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Overdrive Problems

TodE

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So I have had an overdrive issue for a while. It seemed to work ok when I first start out it works fine, but once the oil warms up it "jumps out" of overdrive. It's been doing that for a while. Now it won't work at all.
My first thought that it was low on oil. I checked it, the level was fine. I pulled the solenoid out cleaned the rod and inside the solenoid. I applied 12 volt to it and it pulled the rod in.
I put the solenoid back in. I turned the key on and turned the overdive switch on, I could hear the the relay under the dash "click" and solenoid engage. When I depressed the accelerator pedal part way down I can hear the throttle switch engage. When I depress the accelerator pedal again I can here it disengage.

I have not driven the car since I did the above, so I don't know if I corrected the problem? I didn't really fix anything?
I did see where some people with overdrive problems used a thicker weight oil. I saw some used 50 weight, some use 60 weight in the summer. I was going to use 50 weight. Currently I am using straight (Non-detergent) 30 weight.
This is a BN-1 with a 4 speed transmission installed.
Any thoughts on problem or what brand of 50 weight oil to use? Do they even make a non-detergent 50 weight oil?

Thank you in advance with your help,
Tod
 

Jack T

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Tod,

I don't know if the electric circuit is different on my BT7, but pressing the throttle is not required to engage the OD provided the throttle relay is properly adjusted. With the key on and the gear lever in 3rd or 4th, the solenoid should be energized when the switch is on without pressing the throttle. The throttle switch is part of the disengagement process. Be sure to check the lever on the right side of the unit as described in the workshop manual. I adjusted mine today, and the amount of adjustment between go / no go was miniscule.
 
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Healey Nut

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Is the screen filter in the OD clean . What is the pressure from the OD oil pump ?
 

TimK

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I have a BN7 with side-shift trans. I had a similar problem which I rectified by taking off the side cover and removing sludge from the accumulator area and piston. Also I removed the top cap nut and exposed the ball bearing that serves as a valve. I tapped it lightly with a hammer to insure a good seat. Then I followed the instructions to make sure the lever that lifts the engagement pin when the solenoid is energized was adjusted correctly. After these actions the OD has worked flawlessly. All this work was done with the transmission in place with the trans cover removed.
 

roscoe

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There are many small insidious things that can cause an OD to be intermittant. The most useful tool is the one used to measure OD oil pump pressure. From your description, my guess would be that your OD oil pump pressure is on the edge of being too low to engage so that as the oil thins a bit due to the heat of driving that is drops below nominal and the OD disengages. The tool is made by taking a spare operating valve cap, drill a small passage in the cap and weld or braze an adapter so you can thread on a 0 to 600 psi pressure gage to it. You then drive with this installed in place of the regular cap. Keeping clear of the spinning driveshaft, you can watch the pressure and know for sure if that is the issue. If it is not, it rules out a multitude of potential problems. I suppose if you are a little thoughtful you could actually use the original cap without needing a spare if you made it so you could remove the gage and cap it off for normal driving.
Is it possible that when the OD drops out after warmup, that it reengages if you rev the engine as you drive. If you try this as soon as it happens and it reengages even momentarily it might also point to low oil pressure. Of course there are multiple reasons you can have low pressure and knowing that it is low doesn't tell you why it is low but it narrows the possibilities.
 
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TodE

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What would be an acceptable pressure range? Will the pressure vary with OD engaged or disengaged?

Thank you!
 

TimK

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The nominal operating pressure is 470-490 psi.
 
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roscoe

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Anything under 400 psi is not good. The minimum pressure if I recall correctly is 470 to 490 psi but I know from experience it may operate as low as 400. The pressure if measured at the operating valve as I mentioned above does not change much if things are normal, whether the od is engaged or not. It just changes how the oil is routed. In a freshly overhauled OD the accumulator should hold that pressure for a considerable time even when the engine is off and the OD is not turning its pump. It will eventually bleed off. There is a spring loaded pressure relief ball bearing and seat that determines pump output pressure if the pump itself is not badly worn. A 0 to 600 psi gage gives a nice scale to read and it may be best of a glycerine filled gage is used to dampen out fluctuations. There is a ton of good information on this forum and other places on the internet about the Laycock deNormanville OD in the big Healeys and other cars.
 

CraigC

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If you don't want to cobble a pressure gauge setup together, you can purchase one here---> http://www.geocities.ws/jholekamp/

I purchased one several years ago and it was quite helpful in the diagnosis of my OD problem. Found that the pressure was low due to a weak accumulator spring.

