Front diff to cope with the power of an M57

[Mo Murphy]

13 minutes ago, Snagger said:

92 RR should have had a Borg Warner transfer box, not an LT230.

Or a discovery, same thing, different clothes 😆

It's a 28D suffix E

Mo

[Ed Poore]

Mo having seen you driving a fair bit you are a very sympathetic driver. The stuff that kills transmissions will be being doing silly things that shock load it - your driving style isn't conducive to that. With the auto-box that'll be smoothing things out even more.

I'd focus your pennies on other things but where possible put some money aside to upgrade once you've got it on the road and given it some miles.

[Hybrid_From_Hell]

Ok some info, much of which you may know :

The 6HP26X is a variation of the 6HP26 just for four-wheel drives, so the X at the end just means 4x4 version applications.

 

The Ratios are :

 

Ratio    1st 4.17   2nd  2.33   3rd 1.52    4th 1.14   5th 0.86    6th 0.69

So 6th Gear as you may well know is quite a High Ratio value = Low RPM at cruising speeds

Now my calculator only does 5 Gears !, so I have added in 1.22 TBox and 33" tyres and done just 2nd 3rd 4th 5th 6th gears

The entire calc sheet is loaded below as PDFs, but you can see from this that at 5,000 RPM in top (6th Gear) you'll be doing 167 MPH

 

Soooooooooooooo

I would say "Possibly over geared !!!!!!!!!!!!!!!!!!!!!! "

I have added 3 datasheets from my calc, 

TBox 1.2 + 33s + 6 speed (1st missing so 5th on chart is 6th etc) 

1st is as above, 2nd is with 4.1 CW&Ps, 3rd is with 4.75 CWPs

 

Have a lookie and comment, check I have the numbers right, but I would say it looks like 3.54s may be very wrong !

When I fitted my 342 BHP screaming full race 5.2V8 I was surprised it didn't go better when I built the calculator I thought I had formulas wring, as it showed me as 147 MPH at 4000 rpm, gave the spreadsheet to a guy who was **** hot on excel and it came back as formulas correct ! - tweaked CWPs and TBox and now yes it goes like ****

 

 

Nige

 

 

 

 

with 4.1s.pdf with 4.75s.pdf 1.2 33s and 6 speed.pdf

[Bowie69]

Not knowing where peak torque is, it is tricky to say, but 2100rpm at 70mph does seem a touch over geared, but not much..

 

 

[Mo Murphy]

It's a very common set up on M57 conversions with the 6hp and seems ideal for running across the European motorways, 6th is only slightly higher than my current set up in 5th with 200tdi, lt77S and 1.2 transfer box @ 2300rpm and 70mph. If my 200 can pull it then I'm fairly certain something with double the power and torque will manage 👍

Changing ring and pinion is not a particularly cost effective way of altering ratios for me especially when I have access to 1.4 and 1.6 gear sets for the transfer box.

Thank you so much for taking the time and effort to prepare your considerations. Unfortunately I'm unable to open the .pdf files 😕 is anyone else having trouble ?

Mo

[Bowie69]

Opened fine on my android phone, despite a warning.

You can shove the figures into the ashcroft version, which supports 6 speeds....

[Mo Murphy]

Yup, I've done that already Pete, some weeks ago 👍

Opened the files from the downloads folder 😊

 

Mo

[Mo Murphy]

So what are you thoughts on the front diff Nige ? A good 24 spline and ashcroft shafts ? Forged Cross pin ?

Mo

[uninformed]

2100 @ 70mph is slightly better (lower rpm) than my factory spec BT50 with 3.2Tdci

ill be worse with my M57 6 speed manual set up , but set my cruising speed at 60 (noisy Defender on Australian roads and not my DD). I was also looking for a deep low range 

Tcase ratio swaps are not hard for Mo and reasonably priced if he needs to go to 1.1 or higher 

but just as importantly,  a 24 spline diff of the 4 pin variety should be fine 🙂

[Hybrid_From_Hell]

Front diffs dona lot less work than rear so less stress and less need for big bills 

 

getting a front axle strong is expensive - diff high spec hd shafts hd cvs etc 

id say load wise front 30 rear 70 + or -

so make rear strong @circa 70%

As The rear axle  needs to be the strong one and a pegged ARB )hopefully a Rd128 and not a RD56 which is a lot weaker) is fine 

you shouldn’t consider a ATB for the front as if you do it will drive like a supermarket trolley front goes where you point it while rear goes all over the f place lol

I would suggest 2 routes

Route 1

pegged 4 pin maybe forged cross shaft HD shafts keep cvs as a fuse 

this will be expensive

or

a better route IMHO …

standard casing std CWP std 4 pin leave reat of the axle alone and spend some of the saved money beefing up rear further with HD shafts

 

you could go a 2nd Locker but that adds stresses to things like cvs and shafts and a front locker is not twice as good as just a rear 70/30 comes into play !!

Nige

 

 

[Mo Murphy]

Thanks Nige, the rear ARB diff is your old one 😁

Is a 4 pin for the front difficult to find? 

Mo

[uninformed]

Not sure if out of your budget Mo

 

https://ashcroft-transmissions.co.uk/product/4-pin-diff-centre/
 

https://ashcroft-transmissions.co.uk/product/front-shafts/
 

The one piece cross shaft, while nice, isn’t necessary. There are A LOT of locker rear diffs running around the world with 2 piece cross shafts.

I think your factory CVs will be fine and by all accounts will “wear” better than the softer chromoly upgrades 

[Hybrid_From_Hell]

2 hours ago, Mo Murphy said:

Thanks Nige, the rear ARB diff is your old one 😁

Is a 4 pin for the front difficult to find? 

Mo

😂😂😂👍

 

that’s defo the stronger RD128 so pretty strong and stronger than the earlier RD56

 

add some ashcroft shafts anc flanges and you have a nice strong rear axle 👍