Commodore Diff & Front Brake set-up

[DN2168]

Hi all, I have been told that a VN Commodore diff will fit under an FC if you cut the long side of the diff housing to the same length as the short side, then use 2 short axles. Only have to cut one side of the diff.

Has anybody heard of this or done this conversion?

Next question, what is needed to fit Commodore front brakes, I know Hoppers do a kit, but with work I haven't been able to get them on the phone, so I thought someone on the forum would know....Ken . I have done a search but would like to know what dramas others have had or if it is straight forward.

Thanks,
           Dean.

[FC427]

Hi Dean I run a Commodore diff I used the short Axel for the long side  Housing has to be shortened on both sides to suit FC  and the long Axel is then shortened and resplined [$100] for the short side .... thats what I did .......Front rotors go straight on HQ to WB stubs I run 290mm rotors and 4piston calipers that bolt to original holes but you would need to make a mount to fit VB VR  Commodore calipers.. I have a pair of these mounts  somewhere  but you may as well mount up AU 2 calipers  if you have to make mounts .......FC427.......

[FCOV6]

Hi Dean I run a Commodore diff I used the short Axel for the long side  Housing has to be shortened on both sides to suit FC  and the long Axel is then shortened and resplined [$100] for the short side .... thats what I did .......Front rotors go straight on HQ to WB stubs I run 290mm rotors and 4piston calipers that bolt to original holes but you would need to make a mount to fit VB VR  Commodore calipers.. I have a pair of these mounts  somewhere  but you may as well mount up AU 2 calipers  if you have to make mounts .......FC427.......

 FC427, i am interested in the VN or later commo diff to FC, i'm not familiar with the diffs but is it just a matter of removing the axle tubes from the center shortening and then re fitting ? Is it VN rotors that fit the HQ stubs along with HQ-WB calipers ?

thanks,
Nick.

[mcl1959]

Nick - no commodore rotors will fit with HQ - WB calipers, Apart from the rare 4 cyl Comm rotors, all the early Comm rotors are 22 or 23 mm thick. HQ rotors have a min thickness of 24.5mm so the Comm rotors are below min thickness for the HQ caliper. Will work OK when pads are new, but when pads wear down the pistons are in danger of popping out of the caliper - not what you want at 100 kph!!!!!!!!
Apart from this the offset of the rotor is different so the caliper wont bolt up without spacers.
I have seen cars come into H/S with all sorts of dodgy brakes cobbled together and people wonder why engineering reports came into existence.   In fact I remember a Gold VL Comm on the cover of Street Machine mag with calipers mounted upside down and it was given awards for top engineering.

Re the diff - you make it sound simple but effectively yes that is what you do. Has to be cut squarely and welded back without warping the housing

Ken

[FCOV6]

No worries Ken, i'm not about to as you say cobble a few parts together , i'm working out what can be mixed and matched effectively. When this thing gets on the road it will carry us and my 2 little girls so i wont be doing any dodgies on the brakes. So if the HQ-WB calipers are out will the matching commo calipers bolt up to the stubs ?

[mcl1959]

No unfortunately GMH changed the mounting hole dimensions with Commodore. The one saving grace is the CRS dropped stub (if you can get them anymore) These were available with early Holden caliper mount on one side and Comm on the other side. These allow you to fit up Comm brakes onto the dropped stubs as a bolt up arrangement. This is what I have on my FE.

You can make mounting plates (CRS have a kit) but I never really liked this conversion very much because the difference in the dimensions is only half a hole, so mounting a plate is a bit difficult. This is why CRS use a cut down drum stub axle with a ring bolted to it. The bracket is then bolted to the ring.

Ken

[FC427]

FC427, i am interested in the VN or later commo diff to FC, i'm not familiar with the diffs but is it just a matter of removing the axle tubes from the center shortening and then re fitting ? Is it VN rotors that fit the HQ stubs along with HQ-WB calipers ?

  Hi Nick I never mentioned the use of HQ to WB calipers and Commodore rotors DO go straight on to the stub axles I use these rotors and a set of OUTLAW 4 piston calipers that bolt straight up to the stubs with no modification to stub axle or caliper .....When shorting the VN VP VR VS  Commodore biff it is a lot easer to cut the ends off and leave the center alone ......FC427......
Nick.

[FCOV6]

 Thanks, i'm going blind trying to take all this in !

[NES304]

  In fact I remember a Gold VL Comm on the cover of Street Machine mag with calipers mounted upside down and it was given awards for top engineering. ::

WTF?!!!

[mikey]

In fact I remember a Gold VL Comm on the cover of Street Machine mag with calipers mounted upside down and it was given awards for top engineering.
Ken

Ken,
        I really don't see the problem here, just have to roll the car onto it's roof to bleed the brakes.

Simple really.

Cheers  M

[FCOV6]

I will be going down the HQ stubs commo rotors and commo diff once i collect all the parts, but for now if i fit a commo master/booster will that still work with my current LJ rotors/calipers and HR rear drums ?

[FC427]

FCOV6 I use a VH Commodore V8 booster and a 1'' master cylinder.......FC427....

[FCOV6]

FCOV6 I use a VH Commodore V8 booster and a 1'' master cylinder.......FC427....

 Yeah, i searched and read all the posts on brake upgrades but what i need to know is if i keep my current setup, will a commo master/booster be suitable and not have to be replaced when i fit commo discs f/r ? The fronts will be fine but not sure about the difference swapping rear drums to discs will make if i have the correct wheel cylinders to suit, i guess Ken is the man i need to ask.

[FC427]

 Fronts should  be OK ,Don't know how the rears will go because the 1'' mastercylinder has a built in proportioning valve and you should have the small disc brake rear wheel cylinders fitted  ......FC427.....

[FCOV6]

Fronts should  be OK ,Don't know how the rears will go because the 1'' mastercylinder has a built in proportioning valve and you should have the small disc brake rear wheel cylinders fitted  ......FC427.....

 Thats why i added this -The fronts will be fine but not sure about the difference swapping rear drums to discs will make if i have the correct wheel cylinders to suit.

[mcl1959]

The Commo master cylinders are different for disc/drum and disc/disc set up - the proportion of front / rear ratio is different and a residual valve is fitted in the disc/drum master cylinder. When you change to disc rear the easiest thing to do is swap over the master cylinder at the same time. Be careful with pedal ratios with 4 wheel disc set ups as well. HZ for instance uses a different pedal box for disc/disc cars - if you fit a disc rear end to a HZ, you end up with a soft pedal feel with long travel without the pedal box and booster change.
VT onwards master cylinders are good because they have a "fast fill" section of 1.25 inch at the start of the cylinder followed by 1 inch diameter after that - they give a much firmer feel pedal. Compare a VS Commo pedal feel with a VT pedal feel and you will see the difference.

Ken

[FCOV6]

Thanks Ken, that makes sense, at least then if i stay with the same vehicle/make mc and booster i wont have to change any piping when changing to rear discs.

regards,
Nick.