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Discussion Starter #1
so im trying to work out what diffs i have, to see if thats the cause of my woeful lack of power and struggle up hills, even running 17psi without limp mode. trouble is i dont know anything about diffs really, so i dont know how to tell. all i can do to help is say that ive got 35 inch mud tyres, and in 5th gear at 110km/h the revs sit at 2650. what diff ratio is this likely to be??
 

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GUII ZD30DI Wgn
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If yours has never been changed then look on the aluminium plate near the wiper motor, has diff type and ratio written there
 

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2010 GU DX CRD Grenade :)
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As above, there will be letters and numbers, something like hg46 means h233b diffs and 4.6 ratio.
 

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GUII ZD30DI Wgn
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From an old thread about diffs in GU's

To make it short and sweet look at the compliance plate where the transmission details are, if the last alpha numeric group is HH43 that means it's H260 with 4.375 ratio.

This is what mine has FS5R50B (manual gearbox) HH43 (Diff size and ratio H260/4.375). For the H233b rear end it's HG then ratio I have no idea what the Auto tranny number is, so it may be HG39.
 

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Discussion Starter #5
ill take a look, how would i know if its been changed? ive seen alot of threads about people switching to 4.8 when they run 35s. how will i know if mine are switched (not first owner)
 

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GUII ZD30DI Wgn
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You can count the number of turns relating to axle to driveshaft
 

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Discussion Starter #7
So I’ve had a look and it’s got 4.3 diff ratio . Could that be the cause of the catastrophically poor performance with 35s?
 

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GUII ZD30DI Wgn
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Same as mine which is what I expected, of course it is but the 35's are a bigger problem than the actual diff size. Are you out in extreme mud on a weekly basis? this is the question you need to ask yourself to strike a balance, this forum is full of questions on tyre sizes and fuel eco over the many years it has been going and 35's are a disaster. I think maybe you need to do some soul searching to find out what you really want.
 

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Discussion Starter #9
Same as mine which is what I expected, of course it is but the 35's are a bigger problem than the actual diff size. Are you out in extreme mud on a weekly basis? this is the question you need to ask yourself to strike a balance, this forum is full of questions on tyre sizes and fuel eco over the many years it has been going and 35's are a disaster. I think maybe you need to do some soul searching to find out what you really want.
actually yes, i go four wheel driving almost every weekend, i live south of sydney, near nowra, and have easy access to some great tracks. Im in the process of searching for a set of tyres for daily driving so the muddies can be used only when needed\

edit: i should add its alot of mud driving and rock climbing, so the 35s are very valuable
 

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GUII ZD30DI Wgn
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What you need to be very careful of is the load that 35's put on a ZD30 in basic std form re EGT when you don't have an EGT gauge. Guys who regularly run 35's often change diff ratios and sometimes change transfer gear ratios to overcome the problems, then going back to normal size will be a pain in the arse for you, it is a delicate balancing act.
I don't mean to worry you but I know of a member some years ago who drove continuously on 35's with no gauges on his 2005 DI, then seriously wondered why it holed a piston.
 

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I agree with @geeyoutoo. You need to seriously consider if you really need 35's. They're a big tyre for a stock ZD30.

IMO if you want to keep the 35's, but plan on using something smaller for daily driving, I think you need to look at changing your low range transfer ratio. That way you can have a decent daily but also have better performance IN LOW RANGE when you have the 35's fitted.
 

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Discussion Starter #12
I agree with @geeyoutoo. You need to seriously consider if you really need 35's. They're a big tyre for a stock ZD30.

IMO if you want to keep the 35's, but plan on using something smaller for daily driving, I think you need to look at changing your low range transfer ratio. That way you can have a decent daily but also have better performance IN LOW RANGE when you have the 35's fitted.
When you say stock zd, what do you suggest needs to be done to it to run 36s full time. Would 4.8 diffs be enough, or is there engine mods that must be done, if so what is recommended
 

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When you say stock zd, what do you suggest needs to be done to it to run 36s full time. Would 4.8 diffs be enough, or is there engine mods that must be done, if so what is recommended
We don't know what mods you have, does it have a basic EGT gauge so you can see the effects of extremely high load from the 35's, as said we had a guy blow up his 2005 because of that. 4.6 - 4.8 will do you fine but you will not be able to go back to smaller tyres after, engine will scream.
 

