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I'm fixing my overdrive with a saws-all

roscoe

Jedi Knight
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Those of you with BN-1's or center shift transmissions may not be interested in this. I have been troubleshooting overdrive problems for the last couple of weeks. I have had the oil pump and the non-return check valve out a couple of times, and each time I've taken it for a test ride (with a pressure gage installed at the operating valve)it has operated properly, but not developed as much pressure as it should. More than once I reinstalled the cover and carpet, only to find that after a longer drive I had the same problem. The on-line article by Nelson Riedel is a real gift to all of us. My problem is that when cold, the pressure will build to about 300 psi(I know this is low) and everything works (30W non-deter). Gradually (over 10 to 15 miles) the pressure drops and I end up at about 100 psi and can get stuck in overdrive (if I let it cool off it will disengage and work again), or fail to engage. I've done all the easy stuff like change the accumulator o-ring, checked the operating check valve and the non-return check valve (replaced the ball bearings and lapped the seats, the springs are on order), set the operating valve lift with a dial indicator, etc. etc. I finally had what I think is a bright idea and here-by offer it (probably to find that everyone except for me has already done this). To reduce the time and effort it takes to get the transmission cover off by more than half, I took a saws-all and cut the transmission cover in two, just aft of the shift lever hole. I can now remove only the back half and have access to the operating valve cap, solenoid, and operating lever cover without doing the hokey-pokey with the cover to get it over the shift lever and around the hand brake.
It seems to me that if I'm looking at the pressure with the overdrive off and it drops to 100 psi, there has to be a leak in the non-return check valve or the operating valve. It also does not hold any pressure when I park and shut the motor off, it drops right to zero. I'm signing off until I figure this out. Did Rube Goldberg work for Laycock?
 

Keoke

Great Pumpkin
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Hi Rosco, what you may have is a weak spring behind the non-
return valve or a worn plunger. You might try is; shimming the plunger with small washers located between the plunger head and the spring.---Fwiw---Keoke-?
 
OP
roscoe

roscoe

Jedi Knight
Silver
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Thanks. I've already tried some shims (used some very small washers), and it didn't fix the problem. I've also put some shims (much larger washers) under the accumulator spring against the piston. I've got high hopes for the new springs I've ordered for the non-return valve and the operating valve. I'll let you know. I do agree it must be a weak spring or a leaky seat on the non return valve. It's just hard to make it go away.

Jon
 

Dave Russell

Yoda - R.I.P
Gold
Offline
Hi Jon,
I think you have already done most of the easy fixes to improve shift reliability.
1- Stretch the control valve spring about 1/8"
2- Add 0.125" spacer under the accumulator spring seat
3- Increase pump check valve plunger length from 0.102" to 0.220". I made a new plunger but shims might work.
4- replace the accumulator HOUSING to OD body O ring. I know you changed the accumulator piston ring already, but this is different.
5- Check the oil pump plunger for wear, intact roller, & the drive cam position/condition. It isn't building much pressure. The pump can be removed from the bottom with the OD in place.

Usually the ball valves can be reseated by firmly tapping them into their seats with a brass drift, plus the lapping listed below. Then replace with new balls. The pump CV is 1/4", the OP valve may be 1/4" or 5/16" on some OD's.

As you seem to know, the OP ball must seal on it's outer lower aluminum seat when it is not operated & must also seal on the end of the valve plunger when it is operated. I assume this plunger end is the one that you lapped. I wouldn't use lapping on any of the other seats. Too hard to get all of the grit out without complete disassembly.

I really think you should replace the outer accumulator to OD body seal as the next move. Forgive me if you already have all of this covered. Just making sure. Riedel has it really covered but there is a lot to digest there.

As a last resort, try a little heavier oil such as 20W-50 to see what happens.
D
PS - If the O ring seals on the OD operating solenoid cross rod are too tight it can bind the operate valve mechanism & prevent it from operating fully when the solenoid operates, especially on release. If this happens the pump wont build much pressure. This could be checked by manually moving the RH operating lever. Be sure you don't get your shirt tail in the U joint while test driving.
D
 
