Brake Front-REAR imballance

Description:

My Jeep Brakes lock up the Back brake set when I stop hard-- Burn rubber.
At the same time my fronts are not doing much wheels braking lightly-- but not locking the tires.

All the system is bleed and I have lots of pedel.

I Got 11" brakes on all fours.

The Master Cylinder is on the firewall-- it is from a 1980ish Chevy 1/2 ton PU
It is a dual master cylinder.

There are two hydro fittings on the master cyl. One to the back brakes and One to the front brakes.

The larger of the fittings goes to the back brake set. It is a 3/8 hydro fitting
The fronts have 3/16 fitting

Question--

Is it reasonable to think that I should just trade fittings-- and thus the front brakes would brake harder-- while the backs brake lighter?

Has any one else dealt with this situation?


WILWOOD ADJUSTABLE BRAKE PROPORTIONING VALVE?

Thanks-

 

are you sure the front wheel cylinders are free, and not frozen up ?
are you sure the brakes are adjusted properly, the shoes are contacting the drums before the pedal is applied ?

if yes and yes, then carry on

 

w3srl
and
bkd--

Thanks and this is the case-- That is the fronts have the bigger reservoir . YOur feedback is appreciated. Driving an old Jeep is a real reality check for me after driving my supercharged Bonneville for years.

I just ordered a Wilwood brake proportioning valve off of ebay for the Jeep-- seems like a solution---what do you think?

Part of the Challenge with doing a frame-up rebuild it you put it all together-- then have a lot of bugs to get out of the whole vehicle-- expecially when you switched the engine, brakes steering-suspension and all of that plus more all in one big project. It is actually a real surprize that the Jeep works as welll as it does considering what a massive combo of untested parts it is built-up from and how CHEAP I did it.

When I think about it ----the brakes are not really a perfect match for the MC. The MC was designed for a 1/2-3/4 Chevy truck that had discs in front and drums in back.

I got 1967 front Bronco Brakes that are 11" on the back axle and 1974 Stock CJ 11" brakes on the front. The wheel cylinders on the back vs. the fronts may be as much as 1/4' dia different. The Bronco drums are somewhat different too-- they are very heavy and thick.
This dawned on me after I just looked at the old parts I saved. I replaced the front brake cylinders with new aftermarket ones that I think are 1" dia (not sure) but I remember now that the Broncos were a little different size.

Part of the problem may be that the brake shoes have not seated to the front drums yet. The Fronts have brand new drums and shoew the backs were arched-in and worn in . I got the bronco brakes from a neighbor who put a Dana 44 and disc brakes on his Bronco-- then the brakes sat for like eight years in my garage.

Also I am running really small studded snow tires-- 215s these are only 27 -28 inches tall.

I got a worn set of 31x10.5s I am going to mount in a couple of weeks. Then after the Jeep brakes and tracks good I will save $ for some better tires. I got 4-5 inches extra of wheel well clearance and could run really big tires-- even 37s. BUt that is too big.

And part of my problem is that I was driving the Jeep in metro Denver, Colorado with BMWs,
Hummers, Lexus, and sporty VWs flying all around like wild! Jack-Rabbit jump states and rapid panic stops are the way of driving in this place. 40-50 year old Jeeps and Trucks just cannot compete with agile commuters in this metro traffic. I drove a 40 mile circle to get the Jeep inspected and registared last week and it wore me out driving that old T-90 in big metro city traffic-- I was in a bumper to bumper for about 3 hours too. I live in an area right next to one of the wealthest urban areas in the Nation. Hummers and Escalades with 22" spinner chrome wheels--Brass chrome and coustom plates.

But I am selling my metro Yuppy house and moving 1400 miles back to southern Oregon ASAP-- and I am going to become a Hippy again.

Ever use a proportioning valve?

