Fragile 4WD systems
Discussion
Haha, has someone just had to spend money rebuilding a diff because they ran badly mismatched tyres?!
It's built from moving parts which require maintenance for a start. To work properly there is a certain amount of rotational speed mismatch that they can tolerate. Beyond that and the diffs get cooked (and/or worn) and stop working as a result. Some are more robust than others but damage will still be done even on the toughest systems if you're using them on high grip surfaces like tarmac. Impreza's are pretty tough but even then the viscous diff's have their limits and will only cope with so much. Mechanical diffs are generally slightly tougher but they will wear and need a rebuild in time. It all boils down to appreciating that you have a 4wd system and part of that involves being careful with tyres. Over time I've had a number of 4wd/AWD cars and in every one I have just accepted their design limitations. In the uk that includes; a Cavalier Turbo 4x4, a Volvo 2.4R AWD, a Discovery TD5, a Syncro VW Transporter and now the Impreza.
It's built from moving parts which require maintenance for a start. To work properly there is a certain amount of rotational speed mismatch that they can tolerate. Beyond that and the diffs get cooked (and/or worn) and stop working as a result. Some are more robust than others but damage will still be done even on the toughest systems if you're using them on high grip surfaces like tarmac. Impreza's are pretty tough but even then the viscous diff's have their limits and will only cope with so much. Mechanical diffs are generally slightly tougher but they will wear and need a rebuild in time. It all boils down to appreciating that you have a 4wd system and part of that involves being careful with tyres. Over time I've had a number of 4wd/AWD cars and in every one I have just accepted their design limitations. In the uk that includes; a Cavalier Turbo 4x4, a Volvo 2.4R AWD, a Discovery TD5, a Syncro VW Transporter and now the Impreza.
You'd think that one of the WEAKEST possible AWD systems would be that fitted to the Mk1 Mondeo 4x4, yes? A limited run car 20 years ago using parts they found lying around a Ford warehouse no doubt, maybe bits from the old Sierra 4x4 etc, and cobbled together with a budget of around 50 quid I'd imagine.
Well I've had 2, and the first one I owned ran to 250,000 miles. Never had a diff oil change, had mismatched tyres all round for the 10 years I owned it, got bashed in a field more than once etc, but never complained. Never whined or clunked or anything. When I sold it the 4x4 bits were still running fine.
I find it odd to read about the problems with Volvo etc.
Well I've had 2, and the first one I owned ran to 250,000 miles. Never had a diff oil change, had mismatched tyres all round for the 10 years I owned it, got bashed in a field more than once etc, but never complained. Never whined or clunked or anything. When I sold it the 4x4 bits were still running fine.
I find it odd to read about the problems with Volvo etc.
Compare Haldex to proper Torsen systems in this regard too. The Haldex in my TR struck me as heavy, complicated and expensive to fix. The Quattro Torsen system in my A8 was sturdy and made for a better drive.
Haldex in the TT was an expensive solution to a problem that the Torsen system didn't create!
Haldex in the TT was an expensive solution to a problem that the Torsen system didn't create!
Liquid Tuna said:
You'd think that one of the WEAKEST possible AWD systems would be that fitted to the Mk1 Mondeo 4x4, yes? A limited run car 20 years ago using parts they found lying around a Ford warehouse no doubt, maybe bits from the old Sierra 4x4 etc, and cobbled together with a budget of around 50 quid I'd imagine.
Well I've had 2, and the first one I owned ran to 250,000 miles. Never had a diff oil change, had mismatched tyres all round for the 10 years I owned it, got bashed in a field more than once etc, but never complained. Never whined or clunked or anything. When I sold it the 4x4 bits were still running fine.
I find it odd to read about the problems with Volvo etc.
