MK 5 speed installation - how easy?

[g@z]

Howdy,

I'm looking at picking up a 5speed box for the MK to replace the 4 speed. However it's only the box and not the transfer or shafts. I know I need to alter the drive shaft lengths, but I want to know how easy is it to pull the box off the tranfser case and bolt up the 5 speed?

I'm assuming that the gear box mounts will bolt up, as from memory there is an extra hole to move it backwards.

Anything else I need to know? Thanks.

Regards,
g@z.

[Screwy]

mate, if the motor is to stay in the same position...

the mounts are on the transfer case and need to move back about 7 inches.... which is how long the drive shafts need to be lengthened in the front and shortened in the rear.

transfercase bolt up is as you pull it off, very straight forward.

screwy

[g@z]

So I need to cut'n'weld the original mounts as well as mod the drive shafts.... maybe I should just reco the 4 speed.

Thanks.

Regards,
g@z.

[CB0569]

Hey Screwy.
From memory , the 5 speed that i was going to put in my MK but eventually sold you,the gear lever was under the heater box,cause the 2.8 was shorter than the diesel.I also had to change the bell housings over and as you said the gearbox mounts are in different spots.

[Screwy]

Hey Screwy.
From memory , the 5 speed that i was going to put in my MK but eventually sold you,the gear lever was under the heater box,cause the 2.8 was shorter than the diesel.I also had to change the bell housings over and as you said the gearbox mounts are in different spots.

yes thats correct, to avoid cutting the floor, you need to replace the diesel top cover with a petrol one and also move the box back on the mounts which means mods to front and rear shafts.

screwy

[g@z]

BAH! the 5 Speed I was looking at turned out to be a 2.8 litre TD GQ box.

Back to the drawing board.

Regards,
g@z.

[David_S]

Is the MK the rectangular headlight MQ?

In case you pursue the 5 speed option the following might help. I fitted a 5 speed box out of an SD33 MQ to my P40 engined MQ. Fitted without problems except that I had to shorten the front gearbox shaft where it engages with the pilot bush in the flywheel. Also had to replace the pilot bush as the SD33 shaft was of smaller diameter as well as longer than the P40 shaft. Other than that I had to make new transfer mounts and fit a longer front driveshaft and shorter rear one as you mention. I also substituted the cast steel bell housing from the diesel for the original alloy housing as I reckoned it was stronger.

At the same time I changed the diff ratios from the 3.9 (yes 3.9!) fitted to the P40 to 4.375 ex turbo diesel. 5th gear high ratio was still higher than the 4speed top, but the low-low was a lot lower and more useful. The 5 speed ratios are different to the 4 speed. Specifially; 3.897, 2.370, 1.440, 1.000, 0.825 compared to 3.519, 2.157,1.449, 1.000 for my 4 speed. Transfer ratios were the same at 1.000 high and 2.22 low. Would have been nice to have had a lower transfer ratio. The gearbox/diff combination works well though I still find low/low not low enough at times. The 4.625 diff (SD33 and L28 engines) would have been better offroad but not so good on the highway. Can't have everything.

Cheers, David

[rockrover]

how hard would it be to fit a 5 spd diesel to a L24 engine i hav a four spd at present and is the gearing goin to be ne lower
Cheers Bourkey

[David_S]

I don't know the L24 engine, Rockrover - do you mean the L28? I can't think you would have too much difficulty except mating up the main shaft/pilot bush. According to the parts book the P40, SD33 and SD33T use the same bell housing whereas the L28's is different presumably because of the shorter engine. You would need to check this out before investing in an SD33 (diesel) or SD33T (turbo diesel) 5 speed box.

From the Parts Book it appears that there were two 5 speed boxes. One with ratios 3.897, 2.370, 1.440, 1.000, 0.825 (4.267 Rev) and the other 4.222, 2.370, 1.440, 1.000, 0.825 (4.622 Rev). The former was used as far as I can ascertain with the P40 and SD33T engines and the latter with the SD33 and L28. If you have the L28 engine it would seem preferable to find a L28 or SD33 box. I also note from the Parts Book that from August 1983 the four speed ratios were only fitted to the P40 and the L28, the P40 with the ratios 3.897, 2.370, 1.440, 1.000 and the L28 with ratios 4.222, 2.370, 1.440, 1.000.

Your overall gearing will depend on the particular 5 speed box, the transfer box T130A with 1.000 High and 2.220 low, the particular diff you have with possible ratios varying from 3.900 through 4.111, 4.375, 4.625, to 4.875 and your proposed tyre diameter relative to your current tyre diameter.

When changing my box I set up a spreadsheet where I could fiddle with the variables to come up with the ratios I wanted - specifically a good 5th high for highway cruising at 100kph at 1,800 to 2,000 rpm and a good 2nd low for heavy offroad work.

Hope this is of some help and has not confused you.

