BJ8 Overdrive Oil Pressure

[AUSMHLY]

Hello,

I'd like to check the oil pressure in my BJ8 transmission/overdrive.

The work shop manual, Section G.9 Hydraulic Pressure, says:
A working oil pressure of 470 to 490 lbs. per sq. in. (33.40 to 34.45 kg./cm.2) is required.

The manual does not specify at what rpm or if that's in or out of overdrive (3rd or 4th gear).
What rpm should I be in for 470-490 lbs?

With rear of the car on jack stands I'm able to check this with a hydraulic pressure gauge, but the lbs per sq. in. changes per the rpm.
4th gear 1500 rmp I have 350psi
4th gear 2000 rmp I have 390psi

My accumulator pressure spring has a washer added.
I believe adding a 1/16 washer adds 50psi (I didn't measure that washer when I was addressing another issue.)
I could add a thicker washer, another bandaid or replace the spring.

Car does go in and out of overdrive within 2 seconds. After flipping the OD toggle off (foot off the gas peddle) with just a very light tap on the gas peddle it comes out immediately, but with a little bit of jerk. I've adjusted the throttle switch so that I'm able to pass a 3/16 drill bit between the throttle stop and the stop lever. I remember it coming out slower and smoother before. So I'm looking into if I have the correct oil pressure. Or perhaps I need to fiddle with the throttle switch.

Now my curiosity is focused on do I have the correct oil pressure.
Cheers.

 

[CraigC]

I went through this about 5 years ago.

You should reach operating pressure while still in first gear but definitely in second gear and well below redline, or the shift to third. When you switch on the OD you will see a momentary pressure drop coinciding with the accumulator dumping its pressurized oil into the operating pistons. The recovery to max pressure after that drop should take a second or two.

Overdrive Pressure. Note: I took off in second gear as it was a road that was very slightly downhill. As you can see, the pressure was 450-475 psi and dropped to about 150 psi during the OD engagement after which it recovered to the same initial max pressure.

 

[Healey Nut]

Time to replace the piston rings on the accumulator piston .

 

[CraigC]

More likely a weak accumulator spring. If you have it apart, what is the free length of the spring?

There was actually a Technical Service Bulletin for adding the washer you found.

OD pressure has nothing to do with the harshness coming out of OD. That is a function more of the 8 clutch return springs and throttle switch adjustment. When the solenoid de-energizes, pressure in the operating piston cylinders is dumped, accumulator is sealed and it is the springs that push the sliding clutch back into engagement with the annulus.

 

[AUSMHLY]

Time to replace the piston rings on the accumulator piston .

Do you have to remove the tranny/overdrive to do that?
With the tranny in the car, I've removed the solenoid bracket, the accumulator pressure spring and the spring tube.
Then can the accumulator piston and rings removed?

 

[Healey Nut]

You can remove the OD from the gearbox with it in the car , getting it back in and aligning the double spline on the output shaft into the OD requires the patience of a saint .
You should be able to get the piston out of the OD unit with the OD in the car but it’s finding something to grip it tightly enough Internally so it can be pulled out . I used a pair of long handled circlip pliers that open and grip the harder you grip .
Some ODs have metal piston rings , some are plastic/nylon with O rings .

 

[CraigC]

AUSMHLY, before you rush into plans to replace the accumulator o-rings, there is a pressure test that you did not perform that goes a long ways to checking their condition. It can be done with the car on stands like you have already done. Basically you just stopped short. I am going actually going to suggest that you perform the entire test over, this time recording a video.

First, run the car in gear OD off. Second activate OD and let it run for a little bit(30 seconds?) and switch it off. The last step is to bring the trans to a stop---clutch disengaged and brakes applied or neutral with brakes applied. Now watch the pressure degradation. It should drop SLOWLY. If it drops rapidly, the o-rings likely need attention. I have it on a video, but I'll have to edit it down to a short clip. BTW, you did watch the video I posted, right?

Regarding the throttle switch, when adjusted correctly and with the throttle closed, the slot in the end of the shaft should be about straight up and down.

 

[Bob_Spidell]

Time to replace the piston rings on the accumulator piston .

