48 replies to this topic

[MRLXSS]

If you were in Vic, i would swap you my good 6cyl M20 for you V8 box.

That might be the easiest thing to do mate

[Collo]

Is there a lot of difference strengthwise between the 6 and 8 cylinder boxes?

Thought most of the difference was in the input shafts and ratios.

[rodomo]

Is there a lot of difference strengthwise between the 6 and 8 cylinder boxes?

Correct!
There is NO difference with the internals.
You WONT end up with a stronger box.

[Collo]

Yeah thats what i thought.

[MRLXSS]

Yeah, same box, just different input shaft really.

[MRLXSS]

I'm pretty sure its just the input shaft and bell housing....

[yel327]

As Rodomo says all aussie 4 speeds are the same regardless of whether they are 6cyl or V8. So if you have a V8 M20 you can put a 6cyl M20 input shaft and cover on it and it's the same as any other 6cyl box. Or you can put an XU-1 M20 or M21 input shaft into a V8 M21 box and it's no stronger than an original (but almost impossible to find) 6cyl M21. To go even further, you can put a V8 3 speed input shaft into an M22 6cyl box to make a V8 M22 (never made by Holden), or an M21 V8 input shaft into an XU-1 M20 and make a V8 XU-1 M20 (only ever homogated for L34 but possibly never used). I would always recommend putting a kit through any aussie 4spd before putting it in your car, so it doesn't really matter which one you start out with nowadays as you'll probably have to replace at least the cluster and possibly the input shaft, 1st and 2nd gears as well. So if you want to run one just buy a cheap 6cyl M20 rather than a broken V8 M21 and rebuild it how you wish.

[Collo]

Too slow...
haha

Edited by slr_v8, 08 October 2008 - 06:03 PM.

[rodomo]

When you turn your V8 box into a 6cyl box, you can sell your V8 input shaft and thrust bearing sleeve (and bellhousing if you have one?)for a pretty penny as there are lots of peeps trying to go the other way

[rodomo]

It's a bit involved. Do you have a w/shop manual?

[rodomo]

I googled it and didn't find much.
I can put something together over the next couple of days if your not in a hurry?

[rodomo]

Is it possible to remove the imput shaft and not disturb these bearings??

Yes, but only with a "dummy" layshaft.
Have a good read as you should only drive the layshaft out one way from the box and refit it the same end it came out of.

[surfmaster]

There is more to this than swapping input shafts, you may have to change the cluster and third gear as well depending on the type of box. The V8 input shaft is also longer than the 6 cylinder input shaft.

[yel327]

You used to be able to buy a spacer but it pushed the box backwards a few inches, hence shorter tailshaft and stick in the wrong spot. Once you've pulled the input shaft out and go to change it you chuck the needle rollers and fit new ones. I still wouldn't do it without pulling the box apart and checking it out. They nearly always have buggered bearing surfaces on the inside of the cluster. As Surfmaster says you need to make sure the boxes are the same ratio set before changing out input shafts, but if you need a new cluster anyway it's bugger all more to get the right 3rd gear so it doesn't really matter.

Edited by yel327, 08 October 2008 - 08:13 PM.

[TerrA LX]

I think you should sell/swap your good V8 box for a good 6cly box before you bite off more than you can chew. JMHO.

[TerrA LX]

just slide the gearbox back further on the spline so the gearbox eats more tailshaft?

Good cause that's not all that will get eaten up.

Seriously, this one won't work because that clearance is there so the tail shaft can slide in and out of the box as the suspension goes up and down.