At 09:41 PM 12/18/2006 -0500, Daniel Hackney wrote:
>I'd like to fix what I find to be an annoying trait of my '72 GT:
>the brake and clutch pedals each have a fair amount of side to side play.
>The play exists between the distance tube and the cross bolt, not
>between the distance tube and bushing. Using a caliper, I measured
>the bolt (3/8") to be 0.371" OD on average. The bolt doesn't have
>grooves in it or appear worn in any way. The existing distance
>tubes measured 0.385" and 0.380" ID. The two replacements that I
>purchased (from a reputable supplier) measured 0.392" and 0.387"
>ID. This hundredth is enough slop to translate to a lot of movement
>at the end of each pedal.
>I realize these aren't high precision parts, but surely I can do a
>bit better. Are they all like this, or does there exist a fix that
>I am missing?
I left most of the prior message in tact, as I need to refer to the
details. I am not intimately familiar with the MGB set up. From the
parts books and shop manual it appears to have two short inner steel tubes.
I am intimately familiar with the similar MGA set up. For the MGA
the bronze bushings are short, but there is a single longer steel
tube which is captured between the side brackets and steel thrust
washers with the tight bolt so the steel tube cannot move. The bolts
are often undersize, and the tube bore can be oversize, but it
doesn't matter as long as the bolt tightens up to hold the tube
securely at the ends so it cannot move.
The short bronze bushings are subject to cocking loads caused by
sideways pedal forces. It does not take long for the bushings to
wear enough to allow sideways pedal wobble of 1/4 inch or more. At
about 1/4 to 1/2 inch of pedal wobble the steel thrust washers come
into play to relieve some of the cocking load on the bushings. If
you are careful measuring things during assembly you can reduce the
length of the inner steel distance tube(s) slightly so when the bolt
is tightened it will minimize the side clearance for the thrust
washers. This can help in the long run if you don't want to be
constantly changing the bronze bushings.
As to fit of the bushing on the tube, it is common engineering
practice to make the bushing with nominal bore size and make the
shaft (tube in this case) about 0.002 inch undersize for working
clearance. My experience with MGA parts verifies this practice. When
the bushing is pressed tightly into the arm it may sometimes be
reduced slightly in diameter, and/or the ends of the bushing might be
slightly deformed during installation. If the bushing does not
subsequently fit over the tube you can drive a standard size ball
bearing through the bushing to burnish it back to correct size. The
OD of the steel tube should be ground smooth and correct diameter for
the bearing surface. If the tube OD is more than 0.002 inch smaller
than the nominal size I would consider it to be a defective part.
It is a bit of a pain to R&R the pedals, but the bushings are
otherwise fairly cheap and easy to replace. I spent an extra half
hour once measuring things and adjusting the length of the steel
bearing tube to minimize clearance for the thrust washers. This was
time well spent, as I haven't felt the need to change the bushings
again in a very long time.
1958 MGA with an attitude