Soft Brake Pedal.

[csuengr]

I have had this issue with my 1980 CJ7 since I rebuilt it six years ago. I can push the pedal to the floor. Tires will only lock on dirt, but only the fronts. Parking brake works fine.

Basic parts:
Waggy front and rear axle and brakes with Waggy master cylinder.
95' YJ booster.

I have bled and bled the brakes and no change. Even pulling the thingy out on the proportioning valve while bleeding. The booster push rod is adjusted properly. I know this because if I extend the length any, the brakes drag. No play in the brake pedal. I am wondering now about the pedal ratio and if its not working with my master cylinder.

 

[73CJ]

I'm thinking it might be a bad master cylinder leaking internally.

I've had a few fail like that til I switched to silicone brake fluid.

 

[tarry99]

I have had this issue with my 1980 CJ7 since I rebuilt it six years ago. I can push the pedal to the floor. Tires will only lock on dirt, but only the fronts. Parking brake works fine.

Basic parts:
Waggy front and rear axle and brakes with Waggy master cylinder.
95' YJ booster.

I have bled and bled the brakes and no change. Even pulling the thingy out on the proportioning valve while bleeding. The booster push rod is adjusted properly. I know this because if I extend the length any, the brakes drag. No play in the brake pedal. I am wondering now about the pedal ratio and if its not working with my master cylinder.

You mentioned you have a Booster...............you need about 21 inches of vacuum to make that work properly..................the other problem you have is where you live....................not to say its a bad place but the altitude will effect the ability for the vacuum system to work properly.........Do you have a two stage booster? if not get one and you should have at least an 8 inch diameter sized..........................pedal ratio for Power Brakes should be about 4-5 to 1................if you had a manual set of pedals in there the brakes would be touchy....................my guess is your short on vacuum.

 

[csuengr]

I guess I should have mentioned that the pedal is easy to push. Goes right down. So I have plenty of vacuum. Even when I switched from the 360 to LT1, which has much more vacuum, pedal was no different.

Master cylinder was replaced to no affect.

 

[tarry99]

I guess I should have mentioned that the pedal is easy to push. Goes right down. So I have plenty of vacuum. Even when I switched from the 360 to LT1, which has much more vacuum, pedal was no different.

Master cylinder was replaced to no affect.

That's the point if it had an ample supply of vacuum it would not go down.
I would put a vacuum gauge on it.

 

[mtnwhlr]

My experience with power brakes is lack of vac or a bad power booster not working will cause a hard pedal not one that is soft and goes to the floor. That said I have found it is either a bad master cylinder or air in the lines. I wonder if you didn't get a bad replacement master cylinder or have a bad line letting air into the system.

 

[csuengr]

Uh, vacuum makes the pedal easier to depress. Without vacuum, the pedal is hard to push. So vacuum is not the issue.

 

[Old Dog]

Might be a dumb question but did you bleed the master cyl.?
sounds like a bad master or air in the master to me.

 

[csuengr]

I would think bad master cylinder if the replacement I put in didn't act the same as the old one, that was good, apparently. Replacement was bench bled, and bled again when lines were bolted on. No bubbles that I can find.

 

[IOPort51]

I would think about the residual pressure valve for the rear drums. The rear drums are backing off so far that it takes all your peddle to bring them back in contact with the drum. I do not know where you would find this valve it could be in the master or the proportioning valve. I think you said you replaced the master, did you do the prop valve as well? This opinion is well worth the price you paid for it.

 

[1986cj7]

Do you have self adjusting brakes in the back. If so you may want to check the adjustment. When I replaced all my brake lines and pads and shoes and wheel cylinders I has to adjusted the self adjusting brakes by backing up and coming to a complete stop and going forward and coming to a complete stop about 10-15 times to adjust the back brakes. The parking brake will work even if the brakes aren't adjusted because the parking brake will take out the slack in the shoes. If you don't have self adjusting brakes disregard.

