Overdrive issue

[Stewart]

Lost use of my over drive on the way to the labor day run. Made it to pch with it working and then it quit.

What I know so far

I have power all the way to the solenoid
Changed the solenoid.
Oil level is full 20w50 oil.

So that should take care of the electrical side of the issue so it should be hydraulic. What are the common parts that would fail and since I'm going to be there what should be redone.

[Steve Simmons]

Assuming the lockout switch is functioning, it's possible that the little ball above the plunger is worn or for whatever reason is not seating properly anymore. Replace the ball (it's a standard size but I can't remember what it is - get one at a bicycle shop) and when you put in in place, tap it in with a punch and hammer to ensure the ball and seat are as precise a fit as possible. To do this, I put a dab of heavy grease on a punch and stick the ball to it. Oil will be dripping out so you have to act fast, before the oil liquifies the grease!

[Stewart]

I'm assuming you are talking about the ball in the solenoid assembly or is there another one I'm missing. I did install a new complete solenoid assembly since I had one on the shelf with no change.

[Steve Simmons]

Yes, there's the solenoid, then the plunger that goes through the middle, and the ball on top. Even with a brand new ball it doesn't always seat properly. If it were me, I would take it back apart and hammer the ball in place. A couple good solid smacks will do the job and may return function to the OD. Of course this is a WAG based on reading a forum post, so don't yell at me if it wasn't the problem!

[Stewart]

Should the ball hold it's place on it's own or will the grease hold it in place?

also should I be concerned that there was no oil dripping?

[Steve Simmons]

The ball will fall back out unless the grease holds it there. On mine there was a lot of oil dripping out so it wasn't going to stay there on its own.

Another thought, have you cleaned the screen filter lately?

[Stewart]

I did a oil and screen change about a month a go. Screen was nice and clean. The next time i go under I will check it again.

[tannyo]

John Twist on MGB overdrive.

FAULT DIAGNOSIS

In standard or direct drive-overdrive is on all the time: This situation is dangerous to the gearbox and expensive if not repaired immediately, as reversing the car while in overdrive will burst the one-way clutch. The problem may be electrical (switch has gone continuous) or hydraulic (dirt jammed in solenoid). This situation is extremely rare, but must be repaired immediately.

In standard or direct drive-overdrive shifts in and out: This situation is caused by the failure of the tiny O-ring at the top of the solenoid piston. The solenoid assembly requires three O-rings-change all three. This situation is extremely rare.

In overdrive-overdrive works intermittently: There may be an electrical problem or a hydraulic problem. Try moving the gearlever to the right and/or to the rear-if this allows the overdrive to work, then the problem is the 3/4 electrical lockout switch-this is not uncommon. If the overdrive suggest on and off, low oil in the gearbox could be the problem.

In overdrive-overdrive does not work: Test for an electrical problem by piercing the solenoid wire with your test light with the ignition on, the overdrive switch on, and the gear lever should be hot. If not, test light with the ignition on, the overdrive switch on, and the gear lever in fourth. The solenoid wire should be hot. If not, test the circuit, switch to switch-but the problem is most often the 3/4 lockout switch.

In overdrive-overdrive does not work: Open the bottom of the overdrive unit and clean all the parts-the solenoid, piston, ball, and housing; the oil pressure relief valve; and the oil pump. The most common fault is a sticky oil pump which has stuck down.

In overdrive-overdrive freewheels on deceleration: In this condition, the MGB will accelerate but the free wheeling clutch can allow the engine to return to idle speed while the car is still running down the highway at 55 mph. This is caused by dirty hydraulic components or a fault in the sliding member (cone clutch).

[tannyo]

Here's three more videos on overdrive repair.

104 MG Overdrive Repair Part 1


105 MG Overdrive Repair Part 2


106 MG Overdrive Repair Part 3

[Stewart]

Well I think I found the problem



The silver spring above the plug with the 2 holes in it should be moving.

The plunger was pretty much stuck and took a good blow to free it. Pulled the assembly and gave it a good cleaning and light polish. Seems to be working smooth now. Just need to replace the filter and cover and add oil and hopefully that will be it.

[Stewart]

Its now working better than it has before. It always took a mile or 2 for the initial engagement of the day then it would work fine. Now its works right off the bat. You forget howmuch you use overdrive till it dosent work then you really miss it.

[Jimmy]

If you plan on going farther than the end of your driveway, isn't the overdrive pretty much essential?

[Fifty Six MGA]

Overdrive makes you soft. Real men love 4500 RPM on the freeway.

[gorms68]

Overdrive makes you soft. Real men love 4500 RPM on the freeway.

Well with O/D I'll be going faster at 4500 rpm

[Jimmy]

You saved me from writing it, Chris.