suffering from Diff noise

[miked]

I have done loads of winter maintenace to have a "bob on" Elan. Had quite a few problems that I never had before. Confidence is getting a bit knocked. Not been like this before in over 12 years of playing with Elans.

Help required. Elan S4, on Spyder chassis with 5 years of good motoring since restoration. During the winter I pulled out the diff' as it had oil leaks. It was however quiet. At the same time I removed my TTR solid shafts for a track project. I had the same diff' overhauled. All new bearings and seals. I then did the ally case with bearings and seal etc.
At the same time I fitted a set of sliding spline UJ shafts that I had made up.Done by a proper guy.
I did my first run to Donnington on Saturday. I now have noise that sounds like a light/medium wearing metal sound. It is not there when off the throttle or on it with some power. It is mainly there when just holding the car in between actually accelerating and being off throttle. I think it is probabley there in a duller form when power is applied but exhaust noise screens it somewhat.

I can get up to 80mph and back off and it is quiet.

Diff' is not metal bound. Top mounts are fine. Torque rods and rubber are fine. I actually lowered it with some more washers as it was a bit high. It has the washesr ground with flats as Spyder chassis is different and it is easy for the washers to touch the chassis. Top mounts do not centre the top gap like a Lotus chassis.
I took the car to the Diff' guy and took him for a ride. He says it does not sound like a classic diff noise, he would expect. Only done about 300 miles in it.

I pulled out the diff' this aft' and will take it to him in the morning for a check. The oil looked as though it had gold coloured stuff in it. Also when I got back from the 40 miles (to Preston & back) I reached underneath and I could not keep my finger on the bottom diff' wing, it was so hot. I had only been doing 60mph and no burst of power at all.

I think it is the diff - set too tight. I cant believe this as I took it to proper guys.

I will take the short drive shafts for a balance check, but the guy who did them said he DTI set them up. Also they would surley bounce at 80MPH if it were a balance problem (whether "on" or "off" load) related only to speed. I think they are right, this guy does good work. Also you would not get a metalic noise from shafts. They have brand new UJ's and are all nicely moly' greased up.

Any advise appreciated.


Mike

[steveww]

I had a lot of diff noise on my S4 after fitting new torque rod bushes. Turned out the the cups that surround the rubber/poly bits were just catching the torque rods, hence the noise.

I just drilled out the holes in the cups a bit bigger, problem solved.

BTW it is also quite easy to put the torque rods in on the wrong sides i.e up side down. Don't ask

[miked]

Steve,

I have the rods on with the rise to the diff'. Will check cups but am sure the inner ones are the large hole type from the lower front shockers.

I dont like the amount of heat and the business with a gold colour to the oil. It was not a EP syrup type colour but had gone a milky gold as if tinted by metal.

Thanks Mike

[elansprint71]

Gold stuff in oil is usually brass, where would that come from? Hot diff is not good.

[miked]

UP date.

Diff' colour was the spray they use to check contact marks on CWP. Had diff' re checked. All to bits again. Had drive shafts checked, was told they were 120 thou'out. Even though they don't vibrate at speed. Had a brand new set made up. Fitted new top mounts. Made new 2inch washers with dead close fit to ensure the AVM tubes dont pull and distort.

Tried it and still have noise.

I think I know what it is. Two things.

1) Spyder Chassis's have very little clearance at the front of the diff' top mounts. About 5mm even with flats ground on the washers.

Lotus chasis is in the middle with loads of fore/aft clearance.

2) Also I did not but the poly' bushes back on the torque rods. I used the old rubber type.

I notice last night when in the boot that the top washer on the left had made contact the fibreglass body some 3/8 of an inch to the rear.

I think the natural flex movement of the diff under load is more dramatic than I figured and one side goes back and the other side moves forward into the chassis. Thus grounding the diff' and giving me the wear noise.
Tonight I am going to grind the washers back further and also the bottom metal of the AVM. Also to fit the Poly' bushes on the torque rods to limit the movement.

Am I right in thinking that the lack of donuts and the solid shafts encourage the diff' to move about a bit more. Does the left go rear and down and the right try to move forward and up. (when viewed from above).

Looking at the shape of the old poly' buses it would suggest that only two of the diagonal ones take load when under power due to the inclination to twist.


Mike

[oldelanman]

Hi Mike,
Just a thought......Have you checked that the dirt shield on the diff input flange is not loose or bent and contacting the diff nose ?
Regards,

[steveww]

I have fitted the TTR diff mounts which are a lot stiffer than the original type. These will prevent the diff moving around too much.

[miked]

Thanks, will check diff' input. It is not bent but have not looked at how close.

Re TTR top diff mounts. I had thought about these but heard they are very stiff and could cause vibration. Steve, are your standard TTR or the extra special ones as I am told he has two types.

Mike

[steveww]

Thanks, will check diff' input. It is not bent but have not looked at how close.

Re TTR top diff mounts. I had thought about these but heard they are very stiff and could cause vibration. Steve, are your standard TTR or the extra special ones as I am told he has two types.

Mike

AFAIK they are the TTR standard ones. They are a lot stiffer than the old ones I took out.

[miked]

Went through it all again.

Top mounts (although standard) are not touching anything. Have ground the two flat washers further. The are well clear of the spyder chassis cross member. Fitted some new poly' bushes to the diff' torque rods. Everything is centred great with correct cup washers etc.

Took it for a run. Still have diff' noise. Not on power but just between coasting and tiny throttle. Even at 25mph. Sounds like the prop' shaft rubbing the chassis. (It is not, I have checked)

Input shield is well clear.

I jacked it when i came back from a 5 mile run and the diff' is hot, not mega. I would guess at 50 - 60 degrees C.


Even though the Diff guy has had this in twice I am convinced he has built it up too tight or it has odd wear and he should have said I need a new CWP..

I think I will try and get another 3.77 diff. My mates say to try some of the slippery additive. I have a tube of STP in the garage. What do we think? Am I just masking something or is it a valid thing to do.


Mike

Hump backed with jacking and meddling.

[rgh0]

If the problem is actually inside the diff then trying a different lubricant may at least change the noise and help diagnose it. I would try Redline gear oil as an alterantive to putting in additives.

cheers
Rohan

[miked]

Rohan,

I will get some Redline and try it out.
I suppose it will not harm to get some summer miles on while I source an other diff'. I'll bet that if I had the hood down, I would not even hear this.
However, it is nice to have a quiet drive train wth the hood up.

Thanks

Mike