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Old July 13th, 2019, 09:23 AM   #1
itselliott
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Default Old School brake question

I have been putting off a project for years....swapping both front and rear diffs.

Along with that swap comes OEM "Big Brakes" in front. (Same drum rear)
Having smaller calipers (also oem) previously I am wondering if I need to replace the proportioning valve???
Having bled the system extensively....I cannot get the front , now bigger calipers to extend far enough to grab.....

My thinking is that the prop valve is the issue...???
Is there an OEM valve that must accompany the swap?

Thanks for any help

I don't want to go disc in the rear.
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Old July 13th, 2019, 09:44 AM   #2
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Proportioning valve doesn't do anything besides restrict flow to either the front or the rear depending on where it's set. So if you don't have enough pedal to apply pressure to the drums then the proportioning valve isn't the solution, it sounds like it may be a master cylinder problem, IE not able to move enough fluid in the pedal stroke to move the drums. Did you upgrade the matter cylinder at all when you went to bigger brakes?

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Old July 13th, 2019, 10:11 AM   #3
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Originally Posted by Mihlfeldl2005 View Post
Proportioning valve doesn't do anything besides restrict flow to either the front or the rear depending on where it's set. So if you don't have enough pedal to apply pressure to the drums then the proportioning valve isn't the solution, it sounds like it may be a master cylinder problem, IE not able to move enough fluid in the pedal stroke to move the drums. Did you upgrade the matter cylinder at all when you went to bigger brakes?

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The drums are engaging. Its the new, larger caliper pistons that are not.

The master is a YJ booster /master that is basically new and was working perfectly prior to the swap.
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Old July 13th, 2019, 11:09 AM   #4
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The drums are engaging. Its the new, larger caliper pistons that are not.



The master is a YJ booster /master that is basically new and was working perfectly prior to the swap.
I was thinking calipers and said drums , my bad!

Even after pumping the brakes a few times they won't extend out at all? I would take the caliper off of the rotor and see if they move at all when applying pressure to the pedal. You can get an aftermarket proportioning valve if you want to be able to adjust the pressure to the front and rear but I don't see that solving the issue here.

In theory if you switched to a larger caliper that requires a larger volume of fluid to extend the same master cylinder may not provide the required fluid volume. Make sense?

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Old July 14th, 2019, 02:54 PM   #5
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Yes! exactly what I was going for....now...…….the stupid truth...…….
I had the lines reversed …..front and rear from the Master to the Prop valve.....making the rears "primary" …..DOH!!! ….have not fixed it yet,. but holy cow....been that way for about 2500 miles...…...Never too old to learn .
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Old July 14th, 2019, 04:15 PM   #6
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Probably could do some sweet drifts if you disconnect the rear drive shaft and put it in 4wd

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Old July 15th, 2019, 05:41 AM   #7
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Originally Posted by itselliott View Post
Yes! exactly what I was going for....now....the stupid truth....
I had the lines reversed ..front and rear from the Master to the Prop valve.....making the rears "primary" ..DOH!!! .have not fixed it yet,. but holy cow....been that way for about 2500 miles......Never too old to learn .
Glad you figured it out.

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Probably could do some sweet drifts if you disconnect the rear drive shaft and put it in 4wd

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