BRAKE BOOSTER NEED HELP ASAP!!

[mandoneer]

do any of you know the mounting bolt pattern for a jeep brake booster mine went belly up and I have a ford unit in a box and want to use that but dont know if the bolt pattern is similar I would measure it myself but I am at my shop and my jeep is at my house

[The Anti-Chrysler]

Booster for what??? The Commando? I'm pretty sure it's Jeep only.

[carrotman]

I beliebe that my 76 brake unit was made by General Motors, so you would probably have better luck adapting a GM unit on your Jeep rather than the Ford. But given enough time you can make anything fit. You just have to drill out some new holes and get an adjustable proportioning valve from Summit.

[mandoneer]

thanks for the response but I whent ahead and measured it (had to go home to do it ) and the bolt pattern is the same , the length of the push rod is the same and the dia. of the booster is the same ,the leingth of the booster and master cyl. is a little longer but not much (for commandos at least, not sure about wags )BTW the booster is for a 66 t-bird (I think it is the same booster used up to 75 in all fullsize cars and trucks) so if ford is cheaper than a stock unit it would prolly fit but you would have to take the measurements yourself to know for sure but the left to right pattern measurment is 3.75 and the top to bottom measurement 3.5 on the mounting bolts and the pushrod to the center of the hole is a just at 3 from the back of the booster

[mandoneer]

and why would I need a proportioning valve ? stock it only had a diverter block not a valve

[carrotman]

You would need a proportioning valve if you had front discs, since the Ford unit would have different pressure settings. I guess you have drums all around. I wonder if the Ford unit was set up for drums or front discs? Will make a difference in pressure to front and back. Can you upgrade to front discs?

[mandoneer]

yea the ford unit was set up for disk front and drum rear and I will be doing a disk conversion in a few months or so but right now I have 4 way drum, will I need a proportioning valve? and if so would I need it on the front or rear breaks -cause I know that it takes less pressure to run disk than drum so would I need to put it on the rear ? also I could put the stock master cyl on the ford booster (mounting holes are the same also)but I ned to rebuild it first .Thanks for all the help

[mandoneer]

once I have it on I will test the pressures and if they are the same than I can just go with it ,right? and if they are diff. than should I run the harder pressure to the rear or front with a proportioning valve

[carrotman]

As I understand, disc brakes stop harder, but require more pressure. According to the 76 TSM, "the metering valve delays full hydraulic fluid pressure to the front brakes until the rear brakes overcome retracting-spring tension and the rear linings make contact with the rear drums." With an adjustable valve between the front and rear, you can take the Jeep to a parking lot and adjust the pressure so the fronts and rears lock up at the same time.

[mandoneer]

is that why when I put the booster and master cyl on fluid only came out of the rear port? and not both -(there is a metering valve in the master cyl for a 66 'bird ,I know this cause the 66 'bird definatly dose not have a proportioning valve -but on a side note when I push the pedal down it dosnt come back up on its own -do you think that this is because I dont have the lines connected or a return spring (but I thought the spring was only for making the brake lights turn off not to return the pedal to an up position )and when I connect the lines (or at the least put a plug in the rear port will it transfer to the front ( I dont remember having this prob on the last master cyl and booster I put on the 'bird)or do you think I should just rebuild the jeep master cyl and put it on the ford booster cause that was the reason that I started doing this ( the booster was bad not the master cyl . thanks again

[mandoneer]

and also why would I want them to lock up at the same time I thought that you wanted the fronts to lock up just a hair earlier than the rear ?

[carrotman]

On my motorcycle, I can stop the front discs, or rear disc, or both. In a panic stop, I hit them both, including the clutch lever. I can see the benefits of having the front or rear brakes come on first on your Jeep, but I think Jeep had it right with the rears coming on first, especially on icy conditions. Since it may be a while before you do the front disc swap, why not put the Ford booster on your Jeep cylinder now?

[mandoneer]

but the actual braking force is alot slower with a drum set up than a disk and that is why the rear drums engauge first , not because they actually stop first but because they take more pressure to actuate and apply less stoping force whal braking and if you get in your jeep and get to speed and slam on the brakes you will notice the front end actually does a small nose dive and this is because the rear breaks dont lock up at the same rate witch is what the proportioning valve keeps in check --just because the residual spring pressure is overcome first dosnt mean that the rears are actually locking up / if they did lock up first than you would have the WORST panic breaking handleing and your rear end would slide , the reason the fronts lock first is they make it so the rear end is alot less likely to slide out and therfor gives you better handeling (I use the word lock-up but in all actuality you dont want your braking pressure to be so great that the wheels actually stop moving when you put on the brakes) aside from the loss of handleing the heated rubber actually causes a gas barrier between the tire and the street and in effect lets you slide farther than if your brakes didnt lock up - this is only in a higher speed aspect of the whole picture (at 5mph if you slam on the brakes they will lock up but wont hardly slide cause the kenetic velocity of the jeep isnt as great . DONT read this wrong I truly appriciate the help on this matter and the ideas that you have givin me thanks

[mandoneer]

and the reason it does this in a drum setup is because the lines are ALOT shorter to the front brakes and even though the fluid dosnt compress much it dose compress some and the more fluid will compress more so lets assume that one foot of fluid compresses 1/64 (in a brake line ) than to the front lines (lets assume you have an equiliser link like the rear ) to each drum you are lookin at about 5 feet and the first 2 is shaired so that would be 1/8 of total compression (I dont know the actual numbers but the idea is the same ) to the rear you have 7 feet of shaired line and 6 feet of indiviual line so you would have 13/64 of compression witch would be almost 1/3 of an in so you can plainly see why the fronts would engauge first, see what I am sayin ?

[carrotman]

You are correct, if the master cylinder is the old single cylinder. Is that what you have now? In the newer dual master cylinder, the front and rear cylinders can have different diameters, as can the front and rear slave cylinders. Then physics takes over. Larger piston pushing a smaller piston, increasing pressures, and all. Getting back to a motorcycle with individual front and rear brakes, my legs are stronger than my fingers, so it's easy to lock the rear wheel in panic stops. The back end tries to swap ends with the front. Kind of scary. You could get the proportioning valve and plumb it in to the rear brakes with the adjusting screw under your seat, and you could adjust the pressure so the rears come on hard after the fronts.

[mandoneer]

check this out - after I put the ford booster and master cyl on the commando I started looking at the jeep unit and found a few things that I thought were interesting #1 the P.O. had run the rear port to the front lines and visa versa #2 the booster held vaccum just fine #3 the P.O. didnt remove the pushrod retainer (For manual brakes ) and it was holding the booster valve closed #4 both left and right wheel cyls. were rusted sand not mooving so I got a new jeep master cyl and both wheel cyl and moved the lines to the right places on the new master cyl , I havnt quite finished the change out but i THINK THAT IT ALL MIGHT WORK PROPERLY ONCE i AM DONE WITH THE ORIGIONAL PARTS ! TALK ABOUT A WHOLE CAN OF WORMS HUH !!and my master cyl is the dual thanks for all the help