Race Engine Forum UK

Ok I haven't had a chance to look at the locking ratio yet, but there is definately a knocking.

I had the car out of the garage at the weekend and because I'm still having clutch problems, I had to push it manually. On the way back into the garage there was a definate knock. I felt it trough the body work as it was going back into the garage. Slightly concerned at this.

I have also very strong LSD in my Fiat 131(this is colotti due block diff) and this is usual that you feel the knocking as if it tries to ripp the whole axle off the car but it is very important if this knocking appears when driving straight because if it is then you definitely have a problem ,if it happens only when you turn the car(even slightly) then it is OK. You will have that knocking noise probably all the time with big lock ratio. this is I think the main reason why it is hard to find such diffs in standard cars.

Just like to say, if you do not run the diff in using a figure of eight, then the discs will wear at an angle and will not function correctly.

Andy.

Once I'm legal to drive the car on the road I will be doing the figure 8's and changing the gearbox oil.

Does anyone know where i can get friction modifiers from?

Demon Tweeks sell it.

Andy.

thank you. Will get on the phone to them!

Ok I've got some Redline MT90 and Friction Modifier, although I haven't put this in yet.

I did however jack up the back of the car yesterday to investigate the noise a bit more.

When spinning the wheels there is no noise, so to me that rules out the diff. The only difference I can see between rolling the wheels on the road, and in the air is the angle of the CV joints.

I've had the inner CV joints rebuilt using uprated cages and balls. The car is very low and the drive shafts are at quite an angle.

Is it likely that I'm pushing the CV joints past a comfortable working angle?

Could it be they just need to bed in?

Any advice on this? I can't really think of what else it might be.

Thanks,
Ant

Hi Ant

any news from your diff?

I can positively tell that the banging noise during manouvering or slow (no-power) cornering is the LSD diff, because I have it myself now also with the my new diff...despite having "only" 45% locking rate. And things did not improve despite the fact that I was driving 8-figures till I had blisters on my hands...

However, after discussion with my LSD diff manufacturer, it looks like excessive pre-load is the main reason. You can check pre-load with one tire off the road and the gearbox in neutral. Turn the lifted wheel with a torque wrench by the center nut and measure the breakaway torque (the torque you will need to take the wheel from standstill to rotation).
Mine is 60 Nm at the moment. The pre-load is cause by mechanically squeezing the plates together (or by spring-washers). I will reduce pre-load in my diff next days by putting thinner clutchplates in, which I can get in 1/10 mm reduction-steps.

I am curious to hear about your measurement.

Thomas

Sounds like the same sort of thing. Its quietened down alot to a point where it only does it sometimes, more so when the gearbox is cold.

I have a feelign that some of it is to do with the gearbox oil I'm using. Its only normal 75w90, but I will be changing this out to some redline MT90 in the next couple of weeks. I will be leaving the diff as it stands at the moment. At least for the time being. I will one day have to remove the gearbox as there are a few issues I need to address in the future. They are at the moment the diff noise and any adjustments I need to make. Especually if it doesn't sort itself out. The other issues are that 3rd is normally quite difficult to get engaged even though it has all new synchros, and lastly the clutch is still leaking somewhere. Not by a hugh amount but enough to require a bleed every few days.

I'm hoping that the diff and the shifting will get better with the new oil.

The noise is GONE!!! (in my diff)

It was definitely the preload.
I reduced the preload by grinding off 4/100mm from 2 clutchplates on each side from the diff, which reduced the breakaway torque from 60Nm down to 30-35Nm.
Now the operation is smooth and quiet, NO MORE BANGING NOISE, even during parking manouvering etc.
The engagement of the locking is still smooth...happy me!

Thomas

Thats great news!! I'm very pleased that you've got it sorted.

I'm living with mine for the time being. Currently have bigger fish to fry than a noisey drivetrain. One day though, I'll sort it out. I'm still hoping that some good oil will smooth it out.

I fitted a new LSD to a friends 131 Abarth , supplied unmarked in a box , so had no idea of preload , manufactures etc... had exactly the same banging on it when turning , it frightened the sh.. the unacceptable off me the first time I heard it! Does it eventually go out of it? Bearing in mind it's a road car , and it sounds terrible in town....

Does it eventually go out of it?

Presumably it does.
I did notice a significant reduction in preload on my LSD after the first trackday.

I think the preload is reduced during the first hard use, simply because you grind down some hundreds of a millimeter and/or make all parts really paralell.
So, if you can, get some earplugs and go for some fun.
Maybe its a good idea to do some of this right circle left circle stuff as well to ensure nice equal wear. Be shure to use some engine torque!

Thomas

It depend on what type of LSD it is. It it ues spider gears(ramps) for locking plates intead of springs then you will probably have thi noise all the time as the locking force will be almost the same all the time(depending on torque on the driveshaft). I have such noise all the time in my car and i was daily driving it for a long time and it was a lot of fun and lot of people turned their heads when they ware heard such noise(best was that most of them thought that something is broken :) )

it was a plate diff.