This setup, which is connected the same way as Roscoe stated, will give pressure reading with and without OD activated.
 

Healey Nut

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You need a friendly HVAC guy to convert your OD plug so it has a 1/4” male flare fitting with a schrader valve in it , then you have a 0/600psi gauge with 1/4” female flare adaptor and schrader depressor in it and voila your good to go .
 
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TodE

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Roscoe
So I am not clear where where the gauge needs to be placed? In the Moss catalog, OD page, are we talking about #90 "Plug, threaded" or someplace else?
I don't see a description of "valve cover"? I am using a BN-4 side shift transmission. Is it a "A" or "J" type OD.
In other posts under "OD Problems" as I mentioned before I saw where some guys used heavy oil? I know that doesn't fix the problem it puts a bandaid on the problem, but I am not seeing where you guys recommend that?
Thanks for all the help!
 

TimK

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The #90 plug is the OD Plug described above. The ball bearing I was talking about is the operating valve under plug #90, this plug #90 can be referred to as the “valve cover”.
 

roscoe

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Yes, the item 90 in the Moss diagram is the aforementioned cap on the operating valve, so it is in effect the valve cover. If you Google Austin Healey type A overdrive testing you will find a video of the gage set being used on the bench to test an overhauled unit. Using heavier than recommended oil is something I have no real opinion on as it is meant to operate on straight non detergent 30 weight and that is what I use. People use all sorts of stuff and in my book it is like religion. If it works for you and gets you through the night then more power to you, use what ever oil you think best after educating yourself. There probably is a "best" oil to use and it may not be 30W ND. Heavier oil might be a diagnostic tool in lieu of actually measuring the pump pressure if it makes the OD less intermittant. My 2 cents isn't worth any more than anyone else's 2 cents.
 

CraigC

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Below is a video of the gauge assembly I purchased from JHolenkamp in action. What is going on when the pressure drops is the solenoid activating, opening the operating valve. Once the operating pistons move all the way out, the pressure returns to normal.

I have also included a pic of the gauge I purchased. It uses a bespoke adapter to function as the operating valve cap and connection for gauge.

As an auto mechanic, I could have put together everything I needed to do the same thing, but the time it would take couldn't be justified for the price I paid for the complete ready-to-use unit.

20200618_103222.jpg

 

TimK

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With due respect to those who advocate testing the OD oil pressure, my opinion is that if your OD disengages when the oil warms up, you have a pressure deficiency. Yes, a gauge will verify that but won’t fix it. I fixed my problem (same as yours) by going after the easiest things that could cause a drop in pressure first. The sludge in the accumulator could have easily reduced the pressure as could a partially seated operating valve (the ball bearing), finally an out of adjustment operating lever could also result in intermittent failure. Dealing with these things solved my problem completely. Additional causes could be a weak accumulator spring or worn piston rings on the accumulator piston. Finally, there also could be a worn pump and/or cam that powers the pump. The fixes I did required very little effort and were very effective. I recommend you try them first.
 

roscoe

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Another thing not mentioned is the pressure relief ball bearing seat for the oil pump. This is accessible through the side cover. When I completed my rebuild I was disappointed that the OD was not operating after all rigging, cleaning, replaced the accumulator orings and replaced the oil pump piston because it had been bent because it was installed by the previous owner 180 degrees spun around. Now what? I pulled the gearbox back out and in retrospect I could have done the fix below in place although it would be a bit awkward.

What I found were sizeable corrosion pits on the aluminum ball bearing seat and a slightly out of round ball bearing. The latter was a part I had looked at but not measured and I had neglected to look closely at the seat. It looked like craters on th moon under a 10x glass. I got a new ball bearing or two and glued one to a wood holder, much like a valve grinding tool and applied some valve grinding compound and lapped the seat until I had a smooth surface. The new ball and seat boosted the OD pump pressure by almost 200 PSI and I was in business. No problems since.
 
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TodE

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OK guys thanks for all the great advise! I ordered a gauge from Holekamp. I will check the pressures and test drive. In the mean time, I think I will drain the oil clean the screen and replace with 30 wt. ND oil (which is what's in the OD now.) The transmission and OD was rebuilt when the restoration was done 5 years ago. I have driven the car 1000 miles since restoration.
 

Jack T

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If you can spend a few extra dollars, I would suggest buying 4 qts of Redline MT90 for your refill. The difference in shifting is worth it, and it might help the od as well.
 
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