Final Drive Unit

[Robbie 2B]

On the drive back from Le Mans it became evident that all was not well with the drive to the rear wheels. The initial take up of the clutch resulted in a noticeable clunk and it became harder and harder to pull away smoothly. Get home mode stepped in - max 65, no swift acceleration, etc.

 

Car now on axle stands and the drive shaft and differential have been examined. The drive from the gearbox to the differential appears all OK, UJs in good nick and no noticeable play. However, both drive shafts have a considerable amount of backlash. Thus they can be turned a considerable amount in different directions before 'metal to metal' contact is met.

 

Can anyone provide information on what the allowable backlash should be? The Haynes manual is very limited with information.

 

Prior to going to Le Mans it was noticed that the differential started to make a noise on the over-run. This occurred when the throttle was closed at around 30 and the car was 'freewheeling' in fourth gear. Was this the start of the problem which I missed?

 

Any help, advice or if available maximum allowable backlash reading would be appreciated.

 

Best regards

 

Robbie

 

PS Big thanks to Sir Chris for organising the campsite etc, sterling job - put my name down for next year please.

[Guest chris brown]

Can anyone provide information on what the allowable backlash should be? The Haynes manual is very limited with information.

 

put my name down for next year please.

I don’t know what the tolerances’ are Robbie but it does sound rather excessive, rather than trying to rebuild it (not an easy task) I would be tempted to replace it

 

Your name is now on the growing list

[Guest Ian & Carole]

If it is both drive shafts that have the back lash in them, with them being C/V Joints there really should not be any "slop"

 

Change both shafts.

 

Not worth trying to rebuild IMHO

 

Ian J

[Snapperpaul]

Unlikely that 2 UJ's would be broken at the same time, so i would go with the diff problem.

HOWEVER... with all things car, it could be any of them....So

If you have to change the half shafts or the diff or indeed the propshaft then you will have to dismantle enough of the drive train to replace any or all of these parts.

 

Once you start the process of releasing the halfshafts and the diff, its easy to pull the prop enought to test the UJ's, then have a good look at the halfshafts..... i bet its the dif....

Push fit or bolt on?

Plenty of diffs available and a chance to change ratio if you wish.

[Guest salty_monk]

There is always some backlash but not normally in the CV joints... How are you testing for lash? No good jacking it & turning the wheels without holding the drive shaft still, you'll just be feeling the lash in the diff (and there should be some)......

 

I would look most carefully at the propshaft UJ's first, we know of some failures there & I've never heard of a diff fail..... They do get burnt teeth or the bearing start to grumble but they will go on for a very long time after that.

 

Dan

[Robbie 2B]

Dan

 

Thanks for starting the alarm bells.

 

The prop shaft and UJs are fine, no noticeable play between the gearbox output shaft and input to the differential.

 

The backlash appears to be at the inboard CV joints. If the prop shaft is held solid then backlash occurs on each drive shaft's CV 'can' adjacent to the differential. (See photo, CV 'can' shown painted blue)

 

If the drive shaft is held solid then the inboard CV 'can' can be twisted by about 7 - 10 degrees. Again, if the drive shaft is held solid and the road wheel is turned there is no noticable play in the outboard CV joint.

 

From the above is it more likely that the inboard CV joints have gone and the differential is OK?

 

Any ideas?

 

Best regards

 

Robbie

[Snapperpaul]

There is a thread somewhere about changing these UJ's yourself, what i would do is post in the wanted section of the Locostbuilders site as a lot of them have bits spare when building some of the stranger kits.

Also have a look in your local scrapyards.

 

Just had another look at your photo and you have a push fit diff, no problem but getting more rare than the bolt on joints, also pushfit LSD's are rare, well i have never seen one.

[Andy Spencer]

GBSC have hundreds (literally) of complete Sierra rear ends in the factory, give Richard a call and I am sure he will source you what you need.

Andy

[Guest salty_monk]

It sounds like you are still feeling only the normal play in the diff to me... I think you're barking up the wrong tree.

 

It's only a 30 min job to whip them off though (take them off with hubs intact & slide through the hub carrier.

 

You can then test them for play properly as you'll be able to twist both ends of the joint.

 

If it is the joint you can buy new joints, from memory you simply release a circlip to get them off the shaft (might need a copper mallet to tap them off) then slide the new ones into place.

 

Dan

[Guest timswait]

From what you describe it sounds like play in the diff (sorry, I don't know whether it's a normal or abnormal amount of play), it doesn't sound like your CV joints at all.

[Guest salty_monk]

That's what I said... it also sounds perfectly normal to me. I'd be VERY surprised if it turned out to be a diff problem.

 

You do have oil both in the diff & the gearbox don't you??

 

It's possibly a problem with the clutch, pressure plate, thrust bearing could be shot & making noises or maybe oil contamination or something.

 

Dan

[Robbie 2B]

Thanks to all who have replied.

 

Took the drive shafts out tonight - both solid no backlash at all. Tested them by dangling splined end in soft jawed vice and trying to turned hub - no play at all. The metal can enclosure, surrounding the inboard CV joint, does rotate by about 7 degrees, this being independent of the joint itself.

 

Checked the differential oil level - as per the book 10 mm below the level plug. No noticeable metal filing attached to the level plug's magnetic centre pin.

 

Put wheels back on and tried it whilst on axle stands - clunking problem still event especially when in reverse and dipping the clutch. Too dark and wet to do any more tonight, will try a pin-point the problem when under car tomorrow.

 

Best regards

 

Robbie

[Guest yosamite sam]

are you sure its not the prop uj ? i had a uj fail last year - was noticeable by a. the vibration - b. loss of use of 3rd and 5th gear due to vibration. - rear uj dry as a bone.

 

if it is your uj in the prop or your driveshatfs try commercial propshaft services - team valley - tyne and wear - i am sending mine there next week - balance the prop and replace all cv's - routine maintenance while its apart (there is play in all my cv's - if you just grab hold of the driveshaft and tweak the wheel back n forth you can see play in the cv's - 3-5mm ish, shouldnt really be any noticable.

 

while i'm on here )

 

quick question

i need a cv boot for a sierra drive shaft cv - but is there a one that is a narrow width - because the 'concertina' bit fouls on a chassis cross brace on my rush.. only just fouls but i cant seem to find an alternative to a big hammer to the cross brace. i rang demon thieves and they said the one they supply wont fit a sierra drive shaft which it does look identical to me..

 

anyone a different solution?

 

regards

 

terry

[Guest timswait]

Propshaft or clutch problems sound most likely then. If it turns out to be a prop UJ I wouldn't bother getting your RH prop re-balanced and re-jointed. There's too many doubts over them, look at the other threads in this section, and it's unlikely to be very much cheaper than getting a whole new one made which you can have a whole load more confidence in.

Yosemite-any way you could use a cable tie to to hold the boot in tighter and narrower? I'm not aware of any different widths of boots, but it's quite possible that different third party parts suppliers may have slightly different patterns, maybe you'll find one that's a bit narrower if you just trawl around the motor factors.

BTW Constant velocity (CV) joints and universal joints (UJs) aren't the same thing.

[Guest yosamite sam]

 

thanks - will trawl about - need to get it fixed - what is the difference then?