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LJ Standard disc Brake Improvements

LJ Brakes LC Disc

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#26 grumpy xu1

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Posted 07 December 2023 - 10:37 PM

These guys could be worth a call
https://www.vmaxbrak...-xu-1-1972-1973
 
https://wolfracingpr...-1-my70-74.html


Buy the vmax i reckon.

#27 salamiman

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Posted 08 December 2023 - 08:15 AM

Are you thinking the vmax would hold up better to fading than the 12.7 drilled, Gary?



#28 salamiman

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Posted 08 December 2023 - 10:09 AM

LH/LX/UC disc brake rotors fit straight onto LC/LJ stubs.
 

Dave, can these be fitted with LJ calipers?

 

https://dba.com.au/p...-rotor-dba010x/



#29 rexy

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Posted 08 December 2023 - 01:00 PM

Milled HQ disc with any HQ style caliper you like. 



#30 salamiman

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Posted 08 December 2023 - 03:20 PM

Milled HQ disc with any HQ style caliper you like. 

Hearing you rexy.

 

But want to keep girlock calipers, 108 pcd, & be able to fit 13 inch wheels.(dont want much).

 

Was hoping for drilled XU1 disc's, but not available.

 

Would almost give drilling them myself a go, if I had a pattern, but prob not the smartest of ideas.



Start the engine and let it idle to create vacuum in the booster. Turn off the engine and wait a minute, then pull the hose and check valve from the booster. You should hear the booster take a gulp of air as soon as the check valve dislodges from the grommet. This indicates the booster and check valve are holding vacuum. Refit the check valve and hose to the booster, start the engine and let it idle to replenish the vacuum. Turn the engine off and depress the brake pedal, release and depress again, by the time you release and depress the pedal a third time you should notice the brake pedal become harder to depress as the booster runs out of vacuum.

With the engine idling, depress and release the brake pedal rapidly. You should notice the engine idle quality will deteriorate as the manifold vacuum tries to keep up with the demands of the booster.

To my knowledge if your brake booster behaves as described in the aforementioned tests it is OK.

 

Finally, with the engine idling, have an assistant depress and hold the brake pedal whilst you listen to the rear of the booster. You should momentarily hear air being sucked into the rear of the booster as the pedal is depressed. If the sound stops the booster is good, if the sucking sound is continuous until the brake pedal is released or does not stop even after the pedal is released then the rear seal has failed in the booster.


 

Thanks for this Dave.



#31 yel327

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Posted 08 December 2023 - 04:53 PM

Why don’t you just machine down some HT GTS350 or HG rotors?

https://www.rarespar...-front-ht-hg-v8

Or even a pair of these:

https://www.vmaxbrak...shoC0k8QAvD_BwE

#32 claysummers

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Posted 08 December 2023 - 06:23 PM

You would have to use ktg calipers…………


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#33 yel327

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Posted 08 December 2023 - 06:31 PM

Weren't XU1 discs just machined smaller Holden rotors? 



#34 S pack

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Posted 08 December 2023 - 07:45 PM

Why don’t you just machine down some HT GTS350 or HG rotors?

https://www.rarespar...-front-ht-hg-v8

Or even a pair of these:

https://www.vmaxbrak...shoC0k8QAvD_BwE

I've already posted a link to Vmax slotted XU1 rotors.
 



Weren't XU1 discs just machined smaller Holden rotors? 

No, OEM rotors were cast in the smaller diameter to suit Torana 13" wheels.
 


Edited by S pack, 08 December 2023 - 07:46 PM.


#35 S pack

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Posted 08 December 2023 - 08:20 PM

I wonder if a pair of Girling Bentley front calipers would work with machined down HQ rotors?

Attached File  Bentley Girling front brake caliper.jpg   145.85K   0 downloads



#36 grumpy xu1

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Posted 08 December 2023 - 09:13 PM

Are you thinking the vmax would hold up better to fading than the 12.7 drilled, Gary?




V Max r type, is probably what i will run mate.

#37 dattoman

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Posted 08 December 2023 - 09:33 PM

Drilled are for show

Beat up on them they will craze around the holes

 

If your going to fit the thicker disc you will need to also fit the spacers between the caliper halves

 

Depending on your intended use... pad choices in DB625 shape are varied



#38 claysummers

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Posted 09 December 2023 - 07:13 AM

Weren't XU1 discs just machined smaller Holden rotors?

I believe HKTG are same offset as HR though larger diameter. When fitting Torana discs to HR you have to use the Torana calipers. So I assume that fitting HKTG discs to Torana you need to use the HKTG calipers.


