changing diffs

[slim]

just thinking out aloud at the mo but what is the crack with changing the rear diff does all the axle after come off and be replaced or can just the diff its self be change??( i would like to get more speed at lower revs) as mine seems to rev its nuts off at 70 mph. would it be an easy job to replace?? also would i have to replace the front diff as well as the ratio between them would then be diffrent or does this not matter???

[Smurf]

Hi
I am pretty sure both diffs would need to be the same ratio otherwise one will be driving against the other and will wear very quickly!!
Is your overdrive definitely working ok???

[Morr]

just thinking out aloud at the mo but what is the crack with changing the rear diff does all the axle after come off and be replaced or can just the diff its self be change??( i would like to get more speed at lower revs) as mine seems to rev its nuts off at 70 mph. would it be an easy job to replace?? also would i have to replace the front diff as well as the ratio between them would then be diffrent or does this not matter???

AFAIK you can replace the rear diff in-situ, front I'm not so sure about. If you change the ratio of the rear you must also change the front to match as otherwise selecting 4WD would result in severe transmission wind-up and probable consequent damage.

I note from your response on the poll thread about rpm at 70 that yours is doing 3450 which does seem high, is it an auto? have you checked overdrive etc is working correctly? do you have the correct tyre fitments? These could dramatically alter your rpm at any given speed and should be considered before you go changing any diffs



Edit ** Beaten by Smurf, who can clearly type faster than me

[slim]

AFAIK you can replace the rear diff in-situ, front I'm not so sure about. If you change the ratio of the rear you must also change the front to match as otherwise selecting 4WD would result in severe transmission wind-up and probable consequent damage.

I note from your response on the poll thread about rpm at 70 that yours is doing 3450 which does seem high, is it an auto? have you checked overdrive etc is working correctly? do you have the correct tyre fitments? These could dramatically alter your rpm at any given speed and should be considered before you go changi



Edit ** Beaten by Smurf, who can clearly type faster than me

thanks for the replys u guys, yes it is an auto, the o/d appears to be working ok as when i press it in it drops down a gear and vice verser the tyres i think are standard 265/70/r15 ithink craiglux on this site has the same prob have been in touch with him but he as not yet found any problem as yet!! maybe the diffs that i have fitted are supposed to do this. the thing is i get a little fed up traveiing at 55 mph all the time could well do with a little more speed..........

[Morr]

thanks for the replys u guys, yes it is an auto, the o/d appears to be working ok as when i press it in it drops down a gear and vice verser the tyres i think are standard 265/70/r15 ithink craiglux on this site has the same prob have been in touch with him but he as not yet found any problem as yet!! maybe the diffs that i have fitted are supposed to do this. the thing is i get a little fed up traveiing at 55 mph all the time could well do with a little more speed..........

Well I guess the next step is to jack her up and rotate the wheels to determine which ratio diff's you have fitted. This at least will tell you exactly where your problem lies ........ then just fit a lift and monster tyres to bring gearing back to normal

[slim]

Well I guess the next step is to jack her up and rotate the wheels to determine which ratio diff's you have fitted. This at least will tell you exactly where your problem lies ........ then just fit a lift and monster tyres to bring gearing back to normal

how would jacking her up and rotating the wheels tell me what ratio diffs i have ??

[Morr]

how would jacking her up and rotating the wheels tell me what ratio diffs i have ??

By rotating the wheels and counting the number of turns the propshaft makes you can deduce the ratio of the diff fitted, I think it was covered here recently, I'll try find the info later, meanwhile try a search under diffs on the forum to check

[Morr]

Can't find where I was reading this but I'm 99% certain the following is the correct method, I'm sure someone will jump in if I'm wrong

Jack up 1 rear wheel only, chock remaining wheels securely. Place in neutral, release handbrake. Mark a mark on the propshaft and another on the tyre. Rotate tyre/wheel exactly 1 turn. Meanwhile count the number of turns made by the propshaft, divide this number by 2, this should be your final drive ratio.

This following usefull info is from a previous posting by Elvz .........
If you look on the VIN plate on the firewall you can see the factory code for your transmission e.g. R150F/G145 (on a '89 2.4 Surf)

First character denotes ring gear size. Surf Front diff = F or R (7'5" dia) Rear diff = G (8'0" dia)
Second & 3rd characters denote the final drive ratio and indirectly other information (automatics are fitted with special diffs that are not interchangable with manual ones so they are differently coded)

x06x = 3.889:1
x07x = 3.900:1
x08x = 4.111:1
x09x = 4.222:1
x10x = 4.375:1
x11x = 4.444:1
x12x = 4.625:1
x13x = 4.790:1
x14x = 4.875:1 G145
x15x = 5.125:1
x25x = 4.556:1
x28x = 4.300:1
x31x = 3.909:1
x32x = 4.807:1

Fourth character = number of pinions

2 = 2 pinion
3 = 2 pinion LSD
4 = 4 pinion
5 = 4 pinion LSD

[slim]

Can't find where I was reading this but I'm 99% certain the following is the correct method, I'm sure someone will jump in if I'm wrong

Jack up 1 rear wheel only, chock remaining wheels securely. Place in neutral, release handbrake. Mark a mark on the propshaft and another on the tyre. Rotate tyre/wheel exactly 1 turn. Meanwhile count the number of turns made by the propshaft, divide this number by 2, this should be your final drive ratio.