 

the front wheel cylinders are typically much larger in diamter than the rears, say 1-1/8" vs 1" or even 3/4"

 

It could be that the rear brakes since adapted front Bronco brakes- thus the fronts from a heavier vehicle-- So after thinking about it the backs might naturally be giving slightly more braking than the factory 11" CJ brakes on the front.

Part of my situation with such a customized vehicle made from so many different donor vehicles is brain storming possible bugs in the overall vehicle. So all of your feedback is very useful and appreciated.

It is a real scarry thing to lock your screatching louding ripping rear tires-- and having your Jeep skid a long ways on its rears--- in heavy traffic toward possibly ramming some lawyers NEW 2008 LOW SLUNG CONVERTIBLE BMW who stopped on a dime in front of you. ( Though I must admit is it fun to see some fancy-dan lawyer who - (in his shiney sports boat--all groomed with slicked back hair, brute colone and 1000 dollar sun glasses) get the #$%&... scared out of him by an old red Jeep about to run him over. R) (as you see his eyes in his rear-view mirror-- watching at our quickly approaching bumper at his head level-- )--------( ASIDE FROM GETTING REALLY SCARED MYSELF)

 

Yep - the front brakes do most of the braking because of weight transfer, so they should have the larger cylinders. The master has to deliver the same pressure front and back, regardless of the volume of fluid delivered. A pressure imbalance would set off the warning light (if you had one). Force on the shoes gets larger the larger the cylinder is. A 1 1/8" cylinder makes 2.25x as much force as a 3/4" cylinder.

I'm not sure that a disk/drum master cylinder is what you want. The disk brake wheel cylinder pistons are much larger than the drum brake WC pistons. I would use a drum-drum master if I had a choice. Since you have hanging pedals, I would use a drum-drum MC from maybe a '76 CJ.

 

Yes indeed.

Testing your vehicle in a Metro area is really different from how I did it when I lived in a small rural town.

Personally I do not like to drive a lifted narrow track Jeep on a Metro Freeway. And I avoid it.

I did run the old CJ6 down Denver's Interstate 25 for about 5 miles at 60 mph-- and is was not a very safe feeling experience-- but it was OK-. FRONT END DID NOT SHIMMY even when hitting BUMPS!!!!


BUt it is my belief that an old narrow track Jeep is a 45-50 mph designed vehicle.

People drive their cars here like it was a raceway. Average speed 70-75- with a few always going like 80. If is often( in local news) that a very small agile car gets completely demolished by a heavy truck here in Denver. It is like an everyday thing on the evening news-- some little late model can pulls a quick lane change 'cut in front' with fast stop stunt in front of an 18 wheeler and is actually totally run over and completely transformed into shreaded sheet metal with chunks of wheel rubber, castings and human flesh. This happens when the lane the car changes into is suddenly slowed, just as the car switches into that lane-- yet the person still cuts infront of another vehicle. People who are in a hurry do not seem to realize that all other vehicles can NOT stop, accelerate or turn as quick and eazy as their little sporty cars.

If this were to happen in front of an old Jeep on a metro freeway-- it would be a really bad day for Jeep, Driver and car in front and all directly involved.


So with an old Jeep you want all your steering, suspension, and brakes to work as well as possible-- to avoid running into or having to to manuver beyond your vehicle's ability to stay upright. And you also want to avoid those kinds of traffic.

But even 11" drums vastly our preform the old stock 9" stock brakes== and are pretty cheap and eazy to convert.

And yea-- my front wheel cylinders are free and brand new and bleed. But thanks for asking/ mentioning.

 

Yea--this could be a very good tip. I used a MC that I had quick had access to--
It takes considerable pedel pressure to make the brakes work as it is now and very little foot pedal travel occurs.

I wonder if other MCs have the same mount bolt pattern?


IF not I could redrill-- or make an adapter.

 

Why not just put on the adjustable proportioning valve?

It's not very expensive or difficult.

And it may keep your jeep out of the back of a BMW.

I put mine under the dash so I can reach it from inside but it may be even easier to frame mount it. Once you get it adjusted you don't mess with it much.