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AH 3000 BJ8 overdrive problems

davidb

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Looking for some technical advice gentlemen...

Overdrive works while the oil is still cool/cold, but after a warmup run, the overdrive engages slowly and finally won't engage at all. Is it an oil pressure issue? Solenoid seems to be working fine, and electrics are good. Any suggestions?

thanks
Dave
 

Keith_M

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What kind of oil are you running in the tranny/OD?
 

Keoke

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I'm not an O/D expert--never rebuilt one--but the O/D is kept engaged by high (300psi+) oil pressure produced by a piston pump working against some fairly strong springs. Assuming you're running a suitable oil--30W non-detergent is recommended, I run Redline MT90--the logical culprit is the pump. It's similar to an engine piston, with rings, and the rings and/or cylinder wall could be worn. Also, pressure is maintained/damped by an accumulator, and if it's leaking down it could be at least part of the problem.

Be sure you've ruled out electrical issues--they are the easiest to fix once you've identified the problem.
 

kozelding

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Mine used to do that too. I assume a pump rebuild is eventually in order, but in the meantime I:


- switched from 30 weight to 50 weight oil
- adjusted the operating lever so the ball valve moves up a little more


The OD is still lazy to engage when it gets hot, but at least now it always does (and it won't drop out unless I slow to ~35 MPH).
 
Last edited:

RAC68

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Although there are many things that could affect the operation of the OD, I believe knowing the oil being used and that its up to mark would is the first step to identifying the issue.

Ray (64BJ8P1)
 

Healey Nut

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Second is knowing what the pump pressure is . If it's not over 400 psi when it's hot you will have problems .
 
OP
davidb

davidb

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My thanks to all who took the time to provide their advice/suggestions/experience. It was quite helpful. Overdrives in my view tend to be a Pandora's Box, and I'm afraid to open one fearing what I might find. I currently use Castrol 20/50 in both of my Healeys. The other one works fine, so as suggested, it may be the pump or an adjustment to the operating lever. As mentioned, the electrics appear to be good. Moving to a thicker oil may be a temporary fix. We'll see. It's getting pretty cold up here in the Great White North - getting the beast to start is the biggest issue, let alone the overdrive. Am I right "Healey Nut"?

Thanks again, guys
Dave
 

Healey Nut

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Your using the same oil I use and mine work fine . There no "pandoras box" to an overdrive . Its a hydraulic pump with a wet clutch a big ass set of springs and a diverter valve . The electrics from what you say seem to be working . When did you last change the oil/check n clean the filter ?
Your symptoms seems to be leaning towards worn piston rings which is an easy fix . What you could do if your not up to doing a rebuild is change the oil clean the screen , if that doesn't fix it then you could do an exchange unit from Autofarm in Kitchener .
Where in Ontario are you ? If your close to me I could check your OD pump pressure for you with my adaptors and gauges .
I have rebuilt 3 overdrives so Im quite familiar with their quirks and setup issues .
Starting is not an issue for my cars , they all live in a heated garage
 
Last edited:

Keith_M

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Before you start tearing into the overdrive, it might be worth trying 30W nondetergent oil. Here is a link to an article that tried several types of oil in a Laycock overdrive unit. The important point for your case is that they found that detergent oil tended to foam and affected the oil pressure. If your oil pressure is marginal, foaming might reduce it just enough to make it pop out of overdrive. You might just be able to get by with a nondetergent oil. It's a relatively easy thing to try (compared to tearing apart the overdrive).

https://www.mgtoronto.com/pdf/Tech/Overdrive_oil.pdf
 
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Could it be the switch on the gear shift. When they act up the can mimic a low oil level. Push the gear shift to the right and see if works better.
 

titanic

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One culprit that is easy to eliminate is the adjustment of the operating valve (as mentioned by Kozelding). Sometimes the use of the 3/16" pin does not give enough valve lift and it is necessary to go slightly beyond that. Here is a link to some very comprehensive tech articles on the A type OD, including theory, rebuilding, and trouble shooting. They are from a Triumph site, but the OD is the same. Scroll down to the A type OD sections.
https://www.buckeyetriumphs.org/technical/technical.htm
Berry
 
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