I hope that someone could shed some light on my problems with the brakes on my car. It is a '74 RX-3 that I have fitted T2 calipers with GSL-SE hubs/rotors to the stock strut of the car. The problem is that the brake pedal goes almost straight to to floor with very little attempt to even try to slow the car down. I have rebuild the calipers, master cylinder, replaced the brake booster, replaced the rear wheel cylinders, inspected and bled the proportioning valve, new brake pads and shoes to no avail. I have bled the system about 12-13 times and still nothing, adjusted the travel of the brake pedal to see if that could improve/help with the issue and still no brakes. Is there something I am missing here? Maybe I need a different master cylinder for this set up? if so, which one could I bolt on to this thing that works well??

 

The stock rx3 master is 7/8 bore, you may need larger bore to move enough fluid. I don't understand why the rear brakes don't harden up the pedal even if you don't get good braking effort from the front.

I don't think the stock set up had a proportioning valve. I think its a safety switch to let you know if front and back are way out of balance ie a leak.

I put a 4 piston caliper set up on my rx3, but also upgraded rear brakes to rx7 disk with a LSD diff change.

The vacuum booster is an issue when changing the master. I got rid of the vacuum booster and use a 1 1/8 bore master.

Brakes are very good, loss of vacuum boost not an issue. Stock booster was small any way and all the extra brake capacity works good. Good road feel.

 

Thanks for that information, I plan to upgrade the rear brakes in a short while, but until then, is there a master that can be used with the booster? I will like to keep the booster functional if at all possible.

 

Could not find any kind of direct bolt on. The booster has 3 bolts to the fire wall and the master has 2 bolts.

Did not want to make any new holes in my rx3 so I build an adaptor. Basically a plate that matches the booster on one side and the master on the other side. The plate has a hole for everything to line up.

If you don't know how to do it, get someone who does to do it.

Changing brake set up requires a lot of concideration. They are more important than power changes.

 

only other thing i can think of is did u pump the brakes to close the front pads to the rotors before driving it?

 

RXTASY3, yes, the brakes were pumped several times before driving the car, they have been bleed multiple times so far. EDSRX3, what kind of master did you ended up using? the space there is very small with the strut and reservoir in front of the cylinder itself, but I will like to try this one. I could have some one build the spacer required to mate the cylinder to the booster, that will not be a problem

 

Yes the space is tight. Spent many hours at a parts desk checking specs.

Used a mid 70's Ford master intended for 4 wheel disk. It was the largest bore with the ports on the correct side. Yes it is big ugly cast iron. I've seen other options used by racers that may work. I put a proportioning valve in the rear brake circuit to get the balance right. Used the stock safety valve.

When you mount the master you'll have to build a custom plunger to mate it with the foot pedal mount.

There is also a little trick to use the original RX3 emergency cables with the rear disk conversion to avoid changing them to rx7 cables.

here are a few pics

 

Hmmm. For approx 5 years, i have been using Fb front suspension/brake, rear disc brake conversion, brake booster/master, clutch master and full brake pedal. Had to modify the firewall to accomodate the 4-stud FB brake booster and new holes for fb clutch master. My cars stop on a dime and never had any brake locking issue or whatever.

Most peep run aftermarket front brake conversion and brake master without booster but i didnt go that route since i collected many FB parts plus I am a cheap *** lol

 

Do you think that an FB brake booster could be used with the original pedals? I would like to go this route better since I would like to keep the booster operational. EDSRX3, do you recall for what year/model the cylinder you ended using is? I need to keep all options open....

 

Don't know the model Ford, just remember it did not have power brakes, but had 4 wheel disk.

Like I say there are lots of things to take into concideration. I was also aware of the room I eventually needed to reinstall my rx3s ac system.

Wacky has a lot of experience with these cars, he can give you far more information than I ever could.

Ed

 

Fb booster on a stock rx3 pedal wont work plus it need to be redrilled for fb 4sfud booster. Fb booster is larger than a rx3 so the clutch master has to move closer to the fender. Besides,if you dont change the pedal to Fb, the clutch pedal push rod will not line up with CM. Dont get intimidated with the conversion, its not hard at all, check under my SN...its all there

 

So it looks like it will be a bit more complicated than what I thought. Just to make sure I understand this, if I were to install the FB booster, I will also need to replace the pedals with the ones from an FB also?

 

Here it is
https://www.rx7club.com/old-school-other-rotary-63/rx-3-brake-upgrade-final-result-872738/

 

Also use the rx3 clutch pedal push-rod instead of rx-7. This helps a lot when using very stiff dual diapram pressure plate. Otherwise you may run into issues with clutch not engaging due to not enough travel. Old schools rx adjustable clutch slave push-rod is NLA so switching to a longer clutch pedal push-rod is necessary IMHO. some may say it wil ruin the clutch master but I have had any issues

 

Thanks a million for all that information and the link for the work that needs to be done. Now I will be looking for a set up to star work on this project, time and availability permitting. I hope to be able to get it done before I decide to sell this car, it really is getting me really upset and frustrated not being able to get it even close to what I had in mind....