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HT front end swap
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HKM068 Offline
#1 Posted : Sunday, 6 November 2022 9:54:12 PM(UTC)
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Are the HK HT HG front ends all interchangeable? Looking to do a disc brake conversion on a HT ute.

Does the master cylinder need swapping as well? Booster?

Thanks in advance
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Dr Terry Offline
#2 Posted : Monday, 7 November 2022 6:29:16 AM(UTC)
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Yes, the front suspension assemblies are interchangeable between HK, HT & HG, but to do a disc brake conversion you only need the change from the ball joints outwards.

In other words separate them at the ball joints & just change the outer (stub axle) assemblies.

Dr Terry
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Smitty2 on 7/11/2022(UTC)
HK1837 Offline
#3 Posted : Monday, 7 November 2022 7:49:03 AM(UTC)
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There are two different front rotors as well. HK-HT and HT GTS350 plus HG. The latter are thicker. There is a spacer in the calipers to account for the thicker disc.

You'll need the correct booster and a disc brake master cylinder.

The rear shoes and wheel cylinders are different as well I think.

If you aren't doing it totally original it is probably better to use HQ rotors and calipers on HK-HJ disc stubs. You'd have to get some new rear axles made in HQ stud pattern so all wheels matched, and just use HQ drums. You'll still need the correct HT or HG booster and a HQ disc master cylinder, but you might be able to keep the rear shoes and cylinders as they are - Dr Terry might be able to guide you here. It might need a HQ proportioning valve in the rear brake circuit though.
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Sandaro Offline
#4 Posted : Monday, 7 November 2022 2:04:41 PM(UTC)
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Not to forget that HK front ends have screw in type bushes as opposed to press in type on the control arms
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HK1837 Offline
#5 Posted : Monday, 7 November 2022 2:56:35 PM(UTC)
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Originally Posted by: Sandaro Go to Quoted Post
Not to forget that HK front ends have screw in type bushes as opposed to press in type on the control arms


That won't affect changing the stubs out. Stubs are the same from HK-mid HX then they are machined slightly differently for the alloy calipers from mid HX through to WB. Although having said that I still reckon you could use HZ or WB stubs with earlier calipers, you'd just need to dummy them up and check.

What Sandaro says though has to be considered if you were thinking about changing the whole crossmember. You also have to watch the upper control arm attachment points, they were raised not long into HT (pre GTS350) to improve straight line steering performance but at slight detriment to handling. So if you have a HT front end that isn't a first month HT, it will have the raised UCA mounts. If you used a HK front end or early HT the car will drive and slightly differently.

The HQ brake upgrade on a HK-HG is one of the best mods you'll make, but it means different wheels. If you want to run stock wheels it has to be HK-HG discs. At least you can still buy new HQ-WB rear drums, HK-HG are not easy to find now.

Edited by user Monday, 7 November 2022 3:00:47 PM(UTC)  | Reason: Not specified

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KBM Offline
#6 Posted : Monday, 7 November 2022 6:54:41 PM(UTC)
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I've got a pair of HQ discs drilled to suit HK wheels. Don't they do that anymore?
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HK1837 Offline
#7 Posted : Monday, 7 November 2022 7:47:25 PM(UTC)
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Do HK 5” wheels fit over the HQ calipers? I thought HT-HG might but they are far less backspace than HK.
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KBM Offline
#8 Posted : Tuesday, 8 November 2022 8:47:44 AM(UTC)
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If I remember correctly I had to grind a bit of the casting from the caliper for the standard wheels to spin freely. Mags where not a problem. I put alloy calipers on and there was a bit of shuddering so in the end I went back to standard brakes. Still got the calipers I tried.[img]null[/img]
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HK1837 Offline
#9 Posted : Tuesday, 8 November 2022 8:55:12 AM(UTC)
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Mags will normally fit as most of those 70's mag wheel castings were the same and they just drilled them for different stud pattern. Those look to be HJ cast iron Girlock and later HX half alloy PBR. Those PBR can be problematic but work well if rebuilt properly and they aren't pitted in the alloy bores. From memory the best way to make them work is to find a similar pair off a UC and use the UC alloy bit with the HOLDEN cast iron bit (replace the TORANA bit) - this gives you a top entry brake hose. Probably the best long term ones to use though are the HQ cast iron PBR.
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HKM068 Offline
#10 Posted : Tuesday, 8 November 2022 2:01:42 PM(UTC)
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Thanks for all the replies. Plenty of food for thought there. Nothing too original about the ute so no problems there. I have a line on a complete HK disc brake front end and thought it might be a simpler upgrade but it actually sounds like the HQ option might be better. The wheels that are on it are Torq Thrust style mags with the HT bolt pattern. Nothing too exciting there although I am used to them now.

Just to clarify and compare ...

To keep the original stud pattern, need to fit
- HK-HX disc brake front stub axles
- HK-HX disc brake front hub
- HKT front rotor and caliper (nothing the thicker HG versions)
- HKTG booster and MC for disc brake
- rear wheel cylinders and shoes from a disc brake variant HKTG

To go with the HQ upgrade, need to fit
- HK-HX disc brake front stub axles, facing opposite way to HKTG (ie swap L to R)
- HQ disc brake front hub
- HQ front rotor and caliper
- HTG disc brake booster
- HQ disc brake MC
- proportioning valve (?)
- HQ rear backing plates, wheel cylinders, drums and shoes
- new axles if wanting to keep stud pattern consistent.
- new wheels

What did I miss???

