404 8 speed conversion

[mike97]

Hi,
anyone done the conversion from 6 to 8 speed?, found this excellent site/pdf doc. giving loads of info on the conversion, http://www.robanddenise.com/webpics/tranny.pdf
I,m going to give a go, plus you get more levers to play with

mike

[The Original Donk]

both dave and tristan are in the process of transforming spare gearboxes into 8 speed, but it doesnt allow for a PTO gearbox

[moggs]

the basic 8 speed conversion is a doddle, however mine and tristans is taking a while , we are trying to keep the pto set up also, so means even more levers to play with, problem is space on the already fragile gearbox top.

[mike97]

Got the top of my gearbox in bits and yep, your right the conversion is dead easy, luckily i don't have a pto fitted so i'm going to use the hole where the pto lever goes, and fit a lever to operate the high / low raito.

mike

[Turnip]

I'm going to have ago at the 8 speed thing, but I will use an air cylinder........cos i got air!
One thing puzzles me though? All of these conversion write ups bang on about how you should keep a reverse interlock so that reverse cant be used in high range. Well I reckon I'm old enough and certainly ugly enough to decide when to select reverse? So I lifted my spare selector plate and used the Dremmel to chop off the interlock tongue.
Put it back together and looked forward to being able to meet something in a lane and reverse at more than 1 mph!
Guess what? You can put the reverse /neutral / forward lever in any position in high range.....and it makes no difference at all - yep - all forward gears

[dxmedia]

Had anyone sucessfully completed this conversion? Planning on doing it myself due to the gargantouse gap between 2nd and 3rd.

Also have a PTO, although I've read on benzworld that it's 'possible' to work around the PTO to get the linkage in? Any one done this?


Thanks


Chris.

[mike97]

I've done the 8 speed mod on mine now, really worth doing if you spend a lot of time off road, having the 3 & 4 speed in low removes the huge gap between 2nd low and 3rd high.
I have put the the high/ low lever where the pto lever would go, but the high/ low lever could be put in a few different places with a bit of thought.

regards Mike

[dxmedia]

Thanks Mike,

I've a PTO which I want to keep for hydraulics / compressor and a winch, but i think i'm going to have a crack at it.

Is it as straight forward as the documentation makes out (which does look very simple)?

I was thinking about mounting a lever in front of the gearbox vertically for hi low, but that's just going to be a tinkering thing I suppose unless i can mount on the far side of the pto?

[TigerMog]

I would definitely be interested in having a go at this conversion. Does anyone have a link or info on the how to of it?

[normalbloke]

Dan,
Coming to Slab common on the 4th Oct?

[dxmedia]

[TigerMog]

DX,

Thank you! That document is brilliant. I have been through it briefly, have printed it out and will study it before cracking the tranny open and having a go at it.

Tom,

I am off to play with the muddy bottom 4x4 club in the New Forest Tomorrow, The UK Mogfest at Alconbury on 26-27, and Slab common on the 4th. Now that Tigger is back on the road again I cant wait to play! Are you going to Mogfest?

[dxmedia]

[RobotMan]

Excellent document Mike, Thank you!
I tried compressing it and maximum compression using rar only got it down to 10Mb.

TigerMog,
Yes pictures, pictures and more pictures pretty please
Oh and any chance of doing a bit of a write up or at least pictures and parts list for your LPG conversion. I'll be doing mine as trailering it around is too much grief!

[normalbloke]

Hi Dan,
Wasn't planning on Muddy Bottom.Have you been before?I might pop down if I am free a bit later in the day to watch.
Alconbury is too far for my tastes!Although it should be fun.
If I don't speak to you tomorrow i'll give you a call before the 4th.

[TigerMog]

I am taking a couple days off from work this week to hide in the workshop and fabricate a new bed for ol' Tigger. While I have the back end off I figure is a good time to try and have a look at the tranny and see if i can do the conversion without pulling the cab and or dropping the tranny. I am hoping I can access everything I need through the floor panel or from the back of the cab with the bed gone. I will definitely take lots of pictures and do a full write up when I do it.

Part of the reason for fabbing the new bed is to move my LPG tank. It currently sits in the back of the bed and I dont really like it there to be honest. The goal is to mount the LPG cylinder crosswise on the frame just where it starts to dip downwards towards the tranny. I am then making a new petrol tank to sit on the frame rails full length under the bed. Have to have a few baffles in that I am thinking! The new bed frame will sit over the top of both tanks, will be made of 2x 4 inch steel tubing with all the joints drilled and welded up to make the entire frame into an air tank

So pics and write up on the the tranny conversion, the bed/air tank fabrication, 24v-12V conversion is done (and I am loving it!) will do pics and write up on that, and will take some pics and a write up on the LPG setup as well. Looks like I should have a few posts coming soon.

aahhhh the one bad bit...for the 24V-12V conversion I finally came to my senses and got a new motor and solenoid to convert the old winch instead of buying a complete new unit. Problem is, the new 12V winch motor is darn near a full inch longer than the old 24V unit so the winch wouldnt fit back in the mount anymore ....add that to my "to do" list of fabbing things up next week.

