SteveWallace
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| posted on 4/4/14 at 01:16 PM |
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Viento IVA Fail suggestions for fixes please
I had my IVA test today and failed on 3 points, all of which would have been hard to spot at home. Before I get into that, first of all a big thanks
to Irony on here who came to the test and helped prevent failing on other things. Also, as has been said before, the Nottingham testers do everything
they can to help you get through.
I) Brake bias. We could not get the balance between front and back right. Overall performance and left to right balance was fine. Strangely, fully
adjusting the bias bar from one end to the other made very little difference even though you could see the bar pivot. I was wondering how much
difference the length of the push rods that go into the master cylinders would make. Any ideas or thoughts would be appreciated.
ii) Speedo. Was fine on the calibration up to 50MPH (which is how fast I tested it to at home), but then started to behave very erratically after
that. I'm using magnets on the prop shaft and I could understand it if it had started to read low due to missing a beat, but the reading was
bouncing around both high and low.
iii) Noise. I was worried about this and I ended up with a reading of 101db. I have a few things to try such as repacking the silencer and seeing if
I can find a DB killer that fits the 90 degree outlet pipe.
He also didn't like my chocolate block connectors for the headlights and rear cluster (schoolboy error, I should have seen that one coming), but
we managed to swap them for bullet connectors, which he was fine with.
He liked the overall build quality and I was really pleased that I passed the emissions test and that it self centred enough as those would have been
really difficult to fix.
Having said all that, the drive to and from the test centre was great fun. More so on the way back as I knew that the car was basically OK.
[Edited on 4/4/14 by SteveWallace]
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daveb666
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| posted on 4/4/14 at 01:48 PM |
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Hi Steve,
firstly sorry you failed; I know what that's like!
Do you have any photos of your brake-bias setup? Is it a pedal box?
I'm assuming you know that, when you go back for your re-test they won't recheck anything it passed on first time, so in the interests of
getting a pass on your noise-test you really only need to get the sound down, in as crude a way as possible (but obviously sticking within sharp-edge
tolerance).
With the speedo, can you not use an output from your gearbox?
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keithjardine
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| posted on 4/4/14 at 01:51 PM |
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Good effort so far just a little push now towards the finish line but as you say you know you have a basically OK car fit for the road.
I spotted you parked this morning at the test station and meant to stop but was running late for work.
Can't help much on the fail sheet though
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MikeR
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| posted on 4/4/14 at 02:10 PM |
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As the prop spins faster I'd guess the tollerence between magnet and sensor becomes more critical - how sure are you that the sensor is close
enough and not wobbling?
Assuming the speedo is programmable, how many magnets do you have? Could you half the number?
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loggyboy
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| posted on 4/4/14 at 02:12 PM |
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I) Brake bias. Is the bearing moving within the tube of the pedal or is it fixed, making the par itself move side to side?
ii) Speedo. Completely finger in the air stuff here - but try moving the magnet to another part of the prop, or the the diff flange, its likely the
signal is getting missed or being on a small diameter inst getting enough 'down' time for the sensor to switch between states/
iii) Noise. Your options sound sensible. Try and borrow a meter for a before and after, even if the accuracy isnt there, if you can get a decent
reduction on one meter that reduction should carry over on the IVA meter.
Its unlikely to trigger a meter orienated at the exhaust, but do you have much induction noise?
Mistral Motorsport
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Paul AS
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| posted on 4/4/14 at 02:22 PM |
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Not a bad fail list at all!
On the speedo front, as you're using magnets on the propshaft, there will be less variation, the closer you can get them to a fixed point. If
they are near the gearbox mounting rubber support, the gap will be more variable at different speeds.
Assuming you are IRS and the diff is solid mounted, I would be getting as close as possible to that, and making sure the magnets are at the suppliers
specified gap. Super close is not necessarily the best position.
Alternatively, with has already been mentioned, gearbox output with appropriate convertor is a very reliable way of dealing with the issue, now and in
the future! Magnets have an occasional bad habit of falling off.
Good effort - really close now!!
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davidimurray
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| posted on 4/4/14 at 02:28 PM |
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That's a good Fail - well done
What front pads are you using? My IVA inspector said to use the cheapest pads you could buy as they will bed in quickly and be fine for the test. He
said he sees lots of cars with performance pads that he struggles to bed in.
What rear brakes are you running? If using the sierra drums then the larger drums can be too strong. You can get around this by changing to a smaller
bore rear cylinder. I saw this come up by one builder so did the mod beforehand and flew through IVA. If you need any info let me know as i probably
still have recipts for parts.
Can you get a DB killer before the silencer?
