Brakes upgrade ??

[Bulto]

I have a Jeep CJ 1979 Dana 30 & AMC20 rear diff. with stock brakes & OEM Brake Booster.

I need more power in the brakes because I don’t lockup my 33” tires.
I try to upgrade my brake system:
I change the OEM master cylinder with a Corvette 1980 Master Cylinder.
I removed the stock proportioning valve, because it’s leak. It was replaced by a Wildwood Engineering adjustable proportioning valve in the rear brake line to balance the front and rear brakes. The front brake lines had been replaced with a single drop brake line ran directly from the Master Cylinder to a split tee & connected to the front calipers.

After these changes the Jeep stops better, but don’t lock my 33” tires.

Any ideas ???

Thanks for any help!

 

[tarry99]

I have a Jeep CJ 1979 Dana 30 & AMC 20 rear diff. with stock brakes & OEM Brake Booster.

I need more power in the brakes because I don’t lockup my 33” tires.
I try to upgrade my brake system:
I change the OEM master cylinder with a Corvette 1980 Master Cylinder.
I removed the stock proportioning valve, because it’s leak. It was replaced by a Wildwood Engineering adjustable proportioning valve in the rear brake line to balance the front and rear brakes. The front brake lines had been replaced with a single drop brake line ran directly from the Master Cylinder to a split tee & connected to the front calipers.

After these changes the Jeep stops better, but don’t lock my 33” tires.

Any ideas ???

Bulto,

So Discs in the front and drums in the back? Correct?

[I]A picture under the hood of the booster would be great.[/I]

Locking up your brakes is of course not how the system was designed coming from the factory with 30-31 inch tires...........versus a larger & heavier 33" tire.
Do you know the condition of the Booster? How is your linings front and rear?

First off if you want more force then a Bigger booster like a two stage versus a single would be in order...............you also need about 15-18 inches of vacuum to make the system work correctly.

You said you recently changed the MC...........what bore size is the new cylinder versus the old one?
A smaller cylinder will give you more force but less volume......less volume in the line may not have enough to stop beings the pistons can only travel so far. This is also effected by worn shoes, drums , pucks and rotors as the pistons have to travel further hence the need for more volume...........
There are some real important calculations that need to be followed.

 

[Torxhead]

I am not sure of the improvements with that master cylinder, but I think you should consider an upgraded power booster. There are a few options here so you should research that. Mikes off-road makes a good one and some guys convert to a YJ power booster.

 

[Bulto]

Bulto,

So Discs in the front and drums in the back? Correct?

[I]A picture under the hood of the booster would be great.[/I]

Locking up your brakes is of course not how the system was designed coming from the factory with 30-31 inch tires...........versus a larger & heavier 33" tire.
Do you know the condition of the Booster? How is your linings front and rear?

First off if you want more force then a Bigger booster like a two stage versus a single would be in order...............you also need about 15-18 inches of vacuum to make the system work correctly.

You said you recently changed the MC...........what bore size is the new cylinder versus the old one?
A smaller cylinder will give you more force but less volume......less volume in the line may not have enough to stop beings the pistons can only travel so far. This is also effected by worn shoes, drums , pucks and rotors as the pistons have to travel further hence the need for more volume...........
There are some real important calculations that need to be followed.
[/QUOTE]


Thanks for your response.

Yes, Discs in the front and drums in the back.

I know that; the bigger tire need bigger brakes.

The booster, it's new. 8" dual diaphragm. Ebay listing: (Jeep CJ Brake booster master cylinder NEW w/valve) but I don't use the valve,

MC: it's 1 1/8" bore vs. OEM master I don't know the bore.

I think that bigger calipers it's the way, but not sure.

Note: If I open the adjustable proportioning valve, the rear tires will lock.

 

[tarry99]

Bulto,

So Discs in the front and drums in the back? Correct?

[I]A picture under the hood of the booster would be great.[/I]

Locking up your brakes is of course not how the system was designed coming from the factory with 30-31 inch tires...........versus a larger & heavier 33" tire.
Do you know the condition of the Booster? How is your linings front and rear?

First off if you want more force then a Bigger booster like a two stage versus a single would be in order...............you also need about 15-18 inches of vacuum to make the system work correctly.

You said you recently changed the MC...........what bore size is the new cylinder versus the old one?
A smaller cylinder will give you more force but less volume......less volume in the line may not have enough to stop beings the pistons can only travel so far. This is also effected by worn shoes, drums , pucks and rotors as the pistons have to travel further hence the need for more volume...........
There are some real important calculations that need to be followed.

