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Overdrive mystery on BN2

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bighealeysource

bighealeysource

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Hey all,
Had my overdrive rebuilt recently( by a Healey specialist ) and it works like a champ for the first 30 or so minutes. Crisp engagement, running perfect. But, once the Healey comes up to full operating temp after 30 or so minutes with the trans/OD obviously heating up too, the engagement begins to become sluggish and then will simply not engage at all. I upped the viscosity of the oil from 30 wt non detergent to 40 wt non detergent ( some thick stuff) thinking I was loosing viscosity with the unit heating up the oil. Did make some difference ( maybe 30 versus 20 minutes) as to how long before unit would not engage so thought I might be on right track there. Have double checked the operating valve ( ball bearing, spring, actual valve) as well as replaced the ball bearing on the non return valve. Replaced the relay, new gear switch and new solenoid. Even by passed the throttle switch in case that was the culprit. Had the trans tunnel off and OD will go right into engagement with pressing down on the right side of the operating lever. Triple checked and then some the adjustment of the operating lever and it is spot on. All electrics check out and as I said, unit works perfectly when starting out for 30 minutes or so. Only when fully heated up does it become an issue. If I stop for maybe 20 minutes and start back out, OD will not engage as everything still hot. Let it cool down completely and works perfect. Have even put in Redline MT90 but made no difference so put back in the 40 wt ND. Had thought about trying to find some 50 wt non detergent oil but before I do that, any ideas ???? Have spoken to rebuilder about it and he suspects it to be an electrical issue since OD does work manually. Getting to be a real quick taking my interior out and tunnel off. Taking car back out tonight and one thing I will check again is do I get the solenoid clicking/ operating lever movement once the unit stops engaging. Keep meaning to pull over and stop so I can hear it but always forget to double check - will edit this post with results. Sorry this post is so long !
Thanks
Mike
 
HI it may be the pump. In any case you need to check the pressure in the OD while running hot.
 
Hi Mike
Probably your issue are easy to fix. you can add one or two shims ( hardware washer) to the accumulator spring- normally 0.10 inch thick for increase pressure 15/30 psi sufficient to avoid OD clutch sliding
pressure at the operating valve:
must be 360 psi for early large accumulator
and 450psi for unit with small accumulator
step 18 of https://www.vintagetriumphregister.org/maintain/TransRebuild/OverDriveA02.pdf

and better at
page 5 of Nelson Riedel FAT part IV
https://www.buckeyetriumphs.org/technical/AOD/AOD4/AOD4.htm
 
Thanks y'all ! Was at a big Brit car show in Columbia, SC today, must of had well over a 100 cars with perfect weather. I even snagged a best in class with the 100M. But, as usual, the old OD worked great for about 30 minutes then simply stops working. On the way back home got on the interstate within 5 minutes of starting her up, running 75 like a charm and sure enough, in about 30 minutes, simply stops working and rpms rise up. Not a sudden rise like you might get if disengaging the OD, just gradually went up and was obvious by the screaming engine now doing over 4000 rpm at 70+ that was not in OD anymore ! I was watching and listening like a hawk to avoid a sudden drop out of OD just in case.

Andrea, the articles you linked are fantastic !!!! Sounds like I need to get that pressure tester described that can be used with the OD in place. Plus will reread the idea of putting in shims as believe that can be done with out pulling the OD. Already had the plate off to check out the one valve so although kind of a pain, at least doable with unit in car. ASSUMING I could add a shim/shims as described if enough room to work on the accumulator. I did not pull it out when checking out the valve so not sure about removing it with OD installed. Any thoughts ? Not sure what size accumulator I have with a stock 56 BN2 trans but assuming it to be the larger one since it is an early unit, correct ?

