O/D Diagnosis

[Healeysince59]

My BN1 Overdrive is starting to misbehave. It will engage sometimes and sometimes not. When it doesn't engage, it freewheels. That is, if I back off on the throttle, the engine drops to idle. It pulls when I get on the throttle but doesn't go into O/D. My questions are:

Any idea what's wrong?
Is it about to grenade or is it OK to drive for a while (without using O/D)?

I plan to trailer it to San Diego and would like to postpone major work until we return. I have another O/D that I think is good but I would rather attack it when I have more time. I think the O/D is the only bit on a Healey that I haven't been into.

Thanks in advance for any thoughts

Marv J

 

[TimK]

I just went through my OD (BN7) on Tuesday and got it working again. I did not have your symptoms, but I believe you have a hydraulic pressure issue. It is safe to drive it without OD on. I doubt it will "grenade". See my earlier post on "Overdrive with no oil pressure" for additional information. I don't know what the unique features are for the BN1 overdrive (BN2-BJ8) BN1 differs from the BN2-BJ8 overdrive unit.

 

[Healey 100]

Marv:

Your OD is engaging half way, the clutches are pulling out of direct drive but not getting fully into OD; which is why the engine drops to idle if you let off the gas but can still pull the car when accelerating.

The first thing is to check is your transmission oil level. Low oil will produce this symptom, and the BN1 tranny is notorious for leaking. Pull the fill plug and fill up so it's about a 1/2 in below the plug.

Chances are this will fix the problem. If not, make sure the solenoid is engaging fully and the linkage is adjusted properly. I usually drive the car with the transmission cover off and actuate the OD manually and watch how the solenoid engages it to test the system.

The other possibility is wear in the OD pistons or pump assemblies may be excessive. These units are very tough and few seem to wear out this way. But if so, you may be able to buy some time by putting heavier oil (such as 90W gear oil) in the transmission.

If the OD is not working, it should not hurt your car to drive it direct mode -- provided there is oil in the transmission, be sure to check that right away.

Good luck, see you in San Diego!
Bill S
Albuquerque

 

[Ed_K]

Marv,
If your o/drive is " freewheeling " with the transmission oil at the full mark, drain it out and fill it up with Valvoline VR1 60w.
That cured the problem on my BJ8.
I am certain that the 60w oil is making up for some internal leaking but I have put on several thousand miles and the o/drive is working perfectly. Keoke said he has used 60w VR1 for the last 20 years. He said he switches to 50w in the winter.
Ed

 

[Dave Russell]

60w might well cure the problem. just remember that Keoke lives in a moderate climate. Some pressure tests by "Quantum Mechanics" have shown that extremely high pressures, high enough to cause serious damage to the OD, can be achieved with COLD heavy oil.

To compare viscosities - 60 wt oil at 40 degrees c = a viscosity of 315 cst. This same oil at 100 c. = 24 cst viscosity.

SAE 30 oil at 40 degrees c = a viscosity of 85 cst. This same oil at at 100 degrees c = a viscosity of 10 cst. Original factory recommendation.

SAE 20W-50 at 40 degrees c = a viscosity of 40 cst. This same oil at 100 degrees c = a viscosity of 18 cst.

To compare, Redline MT-90 is a 75W-90 gear oil. At 40 degrees c it has a viscosity of 20 cst. This same oil at 100C has a viscosity of around 18 cst.

Our transmissions can be well below 40 c when cold & anyones guess about the temperature when warm. A good guess is maybe 80 degrees c.

I believe "Quantum Mechanics" INSISTS on 30 wt oil in their newly rebuilt transmissions. Others, including myself have good results with RL MT90. I believe Triumphs with Type A OD's suggest 90 GL4 gear oil which is at 40 c = 205 cst, at 100 c = 18 cst.

I think the best oil is determined by your transmission's condition & the ambient temperatures that the car is run in. Apparently SAE 60 works for the time being in your car.

There is no single correct answer, A viscosity comparison chart is attached.
D

 

[Healeysince59]

Thanks all for the excellent inputs. Since I didn't know what was in the gearbox, today I drained it and refilled with 30w to establish a starting point. I also fabricated an adapter so I could hook up a pressure gauge. I didn't run it long enough to get it really warm but I was seeing 385 psi max. The most important discovery was a weak solenoid. It would pull in part way but not go into O/D until I manually "helped" it. I swapped in a really ugly but functional solenoid from another unit and it's working great.