Thanks for your response.

Yes, Discs in the front and drums in the back.

I know that; the bigger tire need bigger brakes.

The booster, it's new. 8" dual diaphragm. Ebay listing: (Jeep CJ Brake booster master cylinder NEW w/valve) but I don't use the valve,

MC: it's 1 1/8" bore vs. OEM master I don't know the bore.

I think that bigger calipers it's the way, but not sure.




Well there is no weight back there that's why they will lock up in the rear.

You need to check how much Vacuum you have at Idle?

Bigger calipers could be the way but your missing the point...........all brakes systems have to be balanced by pressure & volume......in order to do so you need to know the size of the MC and the bore size of the front calipers and also the rear wheel cylinder size. Along with that the pedal ratio is also important.
If you were to put a bigger bore piston caliper on it that could make it even worst.
Whats the condition of your linings and drums & rotors?

Not to say your system will not work because it already does............but in order to get to the next stopping level you need to fine tune all the variables.

 

[Old Dog]

Terry is there any good web sites that talk about these things?

 

[tarry99]

Terry is there any good web sites that talk about these things?

Dog,........... I'll try to be short on that question. (LOL)

No unfortunately not..............There is a little info here and there but it's more so related to whatever the vendor is selling............its basically up to the individual to make the decision if it complements there application or not.

No one in sales wants to talk about all the variables simply because there are few that understand them and there are just to many variables to every application.

I have learned this years back when playing with road race cars and picking the brains of factory engineers that build components........The basic principles of Hydraulics are quite simple and we have built a spread sheet that helps us with these calculations.
Simply You have to have adequate volume and pressure to mechanically force the piston to do it's work against a drum or rotor.

If the volume increase's based on distance from the MC to the piston and Piston size also increase's at either end the volume of the stroke in the MC piston bore has to increase also. But once you increase volume you decrease pressure and the fun starts to overcome that. Notwithstanding the increase of rotor size and weight also have to be part of the equation. Even just the wearing of the friction surface's will effect your pedal travel as the piston has a longer distance to travel to do the work.

In a pure mechanical system your pedal ratio has to be correct so that your leg can can overcome the additional force required do the work. In the simplest terms your leg on a 2-3:1 ratio can easily develop 200-250 lbs of pressure. But when increased pressure is needed via the pedal the fulcrum can become to far to travel. Obviously when volumes or pressures exceed whats needed mechanically then a booster is necessary.

On the flip side in a short wheel base vehicle like a Jeep to much pressure will get you into trouble as much as not enough.

So that I don't continue to bore you I'll stop here.

That's really just the basics and in no way have I covered all the variables.

 

[Bulto]

Tarry99:

I read The vacuum in the engine: it's -18psi
The size of the MC it's 1-1/8"
The size of caliper; I don't know, but it's stock calipers & rear cylinders.
Pedal ratio I don't know how to calculate it.
The condition of linings it's good, it be used ±10,000 miles.
Drums are very good, rotors new I used ± 8,000 miles.
Front brake pads: used ± 8,000 miles from advance auto parts.

Note: Another idea for my experience with my Toyota Tacoma, it's about brake front pads. My tacoma have excellent brake performance, but I replaced the front pads with advance auto replacement pads. Not recommended, No lock-up, it don't stop as OEM Pads. After tested, I removed & I buy the OEM brake pads, it lock-up, like new.

Do you know any brand of front brake pads to my Jeep that perform very well?

 

[tarry99]

Tarry99:

I read The vacuum in the engine: it's -18psi
The size of the MC it's 1-1/8"
The size of caliper; I don't know, but it's stock calipers & rear cylinders.
Pedal ratio I don't know how to calculate it.
The condition of linings it's good, it be used ±10,000 miles.
Drums are very good, rotors new I used ± 8,000 miles.
Front brake pads: used ± 8,000 miles from advance auto parts.

Note: Another idea for my experience with my Toyota Tacoma, it's about brake front pads. My tacoma have excellent brake performance, but I replaced the front pads with advance auto replacement pads. Not recommended, No lock-up, it don't stop as OEM Pads. After tested, I removed & I buy the OEM brake pads, it lock-up, like new.

Do you know any brand of front brake pads to my Jeep that perform very well?

