Checking the diff oil
Discussion
This may help. Did I write this...did I cock.
(From TVRFreak and The Cerbera Register) as compiled by the great one himself...Joolz.
Differential
Oil
Although some diffs seem to be set very "tight" in their limited slip action, there are a few points to consider before condemning the diff itself. Most likely is a faulty damper. This is very common and some cars are on their second or third set of dampers.
They leak oil from the top seal and eventually give up their damping action altogether.
Remember that TVR use stiff springs and so need stiffly set dampers to control the extending spring during the rebound phase. Any deterioration in a damper action will cause that wheel to skip as the extending spring action isn't sufficiently under control.
As your car is fairly recently made it will have the high mounted rear anti roll bar yes? Well check the bushes on this ... they have a habit of running dry and the bar itself sticks in the bushes causing erratic roll control. If you remove the rear wheels you'll see the pivot mounts for the bar … remove them and force grease between the bar and the bush, then when you refit the bush put a spacer washer between the "U" clamp and the flat plate it bolts to in order to space out and relieve some of the clamping force on the bush itself ... it'll become apparent when you look at it.
You can check if the hydratrak action is correct by doing this test .. pull out of a sharp turning at moderate speed and floor the throttle. Don't load the car up too much sideways…you're trying to just unload the inside wheel .. if the diff action is correct the inside wheel should spin away the excess torque and the car should not slew sideways as you would expect. If the car does slew sideways then maybe the diff action is tightening up. HOWEVER if there is a fault like this with the diff then I would have to say it's very rare .. so rare in fact that I've never seen it in 4 years of Cerbie experience!
More often the diff loses it's torque transfer effect and the inside wheel spinning effect gets worse to the point where you end up not going anywhere! The hydratrak unit itself sits in a fully enclosed housing within the traditional diff casing and as such doesn't lose oil since the special oil it runs in within that enclosed unit forms the fluid for the hydratrak effect … see previous threads for my description of it's working action.
The oil that is changed in the diff at service time is for the output shaft bearings/ pinion bearing and diff carrier support bearings and as such has no effect on the hydratrak action at all. There is no sight line for level check. The level is to the height of the filler plug on the right hand side of the diff casing. The drain plug is at the middle at the bottom of the rear ring of bolts. Should be changed every 12000 miles and also changed at the first service ... only use Mobil SHC80w/140ID oil ... anything else at your peril!
Hydratrak
Inside the diff casing is the Hydratrak unit, it is self-contained and as such does not run in the diff oil, it contains it's own lubricant which forms part of the working mechanism. Consider the scenario of setting off under hard acceleration causing wheelspin or accelerating out of a tight bend. Under this condition a large speed difference occurs across the rear wheels and consequently a corresponding difference at the diff output shafts ( from the Hydratrak coupling). Inside the coupling itself, fluid is forced through small orifices thus effecting a resistance to the differential output shaft speed causing it. Because this action varies as the speed difference across the output shafts, the diff is "user friendly", the wheels cannot become "locked" as in a power-locking type diff for example and so limits effects such as both rear wheels slipping under clumsy downshifts, and the back end of the car is less likely to step out when exiting slow corners for example. The downside of course is that they make the cars very boring to drive (!) - I mean, what's the point of a fast rear wheel drive car that's difficult to get the back end out on? My driving impressions of Hydratrak-equipped cars is similar to cars having no type of LSD at all- i.e. they seem to sit there going nowhere spinning the inside wheel uselessly if exiting that slow corner for example. My advice to anyone who enjoys what rear drive cars are all about is to stick with the ordinary diff... much more fun, much more ‘TVR’.
The Hydratrak works differently to conventional friction LSD's. It forces fluid through small orifices like vane pumps when one wheel tries to spin faster than the other. Great care should be taken when running a car in with this type of differential fitted. Any other oil than the correct grade specified above will wreck the unit.
1) my hydratrak seems to have a bit of a drip. about 3 drops per day. is this normal? could this explain my high speed vibrations/judders which come and go? if so, at what point do i need to refill and how do i do that and what type of oil should i use? Well some oil can blow out of the breather, and if it's only slight then I wouldn't worry.. the diff holds just about 2 litres of oil so it'll take a while to drop to a dangerous level. The recommended oil is Mobil 80W/140 ID . I have heard a resonance coming from diffs before, but it's not very common at all .. does it sounds like a hollow resonance rather than a proper vibration? If so it could be the diff .. but rest assured I've never had to replace a cerbie diff except for one with a manufacturing fault which went "pop”. It's a similar scenario to the thumping noise on tight turns as the preloaded plates free off, it's more a characteristic than an intrinsic fault
You can't top up the hydratrak level .. as you say it's sealed inside .. you can top up the diff oil level though for the crownwheel and pinion lube ..the level plug is 1 + 1/8th inch spanner size and located on the drivers side of the diff - you can't miss it 'cos it's the only big bung on the diff anyway. Recommended oil is mobil 80W/140ID. Total capacity is 1.75 litres on hydratrak cars.