That uses the old Sierra 4x4 system I seem to remember? That's proper solid engineering but it's agricultural compared to what's expected on most cars now and also, hardly fuel efficient. I've always found that the more basic things are, the more they can deal with abuse... Well I've had 2, and the first one I owned ran to 250,000 miles. Never had a diff oil change, had mismatched tyres all round for the 10 years I owned it, got bashed in a field more than once etc, but never complained. Never whined or clunked or anything. When I sold it the 4x4 bits were still running fine.
I find it odd to read about the problems with Volvo etc.
Ennoch said:
That uses the old Sierra 4x4 system I seem to remember? That's proper solid engineering but it's agricultural compared to what's expected on most cars now and also, hardly fuel efficient. I've always found that the more basic things are, the more they can deal with abuse...
I was sure it was similar to the mk5/6 rs2000 setup, with the engine sitting in the fwd layout and a transfer box transferring drive to the rear. The Sierra setup was more like a traditional 4wd setup with the engine sitting in a rwd layout and a transfer box on the side of the gearbox putting drive to the front. I may be wrong but it's just what i've remembered.Steve93 said:
Ennoch said:
That uses the old Sierra 4x4 system I seem to remember? That's proper solid engineering but it's agricultural compared to what's expected on most cars now and also, hardly fuel efficient. I've always found that the more basic things are, the more they can deal with abuse...
I was sure it was similar to the mk5/6 rs2000 setup, with the engine sitting in the fwd layout and a transfer box transferring drive to the rear. The Sierra setup was more like a traditional 4wd setup with the engine sitting in a rwd layout and a transfer box on the side of the gearbox putting drive to the front. I may be wrong but it's just what i've remembered.TooMany2cvs said:
I'm going to take a wild guess that the OP doesn't understand what a viscous coupling is or how it works.
Very wild. I don't have a 4WD. I was asking because I have read a lot about it recently on PH. Just seems like poor design. Gearboxes have lots of moving parts that cope with friction. Diffs should be able to cope, surely.HertsBiker said:
Very wild. I don't have a 4WD. I was asking because I have read a lot about it recently on PH. Just seems like poor design. Gearboxes have lots of moving parts that cope with friction. Diffs should be able to cope, surely.
But it's more like a limited slip diff. When one wheel is slipping, the torque under power is sent to the other, so if you had a severe tyre mismatch, when you accelerated, the torque would go to the larger diameter tyres which is the opposite of what you need.http://www.youtube.com/watch?v=MjaCbpw84kw
snapdragon69 said:
HertsBiker said:
Very wild. I don't have a 4WD. I was asking because I have read a lot about it recently on PH. Just seems like poor design. Gearboxes have lots of moving parts that cope with friction. Diffs should be able to cope, surely.
But it's more like a limited slip diff. When one wheel is slipping, the torque under power is sent to the other, so if you had a severe tyre mismatch, when you accelerated, the torque would go to the larger diameter tyres which is the opposite of what you need.http://www.youtube.com/watch?v=MjaCbpw84kw
HertsBiker said:
Very wild. I don't have a 4WD. I was asking because I have read a lot about it recently on PH. Just seems like poor design. Gearboxes have lots of moving parts that cope with friction. Diffs should be able to cope, surely.
So have a quick google about viscous couplings.Quick version: They use the difference in rotational speeds between the two outputs to heat up the fluid, which becomes rapidly more viscous, locking the two outputs together, to try to ensure they both rotate at the same speed. If one end is rotating quicker than the other because of uneven tyre wear, what do you think that'll do to the mechanicals over - say - 10,000+ miles?
Baryonyx said:
Compare Haldex to proper Torsen systems in this regard too. The Haldex in my TT struck me as heavy, complicated and expensive to fix. The Quattro Torsen system in my A8 was sturdy and made for a better drive.
Haldex in the TT was an expensive solution to a problem that the Torsen system didn't create!
No. It was a solution to a problem that the transverse engine created! Haldex in the TT was an expensive solution to a problem that the Torsen system didn't create!
There's nothing wrong with a FWD bias system like Haldex. It works well in the application that its designed for.
Gassing Station | General Gassing | Top of Page | What's New | My Stuff