If the rings are worn the 'barrel' is likely scored. At least one supplier--AHSpares IIRC--sell accumulators with pistons that use an O-ring instead of metal rings. Earlier O/Ds used metal rings on the operating pistons whereas later ones used O-rings.

Sounds to me like AUSM's O/D is operating normally (I have DWM's 'uprated' accumulator and it shifts only a tad faster). After rebuilding my BJ8's O/D and, finally (I hope), understanding the nuances I've taken to applying a bit of clutch pedal on both engagement and disengagement; done 'just right' there is no jerk at all, all you notice is the change in engine speed. Applying some (engine) clutch unloads the O/D clutch before dis/engagement, presumably reducing wear. Replacing engine clutches is a lot easier than O/D clutches, and I've not seen new O/D clutches for sale; DWM offers relined ones (my BJ8's O/D clutch was still serviceable at 200K miles).

 

[CraigC]

OK, I edited a clip of the accumulator pressure leak down after stopping from the original video. The video linked in my earlier post came from the beginning of the same video. I have included both videos here.

You can see that the pressure dropped while I came to a stop. Once it was down to 350 psi, it decreased quite slowly. I wish I had left the camera running until it reached zero. Sorry for my fat hands near end of clip. Also, for the record, the OD still has its original accumulator parts. This OD was built up from a pile of spares to get me on the road the next day to the 1979 Austin Healey West Coast Meet in Bend, Oregon. My original had suffered a catastrophic failure a week prior.

Overdrive Pressure build-up and activation

Overdrive Accumulator Pressure leak down after stop

 

[AUSMHLY]

If the rings are worn the 'barrel' is likely scored. At least one supplier--AHSpares IIRC--sell accumulators with pistons that use an O-ring instead of metal rings. Earlier O/Ds used metal rings on the operating pistons whereas later ones used O-rings.

Sounds to me like AUSM's O/D is operating normally (I have DWM's 'uprated' accumulator and it shifts only a tad faster). After rebuilding my BJ8's O/D and, finally (I hope), understanding the nuances I've taken to applying a bit of clutch pedal on both engagement and disengagement; done 'just right' there is no jerk at all, all you notice is the change in engine speed. Applying some (engine) clutch unloads the O/D clutch before dis/engagement, presumably reducing wear. Replacing engine clutches is a lot easier than O/D clutches, and I've not seen new O/D clutches for sale; DWM offers relined ones (my BJ8's O/D clutch was still serviceable at 200K miles).

Thanks Bob. The AHSpares O-Ring conversion - Accumulator piston and Accumulator housing both have o-rings. Is this a plug and play replacement that seals better? It's not the same as DWM's 'Uprated' accumulator is is?

You pointed out "barrel" is likely scored... is that the Accumulator housing or what the housing is mounted in? Will the AHSpares conversion address that?

 

[AUSMHLY]

AUSMHLY, before you rush into plans to replace the accumulator o-rings, there is a pressure test that you did not perform that goes a long ways to checking their condition. It can be done with the car on stands like you have already done. Basically you just stopped short. I am going actually going to suggest that you perform the entire test over, this time recording a video.

First, run the car in gear OD off. Second activate OD and let it run for a little bit(30 seconds?) and switch it off. The last step is to bring the trans to a stop---clutch disengaged and brakes applied or neutral with brakes applied. Now watch the pressure degradation. It should drop SLOWLY. If it drops rapidly, the o-rings likely need attention. I have it on a video, but I'll have to edit it down to a short clip. BTW, you did watch the video I posted, right?

Regarding the throttle switch, when adjusted correctly and with the throttle closed, the slot in the end of the shaft should be about straight up and down.

Craig, I did watch both of your posted YouTube videos. Thanks for directing me there.

Here's my results for watching how long it takes for the pressure drop:
Car on jack, 4th gear, od off, 1500 rmp, 450psi.
4th, od engaged drops immediately to 200psi, 5 seconds to 450psi.
4th, od off, goes/stays at 410psi.
Into neutral, brakes on, 410-300psi takes 3 seconds, then 7 seconds to 60psi, that's 10 seconds total.
(I borrowed this gauge and didn't pay attention if it zeroed out or stayed at 60psi).

