J20 Power brake booster and MC

[tngreenmachine]

Ok I got a 75 J20 single diaphram booster and MC.. I also got all the hoses and fittings to hook it to my Disc brakes front and rear. I took out the stock MC a few mins ago and it looks like 2 of the holes for the spacer will bolt right up and I will have to cut 2 new ones. Crawled into the floor between the seat and the pedals and took off the spring and the push rod for the stock MC. The J20 pushrod has a much smaller hole in it and there is not enough material there to make it as large as it needs to be. I was wondering what others did to make the push rod work. I would just weld the old ring on the new MC push rod but I can't remove the new pushrod and I think I would melt some stuff if I welded it in the MC. The answer is probably right there but I can't grasp it right now. Any help?

[FSJGuy]

I think that pushrod is removeable via C-clip or some other contraption. I've never removed them, however.

You can use the FSJ pedal assembly, too. I'm interested to see what you use to get it working.

I'm using an FSJ booster/pedal assembly and am having trouble getting good brakes, but maybe I have air in the line and I just need to bleed them again. I'm taking a break (no pun intended) from the project so I don't drive myself nuts and do something crazy like sell the whole thing for $500. (Forget it, there's already 5 people ahead of you....)

[tngreenmachine]

Ok I took the power brake booster apart as far as I dared to see how the rod was retained. It looks like a tube was built into the back of the booster the rod was inserted and then two spots on the tube were crimped. The end of the rod is a ball. No way to get it out without destroying something that I can see. I also took a look at the pedals today and it looks like the retainer for the push rod is pressed in. If you still have your 715 pedals would you look at them for me and see if there is a way to press out that retainer? I started to take mine out but it will require pulling out both clutch and brake pedal assemblies and I really don't want to go to all that trouble if it is not possible to get that retainer pin out. It also looks like to have full pedal travel the push rod would need to be about 3/4" longer.


I had another thought when I was looking at it today as well. I am wondering if it might be possible to cut the new rod and thread it and do the same to the stock one and actually make it adjustable to a point.. My micrometer guages the stock rod at .33 and the new one at .35. 3/8" is .375 so I figured I would see if it would go up on the old rod and I couldnt get it to start...

If it has to be welded on I will do it, but I sure would hate to cook that seal and my booster not work. I don't know how critical that seal is though because the hole in it is alot larger than the push rod and to seal against the push rod it uses a washer and a spring. Couldn't hold too much vacuum IMO.

[tngreenmachine]

Heh I just thought of something else too.... Taking a piece of flat stock and drilling a hole in it to fit over the retainer pin. Marking it for max pedal travel with the new booster/MC bolted in. Drill that out and then weld the flat stock to the pedal and use a small hitch pin or something that would allow the push rod to swivle to retain the push rod to the flat stock. I think I will go this route as it doesn't require messing up the booster/MC and voiding my warranty on it.

[tngreenmachine]

I ended up using the above mentioned method (flat stock with a 2 holes one slipped over the stock stud and the other bolted to the push rod). I have the front brakes hooked up but I am still waiting on rear brackets so I can't tell you how well the MC works yet. The brakes start at the top of the pedal and it pushes in fine with a minor amount of deflection as the pedal swings into the fire wall.

I think I will probably have to add proportioning valves to both sides and adjust them but I will see how it works first. Going to try and get the 205 in today.

[tngreenmachine]

Now with some pictures...


I made the bracket with a little ear on the back of it thinking I might use a electric brake light switch but I think I have decided on using the pressure switch if it works.

And I couldn't get a bolt into the top hole of the spacer because it interferes with the pedal brackets. I think 3 should be enough to hold it.

[brute4c]

Very nice work and thanks for the pics and detail...very helpful.

[ffdemoss]

Did you weld the flat stock to the brake pedal? Anyone else seen any other methods of hooking a booster to the stock brake pedal? I am getting ready to do mine and want to explore all options.

[randyscycle]

I used a 94 Jeep XJ master cylinder and booster on my 715. I had to drill the stud holes for the booster mounting because it sits right on the firewall. I also had to enlarge the original hole slightly.

The pushrod was too long and the hole too small on the end, so I cut it off and took out the appropriate amount, then using the ring end I cut off the stock master cylinder, I then sleeved the outside and TIG welded them together. TIG allowed it to be welded without a major amount of heat travelling up the shaft. I also clamped two pairs of Vise grips on the shaft as a heat sink, just in case.

I'll try to post up some pics of the pushrod in the near future.

[airborne]

Pic's. My air cleaner is in the way of ANY booster. I have one off a FSJ, but there is NO WAY it's going in. ???????????????????