This following usefull info is from a previous posting by Elvz .........
If you look on the VIN plate on the firewall you can see the factory code for your transmission e.g. R150F/G145 (on a '89 2.4 Surf)

First character denotes ring gear size. Surf Front diff = F or R (7'5" dia) Rear diff = G (8'0" dia)
Second & 3rd characters denote the final drive ratio and indirectly other information (automatics are fitted with special diffs that are not interchangable with manual ones so they are differently coded)

x06x = 3.889:1
x07x = 3.900:1
x08x = 4.111:1
x09x = 4.222:1
x10x = 4.375:1
x11x = 4.444:1
x12x = 4.625:1
x13x = 4.790:1
x14x = 4.875:1 G145
x15x = 5.125:1
x25x = 4.556:1
x28x = 4.300:1
x31x = 3.909:1
x32x = 4.807:1

Fourth character = number of pinions

2 = 2 pinion
3 = 2 pinion LSD
4 = 4 pinion
5 = 4 pinion LSD

very informative thanks very much i will give that a go and post what i come up with.......

[slim]

Can't find where I was reading this but I'm 99% certain the following is the correct method, I'm sure someone will jump in if I'm wrong

Jack up 1 rear wheel only, chock remaining wheels securely. Place in neutral, release handbrake. Mark a mark on the propshaft and another on the tyre. Rotate tyre/wheel exactly 1 turn. Meanwhile count the number of turns made by the propshaft, divide this number by 2, this should be your final drive ratio.

This following usefull info is from a previous posting by Elvz .........
If you look on the VIN plate on the firewall you can see the factory code for your transmission e.g. R150F/G145 (on a '89 2.4 Surf)

First character denotes ring gear size. Surf Front diff = F or R (7'5" dia) Rear diff = G (8'0" dia)
Second & 3rd characters denote the final drive ratio and indirectly other information (automatics are fitted with special diffs that are not interchangable with manual ones so they are differently coded)

x06x = 3.889:1
x07x = 3.900:1
x08x = 4.111:1
x09x = 4.222:1
x10x = 4.375:1
x11x = 4.444:1
x12x = 4.625:1
x13x = 4.790:1
x14x = 4.875:1 G145
x15x = 5.125:1
x25x = 4.556:1
x28x = 4.300:1
x31x = 3.909:1
x32x = 4.807:1

Fourth character = number of pinions

2 = 2 pinion
3 = 2 pinion LSD
4 = 4 pinion
5 = 4 pinion LSD

ok i lifted 1 rear wheel and made the marks on prop shaft and then on tyre did 1 rev of tyre and for some reason the prop only turned 2 1/2 times this cant be right can it??? any way looked on the vin plate and axle code reads G145 i suppose this is a common diff to have so there for i should be geetting around 3000 rpm at 70mph but instead iam getting 3450 ish now this leads me back to my original theory that iam loosing compression poss from head gasket i would think that this could cause this problem what do u guys and girls think

[Smurf]

Hi
Wether or not you are losing compression will make no difference to revs/speed as it is a direct ratio, you may lose power but the ratio can only alter by changing gearbox or diff ratios, not even big tyres will make a difference to the revs relative to speedo as the speedo doesnt know what circumference tyres you have got fitted.
You say your prop turned 2 1/2 times, i supect this may need to be doubled giving you a 4.9/1 or 5/1 ratio which would tally with high rpm at 70.
The other possibility is that your torque converter is not doing its job very well and is allowing too many revs and not transferring the power into drive very well.
My diff shows as G254 and does 3000 @70mph
Hope you can make some sense out of all that. Get your diff ratio confirmed first before you start worrying about torque converters!!!!!
Good luck.

[Morr]

ok i lifted 1 rear wheel and made the marks on prop shaft and then on tyre did 1 rev of tyre and for some reason the prop only turned 2 1/2 times this cant be right can it??? any way looked on the vin plate and axle code reads G145 i suppose this is a common diff to have so there for i should be geetting around 3000 rpm at 70mph but instead iam getting 3450 ish now this leads me back to my original theory that iam loosing compression poss from head gasket i would think that this could cause this problem what do u guys and girls think

As Smurf has said double the figure, (I knew it was either divide or double, but guessed the wrong one - sorry), this would bring you close to 5 which as you say would also tally near to a G145 ratio of 4.875:1
Also agree with Smurf that loss of compression could in no way possible cause the symptoms you describe. You are assuming that the G145 is common (it may be I don't know) why not try to find out from others if they have this diff to assertain their revs at 70mph. Also have you checked your Surf at 70 against another vehicle to ensure that your speedo is reading correctly?

[slim]

As Smurf has said double the figure, (I knew it was either divide or double, but guessed the wrong one - sorry), this would bring you close to 5 which as you say would also tally near to a G145 ratio of 4.875:1
Also agree with Smurf that loss of compression could in no way possible cause the symptoms you describe. You are assuming that the G145 is common (it may be I don't know) why not try to find out from others if they have this diff to assertain their revs at 70mph. Also have you checked your Surf at 70 against another vehicle to ensure that your speedo is reading correctly?

thanks for your help guys i will as you advised run the truck against another car and see what the crack is with that thanks again .................

[AndyLala]

If it helps at all...


I have my rear axle listed as G145
And I run at about 2900rpm to 2950rpm (needle width under 3000) at 70mph.
Auto box 2.4TD.

andyL

[slim]

If it helps at all...


I have my rear axle listed as G145
And I run at about 2900rpm to 2950rpm (needle width under 3000) at 70mph.
Auto box 2.4TD.

andyL

thanks for that m8 its somet to work on it cant be right what iam getting then....