Thump when changing gear

[Moz1000]

Hi Folks

My 4200 CC has a thump when chnaging gear. When the engine and gearbox are cold, the gear change is smooth with no thump. When the engine is up to temperature the same applies, however when the gearbox has warmed up, I get the thump. It happens on up- and down-shifts, and is noticeable when changing to 2nd and 3rd when driving around town. It probably does it when changing to 4th, 5th and 6th, but is not noticeable, perhaps because there's less load.

It feels like when you don't fully depress the clutch in a manual car before shifting gear - you get that thump.

Emblem have had a look at the gearbox mount and say that's ok, and can't find anying obvious. Maybe 'they all do that sir!'. Clutch is the two pronged version with 50% remaining. I'm running the original transmission software. I have tries 5.2mm and 4.7mm for the PIS point (currently 4.7).

Can anyone shed any light on the cause?

Many thanks

Dave

 

[conaero]

Take it to your local indie or dealer and get them to re calibrate the gearbox and reset the PIS point to 4.7-5.2. 5.2 will give softer gear changes.

Incidentally, I have mine set to 4.5, and it changes viscously now...the way it should be.

 

[Moz1000]

Thanks Matt. I should have said that the gearbox was also recalibrated at Emblem. I have had the PIS at 5.2 and now at 4.7 - the thump is the same at each setting.

Dave

 

[conaero]

Ok, well then time to look at the clutch and play in the prop and diff. You can have the backlash measured in the diff, that would be a good place to start.

Failing that, if the gearbox mounts are worn, or engine come to think of it, that could be the source of your problem, but I feel, its probably, like us all, just a sign of getting old!

 

[Parisien]

There is a degree of lurch on standard setting........are you going to get the up-grade done.....its pre2003 4200?


P

 

[Moz1000]

There is a degree of lurch on standard setting........are you going to get the up-grade done.....its pre2003 4200?


P

Hi Frank - yes, it's pre-2003. I have toyed at great length about the software upgrade - spoken to a lot of people, read a lot of forum threads - but so far I'm happy with the original software, perticularly as no-one has said that it will solve my thump problem. The lurch, I can put up with. I'm fearful the thump is something that could get worse.

Dave

 

[Moz1000]

Ok, well then time to look at the clutch and play in the prop and diff. You can have the backlash measured in the diff, that would be a good place to start.

Failing that, if the gearbox mounts are worn, or engine come to think of it, that could be the source of your problem, but I feel, its probably, like us all, just a sign of getting old!

Thanks Matt - yes, I thought it could be the gearbox mounts - but Emblem say they're ok. I think I need to have another indy take a look. What's strange is it doesn't manifest itself until everything's warmed up.

Dave

 

[Parisien]

You'd imagine Emblem would have solved this...or given 1/2 more than likely theories and or fixes.....so according to them...its just normal?

 

[Moz1000]

You'd imagine Emblem would have solved this...or given 1/2 more than likely theories and or fixes.....so according to them...its just normal?

Yes - they say some do it some don't. I don't believe it. Hence this thread.

Dave

 

[CatmanV2]

Mine certainly doesn't

Clunks a bit on downshifts when stopping, but nothing else.

C

 

[mjheathcote]

I would imagine, if it is smooth when cold, and then thumps when warm, when the oil has thinned, that it could be wear in a bearing or something in the gearbox/diff?
Or maybe its the gearbox oil that could do with a change?
What mileage have you done?

 

[Moz1000]

I would imagine, if it is smooth when cold, and then thumps when warm, when the oil has thinned, that it could be wear in a bearing or something in the gearbox/diff?
Or maybe its the gearbox oil that could do with a change?
What mileage have you done?

Hello Mike

The car's done 40000 miles. The gearbox oil was changed per schedule only 8 months/2000 miles ago. It did the thump before this.

Please keep your ideas coming everyone!

Dave

 

[cobratwin]

id say it was a Slight misalignment somewhere the, metal is smaller when cold and when hot its larger with a slight misalignment and if the clutch is correct along with the type of gearbox oil.. it would cause a thumping.