3.46 axle fitted

[rob walker]

Finally managed to get back to the UK, get the car out of store and down to Roger Edwards. They rebuilt and fitted the 3.46 axle. Quality of work was superb and I cannot believe the difference on UK roads that it makes.
Cruising at 70mph (on the sat nav so accurate) she is running at 3,550 rpm which is a much more relaxed pace. I also do not feel it has impacted the acceleration you just have to use a bit more right foot...but more on that in another email.
Overall I am extremely pleased to have had this work done and again Roger Edwards quality of work is outstanding.

[Garry]

Hi Rob
Welcome to the 3.46 club!  World of difference I agree.

Have you plans to do anything about the speedo error and if so what or how.  I have just brought a new speedo in KPH to change over my MPH currently installed.  At the moment it reads 42mph when I am doing 100kph. I would like to try to correct the error in the new speedo if I knew how.
Garry

[rob walker]

I am actually running a KPH speedo. But I tend to have the satnav in the car most of the time. What I may do is make some discrete marks with tipex for 30-40-50-70 although I already know roughly what those speeds relate to. The UK MOT have never picked up on the KPH speedo but as its LHD maybe its ok.

[JamesL]

Here's an odd one

When I swapped axle, I put my Garmin Sat Nav in the car to test the speedo for calibration. And the speedo is pretty much bang on accurate - I too am running 3500 revs for 70mph. But then again, i was before.....

Which means one of three things
a) sat navs don't work properly
b) the speedo had a 10% or so error
c) I already had a 3.46..... (please god no!)

[rob walker]

Here's an odd one

When I swapped axle, I put my Garmin Sat Nav in the car to test the speedo for calibration. And the speedo is pretty much bang on accurate - I too am running 3500 revs for 70mph. But then again, i was before.....

Which means one of three things
a) sat navs don't work properly
b) the speedo had a 10% or so error
c) I already had a 3.46..... (please god no!)

Interesting. On the hire car that my wife was following in we were running at 76 mph with the satnav showing 70 mph, which I estimate is about right given the standard over reading of manufacturers speedos.
This was again checked when I put the satnav into the hire car.
Prior to the axle change with the satnav at 70mph I seem to remember I was running at about 4200rpm.
The odd thing is that I do not think my speedo has changed much either   

[Garry]

Rob and James,
I made an assumption that the speedo cable comes from the gearbox and thus works on the revolutions at that point.  Changing the rear end means if the revolutions remain the same at the rear of the gear box, then the number of turns of the axle has changed eg, the speed increases for the same revolutions or put another way, you get a lower revolution for the same speed. I came from a 4.08 axle to 3.46

The change in my car appeared to be around 6-8 mph.  I had just had my speedo overhauled before the change so hopefully it was very accurate.  I also used my satnav and it was telling me that for 60 mph on satnav the speedo was around 52-53. At 50 mph on satnav the speedo was reading 44-45.  They say that speedos are permitted a 10% variation in manufacture, maybe that is what is occurring.

Some others on here have done axle to rev comparisons and tire/wheel size to speed variations. That will answer the question on exactly how much it should change.

Garry

[rob walker]

James, Garry. Just rereading my notes, for sure the speedo reading has changed I was just focusing on what revs I was doing at a true satnav 70mph. I did not make a note of the actual speedo reading as I only pushed her to 4,000 rpm once and I think it was just above 130-132 kph vs 120kph with the old axle. So I have a gain of about 7-8 mph.
James I cannot understand why your speedo would not show the difference? The satnav has to be accurate. What revs were you doing before the axle switch at a satnav 70 mph?

[Garry]

Rob,

I am going to ask my speedo repair man to build in an error of 8mph or 12.5 kph into the new speedo to compensate.

I can only dream of doing 13-140kph but there are so many speed cameras here both fixed and moving that you would get nabbed in short order and the 100kph or 110kph on the open multi lane highways are very strictly enforced.

What part of Devon are you in.  Wife and I spent a couple of months at a friends house they lent to us just outside Chumley last year.  Beautiful part of the world, hope to get back there for a couple of days on the way to PUB this year.

Garry

[rob walker]

Melbourne to PUB at Blacklick via Devon...gee I am envious.
We are about 7 miles from Chumleigh, you are right it's a beautiful part of the UK. I get back there only on occasional visits even less to Spain now due to work pressures in Istanbul.
In the UK I feel you are okay if you restrict yourself to 75mph on the motorways that's a real reading of 120 kmh plus the 10% error we all know is built into the speedos taking it to 132 kph. I do far prefer trundling along the A roads though with the top down, motorway work is no fun even at the lower revs, but unfortunately if you want to get anywhere quick in the UK its by motorway :'(

[Garry]

Then there is getting home from PUB. Still working on the return trip from Blacklick but at this point planning to drive Route 66 to LA for a week or so.  Will need to hire an open top car I think .

[rob walker]

Got to be an old Corvette then