Cheers,

David

[g@z]

Do you still have the spreadsheet?

Regards,
g@z.

[David_S]

I do but it is a Lotus 123 spreadsheet. I doubt that it would convert to Excel as I must have got a bit carried away producing graphs of rpm v km/h for hi and lo ratios etc. If you want it I could e-mail it to you. It contains a lot of info I researched on gear sets, available diff ratios etc. However I did not realise at the time that there were two 5 speed boxes available.

From memory my approach was as follows. With existing setup I did a series of runs in different gears recording kph and rpm to produce a set of graphs of rpm v kph. I then set up a spreadsheet to calculate the overall gearing in hi and lo range for the various combinations of gearbox, transfer box (hi & lo), diff ratio and tyre size. Overall ratio in any gear = gear ratio x transfer ratio x final ratio x old tyre dia/new tyre diameter. Working back from the tyre manufacturer's revs/kph figure (it allowed for about 3% reduction at 75kph on calculated figure due to tyre slippage) I could then produce a new set of rpm/kph curves superimposed on the original ones for comparison.

My objectives were to have
1) lo/lo of at least 37:1 compared to the original 30:1
2) 2nd lo giving a speed of approx 10kph at 2000rpm (max torque for the P40)
3) Top/hi giving 100kph cruising at or below 2000rpm

Surprisingly this all worked out reasonably well with 235/85 Cooper STTs, an SD33T 5 speed gearbox and a final ratio of 4.375 ex SD33T. Lo/lo went to 37.8 which meant that I was using 2nd lo as my standard offroad gear in mud, hill climbs and river crossings. Previously 1st was too low and 2nd too high. Downhill descents on slippery tracks were much easier in the new lo/lo and I cruise on the highway at under 2000rpm in top/hi but still have plenty of pulling power.

Ideally I would have liked to change the low ratio of the transfer box to drop lo/lo to below 40:1 (2.40 or 2.50 ratios rather than the standarsd 2.22) while still keeping the highway ratios but this is not an easy or cheap option with the T130 transfer box.

For serious offroad work I now run Simex Extreme Trekker 32x10.5x16 which are actually 33s. This has upset the mix slightly as I find 2 lo a tad high. Have to keep the revs over 2000 to keep going. The 4.625 final drive would be better but my on road cruising would suffer. Can't have everything. Might try and coax a little more power out of the old P40 - nearly 25 years old and 250,000km all over the world and still going strong. Not bad for an engine based on a 1948 Austin engine.

Cheers
David

[g@z]

I've got that many Ks on the current L28. To be honest though it's had a rebuild, and i had a Jap import L28 in it for a while. Just shy of 500,000ks in the beast.

Have you thought about dropping a ford 6 in it? I have. Actually saw an EL wagon on a farm with minor front end damage for $1500 so I was looking at that to get all the bits I needed, but the L28 sits on about 3200 at 100 ks hence my desire for a 5 speed to drop the revs, or maybe diff ratios.

Regards,
g@z.

[David_S]

I have sort of got used to the old P40 - plenty of low down torque and not overstressed. Still keeps up with most trucks offroad except when the leaf spring hangers get hung up. Only serious problem with the engne occurred 20 years ago when I broke a crankshaft in a Saudi desert but managed to drive the 1,500 km home.

Cheers, David

[rockrover]

my engine num clearly states its a L24 engine no. on the block the plates say L28 but i was informed it has had an engine swap i dont want a 5 spd petty because of the price and they r farely rare so i thought if possible use diesel 5 spd thanx in advance
Cheers Bourkey

[dromana7411]

my engine num clearly states its a L24 engine no. on the block the plates say L28 but i was informed it has had an engine swap Cheers Bourkey

when i got my patrol it had an l24 in it, but had L28 on the compliance plates. that motor was flogged so i put another L28 in. now its feeling pretty flogged aswell... needs timing done, valve clearances set, possibly the head gasket and some minor oil leaks.

I've got that many Ks on the current L28. To be honest though it's had a rebuild, and i had a Jap import L28 in it for a while. Just shy of 500,000ks in the beast.

but the L28 sits on about 3200 at 100 ks

Regards,
g@z.

iv got a jap import motor in mine, as said above... with the 4 speed i also sit on around 3200 - 3500 at 100ks

[rockrover]

how did u find the L24 to the L28 comparisson i hav heard the L24 and L 28 are of the L series fitted to the nissan cars also does this mean the L24 is 2.4L?
Cheers Bourkey

[dromana7411]

didnt get a chance to drive with it.... went to look at the car... started it up ran nice for the first min... then went clunk clunk, clunk, so we turned it off... got the car home on a truck... then pulled the motor down, (guy said it had been rebuilt recently...) which it looked to have had done, but number 6 cylinder was worn to the bitch, and the piston was slapping side to side, hence the clunk.