mark kibort

I just got back from a Thunderhill race where the ole 928 ran like a champ, sans one noticeable difference...………..it had a weird vibration at 5000 to 5500rpm in gear and under load, in any gear. it doesn't seem to do it in neutral and seems to be smooth as silk with the clutch in and in neutral...……….because it showing this vibration in any gear and at any speed, it seem to me that its pointing to the torque tube ort the 5th gear input. because it is at a specific range of RPM, its puzzling me. ill have to put it on jack stands to listen more closely for its behavior under load..

anyone else have a failure that started out sounding like this?? its a vibration that almost reminds me of the throwoutbearing out of balance when I had a ring clip issue, BUT, that happened at 5000rpm too, but didn't smooth out at 5500rpm...…….and it did it all the time , in or out of gear...….

Let me know any thoughts you all might have on the issue.

thanks

Speedtoys

Look for a weak ignition path. Same exact issues were a corroded gapped weak plug 7 wire into the plug boot. The crimped end failed.

mark kibort

I thought of that for a second, as I had the arc'ing coil low voltage to high, once and that was similar,as the vibration. ……….but I think it was pretty consistent, from 4500rpm up to 6500 and this situation smooths out after 6000rpm... I don't feel anything under no load conditions. (just reving out in neutral..) is that consistant with what you saw too?? , could that still be the situation with a weak or shorting spark?
thanks ill see if I can see anything in the electrical area.
thanks Jeff!
Mk

mark kibort

I also left out another issue I had...……..im running around and the tach and speedo are going wacko... (ironous readings ) and all the warning lights would come on, but it was still running. I started feeling that vibration then. this was qualifying, so I ran about 5 laps and came in after I got a clean lap...…. I turn off the car and turn the key to start off again, and there is absolutely no electrical power... dead... thought it was the kill switch, but all checked out. (battery voltage, kill switch working etc). so, the first place the power cable goes is the starter and alternator. alternator looked secure, and then the open wires to the starter showed the problem. the 10 gauge wire (red) going to the starter was broken off at the ring terminal (two wires attached at one crimp ring terminal). I rig it for the race, and it held, but that vibration was still there that I felt during the session. could the wire having a week connection and breaking occasionally , damaged something ??? (igniters, coils, ecu, etc)?

FredR

Mark,

The wire you refer is not a 10 gauge or any gauge for that matter it is a 10mm2 metric cable that feeds power to the ABS live post. If that cable is down you will not get power to the ABS pump and I would expect an alarm[s] on the annunciator to reflect the condition. Cannot see anyway that would cause your vibration issue though.

Vibrations that appear at a certain rev and disappear at higher revs invariably are resonance issues of some kind rather than wear issues and if the issue appears at the same rpms irrespective of gear then the problem invariably has to be generated by the motor or so logic would suggest. As I can understand the first sign of motor mount issues is when harmonic vibrations appear at 1400 and 2800 rpms and by extension 5600 rpm give or take some rpms. Why you might feel something at 5600 and not the lower speeds I do not know other than as a racer you are likely spending most of your time above those lower engine speeds. Whether or not there are any other likely explanations remains to be seen but your engine mounts need to be eliminated from the investigation first or so I would think. .

mark kibort

Thanks fred!!! Love the knowledge base here. So, that's why my ABS was now working last race. the T1 mustang last race said I was locking up in a few places at laguna. also, noticed I could lock up on demand. even did it in the pits.. no problem no ABS. well, it might not have caused the vibriation issue, but thought since when the wire connection was breaking, that all warning lights were going off like a Christmas tree...… but it kept on running but that vibration was never felt before, even in the prior session that day...….. so it made me wonder if maybe I damaged something electrical...….. Good to hear that you think its not a wear issue , like im narrowing it down to be transmission due to it only happening in gear, and at high rev. (like 5th gear, or torque tube). yes, It does act like a resonance issue., but again, its very similar to what I felt when the throwout bearing was out of alignment. no quite as bad obviously. interesting you think it could be motor mounts..... I know mine are old and compressed, but the engine has always been SO silky smooth at all RPM. …… when it stops raining.. ill look at ignition and see if I can see anything on the motor mounts.. any other ideas????

btw... what Is the best way to fix that small 10mm wire leading to the larger hot 12v wire to the starter motor? crimp and solder a ring terminal on it and join the tightening post????
thanks!!!!