Bulto,

Looks like everything in your Jeep is then factory stock.
Vacuum is Ok and the linings are used but OK.

You did say you changed the MC to a Corvette type that is 1-1/8" bore.
I looked up that 1979 Master cylinder and in my books and it says a 1" bore came stock with it.......for both the power & manual brakes.
Now not to say that a 1-1/8" bore will not work but here again you get into the larger bore more volume , but less pressure syndrome.

1979 was also the first full year that AMC downsized there rear brakes to a 10" x 1-3/4" shoes which were a little small since in 1977 & the better part of 1978 they were using 11"x2" shoes in the rear coupled with there large 3.10 bore piston caliper and 1.250 thick vented rotors up front. Commonly known in Jeep circles as the "Big Brake" Package.
Also in late 1978 and 1979 AMC also downsized there from rotor to 7/8" thick non-vented.
Also interesting enough in 1977 & 78 when Jeeps were equipped with the large brake option (Big calipers & large Vented Rotors & 11"x2" shoes) they were using a 1.062 1-1/16" bore Master Cylinder. When the same Jeeps in late 78 went to the smaller caliper and non vented rotor and the 10"x 1-3/4" shoes they again used the 1" bore master.

Could the bore size be hurting you a little? Probably
Could just the 33" tires be also hurting you some? Yes

I think you brake system is at that point of diminished returns .........the weight ratio it was originally designed for has been exceeded by your bore size being a little to large pressure wise coupled with the extra size and weight of the tires.
You could try a more aggressive friction material on your linings, might help?

Next step might be to upgrade your system.

 

[Bulto]

Tarry99:

Thanks for the info. I save to a file for reference.

My 1979 have rear brakes 10" x 1-3/4" shoes, but in the front have the 1.250 thick vented rotors with the large 3.10 bore piston caliper. I don't know if the previous owner replace them.

My uncle have a 1978 with the stock brake system (Big calipers, large Vented Rotors & 11"x2" shoes) with 31 tires, it have the same problem don't lock-up the fronts but lock-up the rears, same that my 1979.

The difference when I changed the OEM MC with the corvete MC it's that my leg put less force to the brake pedal to stop the Jeep.

I dedicated lot of time to search info to upgrade the brakes, I found many ideas to convert rear to disc brake, (calipers of 300zx, suzuki, cadilac, etc.) but I don't need, because my rear stop very well. (lock-up the 33").
Front upgrade I don't found it.

 

[paparooster]

there is a upgrade out there The Jeep Guy Home Page go to brakes . I just purchased the booster and master , then the gm style brackets , 78 CJ7 the calipers are from a 74 to 77 chevy 4x4 1/2 ton you can get local . I have a 78 cj7 . brake system in my opinion is the sh#@*#t ever made Again in my opinion . my post on my brakes will be updated shortly been on camping trips .

 

[Bulto]

paparooster, Thanks for the info.

Do you know if the GM Style Bracket fit in my '79 Jeep with Dana 30 ?

I check the caliper in Advance Auto Parts, it's true the '78 calipers are a lot bigger than '79.
So, I check my calipers, I 'm wrong, the are the small 2 bolt style, as said tarry99.

 

[paparooster]

I just bought them brackets for my wifes 78 CJ7 with a Dana 30 in it . They fit tight when putting over spindle bolts. Here's some picture of brackets and master combo

 

[Bulto]

paparooster:
Thanks for the pictures.
I think that I have the same Booster & MC Combo, see my picture.
So the only question it's: the GM Style brackets fit in my 1979 Dana 30 ? I need see my Dana 30, to verified this.

 

[paparooster]

• Use on disc brake conversions on Dana 25,27,30, early Ford 1/2 ton This is from his site ...Use on disc brake conversions on Dana 25,27,30, early ford 1/2 .... Here is his # 1-503-869-2072 to call and confrim this would fit .​

 

[paparooster]

sorry about the double copy of what to use on

 

[Bulto]

Hi
Searching a Big Caliper for my father's Toyota Land Cruiser FJ40, I found my Big Calipers upgrade for my Jeep CJ

The list for my Calipers Upgrade:
1. 4-piston style calipers from Toyota T100 4wd 1995 with pads & bolts
2. 3/8 Steel plate to adapt it
3. Custom brake lines
4. Patience and a long time to find the perfect position...
5. couple of

Now, the brake system easily locks my 33's tires in the front.
So, next: rear disc upgrade...