Kriss
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| posted on 25/10/10 at 12:01 PM |
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Large transmission bang when lifting off gas
Hi all,
Went for a drive at the weekend and was worried to hear that the diff or prob and banging loudly when I lift off the gas fairly sharply.
The prop and diff have always bashed when changing gears, but this is very noticable and has not been present before.
any ideas or suggestions on where and what to look for? Prop and engine are mounted nicely, no bolts have come off there.
Its one lou clash/bang when the car is being driven, and power removed suddenly.
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sonic
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| posted on 25/10/10 at 12:08 PM |
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Have you checked the Diff mount bolts and drive shafts if they the Lobro type.
Does your prop have the cush tube fitted,if so check that isnt worn.
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bigrich
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| posted on 25/10/10 at 12:08 PM |
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have your diff mounting bolts come loose, or driveshaft bolts (if lobro bolt on type)
also check prop coupling for security on the engine output shaft.
do a nut and bolt re torque on the driveline bolts just to be sure,
.JPG)
A pint for the gent and a white wine/fruit based drink for the lady. Those are the rules
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irvined
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| posted on 25/10/10 at 02:14 PM |
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Edited as you've already checked the prop bolts...
As above, most likely to be play somewhere in the driveline due to bolts loosening.
Check:
Diff Mounts
Prop shaft bolts
Prop Adapter Nut/Float in Adapter
Reverse box/central bearing mounting
Driveshaft bolts
Does this sound familiar?
Also check the lash in the diff/reverse box. If there is a lot of lash you'll notice quite a wack when you come on/off the power.
[Edited on 25/10/10 by irvined]
http://irvined.blogspot.com
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Kriss
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| posted on 25/10/10 at 02:33 PM |
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will do a full spanner check of drive train first.
I suspect last as the diff has always been loud when selecting gears. under drive the car is fine, but that stroy is enough for me to ckeck and also
the safety of getting hit by the prop.
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Kriss
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| posted on 27/10/10 at 09:42 AM |
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OK, I have been told to look at all the prop bolts, slack in the UJ's, diff mounts, and also check that the spocket nut has not come
off/slack.
still think its my diff back last as its always been terrible!
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chunky2772
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| posted on 27/10/10 at 08:49 PM |
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ive got the same problem mate im useing an mx5 diff but i also have a residial tube on my prop shaft when i lift of the gas a bang comes from what
sounds like the diff the car seems ok when driveing under power ive checked every nut and bolt plus flange adapter nothing is loose my diff is a 4.1
ratio and gives instant engine brakeing. what ratio diff are you useing?
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Kriss
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| posted on 28/10/10 at 07:32 AM |
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Are you bike engine in addition to your mx5 diff?
I have a bog standard 3.62 sierra 4x4 rear LSD diff . My car always made a very loud metal on metal knock when put in gear, but this is more solid and
not related to changing gear.
Any other suggestions and bedt practice for removing the front section of the prop and flange/sprocket adaptor
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chunky2772
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| posted on 28/10/10 at 06:37 PM |
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my bec is powered by a k8 2008 gsxr 1000 my prop shaft is a two part with center bearing. my car is a new build chriss gibbs locost roadster! my mx5
diff has got a little play in the flange (i,e, you can move the flange on the diff left to right about 10mm before the rear wheels move if you know
what i mean) im sure this play in the diff is causing the bang in the rear section of the car. when you lift off the gas the sudden stop on the prop
sort of rebounds the flange on the diff causing that loud bang im sure this is the cause of mine. with engine switched off please try pushing your car
back and forwards when in gear and listen for a slight knocking from the diff. let me know if you hear that slight knock as this will also confirm why
mine is doing the same as yours
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adithorp
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| posted on 28/10/10 at 07:14 PM |
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Is this noise worst than it used to be? I seem to remember you posting about it before.
Is the diff' solid mounted (as most are)? That means that any noise/vibration from the transmission transfers directly to the chassis and is
amplified by the paneling. When you come off the gas in a BEC the lack of flywheel on the engine means the back lash in the transmission is taken up
quicker giving a bigger knock.
Have you had any other BEC owners in the car. That'd give some idea of whether this is unusual.
"A witty saying proves nothing" Voltaire
http://jpsc.org.uk/forum/
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Kriss
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| posted on 29/10/10 at 12:48 PM |
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the bang when lifting off the gas when in gear and the car is moving has never been there before and is very pronounced.
The lower gears and selecting 1st from N has always been loud, and is also loud compared to an R1 MK and Busa Westfield.
Yes the diff is hard mounted straight to the chassis, no bushes.
I think the slack in the diff has got worse following some fairly hard laps at the ring a few months back
checking int eh transmission begins tomorrow!!!
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Kriss
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| posted on 30/10/10 at 02:01 PM |
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OK, so the diff has oil, the diff mounts look fine, all the bolts are in and have not moved, the prop is running round and round smoothly.
Im lost!
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adithorp
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| posted on 30/10/10 at 10:13 PM |
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With the car either on the ground or supported with the handbrake on, in neutral, turn the prop' as far as you can by hand in one direction.
Then turn it the other way.
How much does it turn?
Thats the back-lash. It'll feel worse/more than it is so measure it. Some of it will be in the driveshafts but that should be hardly anything
and you'll only just see it (multiplied 3x at the diff input) if the shafts are OK. The rest is in the diff'. Sierra diff I'd
expect less than 5mm at the diff input (propshaft).
adrian
adrian
"A witty saying proves nothing" Voltaire
http://jpsc.org.uk/forum/
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Kriss
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| posted on 1/11/10 at 11:56 AM |
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hi adi, when turning the prop there is a good chunck of rotation available. I would say it turns 1CM, maybe more when grabbing the prop.
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adithorp
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| posted on 1/11/10 at 04:38 PM |
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That sound a lot for a Sierra diff (freelander ones have a fair bit) and would account for the knock. As you shut off all that play is taken up.
Try marking/measuring how much there is. It always feels more by hand. Is there any movement/play in the driveshafts?
adrian
"A witty saying proves nothing" Voltaire
http://jpsc.org.uk/forum/
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Kriss
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| posted on 1/11/10 at 05:24 PM |
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sure, whats the best way of measuring?
was thinking of drawing top dead centre inline with the top middle of the diff, handbreak on, then turning till I feel load again.
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adithorp
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| posted on 1/11/10 at 07:49 PM |
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Yep, thats about it. Mark (Tip-ex) a point on the flange against a fixed point on the diff then lock the wheels (handbrake on) and turn the prop as
far as possible to take up the play (don't force it) and measure the distance.
adrian
"A witty saying proves nothing" Voltaire
http://jpsc.org.uk/forum/
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mistergrumpy
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| posted on 20/11/10 at 03:02 PM |
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Kriss. Was wondering if you'd got any further on this?
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MikeR
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| posted on 20/11/10 at 04:02 PM |
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if you read his next thread, he's found that one of the bolts is tight, but not clamping the diff. The mounting hole on the chassis appears to
be larger than the bolt.
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mistergrumpy
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| posted on 20/11/10 at 05:27 PM |
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Ah. I'll look now. I get the odd sporadic look on here on my Blackberry so some threads get looked over. Cheers matey.
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Neville Jones
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| posted on 21/11/10 at 05:02 PM |
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If the diff is solid mounted, then start at the diff, and work outwards, checking for broken tubes and/or welds.
All those shock loads have to do something, and eventually every solid mounted diff will either break the mount at the diff, or one of the mounting
tubes or lugs, wherever they may be.
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