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Thread: Another OD question

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    Another OD question

    I have a 1962 tri-carb with an overdrive that I am running Redline MT-90 in. When I flip the switch to switch it into OD there is a delay of 1.5-2.0 seconds before the OD drops in. If I am accelerating from a stop with the OD on, when I get into 3rd gear the OD will have dropped out and will not re-engage until I have built some RMP's. If I am slowing down and shift into 3rd gear it will often drop out of OD and once I accelerate and the RPM's get higher it will again engage. I have just enough play in the gear shift lever to be able to "engage" the OD switch on the gearbox while in 3rd or 4th gear to disengage the OD, but in my normal shifting this does not come into play so I don't think that a worn gear shift lever bushing or a bad overdrive switch are the problem. Any ideas as to what is/are causing this problem?

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    Re: Another OD question

    My first thought is that the pump is worn.

    When you accelerate from a stop, the OD disengages in 1st or 2nd. But having to build RPMs to get it to engage in 3rd or 4th means low oil pressure in the OD.
    John, BN4

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    Re: Another OD question

    When you accelerate from a stop, the OD disengages in 1st or 2nd. But having to build RPMs to get it to engage in 3rd or 4th means low oil pressure in the OD. ----

    -Yep: I agree, check OVD pressure builds up quickly to 450 PSI.




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    Re: Another OD question

    If the screen filter in the OD is clean then you need to check the OD oil pressure 450psi min . Probably need an OD overhaul . New piston rings and operating ball/spring etc .
    "If it aint broke ....dont fix it "
    " Thats not an oil leak ..........its a special automatic British rustproofing system "
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    Re: Another OD question

    It seems to be a concensus and is the way I was leaning also. Thanks for the answers. Any suggestions on who to get to rebuild the OD?

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    Re: Another OD question

    Check the oil pressure before you decide to rebuild . It could be a dirty screen in the OD .
    if you decide to do a rebuild , do it yourself its just an oil pump with a diverter valve ,the hardest part is getting it back on the gearbox due to the double spline arrangement. Thats a patience tester .
    "If it aint broke ....dont fix it "
    " Thats not an oil leak ..........its a special automatic British rustproofing system "
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    Re: Another OD question

    Quote Originally Posted by BruceAllcorn View Post
    It seems to be a concensus and is the way I was leaning also. Thanks for the answers. Any suggestions on who to get to rebuild the OD?


    Check with Bruce @ Healey Surgeons

    OR:

    Billy @ White Post in White post Virginia
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    Re: Another OD question

    Try adding some MT-90 to the gearbox.

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    Re: Another OD question

    The recommendation to check the oil pressure is key here. If the pressure drops much below 450 psi, a lot of odd behaviors will show up.
    From personal experience, the first culprit to consider for the pressure decline is the accumulator spring. Over time, they weaken and the pressure drops. The spring is replaceable without removal of the OD unit. It is behind the cover on the left side.
    In my case the overdrive quit engaging but would kind of "freewheel" if I let off the gas slightly. Measured pressure was in the 350 psi range. Ordered a spring and the side cover gasket from Moss. The new spring was noticeably longer than my old one. After replacement, pressure was up to the 450 psi spec and OD operation was back to normal.
    The pressure gauge setup is a bit out of the ordinary as it needs to install into the operating valve plug. I purchased mine from J Holekamp whose gauges are shown in this link http://www.healey6.com/Technical/OD%20Gauge.pdf. His e-mail address is jholekamp@sbcglobal.net. I don't recall the price, but it was not unreasonable.

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    Re: Another OD question

    Quote Originally Posted by dcarlg View Post
    Try adding some MT-90 to the gearbox.
    Yes, make sure the transmission oil level isn't low before doing anything else. If it's ok, check the screen (behind the big nut on the OD). If that's ok, then rebuild.
    John, BN4

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    Re: Another OD question

    Quantum Mechanics, Oxford CT was recommended to me by folk on this forum. John rebuilt my OD. Parts or full service. Check their website.
    Dale

    BJ7 frame up restoration of "the car that would not be restored"; began Dec. 2005, est. complete 2023

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    Re: Another OD question

    Quote Originally Posted by John Turney View Post
    Yes, make sure the transmission oil level isn't low before doing anything else. If it's ok, check the screen (behind the big nut on the OD). If that's ok, then rebuild.
    Apologies for my ignorance but where is the big nut?

