Tech Tips: Spring 1992

Overdrive Troubleshooting
Overdrive doesn’t work? Here’s how to start looking for the fault! Is the oil level and type correct? If no,change or top up with correct oil. If yes, remove the gearbox cover and loosen the actuating lever, start the engine and drive away. At any road speed over 20 mph, in any forward gear, move adjustment setting lever on r/h side of the overdrive, forwards. If the overdrive engages or merely jolts, the “fault” is in the setting or is electrical.

If nothing happens, return to base, jack up the rear wheels and carefully loosen the operating valve plug (B). Start the engine with high idle, engage 2nd gear and oil should bleed past the loosened operating valve plug. Any air should also bleed past, after which the operating valve plug can be retightened. If no oil bleeds out, the pump is inoperative. Usually this is merely stuck and and can be freed by removal of the oil drain plug (catch oil as it drains out). Inspect filter and clean if necessary. Remove pump body plug (C) to reveal the base of the pump. Tap gently with a blunt instrument. Rotate wheels with gearbox in neutral. Pump should move up and down freely. If pump sticks “down” again and the result of the above procedure doesn’t help, consult your local overdrive specialist.

Leaking Water Pump?
New water pumps can at times leak when first installed, the leak being discovered prior to the startup. This can be a frustrating experience, particularly If you proceed to remove the new pump in order to send it back to your (*%#$**&*%$) supplier for exchange!

The usual cause of a leaking new pump is due to the carbon race water pump seal not fully seating against the back face of the impellor. Since the hard carbon sits against the cast iron or brass impellor with only light spring pressure. It shouldn’t be difficult to believe this to be the source of the leak. The best way to insure that the carbon race is properly seated is to actually spin the pump prior to installation. I do this very effectively by holding the impellor against the wire brush side of my bench grinder. Spinning up the dry pump for 15-30 seconds insures a good lapped seat. Alternatively, new pumps can be installed, but be sure to start the engine without coolant and run it dry for 30 seconds or so. The coolant acts as a lubricant and actually inhibits this important seal break-in procedure.

Is Your MGB Idling Rough? Check This Out.
From the time I purchased my ’79 MGB (about two years ago), it did not have what I would consider a smooth idle compared to other cars. Having owned a ’65 Spitfire along with a ’58 TR3A, I just assumed that all British cars idled a little rough. Every once in a while I would adjust the fast idle adjustment on the carburetor, but it didn’t seem to help much. This summer my MG started idling a little rougher than before. Once again I played with the carburetor, but with little improvement. By this fall, my MG was idling really rough, shaking the whole car. When I gave it a little gas, the engine would smooth right out. I was adjusting the carburetor and gunning the engine a little when I noticed the engine lifting as I gunned it. You guessed it—the motor mount was broken. The first thing you will discover when replacing motor mounts is that the books don’t say much about that area.

After blocking up the front end of the car and placing a jack under the motor, I found that the steering assembly from the universal joint on down had to be removed before I could take off the old motor mount on the driver’s side. After popping off the ball joints on the tie rod ends and removing the bolts that held the steering rack, I broke the vacuum hose going from the manifold to the brake servo unit while trying to pull the steering shaft out of the universal joint. At the time I didn’t think much about It except that I would have to repair the line. Alter removing the steering assembly I jacked up the engine and removed the old motor mounts. Installation of the new motor mounts and putting the steering assembly back together again was quite straightforward. I then tried to repair the vacuum line that I broke, but discovered that it was very hard and brittle. Upon checking the other vacuum lines. I found them to be in the same condition, along with some cracks. I replaced all of the vacuum lines and started the MG to see how it ran.The idle speed needed to be turned down a little, but I couldn’t believe how smooth it was running. By looking at the parts I removed, (the one motor mount
was in two pieces) and the vacuum hoses, I determined that the rough idle was caused by those items and had nothing to do with the carburetor. (Vacuum leaks are often the cause of rough idling and poor running, particularly on the pollution-equipped cars of the ’70s. Terry’s engine mount failure was probably aggravated by his rough running engine. Careful checks of vacuum hoses should be a part of regular preventative maintenance.-Ed.)

Cable Removal
Here’s a tip to make the removal and installation of dash control cables much less difficult. First, disconnect the battery (good to do when working behind the dash as there may be exposed “hot” terminals). Then, disconnect the cable from what it is controlling, for example, the heater valve. Thread an appropriate sized deep-well
socket over the cable to the retaining nut, and with a pair of pliers or vise-grip, turn the socket to loosen the nut. It’s much easier than trying to get a wrench in there.