The low pressure is a concern - should be 450 psi according to the service manual. Since it goes to 385 and holds steady regardless of speed, I think it is being controlled by the relief valve and heavier oil won't do much. I may try some 90wt gear oil and see what that does since ultimately I would like to go to Redline MT-90. I'm running Redline MTL in my BT7 and very happy with it.

Significant further experimentation will wait until after SD. When you get to San Diego (Bill S and anyone else), look for a BN1 with lots of patina (an I mean lots!). My son will probably be driving it but he's a nicer guy than I am. He's driving my BT7 to SD and then we'll trade.

Daves viscosity chart attachment is a keeper - thanks.

Marv J

 

[roscoe]

Last year I started my road tests with an od that didn't work. My pressure gage showed no pressure and I traced the problem to a cracked and bent cam follower at the top of the oil pump piston which had caused the piston to stick in the down position and the spring pressure was not enough to push it back. Eureka, huzzah, I thought my problem was solved and pulled a spare unit apart and got a good lookng pump piston and housing. I installed those (all with the gearbox in place in the car, and was way bummed out to get only very low pressure (about 150 psi). Then I hit the on line articles and the responses from some of the more seasoned forum members. There is always the suggestion around to "stake" the ball bearing onto the seat in the side of the oil pump to assure a good seal. While this may help some, it will not raise your oil pressure very much. The ball bearing and seat are both steel and you would more likely dent the ball as make a better seat. I pulled the pump out and got a 10x magnifying glass to look at the ball and seating area. Craters of the moon! There are 2 different ball bearing sizes so if you go this route, mic the balls and run to your local hardware store and buy some new ones (in CA we have Orchard Supply Hardware and they had them in packs of 5). I took a fresh ball and glued it to the end of an aluminum tube, chucked it in a drill and dabbed some valve grinding compound on the ball. THIS IS WITH THE PUMP REMOVED. It took me half an hour of grinding, cleaning, inspecting, grinding cleaning....before I got a good looking seat. I installed a fresh ball, put the pump back in and, voila!! Pump pressure right where it was supposed to be. My over drive has worked without a hitch ever since (straight 30wt). It probably didn't hurt that I put in new accumulator seals and a shim under the pump ball check valve spring, but I think my main problem after I fixed the pump, was the poor sealing of the ball check valve. It is a difficult job (especially getting the oil pump reinstalled correctly because the plunger is not symmetrical and can be put in 180 degrees out. I think the PO managed to do that and may have caused the damage to the pump in the first place.

 

[pan]

I am glad you found the overdrive problem to be simply the solenoid. A couple of years ago I had similar problems with my BN1. It turned out to be the accumulator, which I replaced with parts supplied by a leading UK parts retailer.
The new accumulator had to be modified but I am now happy to say my o/d works perfectly!
In the warm Queensland climate I use a product called
"Penrite Gearbox 40".
When I was having the problems, the symptoms were similar to yours. The O/D would engage when cold but after about 15 miles started to slip then "freewheeled".
One of the remedies I tried, before the problem was properly diagnosed with a pressure gauge, was changing to 90 weight gear oil. There was no improvement.
One last thing.....the adjustment of the solenoid lever is absolutely critical!!

 

[mrdibbles]

Hey Marv-
There is a Healey mechanic in San Diego named Randy Zoller. He owns a shop called Heritage Motorsports. About 5 years ago I was experiencing your same problems. Only difference is that the solution for me wasn't changing oils or replacing the OD solinoid. I needed to have the entire OD rebuilt. I was wanting the transmission rebuilt too so both were done at the same time. I am not suggesting that you're in need of rebuilding the OD but if you suspect you might it may be a good idea to contact Randy. He's close enough to you that you might be able to drop it off with him on your next trip to San Diego. I highly recommend this mechanic. He's the type that will talk you out of repairs instead of into them (if they aren't absolutely necessary). He has plenty of business.
Regards,
Matt-

Here's the link to his website... mine is the black Healey on the frontpage of his website :thumbsup:
https://www.britishheritagemotorsports.com/