FredR

Mark,

The ABS system does not work too well if there is no power going to it-

I would not say your problem is "not related" to wear as it could be as simple as worn out engine mounts- I know you like to get your money's worth out of parts- do you have Yorkshire blood in you by any chance? If you know the mounts are shot that could be a clue! As a general statement when moving parts on rotating equipment are worn the problem usually gets worse with speed as in a wheel that is out of balance but when there is a critical frequency it tends to be more noticeable at that point thus one becomes aware something is amiss. Bottom line with any problem always try to eliminate the more obvious causes first! Maybe you should consider some of those rebuildable mounts Hans offers? I use a pair of Roger supplied Volvo mounts that I would think are perfectly OK for your use even though there has been debate about them- my track record with the OEM ones is not good to say the least and that when I had the proper trays with cooling ducts fitted!

When it comes to making up such terminals there are different schools of thought or so I found when researching for my engine harness project. The way it works is that you need compression lugs and a suitable crimping tool. The size of the compression lug is determined by the size of cable[s] you want to stick in the thing. Thus if you have a 16mm2 cable [the one to the alternator] and a 10mm2 cable you need a 26mm2 lug with the correct opening size for the mounting bolt [cannot remember that off hand]. In my case I sourced a 25mm2 lug and managed to fit my cables into it no problem. The research I did suggested that crimping and soldering might not be a good idea in combination but I am sure some folks would recommend it. When I removed my cables I dissected the original joint and found no signs of solder so replicated what I saw. Even so it still scares the poo out of me thinking that a joint I prepared and crimped is carrying a live feed that is not fused! I put two layers of shrink sleeve over the terminal as far up the lug as I could as well as the sleeving. If you are still running the original engine harness it is probably shot by now. FYI I ran the live feeds and the other cables in separate runs with heat shrink and sleeving. I also inspected the joints a couple of weeks ago during annual inspection/maintenance to ensure to the extent I could that they were still holding up. If you do attend to the harness the 4mm2 cable to the starter motor solenoid will probably be toast and the 1mm2 blue cable to the alternator is also a critical item, the rest of the cables are less critical but if you are doing one do them all or better, still get a new harness and sleep easy for another 20 years. I dare say you can get metric size cables but in your locale the cables tend to be AWG in even number sizes- easy to go with the nearest size bigger and appropriate crimp terminals to suit.

mark kibort

thanks fred…… getting back to the broken 10mm wire, you say that goes to the ABS pump? but why does the entire car have no voltage …when it was breaking connection, all the warning lights were coming on and the tach and speedo were going wacky! I guess I could pull out the wiring diagrams, but if you have the quick answer, that will be good enough for me.

thanks

Mark

FredR

Really needs someone like Allen to give you their thoughts on that one but if the 10mm2 cable came away from the connector as in the complete cable worked its way out then in such circumstance the other cable [16mm2] to the alternator would be virtually free floating and thus conceivable that there would be little to no current flow coming through from the battery to the alternator. When the engine is on load this should be no problem [I would think] but when the revs drop to idle the alternator is not putting out much and maybe demand outstripped supply and various alarms initiated due to low voltage when there was no back up from the battery.

I know when I fitted a locally purchased belt for the ac compressor, during some maintenance I had not planned for, the bloody thing jumped derailing the alternator and power steering belts- the dash lit up like a Christmas Tree with all kinds of alarms going off but it was pretty obvious what had happened as the voltmeter immediately went to 12 volts instead of the normal 13.5 volts or whatever, the ac packed in and the steering was like wrestling a bear- fortunately I was close to home at the time.

