Master cylinder bore size?

[SDrake]

Shopping for new master cylinder, pedal leaking down slowly on original, and once I enter vehicle identification in various online sources I come up with choices of bore sizes, Rock Auto for instance has 15/16, 1-1/4, and 1-5/16.

I have always liked the brakes on my truck and don't want to mess up the feel. Short of putting my truck out of commission for a while and removing the master cylinder to measure it, what guidance can anyone here give me on choice of size?

I want to put in a good quality master cylinder and was going to order the Raybestos one until I noticed the size was 1-5/16, while all the other brands were smaller. After looking through other parts houses to see if I could reverse engineer this thing I have just wasted a lot of time. So I go to the court of last resort

Actually I am about to call Genos. I usually end up buying stuff from them any way.

I will post the information if I learn anything.

 

[jelag]

you don't want to change the diameter of the master cylinder.. the bore of the master cylinder will dictate the pressure applied to the system based on the pressure on the pedal.... this ratio shouldn't be changed... I can only suggest that you pull the boot off the end of the cylinder and measure the bore.... or go to the dealer with the vin # and get the correct unit... After being in the Clutch & Brake business for 20 years... (now retired) I've never personally seen any single line item in either a Raybestos, Bendix, or Wagner brake catalog that once you dialed it down to the correct vehicle, it gave you more than one choice...

BTW - I'm guessing that any lifetime guarantee master cylinder would be as good as any of the major brands...

Good luck...

 

[sag2]

You can have it off in 10 minutes. Pull it and measure, put it back on to go get the kit and then you will have the correct parts. Although if it were me and I didn't have time I would go to Napa and buy one of every size because when they are closed is the only time I ever find I have the wrong parts!

 

[SDrake]

you don't want to change the diameter of the master cylinder.. the bore of the master cylinder will dictate the pressure applied to the system based on the pressure on the pedal.... this ratio shouldn't be changed... I can only suggest that you pull the boot off the end of the cylinder and measure the bore.... or go to the dealer with the vin # and get the correct unit... After being in the Clutch & Brake business for 20 years... (now retired) I've never personally seen any single line item in either a Raybestos, Bendix, or Wagner brake catalog that once you dialed it down to the correct vehicle, it gave you more than one choice...

BTW - I'm guessing that any lifetime guarantee master cylinder would be as good as any of the major brands...


Good luck...

Followed the idea of checking individual manufacturers catalogs and Raybestos lists the 1-5/16 size that Rock Auto does for Raybestos. My first inclination was just to buy a middle of the line price but Rock Auto listed all these various sizes in the diferent brands as the part for my truck. Remembering that the last master cylinder I replaced on my 94 dodge at 13 years old, pushing 300K failed in another 2.5 years. Got it at NAPA or CARQUEST can remember which. Just decided to at least try to get something better. The failed one was a reman so I am deciding to go new this time. Can't locate a bendix catalogue to see if various manufacturers agree. Took a look at JC Whitney and they listed a 1" raybestos one for my truck.

Looks like I am going to have to go sag2's route but I could quibble on the 10 minutes part although I get the idea of man up and just do it, it is no showstopper.. I see that this one is a bit easier than my 94 was. It is just such a tedious job to bleed and I do not have one of those bleeder tools so tomorrow I will waste most of the day working this out.

If I can detach the cylinder without loosening any of the lines and just spring it forward enough to measure then I will be done in 20 minutes after I round up my calipers.

 

[SDrake]

Found a gold mine. Rock auto has a page with links to all the manufacturers. http://www.rockauto.com/docs/manufacturers.php

Checked the ebendix site and they list one part at 1-5/16' bore size. Agrees with Raybestos so I consider size confirmed. Nice thing about Bendix site is they cross reference part numbers for the master cylinder to several competitors so I am now leaving house to shop with 5 different brands of part numbers that I could go with if I run across one of those.