Alloy tank and diff mounting bolt clearance.

[Bigbaldybloke]

Several questions around the rear end of my car. My original fuel tank is corroded inside so I have purchased a replacement alloy tank from Kelvedon motors. This tank does not have the two "dimples" in the bottom of it to clear the diff mounting bolts. My solution is to fit these bolts from the top rather than from underneath as shown in the manual, then to put a sheet of thin 3 ply wood on top of the existing layer of sound deadening felt plus another layer of felt on top of this. I've checked and the tank and straps will fit on with this extra under the tank. I'm fairly happy with this unless anyone has any big concerns. My next questions are, while doing this should I fit a brace to the diff, it's a Spyder replacement chassis so from checking on here I should be able to do this with the body on. Do I need to disconnect the drive shafts donuts from the diff to do this, and if so should I bite the bullet and fit cv driveshafts at the same time? Lots of questions, but if I'm having to unbolt the diff, it's probably only an incremental increase in labour blood, sweat, tears and money to do it all, but I don't want to get started and find I need to take the body off again. All comments welcome.

[Bigbaldybloke]

A couple of photos of the diff bolts with the nuts on top, fitting the bolts from the top should ensure there is much less protruding into the tank area

[alan.barker]

If you raise the Tank check to see if you can fit the fuel Banjo to outlet.
Alan

[rgh0]

I would still fit the bolts from the bottom as these bolts can break and corrode and removing the tank to replace them will be a pain some time in the future ( and you will be called a DPO )

I would make sure the bolts were cut to the precise length and use a jetnut to minimise the height to about the same as a standard bolt head. If necessary grind a little off the top of the diff mounts to lower the nut protrusion into the tank space.

https://www.pegasusautoracing.com/produ ... ct=MS21042

cheers
Rohan

[steve.thomas]

I've just refitted the tank in my Plus2 and initially I had the same concern in that the dimples are not deep enough to clear the diff bolts. Then I realised that the bottom of the tank is not flat, but angles up and away from the diff mounting so will clear them easily with or without dimples (maybe why kelvedon have done away with them). Without the dimples it might be more difficult to get a spanner on the diff bolts, but its easy enough to loosen the tank straps and raise the back of the tank slightly.

[Bigbaldybloke]

I've only loosely sat the tank in place so will fit it and fully secure it with the straps and have a look to see if there is decent clearance, but it was Kelvedon who recommended putting the bolts in from the top. I think the logic being, it's just rebuilt so it would have new bolts, it's for road use and as it's a newly rebuilt diff, the chances of having to remove it in the next few years is slim. Still the decision of to fit or not to fit the diff brace though, I'm tending towards fitting it.

[rgh0]

With the bolts installed from the top and the tank in place you will also struggle to remove and refit the diff as the bolts need to be withdrawn for that exercise also.

cheers
Rohan

[alan.barker]

+1.
Kelvedon imho are wrong to say fit bolts from top. When the tank was made it was a very simple operation to put the dimples for clearance.
I suggest you fit the Diff brace also.
Alan

[Bigbaldybloke]

There appear to be baffled in the tank exactly in line with where the dimples should be so thats not an option. There seems to be no technical reason not to fit the bolts from the top except that it's more work if I ever want to remove the diff in future.
My plan would be to just push the existing bolts out from the top using new bolts, although if I go for the diff brace then it's not quite so straightforward

[Bigbaldybloke]

Hi all thanks for your collective wisdom and comments. I've now properly trial fitted the alloy tank and the straps to secure it in its final position (I expect it to settle a mm or so once full of fuel). As can be seen from the attached photos, once properly secured there is plenty of clearance due to the sloping bottom of the tank. Putting anything else under the tank would mean the fuel tank banjo fouled the bodywork. I've ordered the diff brace and new mounting bolts so will fit them anyway. Getting the existing bolts out from underneath looks tight on clearance between the diff output shaft and diff casing, but I got them in years ago so they must come out! I'm still tempted to fit the new bolts from above as the likelihood of having to remove the diff again is very slim, given that it's been rebuilt and it will get a fairly gentle life on the roads. When fitting the diff brace have people completely removed the big spacer washers against the frustacone rubber mounting as there is not a lot of clearance between the bottom of the diff and the chassis, maybe around 5-6mm max. I appear to have just one thick spacer washer each side about 5mm thick.

[Bigbaldybloke]

Pictures attached