• Hi Guest!
    If you appreciate British Car Forum and our 25 years of supporting British car enthusiasts with technical and anicdotal information, collected from our thousands of great members, please support us with a low-cost subscription. You can become a supporting member for less than the dues of most car clubs.
    There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Subscribers don't see this gawd-aweful banner
Tips
Tips

BJ8 Overdrive

Share this page

davidb

davidb

Jedi Trainee
Country flag
Offline
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
 
What kind of oil are you running in the tranny/OD?
 
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.
 
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:
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)
 
Second is knowing what the pump pressure is . If it's not over 400 psi when it's hot you will have problems .
 
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
 
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:
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
 
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.
 
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
 
Keith_M said:
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
Click to expand...
Keith, the link does not work in your message. My BJ8 overdrive did work and now does not. I filled it with 20/50 castrol with Zinc and I took it for a test drive. It worked! and then dropped out and didn't work again. I'm going to clean the filter when I find it. Any advice? I just bought it a month ago and I'm trying to trouble shoot everything including my fuel gauge that shows full all the time. ??
 
Bob_Spidell said:
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.
Click to expand...

I'm refuting my own comment, now that I've actually torn into one: There are no rings on the pump, only on the operating pistons and accumulator (either metal or O-rings).

Simple things that can cause an O/D to drop out intermittently:

- dash/fascia switch, esp. if it drops out on acceleration; these have not been highest quality for a few years
- relay; mine became intermittent one time in Canada. I removed it and filed its points in a hotel room and problem solved
 
My BT7 (with a BJ8 gearbox) had the same problem a couple years ago. It would engage but after 5-10 minutes it would disengage and not reengage. I checked all the usual suspects and then came across an article from 1985 that identified the problem. The source of the issue was a worn non-return valve. A weakened non-return valve does not allow pressure to be maintained for proper OD operation. The OD works when cold but once the pressure and temperature increase, a worn non-return valve can't hold the pressure as it should. The plunger, spring and ball are available through Moss (#329-510; 866-070; and 866-080) all for under $20. Replacement can be done by draining the OD oil, removing the gearbox cover, solenoid, and its mounting bracket. The bracket pre-loads the accumulator spring so take your time and follow the instructions in the shop manual. Note the location of the spacer and rubber o-ring on the back side of the bracket. You should now see the hex head of the non-return valve plug. Remove the plug (may be very tight) and then the plunger, spring and ball should come out. Replace all three parts. (In my case, the plunger was worn and comparing the compressibility of the old spring and the new spring revealed a discernable difference.) Assembly is the reverse of removal! The entire process took less than an hour by a true amateur (me!) and I have had no further OD problems in the 6 years since I made the repair. For the small investment of time and money, this fix is worth trying IMHO.
 
Further, it's known the seat for the ball on the check valve can wear or be damaged. Some recommend 'staking' the ball--smacking it with a drift and hammer--to reform a proper seat (the casing is aluminium). David Nock uses a specialty reamer to re-cut the seat (probably the most ideal fix).
 
I've posted this before but staking the bearing into the seat might be effective if the flaws in the seat are minor. I have seen two ODs that had the seat severely pitted. The ball would never seal properly. The special reamer is obviously the best solution but you might not have one in your kit. In lieu of that I have had success with gluing a new ball bearing onto a stick, You could also weld or braze one on a rod if you wanted, slather it with coarse valve grinding compound and spin it in a drill. Once a uniform surface is achieved, move to fine compound and you are done. Clean thoroughly. For the cost and effort it takes, I'd do that anytime the relief valve is exposed for other maintenance.
 
Back
Top