The dreaded MOT Test is now on the horizon and once again I am faced with the dilemma about which garage to go to.

The one that MOT'd and passed her last time (garage:1)

Or the one that MOT's my Merc (garage:2)

Garage:1 is old school and doesn't have the high tech digital read outs, where instead the brake efficiency test shows up on two clock dials and they insist on using a 'Taplow Meter' for Testing the rear brakes.

Because the Axle is fitted with a limited slip diff.

The last time that they did this, I held the Taplow meter in place while the Tester drove my Car.

This was worse than having a Wizdom Tooth removed!

Because when he put the Brakes on, I thought the Meter and Myself were going to go through the Windscreen!

So this time around, why don't I drive the Car while he holds the Meter?

When he put the Brakes on, the Jag stopped so quick the momentum was such, that it felt as if the Meter was being ripped out of my hand, as its a very heavy piece of kit. (for those who may not know)

So good job I was holding it on top of the center Arm Rest almost as if my life depended on it!

But this time if I drive the Car, I am going to be paranoid, that he won't hold onto the Meter as tightly as I did and maybe not hold onto it at all!

Which could send this very heavy little box of tricks, flying towards the dashboard doing untold damage to my pride and joy.

Garage:2 Is new school, where everything is done on digital readouts and they always keep the engine running, for the full duration of the Test!

Not sure why they do that? But I'm going to be Paranoid the Jag will overheat, with the bonnet/hood open, while She is up in the Air.

Garage:2 also does not use a Taplow Meter, they do the whole Test on the Rolling Road.

Is there any possibility that the Rolling Road will damage the Diff or break a Drive Shaft? and if not Why not?

Could the Jag overheat while they keep the engine running throughout the Test with the Bonnet/Hood up.

Not to mention a Tenners £10 worth of Petrol going up in smoke!

Got to think of the environment (not!) you know lol!

Any ideas as to what to do for the best?

 

Old School every time, say I OB ! Place the Taplow meter on the floor with your size tens in front of it and all will be well; Like you, my first MOT (equivalent) over here had the engine running the whole time and I was scared stiff! The rolling road differentially loads the tyres, but not the brakes (I believe), so there is no undue strain on the diff system as the brakes are applied at the same time to each side (obviously), so the RR by putting a higher load on first one side then the other, is just measuring each side's caliper/disc arrangement's comparative efficiency, but the driveshafts as far as the diff is concerned each side are still being gripped by the brake each side. Imagine you are trying to twist your arm with your wrist being held by a giant, only your fiorearm will feel the turning strain, not your wrist or hand. Believe me, if a driveshaft cannot take the strain between the hub and the caliper on one side as reproduced by the RR, you need to know about it ! But do not worry, it will ! Good luck with it. Greg

 

Hi Greg

Thanks,

I was already leaning towards 'Old School' the only problem being that they keep rotating Testers and this is a Garage that 'does repairs' if you know what I mean!

As it helps to fill the coffers, if they find something wrong so they are pretty finicky when it comes to doing the Test, although they somehow managed to miss inspecting the Shock Absorbers.

Which were the cause of the rattling, banging and graunching noises, coming from under the Bonnet/Hood, not to mention that She was bouncing up and down like a Yoyo.

And had so much body roll when cornering, that I thought I was going to fall out!

It also quite an expensive place to have an MOT £55 where Garage:2 only charges £30 but as Garage:2 is much further away, it will probably cost me close to £20 in Petrol just to get there and back! (nice run out though!)

I don't like the Tester driving my Car!

I thought he was auditioning for a role as a getaway driver in one of those action Movies!

But even less I like the idea of him not holding on to the Taplow Meter as tightly as I would and then having it suddenly fly through the Air only to bury itself in the 'burr walnut'

And garages tend to hate it when you try and take Control, as they seem to get the impression, that you are trying to tell them how to do their job, when all I'm really trying to do is to protect my Car.

Garage:2 is much more user friendly and they also know that I am not a 'Punter' but the thought of keeping the engine running all the way through the Test about 20 minutes! is really freaking me out!

To be quite honest, I'm still undecided.

Are Limited Slip Diffs common on other Cars, or is it only on the XJS?

I'm totally out of my comfort zone on this one.

 

I take your point OB. Why not ask garage 2 if they will turn the motor off and only run it during the parts of the test they actually need it running?

No need to worry about the diff! really. Nowadays they tend to fake the LSD by (cheaper) automatic rear disc brake electronic systems that make a single brake caliper grab the spinning wheel when it detects traction and/or rotation speed differences. But lots of sports cars and higher-end cars had and still have real ones.

Greg

 

Hi Greg

Thank you for your responding to my dilemma!

The Merc has never boiled over, while continuous running during the Test but the Jag is a different animal altogether, so not quite sure what could happen.

So I think I'll have a run over there and book her in face to face, rather than to do it over the phone.

Then I can ask them if they would mind, not keeping her running all the time during the test and hope that I get a good vibe.

Garage:2 is tucked out of the way and isn't snowed under with MOT's hence the very cheap price where more often than not they can do it the very same day and also seem keen to preserve their Customer base.

 

Garage #2 seems to be the better choice.

As for the possibility of overheating, why not appeal to enlightened
self interest?

Have a friendly chat with the tester and warn him that your car has
a habit of overheating when not in motion and will puke copious amounts
of lovely slippery coolant all over the nice shiny floor. Best to not run
unless necessary.

On the other hand, you could simulate the situation before going.

Have a good run, turn off for thirty minutes. Open bonnet, idle car
for 30 minutes while watching temp gauge. If it survives at home,
it should survive at the shop.

 

Yes! I think I've now decided that Garage:2 is the One, as they are more user friendly and both of the two testers are as nice as two testers can be and hope that I'm still thinking the same thing after this ordeal is over!