bobfett Posted November 15, 2014 Share Posted November 15, 2014 So, having bought an Austin champ (but yet to pick it up) my mind has turned to working out some fixes. The most pressing issue is a "thrumming" sort of sound when driving. Based on the demo drive, this only happens when in top gear (direct 1:1 through the gear box) and only when "on" the throttle. Come off the throttle and it immediately goes away. Definitely not a problem in any other gear. Only a noise, no vibration or wobble apparent from the front or rear seat. Difficult to tell where it's coming from. As daft as it sounds if it wasn't a "lever directly on top of the box" arrangement I'd be inclined to look for something fouling the linkage in the fifth position. Few thoughts I've had: Internal gearbox fault- seems relatively unlikely as it's a constant mesh box and top is the "simplest" gear? Universal joint- one of the more likely culprits I suspect although it seems a little odd it's only in top (and seems to be as soon as you engage fifth, no evidence seen at the top of fourth). Tyre imbalance (one or between axles)- seen it suggested somewhere that it's possible to get tread "skipping" if there's a difference in rolling circumferences front/back or it's simply a wheel out of balance. Seems unlikely due to the noise stopping when off throttle. Reading it back now maybe it is a gearbox fault. Any other ideas? Quote Link to comment Share on other sites More sharing options...
antar Posted November 16, 2014 Share Posted November 16, 2014 So, having bought an Austin champ (but yet to pick it up) my mind has turned to working out some fixes. The most pressing issue is a "thrumming" sort of sound when driving. Based on the demo drive, this only happens when in top gear (direct 1:1 through the gear box) and only when "on" the throttle. Come off the throttle and it immediately goes away. Definitely not a problem in any other gear. Only a noise, no vibration or wobble apparent from the front or rear seat. Difficult to tell where it's coming from. As daft as it sounds if it wasn't a "lever directly on top of the box" arrangement I'd be inclined to look for something fouling the linkage in the fifth position. Few thoughts I've had: Internal gearbox fault- seems relatively unlikely as it's a constant mesh box and top is the "simplest" gear? Universal joint- one of the more likely culprits I suspect although it seems a little odd it's only in top (and seems to be as soon as you engage fifth, no evidence seen at the top of fourth). Tyre imbalance (one or between axles)- seen it suggested somewhere that it's possible to get tread "skipping" if there's a difference in rolling circumferences front/back or it's simply a wheel out of balance. Seems unlikely due to the noise stopping when off throttle. Reading it back now maybe it is a gearbox fault. Any other ideas? I would not think that it is "tread skip" as the Champ is selectable 4x4. The road test should have been in rear wheel drive only. Make sure the lever in the passenger foot well is pushed forward. Champs suffer from various rear axle problems, worn out phosphor bronze bushes in the trumpets could be the issue. Where are you located ? Quote Link to comment Share on other sites More sharing options...
wally dugan Posted November 16, 2014 Share Posted November 16, 2014 WHEN l worked on champs l was told by mentor when a champ came in with a reported fault with the gearbox which appeared when in fifth and disappeared when the clutch was depressed on over run his words of wisdom were before removing the gearbox drain the oil out of the rear axle and check to see if it is silver in colour and contains swarf l said the noise is in the gearbox he then explained that when there was wear in the crown wheel and pinion noise travels up the prop shaft and appears to come from the gear box in this case he was right Quote Link to comment Share on other sites More sharing options...
snort Posted November 16, 2014 Share Posted November 16, 2014 WHEN l worked on champs l was told by mentor when a champ came in with a reported fault with the gearbox which appeared when in fifth and disappeared when the clutch was depressed on over run his words of wisdom were before removing the gearbox drain the oil out of the rear axle and check to see if it is silver in colour and contains swarf l said the noise is in the gearbox he then explained that when there was wear in the crown wheel and pinion noise travels up the prop shaft and appears to come from the gear box in this case he was right I would agree with this too Wally, having had an axle on a Champ go bang and drop all it oil out of the crack!:-D Quote Link to comment Share on other sites More sharing options...
bobfett Posted November 16, 2014 Author Share Posted November 16, 2014 The rear axle was my first thought too, but it seems odd it's only in fifth (not the top end of fourth where the rear diff would be at about the same speed as the initial engagement in fifth) and to be clear it disappears as soon as you take your foot off the throttle, clutch in or out. Despite this I suspect the rear axle is the mostly likely culprit; just as well I got a second one with it! Quote Link to comment Share on other sites More sharing options...
GeePig Posted November 17, 2014 Share Posted November 17, 2014 I know very little about Champs; however, if 5th is the straight-through gear, then the drivetrain is effectively locked into a solid shaft from clutch to axle. In any other gear the drive goes through the layshaft, so the drivetrain is a solid shaft only from the gearbox output shaft to the axle. Hence the transmission of any noise from the axle to the gearbox will be different when in 5th. trevor Quote Link to comment Share on other sites More sharing options...
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