Brake master adjustment - after axle swap

[Dre]

It's been like two months now since I've been driving my truck after the whole build-up saga and yet I have not adjusted master cylinder to work with the new rear axle. Truck is a 94 Sport - came with drums in the back... I installed newer rear end with disk brakes and never done anything to correct preasure. How is it done?

 

[Dre]

btt

anyone?

I know I should adjust something... just don't know where to start.

 

[NOTAJP]

The only way to correct the pressure is by installing a proporting valve. The ABS does a good job of limiting the pressure to the new rear brakes but a proporting valve is the correct answer. One more addition you might want to make is upgrading to a 1" bore master cyl. This will really bring out the full potential of your rear discs.

 

[Billy177]

i think in the master cylinder there is a plunger kinda thing that you can adjust

 

[410Fortune]

OKay first off did you try a SEARCH yet?

NOTAJP: thats not the ONLY way, in fact the proportioning adjuster after the fact is a band aid, it may help but you will still not have optimum pressure for the rear discs, because you are starting with the wrong master cylinder. I am curious about this 1" bore master you speak of? Can you explain?

Brett's original rear disc brake conversion article touched on how to adjust the plunger for front/rear biast.

I swapped in a disc braked 8.8 about 4 years ago. For the first 3.5 years I ran this sucker with the stock drum master cylinder with the proportioning adjusted. Basically the pushrod that comes through the brake booster is adjustable. If you turn it out (longer) then it sends more pressure to the rear, but takes away from the front, and vise versa. This is a delicate adjustment, and you will end up unbolting, adjusting, and re-bolting the master cyl many times to get it right.
It helps.

HOWEVER I have since gone all the way and FINALLY installed a 95 Explorer (rear discs) master cylinder. This was QUITE a large job. Now the brake line that runs to the rear of my truck (remember BII) would not thread into the new master, and even with adapters it would not be right (it would have taken a stack of 6 adapters to make the correct jump from standard to metric.
METRIC brake lines use BUBBLE flare fitting which are different from standard flare fittings.

I ended up running a new hard line (full brake line) from the new master cylinder, down the frame rail, all the way back to the rear axle.

On my truck I only had RABS (its an 88) so your system may be different.

The braking with the correct 4 wheel disc master cylinder is 5x's what it was with the "adjusted" plunger technique.

I would HIGHLY recommend finishing your rear disc conversion with the correct master cylinder, you will be MUCH happier

Also if you search for this you will see I did a FULL WRITE up of the conversion...and Brett wrote the rear disc conv. bible, which is posted on the main page of this site still I believe........

My BII stops on a DIME! I have switched to ceramic brakepads up front with new rotors, I have replaced all 4 calipers, I removed my RABS system completley, and I run semi metallic pads in the back. Even with 33's, 4.10 gears, a modded 4.0L and tranny the truck stops AWESOME. I imagine that a BII with 4 wheel Explorer discs would stop pretty good, and it does! Even with a 3250# boat in tow..................

There has also been some talk of replacing the vacuum operated brake booster with a HYDRAULIC unit from a superduty........NOW THAT WOULD MAKE FOR SOME IMPRESSIVE BRAKING on an Explorer
food for thought

 

[Dre]

thanks a lot for all the info. I did the search but came with lots of threads that had nothing to do with this... went through numerous pages of gibberish...

I'll look on the main page and probably go for a new master... plunger adjustment might do for now but to get this done the right way I think master replacement would be the best way.

ABS all four on mine - I don't think I need to worry about locking the front but wold like to have more "bite" in the back to help minimize wear on front pads and rotors...

thanks again.

 

[410Fortune]

Dre:

FYI the Chiltons book shows a proceedure for setting the plunger back to Ford specs, it involves actually building a little guide from some pieces of wood.

I did this after I installed the new master cyl.
I still ended up adjusting the biast some more, to get a little more bite from the rear axle, you can definatley tell it is a fine lone between too much and too little....too little, fronts lock up easier, and vise versa....

 

[NOTAJP]

Jamie,
I was refering to the bore size internally of the master cyl. Ford made many different sizes. I know it's been discussed on here before, just not sure where. The 91-94 Exploders had a 13/16" bore. (Please don't quote me for an expert as I'm just flying by memory). The later Exploders had a 15/16" or 1" bore for the disc brakes. All later Mustangs had them as well, making an easy search and swap. I believe the biggest master cyl was the 93 Cobra with 1 3/16" bore for the really big brakes. The downfall is a very firm pedal. Don't know for sure, just from other swappers info. This is what I am looking for along with a dual diaphram booster for super brake power with my soon to be 13" rotors front and rear. I have also kicked around the idea of hydro but that gets expensive really quick.

 

[Dre]

so I should actually look for a 1" bore master and replace it all together? what about fittment onto an existing boster?

 

[410Fortune]

Okay well thank you for ringing that to my attention NOW AFTER the fact! hahaha

I used a 95 Explorer bone stock master and I replaced the booster (my BII has 260K miles on it) with a later model Ex booster of the same size) and installed the new master at the same time....

The BII pedal is very finm copared to what it was stock and the braking response is fantastic. If I had known about the Cobra master I may have tried that with the same $$$

Since my truck is much lighter then a 4 door Ex I assume I am in great shape, where as if it was a 4 door Ex I would still be looking to get more from the system...

13" rotors front and rear? PLease explain...(for lack of me seraching right now)

 

[NOTAJP]

That's the good news. 99% of all Ford master cyls will bolt right up. Just need a m/cyl from a newer Explorer or Mustang with with rear discs.

 

[NOTAJP]

Jamie I think you have plenty of brake power. I only wished my X would stop as well as your BII does.

I'm working it out in my head to get Cobra sytle brakes. The rear will be easy as the Cobra had an 8.8 and 12.5" rear rotors. I think I can fab up brackets for the front. Remember I have a D30 so it'll be a little different and easier, I think. I also have 17" rims to clear the huge brakes. I'm in talks with Wilwood about different setups and 4 piston calipers. They have the rears all setup for about $500 and are willing to custom make the fronts for $1500! I think I'll try my way first to save some $$$.

 

[Dre]

thanks... all the info gives me plenty to work with... before I even tear things apart. For now I'll be looking inot getting a new master.... but at the same time I'll have to adjust proportioning valve anyway... right?