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Discussion Starter #14
We don't know what mods you have, does it have a basic EGT gauge so you can see the effects of extremely high load from the 35's, as said we had a guy blow up his 2005 because of that. 4.6 - 4.8 will do you fine but you will not be able to go back to smaller tyres after, engine will scream.
I have a Tillix and needle setup, running 17 pound boost, boost gauge, egr block, 3 inch straight through exhaust, unfortunately I haven’t got an egt gauge setup yet as I really don’t know how to do it and it’s somewhat expensive to get done. So if I put 4.8 diffs in there, will that be enough to reduce the load on the engine? And will that give the car better acceleration and hill climb
 

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I have a Tillix and needle setup, running 17 pound boost, boost gauge, egr block, 3 inch straight through exhaust, unfortunately I haven’t got an egt gauge setup yet as I really don’t know how to do it and it’s somewhat expensive to get done. So if I put 4.8 diffs in there, will that be enough to reduce the load on the engine? And will that give the car better acceleration and hill climb
Absobloodylutely, but I'll be honest with you, if you don't have an EGT gauge in your DI you are having a lend of yourself, with what you have in your combination an EGT gauge is the most important gauge you could have in preventing a grenade attack, it isn't hard, there are plenty of threads on it, buy a quality gauge, remove the dump pipe and weld in a bung to suit the sender thread 50 to 100mm from the turbo flange (it may even have a bung already in it if it is new).
 

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Discussion Starter #16
Absobloodylutely, but I'll be honest with you, if you don't have an EGT gauge in your DI you are having a lend of yourself, with what you have in your combination an EGT gauge is the most important gauge you could have in preventing a grenade attack, it isn't hard, there are plenty of threads on it, buy a quality gauge, remove the dump pipe and weld in a bung to suit the sender thread 50 to 100mm from the turbo flange (it may even have a bung already in it if it is new).
forgive me if I’ve misunderstood, but I thought egt wasn’t as big of a problem once boost is being properly managed and egr is blocked. why is it so important particularly for my setup? I’ll look into getting it done because I don’t have a welder and I’d rather the job done right. Are 4.8 diffs cheaper than buying new tyres and rims?
 

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It's all well and good to have manual boost control and egr blocked, but that doesn't tell you what your egts are when you're giving it to it up hill... That's where the egt gauge comes into its own. I've got a reasonably cheap saas one in mine that I got from supercheap and it is fairly responsive and getting the same sort of egts that others have mentioned in threads here. If you're keen to go that way, supercheap also sell the weld in bung to fit it, if yours doesn't have one.

What brand is your exhaust? You will be able to see pretty easily if it has one or not...

As for the diffs or tyres, it depends whether you get stuff new or second hand. They will probably be similar cost as you have to do both front and rear diffs....
 

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forgive me if I’ve misunderstood, but I thought egt wasn’t as big of a problem once boost is being properly managed and egr is blocked. why is it so important particularly for my setup? I’ll look into getting it done because I don’t have a welder and I’d rather the job done right. Are 4.8 diffs cheaper than buying new tyres and rims?
Wrong in so many ways, I don't know where you got that from, but as said it is load that sends your EGT up and nothing is going to load like 35's Have told you a couple of times about the guy with 35's on a 2005, no gauge and bang, he thought he didn't need one!!!!!!!!!!!! Boost helps EGT but doesn't fix it, L O A D is what sends it up. I'm running 25psi and can still send mine to over 500c if I try, you have no idea what is happening inside there.
 

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Discussion Starter #19
Okay I’ll get the egt gauge done ASAP, from there I’ll do some cost/benefit decisions on whether to do diffs or drop to 33s or 31s
 

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Thank you, I was beginning to doubt my sanity, willing to spend heaps on Diff Ratios but not an EGT gauge, this did not compute, as someone who went through the grenade issue in 2006 and seen others go through it and spent years trying to isolate the key things that cause melted pistons and I did, so I'm not just relating someone else's experience I can also tell you where the first grenades happened and it was here in Australia,
 
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