automatic clunk

[lyn]

My stag with BW35 auto had a clunk comming or going from park and when gear change, then one day no clunks at all for 3 plus months,woopie,well now its doing it again !! Any idears,
regards lyn

[Philip Wardle]

Clunks are mostly caused by backlash in the differential or joints in the propshaft of half-shafts and can usually be located by inspection, this type of wear tends to be present consistently.

However I also had BW35's on Triumph 2500s where clunks came-and-go as a result of a fracture in the drive plate between torque converter and crankshaft. This takes the form of a circular crack concentric with the crankshaft which can sometimes go away for a while if the broken pieces lock together. But eventually there is a sudden loss of drive once the edges of the crack wear against each other sufficiently to create 360 degree clearance.

[richardthestag]

Like Philip says, I would be checking each UJ; 2 on the propshaft and 2 on each driveshaft, the outer joint on each driveshaft requires that the shaft and hub be removed.

First though what is the engine idle speed, ideally around the 700rpm mark should be good

[Philip Wardle]

Good reminder re idle speed Richard, thanks. It would be interesting to know more about about the static or driving conditions when clunks arise? Any sense of where clunks might be coming from?

[lyn]

its got me beat when cold choke out reving higher than normal,bang it into reverse no problem, but now all thats gone,like over night,seemes to be around auto box.

[gbb483]

clunks came-and-go as a result of a fracture in the drive plate between torque converter and crankshaft.

I was advised that this was a potential cause of a problem I had with a Wolesley 6 many decades ago.

[Philip Wardle]

Interesting ... one instance of the drive plate problem was on a 2500S I bought at 14,000 miles, I think it was about three years old. Although its 12 month factory warranty had expired I wrote to Triumph to ask if there were any known causes to look out for, hoping they might offer some info even if nothing in the way of practical help. After a number of weeks I did get a reply saying that it wasn't a known problem and they weren't able to suggest possible causes. However I seem to remember speaking to main dealerrs and others at the time who seemed to know about it. I had two instances of this, but I'm not sure if both were on the same 2500 S or one failure was on a 2500 TC.

Thinking about this again now, a drive plate fracture sounds more like a metallic rattle than a deep, solid, clunk. And you can often hear it when the car is idling or travelling in-gear as well as during changes - but I'm remembering this from more than 40 years ago. So if this is definitely a clunk the fractured drive plate theory may be a red herring, but I was prompted to suggest it because the problem went away for three months and came back - similarly to my experience.

[lyn]

all tnethoughtd and google the plan is tomorrow to c\take out and check the governer ,proberly a half days work,heres hoping

[Philip Wardle]

Could also look at the condition of the rubber bobbins which support the rear of the gearbox and the nearby brackets supporting the exhaust pipe, e.g. for any failure t that might cause a knock?