You can keep the current diff and tailshaft but to do it properly and not void insurance you need a V8 banjo centre and V8 tailshaft. The difference is the uni sizes, that is all. You'll also want a 3.08:1 banjo as the 6cyl one will be 3.55 or 3.36.

6cyl column setup won't work with the V8, you need a HK-HT V8 powerglide crossover linkage. It goes behind the tranny pan not in front like the 6cyl.

You'll also need the V8 powerglide kickdown linkage plus a HT V8 powerglide gearbox crossmember and speedo cable. You'll have to use a holesaw to drill a new hole in the firewall for the V8 powerglide speedo cable. A blank speedo cable grommet goes in the old hole.

I helped a mate convert a 6cyl powerglide HK Premier years ago using a 308 Powerglide HT Kingswood donor. We tried to use the tail housing off the 6cyl powerglide on the V8 box to keep the 6cyl crossmember and speedo cable but the speedo wouldn't work. With a bit more work (changing drive gears) it might have worked.

Engine mounts on the crossmember are the same. I'd change the mount adapters on the engine to HQ-WB and then run HQ onwards mounts, they are better than HT-HG mounts.

You'll need a 253 accelerator linkage (on firewall) plus the pull rod that connects to the carby.

If I was you i'd sell the Powerglide and buy a HQ-WB RH shift Trimatic. You still need the same V8 upgrade to diff yoke and tailshaft but you can keep the gearbox crossmember and not drill a new hole for the speedo cable. Plus the linkage is far easier, you just need a HG 6cyl auto linkage setup. The Powerglide column will work it or change to a HG auto column. The advantage with the HG column (also later HT) is it has the 3spd auto indicators, the HT one is only 2spd. The only complication with the HQ on Trimatic is it is electric kickdown so you have to rig up a switch off the linkage. Not that hard to do but fiddly.

Edited by user Tuesday, 15 March 2016 6:48:55 PM(UTC)  | Reason: Not specified

The V8 Powerglide crossover linkages will be hard to find - there is so many specialist bits that you really need to pull it off a car yourself otherwise you'll never get them all. Even the pan bolts are longer where the mech attaches to the box. It is a nightmare of a system. Then you have the mechanical kickdown setup on top of that.
Once you've looked further at it keep the Trimatic in mind, it is as period correct for a 6cyl HT as a 253 is as late HT had Trimatic. It is the only V8 auto box that avoids body mods too and no pesky linkages.

12 long hard months I chased this powerlglide transmission.. :)

Ok, you've got me thinking..

I must say I didn't know the later HTs came out with a trimatic. Thought they started with the HGs.

And I can keep the current crossmember as well and save 2-3 hundred in the deal?

Given what you say, I'll have a good hard think..

Thank you very much again.

Cheers,

Darren

Powerglide vs Trimatic.. Now I can't sleep :)

HK1837, you mentioned that the current column linkages would work on the Trimatic, even though it's a 2 sp indicator at the moment. Is it right then that if I kept the current column setup, I could put it in 'drive' and the trimatic will automatically do it's thing through the 3 gears, regardless of the 2 sp column, but I wouldn't be able to select the lowest gear using the column shifter, only 2nd gear?

And what would be required to change the column shifter to, say, an HG (or if I can find one a late HT) ? Does the whole column need to be changed over, or is it just a matter of the shifter section?

Sorry, as you can tell, I'm very new to this, but eager to learn..

And thanks for you post too HGV8 :)

Cheers,

Darren

Wow.. A treasure trove of information, thank you gm5735.

I'll give Dave a call and see what may be available.

Now really undecided between Powerglide and Trimatic, but if Dave has the bits, or at least a handle on whether they can be sourced, the decision may be made for me.

Thanks and cheers,

Darren

Personally I'd 'bite the bullet' & go the TriMatic.

If you drive an HT Powerglide & then jump into a similarly powered TriMatic vehicle, the difference is startling. Unless you've got an engine with Big Block torque, you really do miss that extra gear ratio in the Powerglide car.

I've converted many early Holdens to TriMatic & it makes a new car out of them.

The only deviation from original that I would make is to use the better, later TriMatic, with the electric kick-down. Just fit a small kick-down switch inside the car, near the accelerator pedal. As Byron has said, a bit fiddly, but not rocket science. This also makes the carby linkage simpler in the engine bay.

Other than the cable vs electric kick-down thing, as long as you find a later TriMatic with a RH side shift lever, which were very commonplace in HQ/HJ/HX/HZ, this later box will bolt-up the same as the HT/HG type.

Dr Terry.

It's not 'just' any V8 Powerglide, This box is unique to the HT series.

'Normal' V8 Powerglides, which we see in Australia, have the bell-housing integral with the gearbox & are made to suit the Chev V8 block. The 253/308 of that era had a different bolt pattern to the Chev.

Just for the HT series 253/308 V8, GM-H used the 6-cyl Powerglide main casing, which has a removable bell-housing & cast a unique bell-housing to suit.

Dr Terry

Thank you gentlemen :)

When speaking to Dave, he mentioned that there may also be a difference between the gearing of a 308 and 253 powerglide. His experience is that if you put the wrong one behind the wrong engine you end up with a fuel guzzling slug.. Truth is, I don't know which one I've got. I'll have to chase up some serial numbers.

Everybody has been very helpful and I'm indebted to you.

Thanks and cheers,

Darren

You've been more than helpful HK1837, thanks.

I do have another question though. When you say RH shift, is that when you're looking at the front or the rear of the transmission?

Apologies for my great lack of knowledge :)

Thanks and cheers,

Darren

So not the left side, the other left side.. :) Thank you once again :)