 

[csuengr]

Do you have self adjusting brakes in the back. If so you may want to check the adjustment. When I replaced all my brake lines and pads and shoes and wheel cylinders I has to adjusted the self adjusting brakes by backing up and coming to a complete stop and going forward and coming to a complete stop about 10-15 times to adjust the back brakes. The parking brake will work even if the brakes aren't adjusted because the parking brake will take out the slack in the shoes. If you don't have self adjusting brakes disregard.

They are self adjusting. Been there, done that.

I am going to look at the pedal ratio tomorrow. My Jeep originally had non boosted brakes. Gonna check between it and my dad's CJ, which has factory power brakes.

 

[csuengr]

Pedals between the two Jeeps have the same pedal ratio. Now I have to check the ratio on my FSJ pedal assembly.

 

[csuengr]

So I finally measured my FSJ brake pedal, and the distance between the hinge point and the stud the brake rod goes is ~1" longer than on the CJ pedal. Now I get to have fun pulling my brake pedal out.

 

[tarry99]

So I finally measured my FSJ brake pedal, and the distance between the hinge point and the stud the brake rod goes is ~1" longer than on the CJ pedal. Now I get to have fun pulling my brake pedal out.

What are you trying to accomplish? There is a difference between a non power brake pedal and a power pedal as far as the connection point and the ratio is concerned. Both Pedals should be about 16.5 inches from the fulcrum to the contact push point. The ratio difference for a non power is 6.6:1 @ 2.5"and the power at 4.7:1 @ 3.5".........people using a non power pedal ratio in a power brake setup will have very sensitive brakes as far as the application is concerned.

 

[csuengr]

The pedal in my CJ (1980, non power from factory) and my dad's (1980, power from factory) have the same pedal, hence same pedal ratio. I have a MC from a 1988 Grand Waggy. The FSJ pedal has a distance between the fulcrum (second class lever) and the load that is one inch longer than on the CJ pedal. So, at the moment it appears I am not getting enough stroke. If I move the pin down one inch, it will increase the stroke length and I will get a firmer pedal.

 

[tarry99]

The pedal in my CJ (1980, non power from factory) and my dad's (1980, power from factory) have the same pedal, hence same pedal ratio. I have a MC from a 1988 Grand Waggy. The FSJ pedal has a distance between the fulcrum (second class lever) and the load that is one inch longer than on the CJ pedal. So, at the moment it appears I am not getting enough stroke. If I move the pin down one inch, it will increase the stroke length and I will get a firmer pedal.

I have done numerous pedal changes and although the pedals are both the same overall length the pick-up point normally has only one option standard versus power although I have seen some that have had two holes available. Jeep also used a ratio changing lever type adapter that mounts on the firewall that the booster attaches to.

The ratio's I gave you came from Jeep Engineers.

In order to calculate whether or not your getting enough stroke is just one equation................. but to do it correctly you would first need to know the bore size of your master and the stroke along with the bores and strokes of what brake system you have IE; drum versus Disc. Once you know the total volume requirements of the system then you apply the bore size of the Master and stroke to fit the desired volume............I have an ex-cell spreadsheet here that does that stuff for me if you would like send me a PM and I'll try to help you out.

 

[csuengr]

The thing I did do right is that the MC and all brakes are from a 1988 Grand Waggy I owned, so the MC is matched to the brakes. After insuring everything else is good, the stroke length is my last problem to work out.

 

[tarry99]

The thing I did do right is that the MC and all brakes are from a 1988 Grand Waggy I owned, so the MC is matched to the brakes. After insuring everything else is good, the stroke length is my last problem to work out.

That's great that does make it that much easier...........do you know what the ratio or travel was in the Waggy?
Does your current Jeep have the adapter between the firewall and Booster and same question on the Waggy?

 

[csuengr]

The brake pedal of a Waggy and a CJ are different lengths. The only measurement to compare is the distance from the fulcrum to the load point, which is longer on the Waggy pedal. Don't know what adapter you speak of. I am running a 95 YJ booster with the YJ mounting bracket. CJ booster setups were too expensive, and the YJ booster is a dual diaphragm.

I am at the point where I just have to pull the pedal out, modify it, and test. Bad thing is that the modifying is the easy part.