wheel cylinder bore size

Today I replaced the rear brake wheel cylinders on my 98 caravan
because they were leaking. The ones I bought as replacement have a 3/4
inch bore. After I had installed them I noticed that the old ones have
a 13/16 inch bore. Will there be a problem because of this? The brakes
seem to work fine with the new wheel cylinders.

 

The new ones will have 15% less braking effectiveness (for a given pedal
pressure) - that's 15% less effectiveness just on the rear wheels, not
for the whole vehicle. Since you replaced both sides, you will not have
created a side-to-side braking imbalance. You will have shifted the
front-to-back brake balance so that the front brakes will do more of the
work now.

Since the front brakes are doing 60 to 65% of the braking work and what
you did will not have affected the front brake effectiveness, your total
braking effectiveness (for a given pedal pressure) will have dropped
only 5% - i.e., you will have to push the pedal 5% harder to get the
same braking effect.

It may be that the aftermarket manufacturer consolidated close sizes of
otherwise equivalent cylinders. Should not be a big deal since the auto
manufacturers have as much or more variations in brake balance between
different handling packages of the otherwise same vehicle. Also, people
mix and match different pad/shoe material (i.e., different friction
properties) front to back all the time without giving it a second thought.

IOW, don't worry about it. If you have ABS, the difference from a
safety standpoint will be less critical (since the point of wheel lockup
will be determined mostly by the ABS system rather than the actual
balance of the braking actuators.

You will be seeing slightly more wear on front pads and rotors (and
correspondingly less wear on rear drums and shoes).

Bill Putney
(To reply by e-mail, replace the last letter of the alphabet in my
address with the letter 'x')

 

To clarify - from the factory, the front-to-rear braking balance is
typically designed to be around 60/40 or 65/35. What I explain after
that is that what you did shifted the balance an additional 5% to the
front from whatever the factory design balance was.

Bill Putney
(To reply by e-mail, replace the last letter of the alphabet in my
address with the letter 'x')

 

Good point, Glenn. And the info. could have been passed on to
aftermarket. Or the aftermarket may have just unilaterally substituted
them.

Bill Putney
(To reply by e-mail, replace the last letter of the alphabet in my
address with the letter 'x')

 

If you ordered them from the dealer, your parts department may have ran the
vin number to get those updated wheels cylinders off of the build date. They
were updated due to a brake howling moaning noise (TSB) during slow speed
stop.

Glenn Beasley
Chrysler Tech

 

When I bought a cylinder for my 99 Voyager the aftermarket store asked
me which size I wanted. They carry both sizes to avoid having a
mismatch when you do only one side. I guess that makes it more
complicated.

 

Another reason why I stay away from aftermarket parts. If a part has been
modified to correct a problem, normally the old part get reman and put
back on the market to be resold again.Rather then getting the updated part
from the dealer. Water pumps on the first 3.5 LH vehicles as an example

Glenn

 

there is 2 different sizes so u need to the correct one in and the wrong ones
out they should have asked you at the parts store