What do I need to look into why the pressure drops so fast?
Would the O-Ring conversion accumulator housing/pistion from AHSpares fix this?
Would replacing the accumulator pressure spring help? (Mine has a washer, but I believe there was a Healey tech notice that recommended adding a washer.)
Would replacing the spring/plunger/ball bearing for both the operating valve and non-return valve help?

Thoughts anyone...

 

[Healey Nut]

Try reseating the ball bearing in the non return valve . You need to use a rod that will fit into the the opening where the ball bearing sits , it’s about a 3/16 ball bearing . give the rod a sharp tap with a hammer . The ball bearing sits in an aluminium seat and giving it a sharp tap reseats it and can help it seal better .
before reseating the ball bearing use a magnet to remove it and check the ball bearing is shiny clean and not deformed or has a flat spot etc , any doubts replace it and the little spring and plunger .
make sure where it sits is also clean before installing the old or new one and reseating it .

 

[Bob_Spidell]

Thanks Bob. The AHSpares O-Ring conversion - Accumulator piston and Accumulator housing both have o-rings. Is this a plug and play replacement that seals better? It's not the same as DWM's 'Uprated' accumulator is is?

You pointed out "barrel" is likely scored... is that the Accumulator housing or what the housing is mounted in? Will the AHSpares conversion address that?

Accumulator housing. The housing is mounted in the O/D case and shouldn't wear (note two O-rings on housing except for 'late BJ8s' which have only one).

The DWM accumulator has a larger diameter but, as far as I can tell, is otherwise similar to stock, with steel rings (note one version--smaller dia.--is for 'late' BJ8s, presumably 'Phase II'). About half-way down the page:

Overdrive | Performance Parts | Austin Healey | Denis Welch Motorsport

Overdrive Performance parts from Denis Welch Motorsport.

www.bighealey.co.uk

The AH Spares accumulator appears to be a drop-in replacement, and doesn't include a new spring housing 'sleeve.' The housing has a chamfered pressure relief port, so it doesn't wear the O-ring:

O Ring Conversion - accumulator piston

www.ahspares.co.uk

The 'legend,' as I heard it, is that TR6es used the same O/D as Big Healeys, but DMH thought engagement was too harsh for pampered Healey owners; hence the smaller diameter housing, sleeve and piston (at least, for 'later' BJ8s, with a 'stepped housing'). So, DWM resized the piston, housing and sleeve allowing a greater volume of oil for O/D engagement, and apparently a stronger spring set. The thinking of AH Spares, apparently, is that O-ringed pistons cause less wear to the bores (like used in later operating pistons). My BJ8's housing was scored, but it had 200K miles on it and still operated OK (in fact, I gave mine to another owner to use). Unless you expect to drive your Healey a couple hundred thousand miles or more I wouldn't worry about bore wear. Your housing is likely scored at least a little, but unless the wear is serious--like it got some grit in it--it can probably be used for many more miles. Like I said, your O/D appears to be operating more or less typically; wear in the accumulator, pump itself and operating pistons could contribute to slower activation.

I haven't tried staking the non-return valve seat; David Nock of BCS seems to think the seat should be reamed, and has a special reamer to do it.

 

[roscoe]

Obviously a special dressing tool would be the best way to make sure the relief valve seat is smooth. Here is my experience. While troubleshooting low oil pressure I was able to determine that not only did the ball bearing seat look like the craters of the moon when magnified, the ball bearing was way out of round due to years of wear. I forget the bearing diameter but my local hardware store had them in bulk for pennies. Lacking any sort of purpose made dressing tool, I epoxied a new ball bearing to a wood dowel, liberally applied some valve grinding compound and chucked it in a drill. 20 minutes later and after switching from coarse to fine valve grinding compound I had a shiny new seat. Installed a new ball bearing and voila! Perfect oil pressure.

This may not be your issue but I find troubleshooting usually is more satisfying if you eliminate the easy things first and avoid the forehead slap when you realize you should've done those first.

 

[Bob_Spidell]

That's a great idea, wish I'd thought of it when I had my O/D on the bench (probably worth a few PSI regardless). Probably not a bad idea to replace the check valve's spring; I think 'the book' all but insists the 8 heavy springs that hold the cone clutch together be replaced any time the O/D is worked on (I thought that was overkill, but I did it anyway).