(From TVRFreak and The Cerbera Register) as compiled by the great one himself...Joolz.
Differential
Oil
Although some diffs seem to be set very "tight" in their limited slip action, there are a few points to consider before condemning the diff itself. Most likely is a faulty damper. This is very common and some cars are on their second or third set of dampers.
They leak oil from the top seal and eventually give up their damping action altogether.
Remember that TVR use stiff springs and so need stiffly set dampers to control the extending spring during the rebound phase. Any deterioration in a damper action will cause that wheel to skip as the extending spring action isn't sufficiently under control.
As your car is fairly recently made it will have the high mounted rear anti roll bar yes? Well check the bushes on this ... they have a habit of running dry and the bar itself sticks in the bushes causing erratic roll control. If you remove the rear wheels you'll see the pivot mounts for the bar … remove them and force grease between the bar and the bush, then when you refit the bush put a spacer washer between the "U" clamp and the flat plate it bolts to in order to space out and relieve some of the clamping force on the bush itself ... it'll become apparent when you look at it.
You can check if the hydratrak action is correct by doing this test .. pull out of a sharp turning at moderate speed and floor the throttle. Don't load the car up too much sideways…you're trying to just unload the inside wheel .. if the diff action is correct the inside wheel should spin away the excess torque and the car should not slew sideways as you would expect. If the car does slew sideways then maybe the diff action is tightening up. HOWEVER if there is a fault like this with the diff then I would have to say it's very rare .. so rare in fact that I've never seen it in 4 years of Cerbie experience!
More often the diff loses it's torque transfer effect and the inside wheel spinning effect gets worse to the point where you end up not going anywhere! The hydratrak unit itself sits in a fully enclosed housing within the traditional diff casing and as such doesn't lose oil since the special oil it runs in within that enclosed unit forms the fluid for the hydratrak effect … see previous threads for my description of it's working action.
The oil that is changed in the diff at service time is for the output shaft bearings/ pinion bearing and diff carrier support bearings and as such has no effect on the hydratrak action at all. There is no sight line for level check. The level is to the height of the filler plug on the right hand side of the diff casing. The drain plug is at the middle at the bottom of the rear ring of bolts. Should be changed every 12000 miles and also changed at the first service ... only use Mobil SHC80w/140ID oil ... anything else at your peril!
Hydratrak
Inside the diff casing is the Hydratrak unit, it is self-contained and as such does not run in the diff oil, it contains it's own lubricant which forms part of the working mechanism. Consider the scenario of setting off under hard acceleration causing wheelspin or accelerating out of a tight bend. Under this condition a large speed difference occurs across the rear wheels and consequently a corresponding difference at the diff output shafts ( from the Hydratrak coupling). Inside the coupling itself, fluid is forced through small orifices thus effecting a resistance to the differential output shaft speed causing it. Because this action varies as the speed difference across the output shafts, the diff is "user friendly", the wheels cannot become "locked" as in a power-locking type diff for example and so limits effects such as both rear wheels slipping under clumsy downshifts, and the back end of the car is less likely to step out when exiting slow corners for example. The downside of course is that they make the cars very boring to drive (!) - I mean, what's the point of a fast rear wheel drive car that's difficult to get the back end out on? My driving impressions of Hydratrak-equipped cars is similar to cars having no type of LSD at all- i.e. they seem to sit there going nowhere spinning the inside wheel uselessly if exiting that slow corner for example. My advice to anyone who enjoys what rear drive cars are all about is to stick with the ordinary diff... much more fun, much more ‘TVR’.
The Hydratrak works differently to conventional friction LSD's. It forces fluid through small orifices like vane pumps when one wheel tries to spin faster than the other. Great care should be taken when running a car in with this type of differential fitted. Any other oil than the correct grade specified above will wreck the unit.
1) my hydratrak seems to have a bit of a drip. about 3 drops per day. is this normal? could this explain my high speed vibrations/judders which come and go? if so, at what point do i need to refill and how do i do that and what type of oil should i use? Well some oil can blow out of the breather, and if it's only slight then I wouldn't worry.. the diff holds just about 2 litres of oil so it'll take a while to drop to a dangerous level. The recommended oil is Mobil 80W/140 ID . I have heard a resonance coming from diffs before, but it's not very common at all .. does it sounds like a hollow resonance rather than a proper vibration? If so it could be the diff .. but rest assured I've never had to replace a cerbie diff except for one with a manufacturing fault which went "pop”. It's a similar scenario to the thumping noise on tight turns as the preloaded plates free off, it's more a characteristic than an intrinsic fault
You can't top up the hydratrak level .. as you say it's sealed inside .. you can top up the diff oil level though for the crownwheel and pinion lube ..the level plug is 1 + 1/8th inch spanner size and located on the drivers side of the diff - you can't miss it 'cos it's the only big bung on the diff anyway. Recommended oil is mobil 80W/140ID. Total capacity is 1.75 litres on hydratrak cars.
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