Rear brake upgrade

[Singtoe]

This just came to me. Nobody has upgraded the rear brakes on the 4Runner besides the really complicated disk brake retrofit. Well anywho, I have the answer to the Tundra front brake upgrade.

Bigger rear wheel cylinders.

The stock 4Runner has 13/16" bore wheel cylinders while the same year Tacoma has a 7/8" bore wheel cylinder.

This is a drop in swap with no modications. This will give braking that will match the upgraded Tundra brakes.

 

[SIN-Japan]

Do you mind throwing some pics up of the process?
Very interested!

 

[ShannanC]

[MENTION=59542]Singtoe[/MENTION]

Will a larger master cylinder be necessary or beneficial?

 

[FreshSeabass]

Yes yes, we are all listening! :hungry:

 

[T4R2014]

Have you actually done it and noticed a difference?

 

[A.Wilson013]

Is a 1/16" larger bore really that big of an upgrade? I mean, I am sure anything helps, but that seems quite minimal.

 

[mtbtim]

Is a 1/16" larger bore really that big of an upgrade? I mean, I am sure anything helps, but that seems quite minimal.

I'm sort of wondering the same thing. Also, from what I gather, around 70% of the breaking power comes from the front disk brakes and the other 30% comes from the rear. So, I'm wondering if you can even detect any benefit if you change out your wheel cylinders.
[MENTION=59542]Singtoe[/MENTION], are you saying you've done this already and have experienced improved braking or is this just you hypothesizing a benefit from this modification?

 

[A.Wilson013]

I'm sort of wondering the same thing. Also, from what I gather, around 70% of the breaking power comes from the front disk brakes and the other 30% comes from the rear. So, I'm wondering if you can even detect any benefit if you change out your wheel cylinders.

[MENTION=59542]Singtoe[/MENTION], are you saying you've done this already and have experienced improved braking or is this just you hypothesizing a benefit from this modification?

I think he's back at it again with the sick April fool's day jokes... =p

An ~5% increase of something which think controls ~30% of the braking... That's not much of a difference.

 

[csp]

Pressure drops as the size of the cylinder increases.

Meh.....

 

[Konkordmusk]

[MENTION=59542]Singtoe[/MENTION]

Will a larger master cylinder be necessary or beneficial?

A larger master cylinder will yield less pressure at a given pedal distance, but overall less distance to actuate the brakes. A smaller master cylinder is just the opposite.
I don't think 1/16" of a bore size difference is enough to matter, but for arguments sake, if it were any bigger, there would be brake balance issues.
It comes down to hydraulic mechanical advantage; any old bottle jack is a great example of this. You see how those tiny little pump handle cylinders (Master cylinder) push pressure to a much larger cylinder (slave cylinder) and create enough force to lift a vehicle? If the cylinders were the same size, you would have a 1:1 ratio with no advantage. When you make the slave cylinder larger (or the master cylinder smaller), there is more hydraulic pressure on the surface, increasing your mechanical advantage.
However, the larger the slave cylinder, the more pressure it will take to feed the cylinder with enough brake fluid to operate, robbing the front brakes of their braking efficiency. Using the bottle jack as an example, this would mean you would need many more pumps in order to achieve the same lift. Translating to vehicle brakes, this means more pedal travel.
Again, with a 1/16" bore difference, there should be no noticeable difference.

I would never want to dramatically increase my rear braking power unless I've substantially increased my front brake bore. When braking, there's a lot of weight transferred to the front and I wouldn't want to rob the front brakes of any power because I've installed larger bore rear cylinders.

 

[Singtoe]

But every one is forgetting that when you upgrade to tundra calipers, you are using bigger Pistons giving you even more front brake bias.


The Taco was designed to carry more weight then the 4Runner thus the bigger rear brakes.

My rear cylinder is leaking and I have the taco cylinders ordered.

 

[volkinator]

But every one is forgetting that when you upgrade to tundra calipers, you are using bigger Pistons giving you even more front brake bias.


The Taco was designed to carry more weight then the 4Runner thus the bigger rear brakes.

My rear cylinder is leaking and I have the taco cylinders ordered.

I'm excited to hear if there's any difference. Most of us unworthy members don't need as much stopping power as you do.

 

[I_bRAD]

I think he's back at it again with the sick April fool's day jokes... =p

An ~5% increase of something which think controls ~30% of the braking... That's not much of a difference.

