Disc brake upgrade

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69gladiator
Posts: 231
Joined: Tue Oct 15, 2013 6:10 pm
Location: stratford,ct

Disc brake upgrade

Post by 69gladiator »

Over the Christmas break my son and I decided to tackle the disk brake upgrade on his 69 Gladiator. There’s plenty of tutorials out there so it was an easy job to mount everything up. We didn’t install proportioning valves as it seemed there was no clear consensus on its value.

The truck has a vacuum booster and master cylinder that I bought from j and w several years ago. I thought that it would be a good idea attemp to find a disc brake MC that would fit instead of the stock one that J and W sold me with the booster. I called them and the sold me a MC that would fit the booster and give me a larger front disc reservoir. The booster appeared to be off a early seventies Ford f 250. We matched it up with one from a one that the helpful guys at napa found.
The bore depth and all of the measurements match the original Jeep MC.

We have bled the system several times and very occasionally get a soft pedal. When it works the truck has never stopped better! I asked several mechanic friends who felt that maybe the MC was a bad rebuild so we replaced it. Again we are still getting the soft pedal.

There are no leaks. The rear wheels have been adjusted. One thought is that possibly the booster rod needs adjustment because it holding the plunger slightly open. Or maybe there’s still air in the system. Again I cannot say enough how better the truck stops with the disks.

rocklaurence
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Re: Disc brake upgrade

Post by rocklaurence »

Now, do the breaks come-back on their own or do you have to bleed the system? If pumping the peddle fixes it for a while then Id suspect theMC. However, if the brakes dont lock up like they should it maybe a piece of rust or debris in one of the tubes. I had this issue on an old CJ where the rear brakes were never good and it took a while to locate the clog at the rear tube T fitting.

Topic author
69gladiator
Posts: 231
Joined: Tue Oct 15, 2013 6:10 pm
Location: stratford,ct

Re: Disc brake upgrade

Post by 69gladiator »

Pumping brings back the peddle. This is a new MC because three real mechanics felt that the rubber components in the MC were failing. Going to try another bleed. If it does not work, I think I’ll look at the plunger rod adjustment. Maybe it is slightly holding the plunger in the Mc in a position that prevents the Mc from refilling. The brakes will lock up with a firm peddle 99.5% of the time.
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tgreese
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Re: Disc brake upgrade

Post by tgreese »

Did you bench bleed? Last MC I got had plastic plugs to put in the ports for bench bleed, but that left air in the MC. You need to put hoses back to the reservoir from each port and pump the cylinder until there is no air coming out. Get all the air out of the MC.
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Herk
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Location: Boise

Re: Disc brake upgrade

Post by Herk »

If you have the calipers mounted to the rear (3 or 9 o'clock) the flow bolt that attaches the hydraulic line will hit the shock absorber if you crank the wheels all the way in a tight turn. This will compress the caliper piston enough that you will have a low pedal for the first application after the tight turn. I moved my lower shock mount tabs on the axle in towards the spring about 1/2" on each side and the problem was solved. Also disk brakes are more sensitive to wheel bearing adjustment. Loose bearings will cause a low pedal.

Topic author
69gladiator
Posts: 231
Joined: Tue Oct 15, 2013 6:10 pm
Location: stratford,ct

Re: Disc brake upgrade

Post by 69gladiator »

We bench bled the MC with tubing. Never had much luck with the plugs that come in the box. As I said unless the peddle goes soft, about 1% of the time, I can lock up the brakes when I stomp on the. Otherwise the peddle is high and form. I saw a link on the Early CJ Forum which had you jack up the back of the truck and slowly push the peddle to get out the air trapped in the rear of the MC. Gotta check the caliper. I was thinking about moving the shocks to the front of the axle like on a Cj 5. This project really should not have been such a PIta.

Topic author
69gladiator
Posts: 231
Joined: Tue Oct 15, 2013 6:10 pm
Location: stratford,ct

Re: Disc brake upgrade

Post by 69gladiator »

Herk-Did you cut off the tab and simply re-weld it leaving less contact with the formed portion on the axle? I was thinking of getting a wider piece of steel so there would be the same contact to the formed portion. I got the peddle to drop every time I made a hard right turn. Both shocks have a dent in them now.
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