not pushed far enough back to expose the holes. Some claim the accumulator can be removed and replaced without removing the gearbox and overdrive, but I've never done that.
The critical issue is that the O/D has to generate about 450 psi to operate properly and anything that prevents that will prevent the O/D from engaging.
Good luck with it!
 
Matthew

Welcome to the forum. One of the first things to learn is that while a lot of us know a little a few of us know a lot. Steve Byers is one of those few.
 
Mine recently did the same thing. Worked fine until hot. Eventually, however, it stopped working altogether and did not work when cold. It was the relay in the engine compartment that was the problem in my case.
 
Hello Airwave, and welcome to the forum. I''m going to make a suggestion based on the principle of "what was done last". i'm wondering if when the transmission was out for the clutch job that maybe some trans oil was lost. Check your fill stick indicator and refill if necessary.
 
What kind of oil is in the transmission? The consensus seems to be that 30 wt nondetergent oil is best.
 
Keith_M said:
...The consensus seems to be that 30 wt nondetergent oil is best.
Click to expand...

Not necessarily. 30W non-detergent is what was recommended in the manual when the cars were built last century, and is still an acceptable lubricant (though getting harder to find). I use Redline MT-90 in both my BN2 and BJ8. I put it in the BJ8 to see if the OD would be a bit more responsive--it was--but was surprised by smoother shifting in the gearbox. The downside is a bit more leakage.

The theory on ND oil is that--since it has no detergents or dispersants--it allows swarf to sink to the bottom (presumably building up a layer of sludge). The MT-90 keeps wear metals--mostly brass--in suspension, though I've found they are so finely ground they don't cause a problem (at least, in the 75K miles or so that I've been using it).
 
IMG_20170717_074822949-1.jpgI agree that Steve is spot on. Although there are alternate explanations for your issue, since it seems to work well when the oil is cooler it is likley an oil pressure problem. Likewise,there are several spots in the OD unit where oil pressure can be lost. I've added a photo of a simple tool you can make or have made. All you need is a spare cap that goes on the selector valve, which is easily accessible with the gearbox tunnel off. A 600 psi pressure gage and a tad of welding skill. You remove the cap, drill a small hole in the top and install the cap with the gage. Go for a drive, making sure you are not going to get anything caught in the spinning driveshaft, and watch the pressure gage. I'll bet you see the oil pressure slowly drop to less than 300 psi as the oil warms up. Once the pressure drops off below the pressure needed to actuate the OD clutch the OD will drop off. I don't recall what the drop out pressure is but when i put my car on the road I found that the seat for the small ball bearing used with a spring for the oil pressure relief valve was badly pitted and would not allow the valve to ever close, thus not allowing pressure to ever build. I lapped the seat (for hours) and voila!
 
Last edited:
Bob_Spidell said:
Not necessarily. 30W non-detergent is what was recommended in the manual when the cars were built last century, and is still an acceptable lubricant (though getting harder to find). I use Redline MT-90 in both my BN2 and BJ8. I put it in the BJ8 to see if the OD would be a bit more responsive--it was--but was surprised by smoother shifting in the gearbox. The downside is a bit more leakage.

The theory on ND oil is that--since it has no detergents or dispersants--it allows swarf to sink to the bottom (presumably building up a layer of sludge). The MT-90 keeps wear metals--mostly brass--in suspension, though I've found they are so finely ground they don't cause a problem (at least, in the 75K miles or so that I've been using it).
Click to expand...

I agree there are other oils that will work. I think I remember reading somewhere that detergent oils can foam and cause pressure in the overdrive to drop. My (not clearly stated) point was simply that one might try a different oil to see if that's the problem.
 
Good point on the foaming. When my relay failed my OD disengaged randomly, so if an OD gets quits consistently when hot it's likely low pressure. A different fluid may help, but won't fix the underlying problem. I believe MT-90 is equivalent to 40W or 50W gear oil.
 
Hello all again :smile:

Many many thanks to all of you for your excellent hints and advices, much appreciated !!

I performed easiest tests first as adviced and found out that it is obviously an electro mechanical device problem. It's likely the Solenoid.


Again, many thanks for your help, btw I also found this helpful techical overdrive description (added link eventhough I believe that all of you already know this pdf anyway):

https://www.healey6.com/Technical/Tech-OverdriveTroubleshooting.pdf

airwave

PS Low oil pressure problem; I'm using gear oil: SAE 40 and engine oil: 20w50 motorex
 
Airwave--

I am glad you found your problem.

At the end of your post you say you are using "gear oil", a term which seems to be used loosely.

Make sure you are using an oil that has a GL4 rating which is compatible with yellow metal, such as the synchro rings in your transmission. Many "gear oils" are designed to be used in differentials or transmissions without brass, etc. parts and have a GL5 rating which has higher sulfur and phosphorus contents and will, over time, attack these parts. For more information go here: https://www.widman.biz/uploads/Transaxle_oil.pdf
 
Thank you Michael :smile: as a fact my overdrive (false oil pressure for the Solenoid?) stops working when engine is warmed up, do you think it also might be becuse of the used SAE 40 gear oil ?
 
Hi Airwave,

Welcome. A while back there was a discussion on the effects of using thicker oils in the Overdrive and gearbox. Although gear oil and even Automatic Transmission Fluid are recommended by some manufacturers, my understanding is that a 90W gear oil (equivalent in viscosity to a 40W Motor oil you indicated using) could be a little thick to exit out of the small openings of the accumulator and cause an increase in pressure as the car continues to operate in OD. So, instead of OD loosing pressure as it warms, it is building pressure to a point that it will keep it actuated and will not release even when switched off until the pressure slowly diminishes.

As a check, I would change fluid to one having less viscosity before doing anything. I personally used 30W non-detergent oil for many years and switched to Red Line MTL about 10 years ago. No problems with 30W non-detergent but it was getting difficult to find a good brand.

Just a thought,
Ray(64BJ8P1)
 
I have to agree with the proponents of the correct oil theory. If it is not low on oil then the wrong oil could be the problem as well. My belief is that you can get too thick of an oil. I still use 30w motor oil with no troubles with the trans or OD.
 
vette said:
I have to agree with the proponents of the correct oil theory. If it is not low on oil then the wrong oil could be the problem as well. My belief is that you can get too thick of an oil. I still use 30w motor oil with no troubles with the trans or OD.
Click to expand...
Actually, I use SAE60 in mine, but I have the uprated accumulator.
 
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