Lotus Elan

Rear Disc Runout

PostPost by: tdafforn » Mon Feb 16, 2004 9:56 pm

Hi All,
Just checked the runout on the disc of my newly rebuilt rear
suspension, and it is 0.2mm! This would explain the rubbing on the
wishbone at full droop! Anyhow, the surface of the stub axle where the
disc attaches was trued up by turning on a lathe. By a process of
elimination I have however worked out that it is one of the 3 arms
that is out. What is the best thing to do? should I try and take off
the 0.2 mm or perhaps shim it . (I thought I could make shims out of
some steel from razor blades, should give the right amount adjustment)
What do you all think?
Cheers
Tim
1972 +2S130
User avatar
tdafforn
Fourth Gear
Fourth Gear
 
Posts: 867
Joined: 12 Sep 2003
Location: Kenilworth Warwks.

PostPost by: type26owner » Mon Feb 16, 2004 11:04 pm

Shim it with a high modulus material like steel or stainless shim stock. It's done like that all the time on racecars. Only actual requirement is that it does not extrude from being loaded and the stored energy of the stretched fastener is lost. That would cause a failure. Don't use bronze, brass or aluminum shim stock. Anything with a 3E7 modulus is okay. The hardness does not matter either so razor blades are not absolutely needed. They'll work okay though. I'm curious now. How were you going to shape them without injuring yourself?:huh:
Regards,
Keith
p.s. I'm assuming a washer shaped shim of course. Always maximize the load bearing area.
type26owner
Coveted Fifth Gear
Coveted Fifth Gear
 
Posts: 1616
Joined: 18 Sep 2003

PostPost by: david.g.chapman » Tue Feb 17, 2004 12:08 pm

Tim,

I had the same trouble when I fitted a new rear disc to my plus 2. I used a dial gauge and found the run out to be 20 thou in total! I have got it down to 5-6 thou (less than 4 and ideally less than 2 is the aim) by using a old set of feeler gauges and cutting out C shapes to go under the disc.

I can live with what I have, though, and this has been OK for the last year or so.

Dave Chapman.
david.g.chapman
Fourth Gear
Fourth Gear
 
Posts: 670
Joined: 26 Nov 2003
Location: Writtle, Essex

PostPost by: terryrds » Tue Feb 17, 2004 1:50 pm

I have been told that "the best" way to deal with runout is to take the car to a shop that can turn the rotors while still mounted. The car is put on a lift, the wheel turned, and a device trues and finishes the rotor. Obviously the rotor should be marked for proper reassembly if/when it needs to come off in the future. Anyone have experience with this proceedure? Living out in the boonies as I do, it's not an easy option, but I'm told "the big cities" have shops with this service. Comments? -Terry
terryrds
First Gear
First Gear
 
Posts: 17
Joined: 19 Jan 2004

PostPost by: patrics » Tue Feb 17, 2004 9:19 pm

Hi Tim,
You need to find out if it is the disc that's running out or the input shaft to the hub. Try using the disc from the other side as a comparison. If the shaft is running out get it trued up on a lathe - one that runs true! whilst its on the lathe mount the disc and re clock it. You might have had this problem for some time as I think you mentioned some time a go that you were not happy with the pedal travel. If you need help I will come and look at it for you.
Regards
Steve
patrics
Fourth Gear
Fourth Gear
 
Posts: 520
Joined: 21 Sep 2003

PostPost by: tdafforn » Wed Feb 18, 2004 4:07 pm

The thing has already had one ride on a lathe! The guys who did the work said they would take it back and have a look at it. I guess it is possible that it was not centred properly, or perhaps the assenbly is bent?
I wonder how much a new one is?
Cheers
Tim
1972 +2S130
User avatar
tdafforn
Fourth Gear
Fourth Gear
 
Posts: 867
Joined: 12 Sep 2003
Location: Kenilworth Warwks.

PostPost by: type26owner » Thu Feb 19, 2004 3:05 pm

Tim,
Highly unlikely that a machinist would screw up such a simple task. The ear has been over stressed and bent or it's fatigued and cracking and about to break off. Check and make sure both caliper pistons are free to move and one is not siezed up in it's bore. There's better replacement axles which are a heat treated steel that provides increased tensile strenght. Considering the likely loads encountered with these axles having the additional capacity is a wise decision.
Regards,
Keith
type26owner
Coveted Fifth Gear
Coveted Fifth Gear
 
Posts: 1616
Joined: 18 Sep 2003

PostPost by: tdafforn » Thu Feb 19, 2004 3:57 pm

i checked the runout without the caliper on it but and with a new disc, same result..
I just can't understand how else an assembly which was OK when I took it apart becomes so out of whack when it is trued up..
Ah well, such is life ..
Cheers
Tim
1972 +2S130
User avatar
tdafforn
Fourth Gear
Fourth Gear
 
Posts: 867
Joined: 12 Sep 2003
Location: Kenilworth Warwks.

Total Online:

Users browsing this forum: Pastapesto, snowyelan and 9 guests