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    Re: Another OD question

    Number 35 in the pic.
    From AH Spares website
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    Dale

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    Re: Another OD question

    Number 35a is the screen
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    Dale

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    Re: Another OD question

    All of these things may be possible. One thing that is easy to check if you do have low oil pressure is the seat for the ball bearing which is for pressure relief of the piston type oil pump that runs the OD oil pressure. I know this may be beyond what you feel like doing, it requires removing the side cover after draining the oil. I found bad pitting of the seat and wear of the ball bearing was the cause of my never building sufficient oil pressure, even at higher revs. . Lapping the little seat with a new ball bearing glued to a piece of round 1/4 inch stock and chucked in a drill. Valve grinding compound worked very well. Coarse first then fine. The ball bearing is #36 in the diagram that was posted above. I've posted a photo of the pressure gage I made. The threaded portion is a spare operating valve cap with a small hole drilled through the top, item 28A in the diagram, welded or brazed to a pipe fitting to adapt it to a glycerin filled gage. Just replace the in service cap with this and drive and you see the OD oil pressure and it does not affect the operation. IMG_20190131_142944658-585x1040.jpg
    Jon Robbins
    1956BN-2 (do it all yourself, you'll be glad you did)

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    Re: Another OD question

    Good point. There's a similar ball/seat valve on the shaft that is moved by the activation cross-shaft's cam (I believe it's what allows the pressurized accumulator fluid to move the cone clutch against the brake ring and lock the sun gear). I think if this valve didn't seal it would relieve some of the pressure necessary to activate the O/D. I rebuilt my O/D last year and, IIRC, the shop manual's recommended technique for seating the ball in the seat is to give it a good smack with a hammer and drift (maybe not the exact instructions).

    Side note: As far as I can tell, every incidental ball bearing--O/D valves, seat runners, and others--is 5/16". I bought a boatload from an online supplier of (only) ball bearings.

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    Re: Another OD question

    Quote Originally Posted by RestoreThemAll View Post
    Number 35a is the screen
    Thanks for the info...so if there is crud in the screen it can affect how the OD engages /disengages?

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    Re: Another OD question

    Quote Originally Posted by nevets View Post
    Thanks for the info...so if there is crud in the screen it can affect how the OD engages /disengages?
    If it's sludge, yes. If there's metal in it the O/D should be rebuilt. I've seen some stuff that looks like coffee grounds--just a pinch or two--and it didn't seem to cause any problem (could be clutch material).

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    Re: Another OD question

    Quote Originally Posted by nevets View Post
    Thanks for the info...so if there is crud in the screen it can affect how the OD engages /disengages?
    Any restriction (dirty screen)or leakage due to worn OD piston rings or ball seats will affect flow and how much pressure the OD oil pump produces , all this will affect the operation of the OD and dont forget the gearbox and OD share the same oil .
    "If it aint broke ....dont fix it "
    " Thats not an oil leak ..........its a special automatic British rustproofing system "
    Best Healey in show ABCD Ottawa 2013
    Best Healey in Show Boot n Bonnett Kingston 2013

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    Re: Another OD question

    Quote Originally Posted by Healey Nut View Post
    Any restriction (dirty screen)or leakage due to worn OD piston rings or ball seats will affect flow and how much pressure the OD oil pump produces , all this will affect the operation of the OD and dont forget the gearbox and OD share the same oil .
    Addendum to my previous reply: 'Crud' in the screen does not necessarily require an overhaul of the unit; as Nut points out the O/D and gearbox share fluid, so metal could have come from the gearbox (somewhat normal as synchros, etc. wear). You might get by with a good flush and fluid refill, but if either is making a lot of metal, and you want a reliable car, at least a teardown and inspection is a good idea.

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