[TigerMog]

oh forgot...I got my days screwed up Tom! Muddy Bottom is tomorrow, Sunday....wasnt today! Will be my first time out there, but it is close to home so I think definitely worth a look. Hopefully see you there!

[lemansred]

[dxmedia]

[mike97]

Yep, as dxmedia said, I'm sure it can be done if you have crawler gears. After all, your not actualy adding any more more gears to get 8 speed, just changing the selectors so you can access 4 gears in low instead of 2.

Regards Mike

[TigerMog]

OK, so I got the bed off the truck, got the LPG cylinder mounted to the frame now and am nearly done with making the new bed (dump/tipper type). The new petrol tank is a work in progress that will sit on the frame rails under the new bed. I went out to Muddy Bottom today and had a ride in Mike's 4 door that has the 8 speed conversion done...WOW! I was instantly sold on the two extra gears. They are exactly what is needed for playing off road. They fit the gap perfectly of not too low (current 2nd gear) and not too high (current 3rd gear). Came home tonight, read through the instructions one more time and will crack the tranny open tomorrow. I cant wait for that conversion. So....8 forward gears, 4 reverse, and then add on a 4 speed crawler box? hmmmm should be interesting! Pics and write up will follow!

[lemansred]

Hi Just did 8 speed conversion while fitting new gearbox to comp MOG busted original gearbox (20 mph in to solid concrete block with debeaded flat right hand front tyre ) not a good idea broke transfer case clean off and yes grown men do cry when it come to there unimogs !!!

what amazed me is the condition of the internals of the gear box
comp MOG is a 1960 model thats 50 years old and the gears are as new
I'm going to weld box back together and keep as spare

Two things worth a mention re downloaded instructions
1, To stop PTO gear from sliding back ang forward it says to centre punch or use cold chisel to put mark in shaft it don't work shaft is harder than both and I didn't want to put tack of weld on shaft
solution clean shaft where gear slides and put some Loctite stud locker on shaft slide gear in to position it ain't going nowhere
another solution would be to mark cut and weld original PTO fork to side inspection plate but i throught of that after I'd loctited gear in to position
2,I used the standard 35 mm reach forward reverse lever to engage high and low range to work out the height the plate had to be at all I had to do was measure how far down the forward reverse cross arm is

The hardest thing I found about doing coversion was getting my head around the instructions but if you do it step by step it not that hard

[minimog]

was just going to offer you a gearbox then looked where you are
good luck in welding the box back together hope its not made out of the same stuff as the bellhousing which basicly you cannot weld(see moggs post about the dam thing)

[lemansred]

I'll let you know how I go with the welding if its cast steel it shouldn't be a problem if its cast iron it will be a bit harder to weld if it won't weld I'll put a glass top on it and use it as a coffee table Ya right I could you imagine the wife letting that happen !!!!
If i can work out how to post pics I'll put a couple of the broken gearbox up
I was real lucky getting a brand NEW gearbox still in the crate packed in 1985 only 300 k away from home
PS I like your quote about if you can't fix with hammer its proberly electrical

[lemansred]

Just found a issue with 8 speed conversion and crawler gears it is possible to shift into high range (mainshaft engaged) with crawlers engaged potental disaster
Luckerly we still have gear box out and found problem when checking shift patterns ect
what happens is when you have
1,crawlers engaged
2,forward/reverse lever in neutral
3,high/low lever in low
you can pull high/low lever into high which and tries to put forward/reverse lever into forward thus locking gearbox into 2 gears
The problem as i see it is you are relying on the reverse lockout and shift indents to keep shift in right place which is not as positive as the original shift pattern not a problem if you know your shift patterns
but to make it Idiot proof (ME) i'm of welding a bracket off the crawler gear shift and rod to high/low lever to lock high/low lever in low when crawlers are engaged but still let high to be engaged when crawlers are disengaged
question has anybody came across this problem before and solved it any other way?

[Turnip]

Keep us posted on this one - because I am headed the same route! Which method of high / low engagement are you using? I am looking at extending the PTO lever right through the shift plate and directly engaging the slider then activating the PTO vis a rotational lever (like the crawler) through the box top breather.