Overdrive engaging with time delay

[Healey Nut]

Has the OD ever been rebuilt ?
if not then chances are that’s where this is heading
your Accumulator piston rings are probably worn out And the OD is probably full of metallic sludge .
pull the OD and rebuild it , they are not complicated , take your time lay out the parts methodically on the bench .take notes , pictures etc .
clean everything scrupulously clean . Replace anything that looks worn , piston rings , seals , springs ,ball bearings , gaskets etc .
the actual rebuilding of the OD is a 5/6hr leisurely job once it’s on the bench . Including lunch .
a good set of hand tools and something to wash parts in solvent and a compressed air source is all you need .
use the compressed air to blow out all the oil galleries etc to make sure nothing is blocked up .

 

[Bob_Spidell]

The usual recommendation is to stake--i.e. strike the ball against its seat--with a hammer and suitable drift. I did this when I rebuilt my OD on my BJ8, but the OD was operational before and after so I don't know how much good it did (apparently, it did no harm, which is a good starting point). A well-known Brit car mechanic told me this, and I've not heard of lapping the ball against its seat; intuition tells me this is a bad idea because aluminium is so soft (it's not like lapping valves, where both surfaces are fairly even hardness). Here's a discussion about lapping vs. staking on a site where homebuilt aircraft owners congregate:

https://vansairforce.com/community/showthread.php?t=171611

Sounds to me like you need to drop the pump piston and have a look at it; mine had over 200K miles on it and was still serviceable--my accumulator piston and sleeve were worn--but one little piece of grit can ruin your day.

 

[roscoe]

Something bothers me a out your post. My suggestion was to dress the ball bearing seat on the PRESSURE RELIEF valve, which is under the left side plate that holds the overdrive solenoid not the operating valve on the top right side of the gearbox. You need to drain the box to open this up. The pressure relief valve seat is something you can actually see when the thing is opened up. I no longer know what to suggest other than removing the operating valve, cap, spring and ball bearing and then the shaft below that, which has some very small passages in it which may have been clogged and flushing the heck out of it with some petroleum solvent and using compressed air to clean it out. You may also have jammed the shaft below the ball and it needs to be able to move freely, up and down. Normally you can remove the vertical operating shaft with a magnet. You need to look for the overdrive manual on line or reference the Healey shop manual to see what I'm talking about. Moss has good illustrations too.

Also, did you measure the old ball bearing? Using it to dress the seat is probably not a good idea. Use a sacrificial new ball to do that then put in a fresh one. I truly hope this helps and am sorry if there was a misunderstanding about what I was saying.

 

[Bob_Spidell]

ps. If you decide to do an OD overhaul--might as well go through the gearbox while you're at it--let us know; I have some experience to share from a shadetree mechanic's viewpoint.

 

[Bob_Spidell]

... My suggestion was to dress the ball bearing seat on the PRESSURE RELIEF valve, which is under the left side plate that holds the overdrive solenoid not the operating valve on the top right side of the gearbox...

Disclaimer: I'm not being argumentative here, I would like clarification myself.

What you're describing I believe to be a check valve, that allows fluid pressurized by the pump into the accumulator. When I had my OD on the bench I looked for a relief valve--as the pump is positive displacement it can theoretically produce infinite pressure (something would explode first, of course)--and the only thing that could possibly be a pressure relief mechanism is a hole about halfway back on the accumulator sleeve*. The accumulator spring is the only thing that could regulate over 400psi, when its piston is pushed back to the hole fluid will flow through the hole and relieve pressure.

* Moss doesn't have a picture; it's part# 81 on page# 60 of their latest catalog.

 

[Healey Nut]

Disclaimer: I'm not being argumentative here, I would like clarification myself.

What you're describing I believe to be a check valve, that allows fluid pressurized by the pump into the accumulator. When I had my OD on the bench I looked for a relief valve--as the pump is positive displacement it can theoretically produce infinite pressure (something would explode first, of course)--and the only thing that could possibly be a pressure relief mechanism is a hole about halfway back on the accumulator sleeve*. The accumulator spring is the only thing that could regulate over 400psi, when its piston is pushed back to the hole fluid will flow through the hole and relieve pressure.

* Moss doesn't have a picture; it's part# 81 on page# 60 of their latest catalog.

I think ??? Roscoe is referring to the “non return valve “ which is screwed into the side of the pump body .see Moss drawing items 100to 105ish

 

[roscoe]

I'm referring to the pressure relief valve ( called the pump valvemin the manual) that is at the base of the OD oil pump. The spring loaded ball bearing keeps the port closed until the pump reaches operating pressure and then pops opened for very brief intervals to regulate the pump output pressure to the range of normal operation ( more than 400 psi). The pump would put out more pressure, possibly to the point of damaging itself if the relief valve were stuck shut and if it doesn't properly close, it allows pumped oil back into the resevoir at the bottom of the engine and proper pressure won't build.

 

[Bob_Spidell]

You really think that dinky little spring can hold over 400psi? I'll leave it at that.