OP
roscoe

roscoe

Jedi Knight
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So the saga continues. When I first put the car on the road a few weeks ago I had no overdrive at all. I pulled the oil pump because I was getting no pressure. I found that the roller fork on the end of the pump piston was bent and the piston was sticking in the cylinder. It appeared that the piston/roller assembly had been installed by the previous person with the thick side of the fork against the steel pin that protrudes from the casing (I believe to prevent the piston from rotating, i.e. to keep the roller rolling on the cam rather than turning sideways). I happened to have a spare overdrive assembly, so I pulled the pump out of that. It looked pristine. Since installing that one I have been battling low pressure. I have found two things that are related that are probably causing my problem. Bear in mind that both overdrives were improperly assembled by folks unknown. One problem was that in addition to the bent piston, the ball bearing in the non-return check valve (of the spare pump I had) was the incorrect size. I'm not going to put it all back together until Monday, when I should get some new springs for the two ball bearing valves. Also after spending quite a bit of time with a magnifying glass looking at the ball seat in the pump body, I found that despite my lapping the seat(which is machined in the steel of the pump body) the seat looked like the craters of the moon, full of corrosion pits. I had put some fine valve grinding compound on a 5/16ths" ball bearing and spun it a few times. It looked OK using my reading glasses. Wrong. When I had it out this time I realized that it should have had a 1/4 " ball bearing and needed to be lapped properly. It took me 15 or 20 minutes of lapping with several ball bearings to get a seat that looked as it should. Staking the ball to the seat with a brass drift would have done nothing in this case. The latter was suggested in both articles I've read. So the pump is back in with the proper sized ball and a good seat. I'll let you all know what happens next week. Thanks for all of your suggestions.

Jon
 
OP
roscoe

roscoe

Jedi Knight
Silver
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It is too late in the evening to take the car for a drive, but things went well when I assembled the overdrive this time. I now have close to 500 psi operating pressure. With the driveshaft disconnected in the barn, the overdrive shifts in and out smoothly and once pressure built up it stayed around 350 psi when put in neutral. I watched the gage for a couple of minutes and saw only very slight movenemt downscale, until I moved the operating valve lever. So far, all as it should be. I also spent quite a bit more time setting up the operating valve lift. I selected .020" because it seemed like an average of everything I'd read. I made a small tool which consisted of a ground down 3/16ths in bolt that had a concave cup on the top of the head that sat nicely on the ball, and then put a small nut on the shank that kept the bolt straight up in the threaded bore of the operating valve. I set the dial indicator on that. I think that the new non-return valve and operating valve springs made a difference. Based on what you read about springs, they tend to get weak/shorter as they age. The new springs were a tad longer and not as stiff as the old springs (old= work hardened?). When you think about the non-return valve, it seems to me that it would actually be closed with only a little spring pressure, as the pump reaches the bottom of the stroke and pressure is essentially equal on both sides of the ball. So perhaps the spring only needs to be stiff enough to give the ball a bit of a push towards the seat, and the softer it is the easier it gets pushed off the seat to allow pressure in. Dressing out the seat probably made the most difference. Unfortunately you can't really do this and inspect your work without pulling the oil pump. Always remember to take the non-return valve parts out before you pull the pump. I also changed the rear overdrive seal which was leaking pretty badly. I shall report on the road test. I am a huge fan of a test gage. I bought a $20 glycerine filled gage and welded a steel adapter to a spare operating valve cap with a 1/16th" hole drilled in it. Half an hour to make and saved days of troubleshootng.
 

Keoke

Great Pumpkin
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Well Roscoe, those pressures sound more like it and it seems you are now on the road to recovery.---Keoke-- /bcforum/images/%%GRAEMLIN_URL%%/thumbsup.gif
 
OP
roscoe

roscoe

Jedi Knight
Silver
Country flag
Online
One last note in this thread for those interested. The test drive went very well. Everything works as advertised. Thanks again to you for your suggestions (Keoke and Dave R.). This being my first automotive restoration, and an older British car at that, my learning curve has been very steep. My trouble shooting flow diagram is someting like this : Step 1, go to British Car Forum and ask.....no, wait, will I look like a dope?, better troubleshoot some more. Step 2, see step 1 and use the archives this time. Step 3, find most likely answer and apply to my car. Step 4, have an adventure. So far I've had a flat, run out of gas, gotten stuck in overdrive, had an axle seal leak, found out that it is not really possible to drive at any speed with the windshield folded without goggles, and been all ready to go for an evening drive with my wife and found that the generator had just stopped working and I had only one headlight operational. Man, this is fun.
 
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