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#39 yel327

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Posted 09 December 2023 - 08:45 AM

I believe HKTG are same offset as HR though larger diameter. When fitting Torana discs to HR you have to use the Torana calipers. So I assume that fitting HKTG discs to Torana you need to use the HKTG calipers.


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I always thought that XU1 rotors were essentially the same as HT GTS350 with metal missing off the outside diameter. Essentially, they'll go on the XU1 hub. But I just had a look and there is a slight difference in offset:

 

A = diameter.

B = front to back (height when laid flat).

C - thickness when new.

E = centre bore size.

 

HK-HT:

 

A = 270mm

B = 55mm

C = 12.7mm

E = 72mm

 

HT GTS350 and HG:

 

A = 270mm

B = 56.5mm

C = 15.9mm

E = 72mm

 

LC/LJ 6cyl:

 

A = 256mm

B = 60mm

C = 12.7mm

D = 72mm

 

XU1:

 

A = 256mm

B = 60mm

C = 15.7mm

D = 72mm

 

So it looks like the GTS350 rotor is thicker either side of centre as it gets taller (dimension B by half of the thickness increase. But the XU1 doesn't, all the extra thickness is on the outside of the disc as its height (B doesn't change). Assuming the above DBA data is correct of course.


Edited by yel327, 09 December 2023 - 08:47 AM.


#40 S pack

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Posted 09 December 2023 - 08:51 AM

I always thought that XU1 rotors were essentially the same as HT GTS350 with metal missing off the outside diameter. Essentially, they'll go on the XU1 hub. But I just had a look and there is a slight difference in offset:

 

A = diameter.

B = front to back (height when laid flat).

C - thickness when new.

E = centre bore size.

 

HK-HT:

 

A = 270mm

B = 55mm

C = 12.7mm

E = 72mm

 

HT GTS350 and HG:

 

A = 270mm

B = 56.5mm

C = 15.9mm

E = 72mm

 

LC/LJ 6cyl:

 

A = 256mm

B = 60mm

C = 12.7mm

D = 72mm

 

XU1:

 

A = 256mm

B = 60mm

C = 15.7mm

D = 72mm

 

So it looks like the GTS350 rotor is thicker either side of centre as it gets taller (dimension B by half of the thickness increase. But the XU1 doesn't, all the extra thickness is on the outside of the disc as its height (B doesn't change). Assuming the above DBA data is correct of course.

You hit the nail Byron. This is the reason why HT GTS 350 and HG require that caliper to stub spacer plate for correct alignment of caliper to rotor and XU1 don't.
 



#41 dattoman

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Posted 09 December 2023 - 10:13 AM

And thats why the T+G has a thin spacer between the stub and the caliper

 

Same calipers used on Torana and KTG

Except the thicker disc runs a spacer between the halves



#42 UCSLE

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Posted 09 December 2023 - 07:17 PM

You hit the nail Byron. This is the reason why HT GTS 350 and HG require that caliper to stub spacer plate for correct alignment of caliper to rotor and XU1 don't.
 

the spacer should be only 1.6mm  , the different stub axle offset makes up for the rest



#43 claysummers

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Posted 09 December 2023 - 07:40 PM

For the record, I have:

HD HR
A = 253mm
B = 50mm
C = 9.7mm
D = 72mm


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#44 claysummers

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Posted 09 December 2023 - 08:19 PM

I believe the hubs are all the same except HD HR.


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#45 yel327

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Posted 10 December 2023 - 09:35 AM

the spacer should be only 1.6mm  , the different stub axle offset makes up for the rest

 

GTS350 and HG rotors are 1/8" thicker so the spacer inside the caliper halves should be 1/8" and the caliper spacer half of that is 1/16" which is 1.59mm.

 

I've never really taken mush notice of them though to be honest, I've always upgraded them to HQ-WB brakes and all the complete cars I've had have been HK, only bought HT GTS350 and any HG as shells or half wrecked out already. 



#46 claysummers

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Posted 10 December 2023 - 10:49 AM

Same as xu1 3mm

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#47 S pack

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Posted 10 December 2023 - 10:54 AM

Same as xu1 3mm

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Agree, the same 3mm caliper spacers are used in HT, HG, LC & LJ calipers with 15.6mm rotors.
 



#48 yel327

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Posted 10 December 2023 - 11:24 AM

Same as xu1 3mm

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Yes, 3.175mm

#49 claysummers

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Posted 10 December 2023 - 03:12 PM

1/8"

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#50 salamiman

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Posted 11 December 2023 - 08:59 PM

went for these 

 

https://www.vmaxbrak...-xu-1-1972-1973

 

with theses spacers

 

https://www.powerbra...size1/offset/0?

 

Hopefully will get time to fit over the christmas break & will report back.

Cheers for all the help.







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