FE-FC Holden Discussion Forum

Hi,

I am currently dismantling a HR rear end that I will be fitting to my FC. I am wondering whether I will be able to use the HR rear brakes or whether I need to fit HT HG brakes. The reason that I ask this question is that I wish to run HK-WB stubs with P76 discs, Ideally HZ alloy calipers, Holden 1" master cylinder and HT HG double diaphragm booster.

The other question is will the HT HG brakes fit onto the HR housing? Will I also need to run a proportioning valve?

Any thoughts on the above would be muchly appreciated.

Keith

I have LH Brakes on the front of mine and I am using HR (Disc front) Drum brakes on the rear.
Previously I had LC brakes on the front and had no problems over a few thousand miles of travelling.

The HR rear brakes will be fine. I think the double diaphragm booster is an overkill though and will take up a lot of room in the engine bay. A single booster will be just as good or one of the 7 inch double boosters would also be a lot less bulky.

You could run a HQ proportioning valve just to make sure rear brakes don't get too much pressure under emergency stop.

A lot of people don't understand the function of a proportioning valve. They leave it out and give the car a drive and all feels fine so they think it is not needed at all.
The only time a proportioning valve comes into play is under a very heavy brake load and its function is to limit pressure to the rear wheel cylinders under high load and therefore stop rear wheel lockup in an emergency. Rear wheel lock up is the last thing you want in an emergency as this gives the vehicle every opportunity to spin around out of control.

Ken

Thanks for your reply Ken,

My major concern was that as I will be going to 14" rims, the HR braking area would not be big enough and the additional tyre height would create extra leverage on the rear brakes, thus getting to the point it would be almost impossible to lock the rear wheels due to the additional leverage created by going to the 14" inch wheel. I understand that the rear brakes are 9" or 229mm in diameter, but I do not know the surface area of the brake shoes.

I have compared the original 6.40 x 13 diameter of 23.54 inches, which when converted to metric equates to aproximately 598mm. The tyre that I am thinking of running on the rear would probably be a either a 215 or 225/60/14 with either 616mm or 622mm diameter respectively.

By increasing the diameter of the tyre, I don't know how much extra leverage that would create, and therefore would I need to go to the HT HG 10" drums, again not knowing the surface area of the shoes and the potential increase of braking effect.

I also understand that the double diaphragm booster is probably overkill as you suggest. I am also aware that one would only have to "breathe" on the pedal to make it stand on it's nose. I also understand that the FC are a far light car than the HT HG, that the brake system was designed for. I take on board your point about the proportioning valve, but would there be too much pressure with HR brakes with the additional leverage that would be created by fitting the 14" rims.

Keith

Hi Keith

Before we started modifying the van, it ran a HR diff with HK-TG drums on rear and had HK-TG discs on the front.  So to answer one of your original questions - yes, the HK-TG drums will bolt straight onto a HR diff. 

In relation to the need to run a proportioning valve - the use of an adjustable proportioning valve is probably a good thing to make sure the back brakes don't lock up.

In changing to 14" rims and your proposed tyre sizes, any leverage issues with HR brakes would probably be marginal as most of the braking force will be on the front discs.

John

Keith if you are going to use a commodore 1'' master cylinder as you mentioned  it comes with the proportioning valve built in to it so no need to fit an in-line one bias should be OK ........FC427.......

Gidday Keith

Another thing you will have to consider is that the offset of the HT backing plate is too deep and you will have trouble with putting the drums on. I solved this by using a HZ backing plate which has a shallower offset and required no further mods. everything else is HT.

HTH


Denis