Many thanks,
Mike
 
Your OD accumulator can be large if original but it can be modified to small by one PO- one important ADVISE-- you must be sure that OIL PRESSURE are dropped at LOW level -before any operation on OD!!!
OD OIL MUST be discharged before the accumulator shim modification- OD can be MOD on situ-- but is better if you have the assistance of one AH experienced mechanic- this is the best way to make one correct and easy and fast operation
 
Hi Mike/Andrea,

I have been following the posts and the symptoms of the failure seem to match the conditions experienced by a friend with an aeration problem brought on by and incorrect fill during a change. As with you, he would set off and drive for a short while until the OD would act up and soon after totally disengage. Not being an OD internals expert but is there some way that aeration is being introduced into your OD/Transmission during your drives and becomes more prevalent when the oil’s viscosity reduces with increasing temperature?

Just a thought.

All the best,
Ray (64BJ8P1)
 
Hi Ray
Can be one idea but very difficult to find
Mike must see a pressure gauge tester at cold and warm OD to have one idea to how much the pressure drop - my opinion is that Mike WT 90 Redline was one of better oil choices for AH OD
-bubble of air can be the source of problems- but the disengage in the Mike OD are very repetitive .-air bubble can find one way to exit from OD case when you open the pressure valve for control
Your friend matured one strategy to avoid the aeration of the oil? or for eliminate the problem? is sufficient to empty completely the OD, and waiting 12h before refiling it with the same (or new) oil?
 
Mike,
I had exactly the same problem with my overdrive. The problem in my case was the accumulator. After the transmission was overhauled, my o/d was OK for about the same time, maybe less in our warmer climate. I hadn't had anything done to the o/d because it was operating OK pre transmission work. I reckon the thorough clean that was done during the work removed sludge that was maintaining pressure. Anyway, I did all the tests that you did before testing the pressure. Sure enough,once the oil reached operating temperature the pressure dropped from 450psi to 150psi. A new accumulator from a UK supplier fixed it, but what was interesting was that a second o-ring groove had to be machined into the new accumulator body before correct pressure could be achieved. I reported this to the supplier but did not get a positive response. I didn't ask for a refund or anything, I just wanted them to be aware that the part, that was to later model specification, did not necessarily suit earlier cars.
Alwyn
 
Hey y'all,
As usual, thanks to everyone that posted on here. I had the unit rebuilt by Healey Surgeons and Bruce and Inan Phillips have been great in trying to help me figure out what is going on. If I was close Bruce would go over everything at his shop in Maryland but that is not the case with me in South Carolina. Will ask him about the pressure test issue and see what he thinks. I am sure he bench tested it but since everything has to heat up a bench test would not reveal the problem - I think ! So, sounds like I need to pick up a pressure test gauge and going to see if Bill Bolton still has those available. Think I could run it on jack stands which is one method even suggested by the manuals to check operating lever. Just take it out and get everything up to temp, bring it back in, strip out the interior - have become a pro at that - put on jack stands, relieve the pressure as required, install the gauge, and see what we get ! At this stage I will be happy if it does drop down so I can fix with OD installed versus having to pull it again. Install some washers and try it again. Guess if all this does not work, then I'll just put in a 5 speed kit. Kidding - saw one of those installed on a 54 BN1 at the show on Saturday and that gear shift lever right in the middle of the tunnel just simply looks weird and wrong. Now if you could still have a side shift gear lever placement, might be another story. I promise I will not do that !!!
Thanks,
Mike
 
Hey all,
Finally able to run a pressure test today on the Healey OD. Starting out cold, pressure came up to about 400#, maybe a tad more, but hard to see while driving and staying on the road. But 400 or close. Engaged overdrive and went in perfectly, pressure dropped, maybe to 250 - 300, but came back up almost immediately, couple of seconds as most say. SO, working right when cold. Ran around for about 30 minutes and OD still working, but at 55 mph, pressure with OD off running 300 to 400 pounds, engaged OD and pressure dropped to 250 +. Could tell it was getting to the stage where OD would not engage and pressure while still in OD stayed at the 250 to 300, depending on speed in 4th gear. So... appears as though the accumulator spring will not hold the pressure when OD oil is heated up. Based on the websites recommended by Andrea, I should be running 360 for an older spring and 450 for the newer. Not sure which one I have as have not taken it apart so will not determine that until I do later this week. Going to add two washers, ones I have are .065 thick. That seems to be the usual recommendation. Any thoughts or suggestions ?
Thanks and Happy Easter to all,
Mike
 
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