Rear Disc Swap

[Daedalus]

Anyone know if it'd be possible to swap the rear drums out for discs from the Cruze?

The Cruze has a twist beam rear suspension like the Sonic (though some have Watts linkage and some don't) and some trims come with rear discs or rear drums.

Attached here are the two rear suspension diagrams for a 2011 Cruze. It looks like if you can easily swap from drums to discs, that it might be possible to take the rear discs from a Cruze and put them on a sonic.

With Drums

With Discs

(I only wish I had a rear suspension diagram for the Sonic to compare)

They are so similar it looks like the swap would be an easy bolt off, bolt on affair (from Cruze to Cruze). Remove all Drum parts down to the twist beam, put on caliper carrier, dust shield, hub, disc, caliper, and then connect everything back up (speed sensors, brake lines).

Does anyone know if the rear wheel hubs on the Sonic share the same part number as those on the Cruze. If so, that may be a big clue into whether these parts will swap out.

On a slightly related note, does anyone know the disc diameter in the front for both the Cruze and Sonic? If the Cruzes are bigger, that might open up the possibility of an OEM Big(ger) Brake Kit.

 

[Daedalus]

Thats the Sonic's rear suspension but it doesn't tell much.

 

[laborsmith]

Sonic Front 10.9
Cruze Eco Front 10.8 Rear 10.5

Per Car and Driver November 2011

Laborsmith

 

[Papasonic]

There still is more to the swap; The hydraulic system would have different size master cylinder pistons, and a differently calibrated proportioning valve.

You would also have to address this issue.

 

[Daedalus]

There still is more to the swap; The hydraulic system would have different size master cylinder pistons, and a differently calibrated proportioning valve.

You would also have to address this issue.

Possibly. The sonic and the Cruze might share master cylinders and prop valves.

EDIT: I just did a quick search. The master cylinder is the same between all Cruze models whether it has rear discs or drums. Also it looks like the Cruze has electronically distributed brakes (like my old Legacy GT and WRX had) so it'll distribute more or less stopping power to the front or rear automagically. This part is also the same for all Cruze models.

Here are some images:

Part #12 in the first image and #11 in the second is the Electronic Brake Controller thingy.

Disc

Drum

Unfortunately, one thing that IS different between the Cruze discs and drums are the brakes lines. That might not be that difficult of a fix though.

Still a lot to think about. Especially since I don't even have a Sonic yet (and am unsure that I will anytime soon). Just brainstorming.

 

[Danny5]

Unfortunately, one thing that IS different between the Cruze discs and drums are the brakes lines. That might not be that difficult of a fix though.

They're not as different as you may think. The drum brakes have solid lines, with a flexi line for suspension movement, while the discs have a flexi line for suspension movement, and then a flexi line for the floating caliper. This is a pretty minor difference...

 

[oldertech]

Have you thought about maybe the ecu could have different instructions for the drums vs. discs for the antilock/traction control to work properly?

 

[laborsmith]

The possibility of importing the Cruze rear disc brake system to the Sonic is intriguing. I see reprogramming the BCM as one of the lessor obstacles. Several years ago I put a Wilwood big brake fronts kit on my Cavalier, and it worked very well, but I was never able to find a kit to upgrade the rear drums to discs. Using the Cruze rears as if a kit makes the upgrade sound feasible.

I have found rear disc brake upgrades, but the ones I have found are not drums to discs but rather larger disc or more pistons etc to replace OEM discs.

On second thought, the BCM may be a greater obstacle than I above asserted due to safety considerations. Hopefully we can keep this discussion going and maybe come up with a way to make it work.

Laborsmith

 

[BoG233]

I did a rear disc brake swap on my 99 dodge ram and my 95 jeep wrangler . Both kit incorporated drum e brakes in the center of the brake and had a disc around the out side .
The 99 dodge had the anti lock brake censer on the pumpkin . And no anti lock on the jeep . If a brake company comes up with a brake kit it will have to include a reflash of BCM . and the lector ring relocated I think .

 

[Daedalus]

I'm not sure that flashing or replacing the BCM is necessary in this case. We are not substantially (or if at all) upgrading the braking performance of the car. Just replacing the rear drums with a better looking and easier servicing unit. Not only that but the rear brakes are not responsible for much of the brake power.

Subaru has been using Electronically Distributed Braking for many years now. This hasn't stopped the WRX guys from upgrading their smaller discs and calipers to the larger H6 (Legacy) or STI pieces.

 

[Daedalus]

Parking brake cables are different between disc and drum on the Cruze. Though if you see, the rear drum or caliper are used to handle the parking brake duty. Not a separate inner-disc system.

Drum

Disc

 

[Gimpster]

Looking at the Cruze EPC diagrams there, I'm guessing this will be similar to swapping a 92-00 Civic to disc... assuming the Cruze parts fit. In that case you simply unbolt the drum spindle from the trailing arm (torsion bar in our case) and plop on the disc spindle/hub/rotor. I guess who knows though until you dig into this more.

Do you have an EPC diagram of the hydraulic system? Most cars I've swapped to disc in the rear all that was really different was the rubber line itself.

I also agree that BCM might be moot assuming you get all the right reluctor setup on there, not that huge of a change?

 

[laborsmith]

It will be several weeks, but when the Borla full bolt on exhaust comes in, I will go over this idea of using the Cruze rear discs with my mechanic. If this is workable, it could definitely be better than waiting for some company to come out with a kit.

Laborsmith

 

[Daedalus]

Looking at the Cruze EPC diagrams there, I'm guessing this will be similar to swapping a 92-00 Civic to disc... assuming the Cruze parts fit. In that case you simply unbolt the drum spindle from the trailing arm (torsion bar in our case) and plop on the disc spindle/hub/rotor. I guess who knows though until you dig into this more.

That's the hope!

Do you have an EPC diagram of the hydraulic system? Most cars I've swapped to disc in the rear all that was really different was the rubber line itself

For the Cruze I posted them here: http://www.sonicownersforum.com/forum/post7928-5/

I can't find any for the Sonic yet.

 

[Daedalus]

It will be several weeks, but when the Borla full bolt on exhaust comes in, I will go over this idea of using the Cruze rear discs with my mechanic. If this is workable, it could definitely be better than waiting for some company to come out with a kit.

Laborsmith

This would be awesome! Maybe bring some of the diagrams in with you to see what they say.

 

[Daedalus]

This discussion is now moot since the Sonic RS has rear discs.

 

[Danny5]

This discussion is now moot since the Sonic RS has rear discs.

It's not moot until someone has done the swap! We still need part numbers and what is inolved.

 

[laborsmith]

While waiting for RS parts availability, there is an interesting development being discussed on CruzeTalk: Rear Brake Conversion

Laborsmith

 

[sonicR]

This is why I joined.. Thanks fellas, this sounds good. Ill see wanr I can do on my end

 

[SonicBoy24]

It will be several weeks, but when the Borla full bolt on exhaust comes in, I will go over this idea of using the Cruze rear discs with my mechanic. If this is workable, it could definitely be better than waiting for some company to come out with a kit.

Laborsmith

Any updates on this?