Cheers

Edited by user Tuesday, 8 November 2022 2:10:46 PM(UTC)  | Reason: Not specified
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Dr Terry Offline
#11 Posted : Tuesday, 8 November 2022 2:09:37 PM(UTC)
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To go with the HQ front disc upgrade, you can stick with the HK/T/G booster & m/cyl, they will work fine &. the HQ won't fit easily anyway.

Also stay with the smaller HK/T/G rear shoes & cyls.

Also the HQ rotor & hub are one-piece, they don't separate.

Dr Terry
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HK1837 Offline
#12 Posted : Tuesday, 8 November 2022 3:01:24 PM(UTC)
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Follow Dr Terry's advice. I've added some comments in red

Originally Posted by: HKM068 Go to Quoted Post
Thanks for all the replies. Plenty of food for thought there. Nothing too original about the ute so no problems there. I have a line on a complete HK disc brake front end and thought it might be a simpler upgrade but it actually sounds like the HQ option might be better. The wheels that are on it are Torq Thrust style mags with the HT bolt pattern. Nothing too exciting there although I am used to them now.

Just to clarify and compare ...

To keep the original stud pattern, need to fit
- HK-HX disc brake front stub axles
- HK-HX disc brake front hub No. Not required.
- HKT front rotor and caliper (nothing the thicker HG versions)
- HKTG booster and MC for disc brake
- rear wheel cylinders and shoes from a disc brake variant HKTG

To go with the HQ upgrade, need to fit
- HK-HX disc brake front stub axles, facing opposite way to HKTG (ie swap L to R) No, just put them on the same way they go on a HK-HG
- HQ disc brake front hub As per Dr terry's advice, it is all one piece.
- HQ front rotor and caliper Ditto.
- HTG disc brake booster
- HQ disc brake MC You can use this or a HK-HG one as Dr Terry says. I think there is only one you can buy now anyway and the reservoirs are back to front so you need to bend the pipes to swap them over or get new ones made.
- proportioning valve (?) This was located on a HQ basically where the front and rear pipes join under the car, on the inside of the sill behind the front door. I think you only need this if you don't run the small HK-HG disc setup rear cylinders and shoes to match. You can buy aftermarket adjustable ones too.
- HQ rear backing plates, wheel cylinders, drums and shoes Keep the HT backing plates and shoes, just need the HQ drums if changing axles to HQ pattern. Check with Dr Terry if you can keep the all drum brake shoes and wheel cylinders if you run the HQ prop valve
- new axles if wanting to keep stud pattern consistent. It is probably better to do this than redrill original axles. The HQ centre bore is bigger too so the drums and wheels are only supported by the studs unless you get bore adapters machined up and fitted.
- new wheels

What did I miss???

Cheers


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HKM068 Offline
#13 Posted : Tuesday, 8 November 2022 10:16:51 PM(UTC)
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Thanks so much for the clarifications. Much appreciated.

Originally Posted by: Dr Terry Go to Quoted Post
To go with the HQ front disc upgrade, you can stick with the HK/T/G booster & m/cyl, they will work fine &. the HQ won't fit easily anyway.

Also stay with the smaller HK/T/G rear shoes & cyls.

Also the HQ rotor & hub are one-piece, they don't separate.

Dr Terry


This would certainly simplify the HQ upgrade option. Thanks!


Originally Posted by: HK1837 Go to Quoted Post

- HK-HX disc brake front stub axles, facing opposite way to HKTG (ie swap L to R) No, just put them on the same way they go on a HK-HG


Not sure where but I thought I read that the HQ callipers had the bleed nipple on the opposite end so needed to be mounted on opposite sides. Have my wires crossed somewhere on this by the sounds of it. Thanks.


Originally Posted by: KBM Go to Quoted Post
I've got a pair of HQ discs drilled to suit HK wheels. Don't they do that anymore?


This sounds interesting. I wonder if the HQ rotor/hub assembly is (still?) available undrilled. Might that be a simple way to keep the same stud pattern all round? Notwithstanding the ID of the wheel centre matching the hub (ie not hanging not the studs).

HKM

Edited by user Tuesday, 8 November 2022 10:22:53 PM(UTC)  | Reason: Not specified
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HK1837 Offline
#14 Posted : Wednesday, 9 November 2022 6:10:11 AM(UTC)
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You have to have the bleed nipples upright, and that might mean moving the calipers from side to side. HQ-WB stubs are the same basic thing as HK-HG but they are swapped side to side - they are one of the few things that are L&R in the HQ parts book that have an even number on the left side of the car, the reason being they were an odd number on a HK-HG but moved to the other side of the car on HQ. So thecnically you might be right, what I was getting at though was you just get whatever discs stubs you can and put them on as per they were on a HK-HG.

I think Hoppers can get them drilled for you. They aren't cheap, and the folly with this is you have to do it again when you replace them.
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HKM068 Offline
#15 Posted : Wednesday, 9 November 2022 8:10:23 AM(UTC)
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Again, thanks for the reply. That all makes sense now ... I think.

There'll be no racing in this ute so unlikely to go through a set of rotors any time soon. I'll give Hoppers a call at some stage and see what they say.

HKM
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KBM Offline
#16 Posted : Wednesday, 9 November 2022 9:47:40 AM(UTC)
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Just checked and DBA still sell undrilled HQ discs. Maybe a brake or diff shop can drill them for you. diff shops make new axles which need drilling so maybe a good place to start.
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HK1837 Offline
#17 Posted : Wednesday, 9 November 2022 11:43:59 AM(UTC)
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If you can check the centre hub size on both HK-HG and HQ to check they are the same. I have an older memory they are actually the same, 72mm maybe? Long time since I did this.
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