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Smoking Frog
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| posted on 4/4/14 at 02:40 PM |
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Bad luck and well done for having such a small fail list.
quote:
I) Brake bias. We could not get the balance between front and back right. Overall performance and left to right balance was fine. Strangely, fully
adjusting the bias bar from one end to the other made very little difference even though you could see the bar pivot. I was wondering how much
difference the length of the push rods that go into the master cylinders would make. Any ideas or thoughts would be appreciated.
If ajustment has no or little effect it is could be that the push rods need to be unequal lengths. As shown here:-
https://www.rallydesign.co.uk/balancebar.php
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MikeR
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| posted on 4/4/14 at 03:41 PM |
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If you need to stick with magnets another option is to put them on a wheel with the sensor mounted off the hub carrier. Means youll have longer
between pulses & a fourth less of them (approx depending on diff).
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SteveWallace
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| posted on 4/4/14 at 04:33 PM |
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Thanks for the advice.
I) I'm going to try moving the speed sensor to the diff driveshaft flange. This will cut the rpm that the sensor sees by a factor of 3.62, so
since its a problem that only happens at prop shaft revs above 50mph I should be OK as long as it doesn't obviously pulse at low revs. This
will also have the advantage of being much easier to access to adjust. Where it is now is a PITA and was really tricky to get to during the test.
Pads are standard Sierra front and back
ii) I had another look at the bias bar and I think that the clevis for the rear brake is binding against the tube that the bias bar sits in.
I'll also try to play with the lengths of the push rods. thanks for the link to the Rally Design notes
 
Description
iii) I'll repack the silencer with Acousta-fil and also see what I can put in the pipe to restrict the flow a bit. Before I take it to bits
though I'll measure the level again with my I-pod - not absolutely accurate, but should be good for relative difference now that I know what
99db on the I-pod means in terms of the official meter (i.e. 101db)
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jollygreengiant
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| posted on 4/4/14 at 05:33 PM |
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On mine, I put some large washer between the clevis and the tube as per picture below. Mine was disc brake all round if that helps. On front to rear
balance it went straight through (which was good because I'd already pinned it).
hope this helps.
Extra edit bit.
I set the balance up with all the wheels off the ground, helpers at the front and rear wheels turning them while I put my foot on the brake to work
out where the fronts bit/locked up and where the rears bit/locked up. When I was happy with where it was that's where I locked and pinned it.
(IF it failed like that then I would bring it back and sort it at home as de-pinning would have be a mare at SVA). So, IF yours is disc all round,
then, you should end up with the balance bar somewhere near mine. IF it's not, then might you have the master cylinders the wrong way round.
[Edited on 4/4/14 by jollygreengiant]
Beware of the Goldfish in the tulip mines. The ONLY defence against them is smoking peanut butter sandwiches.
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serieslandy
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| posted on 4/4/14 at 06:05 PM |
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Well done today, although its a fail  its not a bad one.
I had a problem with my racetechnology dash 2 when I had the wheel speed sensor on the prop shaft due to it moving too fast.
I ended up fitting the sensor into the rear upright with a bolt head stuck to the drive shaft, as (for me) it spins 3.92 times slower than the
propshaft. It might be worth considering.
My car isn't on the road yet but that is tested upto 60mph.
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rusty nuts
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| posted on 4/4/14 at 06:20 PM |
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From your photo there doesn't seem to be any clearance between the clevis"s and the brake pedal , you need a little to allow full
movement of the pedal without the clevis's fouling the pedal iirc the Rally Design and the OBP websites give advice on bias bar set up . I
take it you have too much bias to the rear brakes? Altering the pushrods length may?? have some effect? Another possible solution is a different bore
master cylinder, My Luego supplied pedal box came with 2 different sizes, the larger went on the rear brake circuit I believe. I had the same
problem at SVA but was able to tweak the bias to sort it out
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britishtrident
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| posted on 4/4/14 at 08:01 PM |
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Brake bias bars only work well if the setting is within a few turns of the central position. The side clearances between. the clevis are critical,
too small a clearance and bias setting will have very limited range, too large a clearance and system will not fail safe in the event of a circuit
failing.
Your problem may well be a front brake pad material is but the sure fire way to fix is to reduce the force acting on the rear pads. The options for
this are (1) fit a bigger bore master cylinder in the rear circuit. or (2) Fit a smaller bore cylinder in the front circuit (usually not a good
option) or (3) fit smaller bore rear wheel cylinders or (4) fit a pressure limiting valve in the rear circuit.
[Edited on 4/4/14 by britishtrident]
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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mccsp
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| posted on 4/4/14 at 08:09 PM |
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Hi,
Couple of thoughts.
What master cylinders are you using? The velocity instructions suggest non equal sizes. Does the Viento? If so are they defo the correct way round?
Biggest on the front axle. Easy mistake to make.
I failed my original sva as a result of the speedo fluctuating, are you sure the mount for the sensor stiff enough? Had to stiffen mine. It is mounted
on the diff input. I suspect it now gets a bit warm as every now and then on a long drive it stops working, but then starts again if I stop for a
while.
