2WD diff ratio too low...

[isuzulady]

A 1989 TFR Isuzu, 2.5 litre diesel 4JA1 motor now fitted in place of original 2.2 litre motor. The original diff ratio is really too low for my use. Is there a higher ratio diff that I can fit please? (maybe the 2.5 model has a higher diff ratio?).
Many thanks for any help/advice.

[geeves]

2 easily available diffs are 4.3 and 4.56. These are for the 4wd models but should fit the 2wd as well.
You will have to assertain your ratio by either the code on the chassis plate ie ST5 = 4.1 , HC5 = 4.55 , S2J =4.7 and S7C = 4.3
or
Lift one wheel and rotate it while watching the driveshaft Count the revs of the driveshaft for one turn of the wheel then divide by 2 ie 4.3 dif the wheel rotates once for 8.6 turns of the driveshaft

[isuzulady]

Thank you geeves I will jack a wheel up and do the count bit.

[isuzulady]

Hi
I have counted the times the drive shaft went round (even I could count and remember the times ) it was 2.25 =1.12 ? it has 14inch wheels and road tyres on the wheels.

When I go to get another diff what do I look for on it so I know what I'm getting is what i want like do they have numbers on them?

[geeves]

MMM Im just going out to my wagon now to jack it up and make sure I havent got my divides and multiplies mucked up. If it was multiply you would have 4.56.
back soon

[geeves]

Sorry try multiply. ie 4.56
As for the type of diff. There are 2 possibilities 10 bolt and 12 bolt. In the 4wds you get a 12 in the back and 10 in the front. I would hope but cant guarantee yours is the 12 bolt as well. A quick look at mine didnt find any external differences maybe someone else knows.
If you are in Wellington I have a 12 bolt 4.3 open diff you can have. They are heavy to change and a little fiddly but not so much so that you need special tools

[isuzulady]

Hi

O.K. I am back to my ute had to go toe lderly neighbour and get her water pump going again. My diff has 10 bolts. I will have to get my
neighbour to fit it if / when I change it. What started me on this track was I get the feeling to change to a higher gear when I am already in 5th gear, like I have revs going to waste.I get around 13 km litre but I do drive steadily

Should I measure between where springs sit and edge of where wheels go and then back to the centre of diff.would a diff of a MU of the same year fit ? and what about one of a bighorn . I am also thinking about taking my overalls to town and going to a wrecker armed with my newly gained knowledge .

Thank you for your help I wish you and all that matter to you all the very best for the festive season.

[geeves]

I would only change the head not the whole thing. The Mu and ubs 55 bighorn complete diffs are the same length but the spring mounts are in different places. the ubs69 and ubs73 bighorns have coil springs.
Also the designation of 10 bolt and 12 bolt refers to the crown wheel bolts not the outside. I have 10 bolts in both my 10 bolt front and 12 bolt rear diff.
To change the head you just chock up the rear end and take off the wheels Take off the brake calipers (disk brake) Pull off the disk undo the 4 bolts each side that hold the axle in pull them out 6 inches or so. Remember to drain the diff first next time. Then take off the driveshaft and undo the 10 bolts that hold the diff head in. then the fun starts. The head weighs between 30 and 40 kg When I changed mine to LSD I lowerd the car after taking the wheels off so I could lay uder the diff with about an inch of clearance I just pulled the diff forwards onto my chest then wriggled forwards and gentaly rolled it to the ground I also found the reverse of this the easiest way to get the new one back in. You need sealant on the mating faces and the smell of dripping diff oil takes several days to wash out of hair. Then its just the reverse to put it back.
Think safety while working under the car while on blocks. It it falls on you it will kill

[geeves]

13 km per liter is good. Thats the same as 7.6km/100km or 36MPG. The same as My Toyota Carib and the work corolla (both petrol)
What revs are you doing at 100kph

[James W]

Re safety while underneath your vehicle on axle stand or whatever. I like to lie the tyres down flat on the ground and under the rear door sills. Perhaps add a block of wood if there is a big gap. It's not an ideal support, but if you are on axle stands then at least you have some redundancy.

[geeves]

I agree. A tyre with a lump of 4x2 (50x100) long enough to sit on the tyre both ends will happily support the car and wont fall over so makes a good secondary stand. I do this as well as the trolley jack and axle stand every time I have to work under the car with a wheel off.
Ive had 2 cars fall off jacks and got trapped under one. Luckily it was only an Escort and still had its wheels on. I get a little paranoid these days