Disco transfer box

[kevinf]

Due to my td5 110s gear box developing a terminal noise, sounds like a tooth broke off the layshaft the box will be coming out in the near future, so it will time for a new clutch etc and maybe a x-brake also think its time I tried disco high ratio gears in the transfer box! My question is I,ve heard all the positive reasons for the change, any reasons not to do the change?
Also for the donor transfer box what year discovery and what engine sould it have?
I think a have heard some where that the v8 one is too highly geared!

Cheers kevin

[Budgie]

This a new one on me, although I put a Defender transfer box into a 300 TDi Disco to allow for better road manners with 33" tyres fitted.
I guess you're looking to increase the high ratio for better cruising?
The one thing I would say, having done the Disco, is don't go much larger than the standard dia tyres or you'll be over geared in high ratio, as I was with the Disco.
This means changing gear later to keep the revs up, only being able to hold at 30 mph in 4th not 5th and struggling to maintain a sensible motorway speed when going up hill.

[Saffy]

5th become like an overdrive. It's nice to potter around in 4th.

Anyhow..... you will want the latest and least miles transfer box you can find. Getting one off a td5 disco is a minefield and you don't sound too clued up to navigate it. You'll need to source one that still has the same features as your defender - difflock for instance - later td5 disco may not have difflock. Even if it doesn't have difflock stick inside the cabin the tranny up to a certain year still had the stud on the box for the lever so can be used, later one have the difflock removed from the box totally. Also if your speedo cable goes into your existing tranny then make sure the replacement box has that arrangement also. Disco td5 often get the speed/rpm from the ABS system and the speedo take off is blanked. I have a td5 disco box on mine and I had to frankenstein it with an old defender box to regain the speedo. AlsoI had to buy an expensive replacement input gear to drive my PTO winch as Landrover as part of cost cutting didn't put any PTO dog teeth on it (disco doesn't use the PTO feature). Also the rear output flange is likely to be different and need swapping off your old one so that you can fit the rear propshaft!

A box off a 300tdi D1 would be easiest if you can find one that not worn so much its not worth the effort as it will be pretty much same spec without worrying about difflock/speedo etc.

The ratio's are usually on a label but you can use the stamped serial number to work it out. You're looking for a 1.2:1 ratio   (1.222 for D1 and 1.211 for d2) Stay away from the d2 boxes with suffix 70D in the serial number as those are the ones without difflock.

The serial number will be stamped in one of 2 possible places, either on the bottom left of the main casing or on the earlier vehicles right at the bottom of the left hand side face of the main casing obscured by the exhaust pipe in which case you will need a knife (to scrape the muck off) and a mirror. You are looking for Eg. "28D123456E, we are interested in the first three and the last, i.e. we call this a "28D suffix E".

List of Serial numbers and corresponding Ratios:

All stock LT 230"s have a low ratio of 3.321, the following list refers to the high range ratio.
12D = 1.667 LT 230R
13D = 1.410 LT 230R
14D = 1.003 LT 230R
15D = 1.192 LT 230R
20D = 1.667 (2.5 N/A 110)
22D = 1.410 (all 4Cyl 90/110 bar above)
25D = 1.410 (V8 110 LT 85)
26D = 1.003 (RR Classic 3 speed auto)
27D = 1.192 (early RR Classic)
28D = 1.222 (RR and Disco I)
29D = 1.192 (V8 90 LT 85)
32D = 1.222
34D = 1.410 (2.0 Disco I)
36D = 1.211
38D = 1.211
40D = 1.211 (NAS/Japan 90&Disco)
41D = 1.211 (Disco II, diff lock stud)
42D = 1.211 (Disco II, diff lock stud)
43D = 1.410 (90/110 TD5)
57D = 1.410 (90/110 TD5)
61D = 1.211
62D = 1.211
68D = 1.211
69D = 1.211
70D = 1.211 (Disco II, no diff lock)

[kevinf]

thanks for the feed back guys, re budgies post the vehicle runs on 235/85/16 tyres (31 inch I believe) so I don't think tyre size should cause any problems.
re saffys post I could get away with swapping the high/low gear cluster and re-using my existing box so lack of diff lock and speedo drive wouldn't be an issue, but didn't know if the d1 transfer box would be a suitable donor box, correct me if I am wrong but looking at the list you posted, a 300 tdi d1 1.22 transfer box would be ideal!
just so we are clear my vehicles a td5 110 with electronic speedo driven from the transfer box, the vehicle doesn't have ABS
I am just watching one on eBay  with no bidders yet


cheers kevin