David Farmery Posted October 5 Report Posted October 5 My 4A is now in the road after a nut and bolt rebuild including new chassis (unexpected cost!) engine rebuild and suspension. When changing up from 2nd to 3rd and 3rd to 4th I’m experiencing a jerking movement and only by manipulating the clutch am I able to smooth it out. It’s a 3.7 diff, overhauled a few years ago by someone recommended by Register members, so not really thinking it’s the diff but could be wrong, hopefully not! I checked one of the rear wheels for play; holding the wheel at 3 and 9 o’clock there is 3/8” play measured relative to the outer edge of the 16” rim. Is this sufficient play to cause the problem? All UJ’s have been renewed; propshaft balanced. I’d be grateful for any ideas as to what might be the cause. Quote
ctc77965o Posted October 6 Report Posted October 6 Rear Wheel Bearings? Sticky halfshaft splines? Binding brake? Rear Wheel Alignment? Quote
Z320 Posted October 6 Report Posted October 6 (edited) Hi David, slowly driving below 2,000 revs is difficult? Specially under low load, in roundabouts, in town traffic, stopp and go? This my 4As problem. Ciao, Marco Edited October 6 by Z320 Quote
John Morrison Posted October 6 Report Posted October 6 David, I checked one of the rear wheels for play; holding the wheel at 3 and 9 o’clock there is 3/8” play measured relative to the outer edge of the 16” rim. Is this sufficient play to cause the problem? I don't know whether it would be the cause of your issue, but it is too much play, and I'd be looking at wheel bearings. You say jerking, does anything happen if you simply raise and lower the throttle, but do not change gear? John Quote
jerrytr5 Posted October 6 Report Posted October 6 Is that rear wheel movement replicated at 6 & 12 o'clock? If so, far too much & indicates wheel bearing wear. If only in one plane then possibly loose bolts holding hub to trailing arm (stripped thread?). Other thing to check for 'jerking', maybe drive or propshaft phasing? Jerry Quote
David Farmery Posted October 6 Author Report Posted October 6 3 hours ago, John Morrison said: David, I checked one of the rear wheels for play; holding the wheel at 3 and 9 o’clock there is 3/8” play measured relative to the outer edge of the 16” rim. Is this sufficient play to cause the problem? I don't know whether it would be the cause of your issue, but it is too much play, and I'd be looking at wheel bearings. You say jerking, does anything happen if you simply raise and lower the throttle, but do not change gear? John Hi John, yes raising and lowering the throttle induces the jerking. The play I described is rotational as opposed to vertical. 1 hour ago, jerrytr5 said: Is that rear wheel movement replicated at 6 & 12 o'clock? If so, far too much & indicates wheel bearing wear. If only in one plane then possibly loose bolts holding hub to trailing arm (stripped thread?). Other thing to check for 'jerking', maybe drive or propshaft phasing? Jerry Quote
David Farmery Posted October 6 Author Report Posted October 6 Just now, David Farmery said: Hi John, yes raising and lowering the throttle induces the jerking. The play I described is rotational as opposed to vertical. Just now, David Farmery said: Hi John, yes raising and lowering the throttle induces the jerking. The play I described is rotational as opposed to vertical. 5 hours ago, ctc77965o said: Rear Wheel Bearings? Sticky halfshaft splines? Binding brake? Rear Wheel Alignment? 5 hours ago, ctc77965o said: Rear Wheel Bearings? Sticky halfshaft splines? Binding brake? Rear Wheel Alignment? Rear wheel bearings have been mentioned but I’ll look into your other suggestions. What are you meaning by ‘sticky’half shaft splines? Quote
trchris Posted October 6 Report Posted October 6 Hi David Is there excessive backlash in the differential? And as mentioned are the drive shaft splines worn ? Both could give you the symptoms you described also has the gearbox and overdrive been overhauled? Chris Quote
David Farmery Posted October 6 Author Report Posted October 6 7 minutes ago, trchris said: Hi David Is there excessive backlash in the differential? And as mentioned are the drive shaft splines worn ? Both could give you the symptoms you described also has the gearbox and overdrive been overhauled? Chris Hi Chris Gearbox and diff overhauled by Mike Papworth so can’t see that they’re the problem. Hubs were also overhauled so may be it’s the splines. I mentioned about the 3/8” rotational play, be interested to learn from people like yourself who have more experience than me of the rear end stuff, if that that amount of play would indicate spline or bearing or wear (or may be both). Would any movement at 3/9 and 12/6 o’clock indicate just bearing. David Quote
Chris Hale Posted October 6 Report Posted October 6 (edited) 16 hours ago, David Farmery said: I checked one of the rear wheels for play; holding the wheel at 3 and 9 o’clock there is 3/8” play measured relative to the outer edge of the 16” rim. Is this sufficient play to cause the problem? Yes you should not be able to feel any play when rocking the rear wheels. Play indicates worn wheel bearings. Not something that’s easy to adjust by most of us I would suggest and really means you need to replace your rear hubs. Rotational play would indicate worn drive shafts or diff to me Are your wheels really 16” or is that a typo normal size is 15”? Edited October 6 by Chris Hale Quote
