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Another OD question

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BruceAllcorn

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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?
 
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.
 
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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Last edited by a moderator:
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 .
 
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 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 .
 
BruceAllcorn said:
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?
Click to expand...



Check with Bruce @ Healey Surgeons

OR:

Billy @ White Post in White post Virginia
 
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 https://www.healey6.com/Technical/OD Gauge.pdf. His e-mail address is jholekamp@sbcglobal.net. I don't recall the price, but it was not unreasonable.
 
Quantum Mechanics, Oxford CT was recommended to me by folk on this forum. John rebuilt my OD. Parts or full service. Check their website.
 
Number 35 in the pic.
From AH Spares website
 

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Number 35a is the screen
 

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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
 
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.
 
nevets said:
Thanks for the info...so if there is crud in the screen it can affect how the OD engages /disengages?
Click to expand...

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).
 
nevets said:
Thanks for the info...so if there is crud in the screen it can affect how the OD engages /disengages?
Click to expand...
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 .
 
Healey Nut said:
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 .
Click to expand...

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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