mark kibort

Makes sense...… Yes, the 10mm broke free, but Is this the main line from the battery positive? anyway, yes ive had the alternator go bad during a race. I don't know if all the warning lights went on, but I do remember getting a real big battery and running the next race only on the battery for 30min. the only diff is that the overall voltage of the system is under 12volts where when the alternator is working, its more around 13.. (maybe this changes things in the ecu, for timing, mixture , etc)….
in checking the wiring diagram... I don't see how the ABS is fed off this power line, it seems to be the smaller wires feeding the EZK as well. if that source was cut, I would guess the car wounldnt run. anyway, ill find a way to get another ring terminal to attach to this wire, as the reason it was broken is that it had an extreme bend in it at the junction point … I cant see exactly what wire this is from the battery on the diagrams. there are 3. the lone single comes from the fuse panel from the starter relay..

this is the easy fix.... just splice back in the wire. my real concern is that vibration its possible to be a resonance of the engine, but it was so all of the sudden...… so, im thinking something is out of balance like the torque tube and a bad bearing, but there is no noise associated with it. power is good too, as there is no variations to the smooth power.... that vibration due to the coil arcing was pretty noticeable and hurt power too.

once it stops raining. ill pull it out and start doing some tests
thanks for the help

Mk

FredR

Mark,

Given the 10mm2 cable came out of the common terminal they were crimped into I think you need to start thinking "big picture" here. Undo the cable the fires the solenoid on the starter, undo the cables on the power terminal of the starter and tie some chicken wire [about 1m or so] onto the terminal of the 16mm2 cable ensuring it will not drop off and pull the cable through to the alternator such that the chicken wire acts to retain the routing. You should then remove the cables from the alternator and then try to remove the orange fibre glass sleeving so that you can inspect the condition of the cables. Do not be surprised as to what you will likely find.Expect to see discoloured insulation [brown rather than red], cracked insulation or insulation that simply falls off if you attempt to bend the cable at all. Take a look where the 16mm2 cable enters the hot post- is that brown and the insulation in poor shape?- that is open at the moment. You should plan on replacing these power cables. Take a look at the cables entering the 14 pin connector from the engine bay -what kind of shape are they in?- take some pics of what you find and post them if you can.

Remember that the big cable from the battery runs to the starter motor- from the starter motor two cables run to the alternator [16mm2] and the ABS post [10mm. At the alternator you have two 16mm2 cables in one terminal- the 16mm2 cable from the starter motor and the 16mm2 cable to the hot post next to the 14 pin connector. the latter feeds the central electrics. At the positive terminal of the battery there are several smaller cables that feed the fans and the ignition system plus whatever. When a cable in this system breaks free there has to be a good chance that something in that circuit earths accidentally and that is not good. If that happens you will probably get all kinds of alarms even if it is just a transitory earthing event.

mark kibort

I think It is the curved "brown" wire crimped together with the larger wire on the starter. Picture attached of the IMI starter on another car. (not mine)

so this wire goes to the ABS? and also cuts out all electrics, but allows the car to run on the battery? btw. the wires all look pretty good and not toasted, especially in the alternator. (I was just in there a little while ago replacing the alternator armature)

FredR

Mark,

Those cables are typical of ones that are fubarred- they are not brown naturally they are supposed to be fire engine red. Look inside the insulation and I'll bet they are corroded with signs of green copper oxide and pretty much the same all the way along. Whilst in the sleeving you cannot see what condition the cables are in- chances are they are at their worst at the point where they loop around the alternator.

Time to do a thorough examination of your engine harness me thinks or more to the point, replace it in all likelihood- they are pretty much all like that [or worse] by now.

mark kibort

Fred, That picture is NOT my car, but ill take a shot when I get under the car again. the one thing working to my advantage, is that my car has only seen water a few times in the past 20 years. when I installed the engine 10 years ago, the harness was in really good shape, sans all the hacking up near the computers for wiring mods. near the alternator , they did look very good there too.

ill send a pic when I get under the car so you can see my "field hack" fix to make the race last weekend.

thanks again!

GregBBRD

Might be too obvious to suggest, but I'd pull the drain plugs and see what is on the drain plug magnets. You can also run a "magnet on a stick" in the front drain and fish around for "big pieces" that might not come out on the drain plug magnets.

To keep your racing budget "in check", if you drain the oil into a clean pan, you can probably re-use it. (Paint strainers work pretty good to remove the giant chunks.)