HQ 173 - 308 three on the tree conversion

[Crock]

So i have a HQ wagon

Its currently running a 173 with 3 on the tree

I got a donor car with a 308 and trimatic that i was going to throw in it

I have now decided to only change the motor and keep the manual trans as i have been told its not a problem to do

As far as i can gather all i need is a longer input shaft, V8 Bell housing and V8 clutch/pressure plate is this correct?

Also do i need to change the wiring loom or is it the same?

Is there a difference between a V8 3 speed box and a 6cyl other than the input shaft?

Will a M21 imput shaft fit in my 3 speed box?

I have managed to get my hands on 2 bell housings for the 308 one is standard length of 190mm which needs the longer input shaft, The othe has been shortened to 160mm so that the imput shaft doesnt need to be replaced (apparently) This would mean that i would only need to lengthen the driveshaft but it would also mean thet the gearbox would move 30mm closer to the front of the car

Would the linkages for changing gears still work?

Thanks

[flyingbrick]

All I can add is that rather than changing linkages and driveshaft you could maybe just move the engine back 30mm. Easy.

[Threeonthetree]

Throw the shortened bellhousing in the bin/Trademe. 

Or sell it to the Stockcar guys. Those bellhousings have their origins in stock car racing and were made to allow them to run a standard short input shaft (six cylinder) three speed gearbox behind a Holden V8. This is because the genuine V8 gearboxes were often expensive and hard to come by. If you use this bellhousing your column-change linkages will not line up so you won't be able to select gears. This is very time consuming to fix as the linkages aren't designed to extend further and still operate in a way that will allow successful gear selection. Best avoided.

 

You are correct in saying that with the proper V8 manual bellhousing, the only other things you will need are the correct clutch and flywheel, a V8 length gearbox input shaft (and shaft cover) and a set of standard V8 HQ-WB engine mounts. With this combination, everything will bolt in, line up and your current three speed manual linkages will still work as the gearbox will not move relative to its original position.

 

Holden 3 speed manual gearboxes were used behind both V8 (253/308) and six cylinder (161, 173, 179, 186, 202) engines. The V8 version has a longer input shaft than the six cylinder version. Apart from that there is NO real difference between the two gearboxes. They are of equal construction and strength. Many people think that the V8 gearbox is stronger but this is untrue. They are the same, only with a longer input shaft to account for the shorter overall length of the V8 engine when compared to the six cylinder engines.

 

The three speed gearbox is called the M15, regardless of V8 or six cylinder application. An M20, M21 or M22 Four speed V8 input shaft will not fit the M15.

You will have to find an input shaft specifically from a V8 M15 three speed gearbox. Or better yet, it may be easier to find a complete V8 three speed M15 gearbox.

 

The wiring loom itself will remain unchanged. The only parts you'll touch are the positive feed to the ignition coil, oil pressure sender wire, coolant temperature sender wire, Starter motor wiring is on the same side for both V8 and six cylinder and should reach both. You'll need to earth the V8 engine from a different point though. Either way, the wiring is extremely simple.

 

Let me know if you have any other questions.

Cheers.

[Crock]

Thanks for that threeonthetree

I was hoping you would have something to say about it as i have read your forum from when you were doing a similar conversion on a station sedan!

Do you still have those gearboxes stored under your house?

Do you know where i might be able to get a shaft cover?

[Crock]

Will the cover off the Trimatic box work?

[Threeonthetree]

Thanks for that threeonthetree

I was hoping you would have something to say about it as i have read your forum from when you were doing a similar conversion on a station sedan!

Do you still have those gearboxes stored under your house?

Do you know where i might be able to get a shaft cover?

 

The gearboxes I had have all been sold, sorry. The shaft cover is difficult to find on its own. They are either attached to a V8 3 speed manual gearbox or don't exist. There's not usually an in between.

However you can simply re-use the existing six cylinder cover and weld a piece of equal diameter pipe onto the end of it in order to extend it. I would only do this if you manage to source a 3 speed V8 manual input shaft though. But otherwise, I would just go about sourcing a 3 speed V8 manual gearbox as they are much easier to find than the individual bits themselves.

 

Will the cover off the Trimatic box work?

 

No. They are completely different.

[dr.wylde]

If I may add my 2 cents here. 

 

once you have all the correct parts to run a column shift manual v8 in the car, you will not be able to run much in the way of aftermarket headers/extractors on the RH side as the shifter linkages will be in the way. without some cutting and welding of the pipes.

 

That is of course if your going to chase a few more neddies out of said V8.

[Crock]

Thanks for your 2 cents

I am putting headers on

Do you think it's major work to cut and weld the pipes?

[Threeonthetree]

Thanks for your 2 cents

I am putting headers on

Do you think it's major work to cut and weld the pipes?

The best way to check will be to test fit them once the engine is in, then make some tweaks from there.

You may get away with modifying your pipes but you won't know until you try them out.

[OSM Garage]

Neal, do you know what the measurements are between the two boxes?

[Threeonthetree]

Sorry, just saw this now.

 

I was pretty slack and never measured the two side by side. The V8 input shaft is about and inch (maybe just over that) longer than the six cylinder input shaft. It protrudes out the front of the bellhousing when viewed from directly above. If you have a picture etc I can tell just by looking, sorry for not having the measurements though. I knew there was something I forgot to do when I had those V8 3 speed gearbags haha.