 

[roscoe]

Oops. I hate spreading misinformation. Bob is correct. What I have been thinking was the pressure relief valve is in fact a one way check valve. The pressure relief takes place in the accumulator section. I got that into my head when I corrected a lack pressure by dressing the seat for what is referred to as the pump valve. If this check valve has a significant leak, it may not allow operating pressure to build as was the issue for me. Sorry for the confusion.

 

[Bob_Spidell]

No problemo, Roscoe (I've been a superspreader of misinformation on occasion). I've been both fascinated and perplexed about the OD operation for years; it took me a while, staring at the OD in pieces on the bench, to understand its working (and I may still have it somewhat wrong). I never understood why there wasn't a pressure release mechanism--it was never explained in any of the literature I read--until I pulled the accumulator sleeve out and had an 'Aha!' moment.

According to legend, Healeys have a somewhat restrained OD engagement, because DMH thought it might be too abrupt for us Americans; DWR has a heftier accumulator--without a sleeve--which cuts engagement time a bit (other LBCs, Triumphs in particular, used similar from the factory). There are lots of opinions on how to employ the OD, but after seeing the cone clutch on the bench I've started slipping the engine clutch a little on both engagement and disengagement, as just throwing the switch is somewhat akin to dumping the engine clutch. New cone clutches aren't available that I know of, but DWR has relined ones on exchange. The cone clutch in my OD was still serviceable at over 200K iles.

 

[Michael Oritt]

Or perhaps system voltage is low when the car first starts (and is cold) but builds up after a bit of running, which translates to more power for the OD solenoid to pull in?

 

[John Turney]

...
According to legend, Healeys have a somewhat restrained OD engagement, because DMH thought it might be too abrupt for us Americans; DWR has a heftier accumulator--without a sleeve--which cuts engagement time a bit (other LBCs, Triumphs in particular, used similar from the factory). There are lots of opinions on how to employ the OD, but after seeing the cone clutch on the bench I've started slipping the engine clutch a little on both engagement and disengagement, as just throwing the switch is somewhat akin to dumping the engine clutch. New cone clutches aren't available that I know of, but DWR has relined ones on exchange. The cone clutch in my OD was still serviceable at over 200K iles.

I had my cone clutch wear to the point that the OD would not disengage unless I put the trans into reverse. At a stop, of course.

 

[Keoke]

You really think that dinky little spring can hold over 400psi? I'll leave it at that.

Yeah Bob ;
My OD shows 450 PSI at full operating Pressure when working properly ??

 

[Madflyer]

Socially distanced and this forum can't be better than this CA To Canada. If going 2000 RPM why go into OD 3,000 is a good number my cam comes in at 3,500 so back to 3,000 in OD. Unit pressure and filter and oil level are about it or rebuild. Madflyer

 

[Bob_Spidell]

I had my cone clutch wear to the point that the OD would not disengage unless I put the trans into reverse. At a stop, of course.

Wow, that's WORN! It's recommended--strongly--that you replace the 8 very strong springs in the front stage of the OD, but that's to hold the cone clutch together with OD disengaged. I can't visualize how putting in reverse would release the clutch without damaging the unidirectional clutch.

How many miles on yours?

 

[Patrick67BJ8]

I always start troubleshooting the OD by checking the fluid level. If good then I check the solenoid. With the car stopped, engine off, turn on electrical power, OD switch on, and trans in neutral take hold of the gearshift lever and go from neutral to the 3rd & 4th gear gate and listen for the click. If it does click you have electric power, however, it doesn’t mean the solenoid is good with enough strength to operate correctly.

 

[John Turney]

Wow, that's WORN! It's recommended--strongly--that you replace the 8 very strong springs in the front stage of the OD, but that's to hold the cone clutch together with OD disengaged. I can't visualize how putting in reverse would release the clutch without damaging the unidirectional clutch.

How many miles on yours?

The OD, and trans, were rebuilt when that started happening. It's fine now. As I said, I wasn't moving, just enough to retract the clutch.

I have no idea how many miles, it's not the original engine/trans or differential.

 

[Bob_Spidell]

Makes sense; if it's jammed-in one way, going the other way would get it out.

 

[Tomblin]

I was able to successfully fix the overdrive problem without removing it from the car, as suggested above by Jon. In this case, in addition to cleaning things up in the operating pump, it was necessary to get to the non-return valve on the pump and clean that up as well. This requires removing the solenoid bracket, which is more of a box on the later cars. When I pulled the ball out with a magnet, I saw there was some metal residue on it which was probably causing it to fail to seal. I sprayed a light solvent into the valve area and then blew it out, put things back together and got very good hydraulic pressure. Now when I flip the overdrive switch, the overdrive kicks right in. Jon recommends trying to do it yourself, and I agree.

 

[Bob_Spidell]

I don't recall if you mentioned draining the gearbox and OD, but since you found metal on the check/non-return valve I'd recommend doing that. If possible, either--or both--strain the (warm) oil through a fine fabric, or into a very clean pan which you can sift with a magnet. Of course, you'll want to have a good look at the screen and magnets in the big OD drain plug. As you've seen, there are some fine passages in the OD; a little bit of brass-colored 'shake' wouldn't bother me, but if there's a lot of magnetic material I'd be concerned.