Tech Tips: Fall 1993

Climb Every Mounting

If you own a late MGB 1974 1/2 to 1980, and contemplate rebuilding the motor, changing the clutch or motor mounts, you might consider this tip that will make life a lot easier.

Countersink the fuel pump hole and block off the plate. Replace the screws with countersunk Phillips, slotted or alloy screws. This will make installing the left hand motor mount bolt so much easier. Moss part #323-280 is just the job for this operation. 

Handling With Care

I am gradually getting to know my 1964 TR4, nut by nut and bolt by bolt However, having completed major repairs I was ready for a summer of driving, however the handling of the car was abysmal.

The problem was vague and there were a number of front end problems that could be contributing to it. The TR seemed drift left on acceleration, drift a little to the right when I braked, but would drive reasonably straight with my hand off the wheel at a steady speed. Was this suspension, bearings, tires alignment or what? Braking was also a problem: initially I had trouble with the hose that runs to the rear brake lines on the differential and axle. That hose had become swollen on the inside, making the rear brakes slow to respond and slow to release (hence the brakes stuck). This trouble was described in the Moss TR2-1 catalog and was easily remedied.

After fixing that problem I then had persistent difficulty with a spongy brake pedal; there was no apparent leakage of brake fluid but despite repeated bleeding of the brake lines, the first pedal depression was spongy but the second and third “pumps” were very firm.

During the off season I rebushed the suspension and replaced the springs and shocks and as usual I made even more amazing discoveries that made me wish I had never risked driving the car before the repairs were carried out. For instance 3 of the 4 trunnion pins were broken! However during this work I noticed that the left front brake hose was a little frayed and I decided to replace both hoses. It was about this time that a possible solution to the handling problem came to me…if the left brake hose was swollen inside and nearly blocked, it would cause a delay in left braking, a soft brake pedal (as brake fluid slowly flowed past the obstructed hose to fill the chambers in the left brake. It would drift initially to the right as the right brake acted first, and later drift to the left as the left brake was slow to release (since the hydraulic pressure would be released more slowly).

Eureka! In fact when I removed the hoses I found exactly what my theory had predicted-the right hose was clear, while I couldn’t blow air through the left hose, and after installing new hoses and bleeding the system, the sponginess was gone from the brake pedal. The handling and the ride were also much improved.

I really should have known better, after all I had already had the experience of a blocked brake hose on the rear, and I suspect that brakes are often over looked in handling problems. I am convinced that the safest plan in to regularly inspect and at least replace all the rubber components that have anything to do with safety or performance (brakes, steering). After all, you only have one life!

More Skinners Union Stuff

We know that the balancing of S.U carburetors requires the removal and replacement of the anchoring nuts and bolts, and washers for the air cleaners. We also know the contortions required to replace the washers and nuts up under the carbs (as well as the kneeling, searching and cursing when we drop them – twice!) I think the following might simplify the problem.

The holes in the carb flanges that the 1/4″ (.250″) air cleaner anchoring bolts go through are .257″ plus (at least the ones for my BN-1 Austin-Healey “H” carbs are) and this just happens to be the recommended hole size to install 5/16″ X 18 helicoils. Run the 5/i6″-18tap in a hclicoil kit into these holes with the wing nut tool. The insert may be a little long for the thickness of the flange but screwing a 1/4″X 18 bolt through will break off the little ‘tang’ and set them.

Now the removal and replacement of the air cleaners is from the outside, and washers and nuts under the carburetor are not required. This method can also be used on other British cars with the same set-up.

(Our technical boffins advise that this will not work on MGBs that have throttle cables held on by nuts on the back. —Ed.)

A Plug for Calipers

When rebuilding disc brake calipers, your shop manual or other service instructions probably recommended removal of the pistons by using pressure from the hydraulic system. However, this method is not only messy, but inhibits the work by allowing removal of only one piston at a time. It also forces you to work on the caliper under the confines of the wing while it is tethered to the chassis by the brake hose.

However, there is an alternative mechanical method which permits removal of both pistons at once while allowing you to do the work off the car. Remove the caliper assembly from the car, disconnecting the hydraulic hose at the caliper. Determine the inside diameter of the caliper piston, then visit the hardware store and find a plumber’s “test plug”, or try the auto store for the rubber plug used to replace the steel expansion plug in a cylinder block core opening. Both are rubber sleeves with concave washers at each end and a center bolt used to compress and swell the rubber sleeve. Choose one of a diameter as close as possible to the piston bore.

Now cut a piece of 1/4″ x 1″ steel strap about 6″ long and drill a hole in the center that will fit the bolt in the expansion plug. Install the strap on the center bolt with the nut finger tight and cut off the bolt flush with the nut.

Insert the plug in the piston bore, install the strap and tighten the nut securely to cause the plug to grip the inside of the bore. If the plug should prove too small to expand enough to grip the piston, securely wrap a few turns of rubber tape around it until it is large enough to grip as needed. Rubber tape is far better than plastic or electrical tape because it will expand with the plug-having good friction characteristics.

Once the plug is tight in the bore grasp the caliper and tool assembly with both hands, placing the thumbs on the back of the opposite cylinder and the lingers around the strap. Squeezing the hands closed will extract the piston from the bore. Then repeat for the opposite side. Either this tool or a C clamp can be used to install the pistons following the rework.