Dale Moore Posted October 6 Report Posted October 6 If that's 3/8 in. rotational play throughout the whole drive to the gearbox, I wouldn't say that's too bad. Are you sure is not just a sticky throttle linkage? Dale Quote
trchris Posted October 6 Report Posted October 6 (edited) Hi David Place one hand at 12 the other at 6 push and pull and see if any movement if so wheel bearing is worn please do not buy reconditioned hubs always buy new, moss have them on offer l believe, if by slightly rocking the wheel back and forth there’s movement suspect splines or drivetrain problem sometimes easier to inspect by being underneath whilst someone rocks the wheel. If you have any doubts I’m sure a mot garage would quickly put it on a lift and check for you Chris sorry if I’m teaching you to suck eggs Edited October 6 by trchris Quote
Drewmotty Posted October 6 Report Posted October 6 Is this just the “kangaroo petrol” jerky throttle response which has plagued some of us for many years without any definitive cure? Quote
Z320 Posted October 6 Report Posted October 6 (edited) Hi, down under the car I had 5 mm play on the ingoing flange of my diff, that#s about 7°. Im 2021 with the diff out this was 8 mm, so I changed the planet gear shims together with my experienced mate Gerhard. This dropped the play down to 0.4 mm (I had to measure this with a gauge) and the jerking was noticable reduced. . But this summer was a pain again and today, only 4 years / 13,000 miles later I measured 5 mm play again (diff in the car). During winter it comes out again to fit new shims. IMO another issue is the TR4 trottle lever. The way it is angled 70° up and nearly 90° to the linkage it pulls on the linkage max (for example 15° / 25 mm) with the result of a sudden carb reaction. I lowered the lever down to 20° and the linkage flat connected, this pulls less (half the distance / speed) on the trottles. Best example is Stuart, who did that like shown on the photo below. His lever is down to about 5° (?), this pulls on the linkage / pistons of his Dellortos maximum slowly! He shows the photo above in 1 or 2 threads. Ciao, Marco Edited October 6 by Z320 Quote
David Farmery Posted October 6 Author Report Posted October 6 2 hours ago, Dale Moore said: If that's 3/8 in. rotational play throughout the whole drive to the gearbox, I wouldn't say that's too bad. Are you sure is not just a sticky throttle linkage? Dale That’s a point Dale, I’ll have a look at that Quote
David Farmery Posted October 6 Author Report Posted October 6 2 hours ago, Drewmotty said: Is this just the “kangaroo petrol” jerky throttle response which has plagued some of us for many years without any definitive cure? Mmm, you’re not the first to mention that; throttle linkages are all new so may need bedding in. Carb linkages seem ok but I’ll have a look at the pedal. Quote
Drewmotty Posted October 6 Report Posted October 6 I don’t think that it’s the linkages. I changed to a cable system but the kangaroo petrol persists. It’s much less noticeable when I have Weber’s fitted so carb related in my case. Quote
ctc77965o Posted October 6 Report Posted October 6 11 hours ago, David Farmery said: What are you meaning by ‘sticky’half shaft splines? The shafts have a sliding joint which moves as the rear suspension extends/compresses... if this sliding joint is stuck or it binds-up when transmitting power then it interrupts the free movement of the rear suspension and can give a twitch/jerk when it lets go (starts to slide). Quote
David Farmery Posted October 7 Author Report Posted October 7 13 hours ago, ctc77965o said: The shafts have a sliding joint which moves as the rear suspension extends/compresses... if this sliding joint is stuck or it binds-up when transmitting power then it interrupts the free movement of the rear suspension and can give a twitch/jerk when it lets go (starts to slide). Suppose I could remove the shaft and try and free it up or is it a case of buying new; if the bearings are suspect then I might as well buy new hub/shaft Quote
ctc77965o Posted October 7 Report Posted October 7 Before you start buying stuff suggest further analysis of where this Jerk is coming from... exactly what conditions provoke the jerk? Particular speed, throttle/brake/clutch position, steering angle, road condition, selected gear? Quote
jerrytr5 Posted October 8 Report Posted October 8 Post 1 mentions all u/j's being replaced. I would have thought you would notice any issues with splines when that was done. Jerry Quote
David Farmery Posted October 8 Author Report Posted October 8 11 hours ago, ctc77965o said: Before you start buying stuff suggest further analysis of where this Jerk is coming from... exactly what conditions provoke the jerk? Particular speed, throttle/brake/clutch position, steering angle, road condition, selected gear? Wise comment! Fool and his money easily parted🥴 Quote
David Farmery Posted October 8 Author Report Posted October 8 2 hours ago, jerrytr5 said: Post 1 mentions all u/j's being replaced. I would have thought you would notice any issues with splines when that was done. Jerry Hi Jerry TBH, I never checked the splines before I let Mike have the gearbox, hubs and shafts .David Quote
jerrytr5 Posted October 8 Report Posted October 8 If Mike P rebuilt the driveshaft/hub assembly then you can pretty much guarantee they are fine otherwise he would have told you. Jerry Quote
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