Why do it the easy way, when I can do things my way!
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CosKev3
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| posted on 4/4/14 at 08:21 PM |
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Not a bad list,well done 
quote:
Originally posted by mccsp
Biggest on the front axle. Easy mistake to make.
Wrong way around I think!!
Smaller to front brakes ain't it?
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mccsp
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| posted on 4/4/14 at 08:33 PM |
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Will check mine tomorrow, all I know is I failed on brake ballance and also couldn't get it to pass on the bias bar alone and ended up swapping
the master cylinders round and passing
Why do it the easy way, when I can do things my way!
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The Black Flash
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| posted on 4/4/14 at 09:35 PM |
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quote:
Originally posted by SteveWallace
iii) I'll repack the silencer with Acousta-fil and also see what I can put in the pipe to restrict the flow a bit. Before I take it to bits
though I'll measure the level again with my I-pod - not absolutely accurate, but should be good for relative difference now that I know what
99db on the I-pod means in terms of the official meter (i.e. 101db)
A cheaper option (since you don't need to worry about the emissions probe) is to make up a disc of metal, with two legs at 90 degrees to it, and
wedge it in the end of the exhaust.
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loggyboy
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| posted on 4/4/14 at 09:40 PM |
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quote:
Originally posted by CosKev3
Not a bad list,well done
quote:
Originally posted by mccsp
Biggest on the front axle. Easy mistake to make.
Wrong way around I think!!
Smaller to front brakes ain't it?
That was always my understanding, larger on rear.
Mistral Motorsport
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adithorp
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| posted on 4/4/14 at 10:28 PM |
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Yes' larger dia' cylinder on the rear, smaller on the front, push rod adjusted to be longer on the front and slight play between the
clevis' and adjuster tube.
"A witty saying proves nothing" Voltaire
http://jpsc.org.uk/forum/
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AvonJas
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| posted on 4/4/14 at 10:29 PM |
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Hi Steve , unlucky with the fail, but not to much to sort out . Regarding the speedo it seems like the problem I had , if you move the magnet onto
the driveshaft don't think you will have a problem ,sorted mine out . Good luck with retest .
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mccsp
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| posted on 5/4/14 at 08:52 AM |
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Morning guys.
Everything I have read backs up the above, including the luego build manual, so apologies for the misleading post.
However, I have a 0.7" master cylinder and a 0.625" master cylinder, which were originally fitted with the larger feeding the rear.
I failed the brake test due to longitudinal brake force not being met.
I am running sierra rear calipers and 265 x 10 mm wilwood powerlite front calipers for the cirtina uprights and a bias bar.
Because I was nervous about the brake bias I hadn't locked the bias bar. Adjustment of the bar didn't resolve the issue and we did drive
around the test facility to bed them in as well.
Having switched the master cylinders around to having the larger cylinder on the front, I was able to pass the test with a relatively neutral bias
set-up. I am not running any sort of servo and I have always been very happy with the performance of the brakes.
Why do it the easy way, when I can do things my way!
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DanP
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| posted on 5/4/14 at 09:53 AM |
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Hi Steve,
Sorry to hear you failed, but the list doesn't sound like its too bad, you'll be on the road soon!
The brake bias on mine was ok after I bedded the discs a little, I set the bias the way that JGG did.
Whilst you are adjusting make sure you get some washers in between the tube and Clevis', I didn't originally and a after a few thousand
miles the brakes started to stick because the bias system was getting stuck when I took my foot off the brake.
Regards,
Dan
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SteveWallace
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| posted on 5/4/14 at 04:11 PM |
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I've checked the master cylinders and I do have the bigger one on the back brakes. I think one of the problems is that the clevis pins are too
close to the tube that the bias bar sits in. I had a close look after the run back from the IVA place and following the posts on here and it looks as
though the rear one is catching on the tube stopping the bar from pivoting to its full extent (has a score mark down the side of it). This would
increase the pressure on the back brakes.
I'll move them out a bit if I can, the problem is that its a PITA to remove the pedal box due to access to the bolt heads with the rest of the
car now built around it. I may be able to undo the push rods and turn the clevis in situ.
WRT the noise test, I should have done more research on the rpm at peak power (test done at 3/4 of peak power RPM). I took the number off some dyno
curves that I found on-line, but I now realise that they were for tuned engines. I'm running the standard ECU for the IVA (I have a separate
tuned one but didn't want to risk it on the emissions) and if I use BMW's own peak power data I can drop the revs that the test is done at
by about 400rpm which should help a lot.
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DanP
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| posted on 5/4/14 at 04:18 PM |
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Unscrew the push rods from the clevis, that's what I did when I had to put the washers on, use two nuts locked to give you some purchase.
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