QUESTION
Currently I don't have a differential brace installed on my Lotus Elan
I added 1.5mm shims today giving about 3mm at the top and maybe 2mm at the bottom.
Test drive proves an 85% improvement.
I can induce some NVH but normal driving is ok.
I think I'll have to live with this compromise at present.
One thought I had would be a flanged rectangular hole directly below the diff flange?
Perhaps an addition required on Elan chassis?
M.K. - Wonga Park, Melbourne
ANSWER
The addition of a differential brace (2.5mm thick mild steel) plus a 2" diameter washer 1.5mm thick should provide optimum spacing at the top of the differential and the bottom.
Installing a differential brace is a excellent addition/improvement and can be thought of as a form of insurance.
This simple component prevents damage to the upper differential mounting lugs and avoids the subsequent replacement costs of the rear alloy housing.
Elan differential braces are available from Lotus Marques and are supplied with a longer bolt plus washer for the top fixing point.
If you still find you have mechanical contact between the the differential and chassis, then this needs investigating.
The clearance between the differential and chassis tray should not be increased by cutting a relief hole as this will compromise the chassis.
From experience, it is not necessary to modify the chassis but investigate the cause of the problem.
Four possible explanations as to why you may have limited clearance -
1) The lower chassis tray may have sustained accidental damage
This has been observed here in my workshop and it has been necessary to use hydraulic rams to gently stretch a slightly damaged Elan chassis to extract the differential from it normal location.
2) Check and make sure the large diameter steel limit washers are located either side of the upper differential rubber mounting.
These limit washers are important as they control the maximum vertical movement of the rubber mounting and differential.
If the upper limit washers are missing, then the differential will tend to move downwards and the clearance between the casing and chassis tray will be reduced.
3) The differential upper rubber mounts may need replacing.
With age and use the rubber mounts sag (and worse case can fail) allowing the differential casing to move closer to the chassis tray.
4) The original cast iron differential nose may have been changed.
The original casting number is 105E2045B and is located on the driver side of the casing.
This can be substituted by using the later Ford Escort differential and casing.
The part number for this component is 73AG4025CA and is located on the passenger side of the casing.
The Escort unit differs in number of ways including the casting itself.
From experience it has been necessary to grind off the casting flashing closest to the chassis tray to improve the clearance during installation.
With the thorough investigations you have carried out so far, I suspect you maybe chasing a hidden problem
It would be worth checking the bolts and chassis integrity where the upper differential rubber mounts are secured to the upper cross-member.
From experience, the chassis around the two rubber mounts has been observed to have been cracked or completely broken on some Elan's we have previously worked on.
I would encourage you to investigate further to determine exactly what is the cause of this unusual problem.
Copyright © 2012 Lotus Marques
Currently I don't have a differential brace installed on my Lotus Elan
I added 1.5mm shims today giving about 3mm at the top and maybe 2mm at the bottom.
Test drive proves an 85% improvement.
I can induce some NVH but normal driving is ok.
I think I'll have to live with this compromise at present.
One thought I had would be a flanged rectangular hole directly below the diff flange?
Perhaps an addition required on Elan chassis?
M.K. - Wonga Park, Melbourne
ANSWER
The addition of a differential brace (2.5mm thick mild steel) plus a 2" diameter washer 1.5mm thick should provide optimum spacing at the top of the differential and the bottom.
Installing a differential brace is a excellent addition/improvement and can be thought of as a form of insurance.
This simple component prevents damage to the upper differential mounting lugs and avoids the subsequent replacement costs of the rear alloy housing.
Elan differential braces are available from Lotus Marques and are supplied with a longer bolt plus washer for the top fixing point.
If you still find you have mechanical contact between the the differential and chassis, then this needs investigating.
The clearance between the differential and chassis tray should not be increased by cutting a relief hole as this will compromise the chassis.
From experience, it is not necessary to modify the chassis but investigate the cause of the problem.
Four possible explanations as to why you may have limited clearance -
1) The lower chassis tray may have sustained accidental damage
This has been observed here in my workshop and it has been necessary to use hydraulic rams to gently stretch a slightly damaged Elan chassis to extract the differential from it normal location.
2) Check and make sure the large diameter steel limit washers are located either side of the upper differential rubber mounting.
These limit washers are important as they control the maximum vertical movement of the rubber mounting and differential.
If the upper limit washers are missing, then the differential will tend to move downwards and the clearance between the casing and chassis tray will be reduced.
3) The differential upper rubber mounts may need replacing.
With age and use the rubber mounts sag (and worse case can fail) allowing the differential casing to move closer to the chassis tray.
4) The original cast iron differential nose may have been changed.
The original casting number is 105E2045B and is located on the driver side of the casing.
This can be substituted by using the later Ford Escort differential and casing.
The part number for this component is 73AG4025CA and is located on the passenger side of the casing.
The Escort unit differs in number of ways including the casting itself.
From experience it has been necessary to grind off the casting flashing closest to the chassis tray to improve the clearance during installation.
With the thorough investigations you have carried out so far, I suspect you maybe chasing a hidden problem
It would be worth checking the bolts and chassis integrity where the upper differential rubber mounts are secured to the upper cross-member.
From experience, the chassis around the two rubber mounts has been observed to have been cracked or completely broken on some Elan's we have previously worked on.
I would encourage you to investigate further to determine exactly what is the cause of this unusual problem.
Copyright © 2012 Lotus Marques