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
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