Thread: Isuzu Gearboxes calculations ??

Bloody Microsoft re-booted my machine overnight and excel didn't autorecover the spreadsheet, now I have to do it again!

At least I have the image files.

Here's a spreadsheet I made some time back.

Change the orange cells and it should fill out the rpm's for you.
There are three tables to compare the LT95, LT85 and Isuzu/LT230 combo.

I think I got the ratios from ashcroft.

My gearing calculator is in the spreadsheets thread - in zip format.

It has a summary sheet that compares many options using the popular/useful combinations of gearboxes and transfer cases for the 4BD1/T, which are on individual sheets.

Thanks guys.

In following up on Ben's comments about the Q box, I wend to Graeme Cooper's on the way to work. They looked up one of their training manuals which specifies the Discovery 1 had 28D (? LT230T)

• suffix up to "F" 1.222:1 26 tooth input gear.
• suffix "F" 1.214:1 28 tooth input gear.
• suffix "G" 1.211:1 38 tooth input gear.

So perhaps I'll be lucky.

Originally Posted by Lotz-A-Landies

Thanks guys.

In following up on Ben's comments about the Q box, I wend to Graeme Cooper's on the way to work. They looked up one of their training manuals which specifies the Discovery 1 had 28D (? LT230T)

• suffix up to "F" 1.222:1 26 tooth input gear.
• suffix "F" 1.214:1 28 tooth input gear.
• suffix "G" 1.211:1 38 tooth input gear.

So perhaps I'll be lucky.

I can't see how that could be correct and it conflicts with Ashcroft's info.

38 tooth input gear should be the Q case. You cannot make a 38-tooth input gear with T-size teeth.
My broken Q case posted above was a 36D from a late model Disco 1.
The case I replaced it with was a 28D 1.222

28D = 1.222

29D = 1.192

32D = 1.222

36D = 1.211

38D = 1.211

40D = 1.211

41D= 1.211

43D = 1.410

47D = 1.667

57D = 1.410

59D = 1.211

61D = 1.211

62D = 1.211

68D = 1.211

69D = 1.211

70D = 1.211

If you already have a t-case, just pull the pan off and you can see instantly if it is a Q-case or not.

Q gears are on the right of the equivalent gears in a T transfer case in this pic.

Hi Ben

Only suggesting that is the information sheet from Jaguar Rover Australia's training manual. It also talks about the currrent Defender at that time being a 22D.

The text states: " ... In its original form it was designated as LT230R. With the replacement of the radial intermediate bearings with tapered roller bearings the designation was changed to LT230T. This specification is still being ustilised in present versions of Discovery and Defender and also for Pre-3.9 litre Range Rovers. ... This makes the information early 1990's and not necessarily contradictory to Ashcroft's or your information on later boxes or the ones in the 3.9 litre RRc.

It is possible the LT230 I have will be one of the earlier 1.222 or 1.214 boxes, but I'm still not convinced (given the 3.9 and R380 in the D1).

Originally Posted by Lotz-A-Landies

...

It is possible the LT230 I have will be one of the earlier 1.222 or 1.214 boxes, but I'm still not convinced (given the 3.9 and R380 in the D1).

Is your case a 28D or 36D prefix?

Originally Posted by isuzurover

Is your case a 28D or 36D prefix?

Don't know yet, it is located at Leppington 40 Km from home and 50 from work.

I can only get out there on weekends.