To be fair, the braking force is a function of the piston area, not diameter so in reality it's more like a 15% increase.

 

[csp]

Front/rear bias is controlled by the proportioning/combination valve.

Braking hydraulics are complex. It isn't as easy as installing something bigger and therefore it must be better.

 

[SnowLizard]

interesting.... but
:worthless

 

[Drcoffee]

The question isn't can you go bigger on the back, but should you go bigger on the back?

I am no brake expert but I do know that the rears should never lock up sooner than the fronts. The ass-end will become unstable. You want the force to be on the fronts and the rears to drag like a parachute to keep the vehicle in a straight line. This is one upgrade I would not do.

 

[StreetCreeper]

interesting.... but
:worthless

I agree completely! Until we see some wheel cylinder pics, I'll post a picture that I find strangely interesting...uh look at all that...uh seaweed!

 

[Drcoffee]

What seaweed? Oh mama! :hungry:

 

[poleclimber63]

Subscribed!

But every one is forgetting that when you upgrade to tundra calipers, you are using bigger Pistons giving you even more front brake bias.


The Taco was designed to carry more weight then the 4Runner thus the bigger rear brakes.

My rear cylinder is leaking and I have the taco cylinders ordered.

I've been following your posts on this forum for years and I have a great deal of respect for your contributions!! So, thanks, ahead of time!!!
If and when you do this, I'd be very interested in how it behaves and any issues you have!
I did the TBU last Fall and love the increased stopping power and brake response--- looking forward to the extra braking, while towing!

I just finished a drum to disc brake upgrade on my sons' Mitsubishi Eclipse and I'm really impressed by the improved brake response, yes, the pedal response changed ie. slightly softer and slightly more travel but it's not a concern. Also, a workmate mentioned what he did to his 01' Dodge, a few years back, to settle down his rear end swing. His truck had drum brakes (like our 4Runners) and he swapped out his wheel cylinders to ones with a 20-30% larger area. He says it really stabilized the rear providing significantly more braking response to the rear. Believe it or not, he used 94' Chevy 1 ton wheel cylinders on his 01' Dodge 3/4 ton Cummins, with only a minor brake line mod, without having to fool with the proportioning valve.

so, I've been pondering your exact idea! I've just thought about it and done no research as yet.... your proposition maybe just what the doctor ordered!

I do acknowledge comments by other members about master cylinder sizing, balancing issues and I have observed changes in pedal response after the TBU.:rain:
However, I'm very interested in seeing how this plays out. If you pursue this, please update us!!!!
op2:

 

[JayRolla]

I've been following your posts on this forum for years and I have a great deal of respect for your contributions!! So, thanks, ahead of time!!!
If and when you do this, I'd be very interested in how it behaves and any issues you have!
I did the TBU last Fall and love the increased stopping power and brake response--- looking forward to the extra braking, while towing!

I just finished a drum to disc brake upgrade on my sons' Mitsubishi Eclipse and I'm really impressed by the improved brake response, yes, the pedal response changed ie. slightly softer and slightly more travel but it's not a concern. Also, a workmate mentioned what he did to his 01' Dodge, a few years back, to settle down his rear end swing. His truck had drum brakes (like our 4Runners) and he swapped out his wheel cylinders to ones with a 20-30% larger area. He says it really stabilized the rear providing significantly more braking response to the rear. Believe it or not, he used 94' Chevy 1 ton wheel cylinders on his 01' Dodge 3/4 ton Cummins, with only a minor brake line mod, without having to fool with the proportioning valve.

so, I've been pondering your exact idea! I've just thought about it and done no research as yet.... your proposition maybe just what the doctor ordered!

I do acknowledge comments by other members about master cylinder sizing, balancing issues and I have observed changes in pedal response after the TBU.:rain:
However, I'm very interested in seeing how this plays out. If you pursue this, please update us!!!!
op2:

I dont understand the 20-30% larger surface area from changing the brake cylinder. All the cylinder does is push the drum breaks against the drum with a little rod. The setup of the drum assembly does the rest of the work. Now if it has more pushing force to cause a harder clamp then it could help. But its not like a caliper where larger calipers can take bigger pads to get more surface to clamp. Larger rear cylinders wont change the pad surface.