knocking noise from the rear

[chris52]

I have a knocking noise coming from the rear of the 3000ml. It sounds like a cross between a noisey drive shaft UJ and the exhaust banging on the chassis, it's only there when you are accelerating you can hear it in any gear, it's not overly loud so once you get going it's hard to tel if it's still there. Setting of you can hear a knock knock knock, if you on a quiet road in say 4th if you put your foot on the loud pedal you can hear it but as soon as the foot is of the gas it's gone. So today I pulled the drive shafts and checked the UJ's even though they are all new also checked the prop and made sure the exhaust is not catching anywhere. All checked out OK with no issues. The diff which is the TR6 type is also fully recoditioned and seems to be OK I do have a bit of play if I hold the prop and one wheel I can turn the other maybe 3 or 4 minutes if think of the whhel as a clock but I would expect that is due to the internal spiders.
I have only done about a 100 miles in the car since its rebuild, I did have to swap the engine that was noisey but don't remember having this clunking knocking noise so maybe I've done something while swapping the engines?
Any ideas would be great of what to look at next .

[chris52]

Cheers Guys
I must admit I was very unsure how tight the front bush bolt should be. It is basically two lumps of rubber squashed either side of the mounting yoke by a 5/8th bolt and two big washers is there a torque setting for this?
Chris

[chris52]

Well this one has got me baffled, checked everything was nice and tight. Checked all the UJ's checked the diff hanger made sure the brakes were all OK. Took it out for another spin and knock knock knock. So got the car back jacked it up removed the wheels lowered the car on to blocks under the rear hub carrier so the suspension was at normal ride height and Started her up. With the car in gear I got a mechanics stethoscope on the differential no noise I know that there was no load but if there was a problem I'm sure you would have heard something.checked the oil and all good listened at the hubs and the same all quiet. Checked the exhaust and nothing loose or close to catching. Not been out in the car since as it started raining but as I haven't actually found or repaired anything I'm guessing it will be the same.
No idea what to look at next.
Chris

[chris52]

Not the hand brake cable checked that. Will look further forward.
Cheers Chris

[chris52]

Cheers D but checked those also. I will find it eventually

[chris52]

TVRMs said:

Diff on its way out?

Diff is fully rebuilt and have checked it. It will end up being something daft. The main problem in finding it is it's hard to know if it's always there as its not very loud and the car is pretty noisy anyway. You can hear it best when your driving on a very smooth road. Take you foot of the gas and it disappears back on and there it is again it doesn't matter what gear your in and you can also hear it when setting off. I can't quite decide if it speeds up the faster you go as when you accelerate the noise of the engine drowns it out. Would just like to find it damn annoying more than anything. I thought it may have been coming from in the fuel tank area but have had it all out and nothing in there that can knock.
I will try get it down to work over the next week or two and get it on a ramp and just check everything underneath.
Thanks for the suggestions
Chris

[chris52]

Cheers John yes did check it and couldn't see any cracks movement or problems with it. It is something of concern as I should have had strengthened while it was off. Schoolboy error on my part as they are a pain to get off once the body is back on. I could do with getting a spare really to have welded up and ready to put on so I can do it in one go.
Chris

[chris52]

Well it's coming from the rear, the only thing that I haven't removed and checked is the diff so I guess it's time to pull it out, a job that I really didn't want to have to do with the body back on hence having the diff rebuilt to try and stop this happening. Anyway a mate is coming over in the morning for a second opinion before I start the job. Well p@@@ed of at the moment. Won't be ready for BHP season opener.

[chris52]

Diff is out and can't find anything wrong with it. Very smooth no damaged teeth no play. The carrier has no cracks But where the rear bush mounts was a bit misshaped and the bushes inner sleave can slot through the bolt hole. Had a chat with Adrian and he will be sending me a recon heavy duty carrier and new rear bushes. Fingers crossed this sorts it all out.
Thanks for all the help
Chris

Edited by chris52 on Sunday 3rd April 20:36

[chris52]

Mine is the Tr6 diff so wouldn't really help you. The Carrier and the way it's mounted it totally different.
Chrisb

[chris52]

Starting to get fed up with this now. Had the diff out found a possible rear bush and carrier issue got a beefed up carrier from Adrian and new rear bushes. Checked all the drive shafts hubs prop etc pulled the back of the diff and checked all the brearings and gears and all good just got it all back together tonight and test diven and exactly the same power on clunk clunk clunk power off all quiet more noticeable when going up hill but can't hear it when on full power. Can't really feel it no vibrations sounds a bit like a dull UJ sound but they are all new and fine. No idea what to look at now. May have to just put up with it until it either disappears or gets a lot worse but does take the shine out of driving it.
Chris

[chris52]

V6Pushfit said:

I had a similar clunk particularly when taking up power or coming off power. After numerous diff changes it turned out to be a worn driveshaft spline. I had looked at UJ's and they were ok and only later looked at splines - movement was minimal but still noticeable when doing it by hand but the tiny click was enough to resound when driving to give a loud almost thump type noise.
Any use?

Cheers for the advice but I did try this and did find one that had a small amount of play in so replaced it but made no difference. It was suggested earlier that it may be further forward I have checked the gearbox mounting and engine mounts also the exhaust. Clutch feels fine checked all bellhousing bolts as well. Handbrake cables aren't touching anything plus if you put the handbrake on while drivingitmakes no difference to the sound. No idea where to go next. Was thinking of driving down to BHP on Sunday but not sure I dare risk it. It must be something

[chris52]

bluezeeland said:

- Rear hubs to upright bolts ?

-lower rear uprights to wishbone pin ?

-g/b rear mount ?

-engine mounts ?

All checked and good I think it must be internal on the diff. I have another diff on its way a known good one so will try this. If this doesn't work then I will have to admit to being beat and see if it get worse which will help find the fault.
Thanks for the help Chris

[chris52]

TVR Beaver said:

I mean.. it's that loud isn't it

It's one of those noises that just spoils your driving as your always listening for it. Your right it isn't loud and most of the time you can't hear it above the exhaust and road noise, but it's there and needs sorting.
New diff now acquired so will be fitting it over the weekend. This diff has a lot less free play on the prop pinion so may be that the guy who rebuilt mine didn't do a good job or missed something he was recommended by other Tvr guys that have had them rebuilt by him with no issues. He also rebuilt the Vixen diff so hopefully that will be ok.
Chris

[chris52]

Before fitting the replacement diff as it needs a new front oil seal which is on its way to me I decided to do some measuring of the backlash on the diff. DTI gauge on the ring gear and measured the free play. Triumph quote 0.004" to 0.006". The one that I had rebuilt was 0.0118". The second hand one that I have just bought the backlash 0.0055 so within tolerance. I don't know if this will cause the noise I cant find anything else wrong with it but this is pretty disappointing to say that a well known rrecommended axle specialist would allow this to come out of there workshop like this.
Would appreciate any opinions on what basically double the backlash will do and if it's possible this will be the cause of the noise.
Chris

[chris52]

Replaced the diff and the noise has now gone so must have been something in the diff. I have sent it back to the rebuilders to find out what was up with it and get it sorted as I will put it back in the car at some point as the one in now has a small oil leak.
Chris