13 replies to this topic

[Stu.]

I am currently overhauling the brakes on Molly (drums all round) and have her up on 4 axle stands.

 

I have noticed that when I rotate the offside front hub it gets stiff to turn at one point then goes easy again. When it gets stiff on rotation the hub assembly rises and falls at the stiff point.

 

I'm guessing this may be a bent driveshaft or an issue with the inner or outer CV joint or a damaged bearing, but wondered if anyone had similar experience, or could give me some advice ?

Edited by Stu., 09 October 2013 - 10:15 PM.

[Ethel]

Is that with the drums still on? could just be an ovalled drum, and the reaction to turning the sticky drum that's lifting/compressing the suspension. I don't think a bent shaft would have much effect at low speed, they are cv joints at both ends: designed to work with the shaft at a wide range of angles.

[Stu.]

No it does it when the drum is off the hub. It does not do it on the near side so I think something is not right ?

Edited by Stu., 10 October 2013 - 01:48 PM.

[tiger99]

It could be a bent shaft, but only if it is rubbing on the subframe at the point where the effect is seen. Check carefully as you turn it that there is clearance between shaft and subframe. If it is rubbing all round, you need new rebound rubbers to reduce suspension droop. If it rubs at one point, the shaft is bent, or one of its ends (CV or pot) is damaged and forcing it to run off-centre. Check also that the pot joint is not wobbling around, which is a sure sign of diff failure. You can easily spot a bent shaft by observing the clearance where it passes through the subframe as the wheel is rotated.

 

A CV joint which is in a thoroughly dangerous condition may also monentarily lock at certain rotational positions, which may force the hub upwards, but if it was that bad it would have been clicking badly during tight turns for some time. An inner pot joint in theory could do the same.

 

A bearing failure, by itself, can't make the hub rise.

 

If this is an early car with rubber inner joints, it is most likely that the rubbers have failed, allowing the shaft to run off-centre at the inner end. When that happens there will often be evidence that the U bolts have been contacting each other.

[Stu.]

Molly's a 79' mark 4 or 5 (I think) so not really early.

 

I should have pointed out that the diff / gearbox moves a little bit when rotating the hub at the stiff point. Would that help to give you any indication of cause ?

 

Thanks for the advice, its appreciated.

[tiger99]

Well, if something is locking up the CV or pot at a certain angle, or if the shaft is bent and hitting the subframe, that will apply force to the diff as well as the hub, so it does not eliminate very much. If you have confirmed that the shaft is not contacting the subframe and there is not a lot of play between pot joint and diff, the shaft will have to come out for a more detailed investigation.

[Ethel]

If you can see it touching the subframe, sit her on an axle stand and jack up the bottom ball joint until it clears the frame so you can retest. If you've driven the car, I'm sure you'd have noticed a bent driveshaft at speed.

[Stu.]

The driveshaft clears the sub frame between the hub and the diff. I did jack up the hub yesterday evening and found that the stiff turning disappeared. I also noticed that the driveshaft is bent a little bit. I think I'll wait until I can road test to see if I get any issues, if not I'll add a new shaft to my list of repairs

 

Ethel, I'm not able to road test the car yet as I've recently aquired her from a reletive. The car's been in storage for 8 years and I'm working through a list to get her  ready for MOT.

 

Thank you both for the advice. Very much appreciated

[xrocketengineer]

For what its worth, many years ago, we had a 1968 VW Kombi that had developed a strange behaviour. When driven slowly at constant speed in first gear, you could hear the engine RPM go up and down at regular intervals. When the van was jacked up we noticed that the left rear wheel had a very tight spot as it was spun around. We removed the axle and noticed that the outer CV joint was very tight at one spot and very loose on the rest. When we took the joint apart, we found a big chunk missing on one of the balls and a lot of damage on the race for that ball. A new CV joint solved the problem.

 

Hope that helps,

Ivan

[Stu.]

Yes thanks Ivan,

 

I need to change the outer CV joint gaiters on both sides, so I might remove the driveshaft assembly and inspect the inner joints for wear and damage while I'm at it.

 

Thanks for the advice.

[tiger99]

Check the ball cage for side wear in the slots, because that is the usual cause of CV joint problems. If the balls are not accurately constrained in one plane, they have two stable states, some deflected inwards, the others outwards, and in that condition free rotation at an angle is not possible. The clicks from a failing CV joint are the balls forcibly being flicked from one side of the slot to the other. Eventually it locks up at an angle at speed, or the cage breaks, and in either case it can get very nasty indeed. If you are very lucky it just spits out all the balls and loses drive, but the one I saw in about 1970 ended up in a moderately nasty crash, with the driver going to hospital. That was an 1100, not very old. Actually, few of them ever became old, as they rusted about as fast as an Alfasud or Lancia Beta.

 

I experienced one in a Talbot Express van, when the cage, of sintered metal and I suspect inadeqate strength, broke. Suddenly, and with no prior warning such as clicking, the steering was kicking furiously and pulling strongly to the left. It took all my strength to prevent it crashing off the M25 and stopped on the hard shoulder. Had it been the drivers side, pulling to the right, I likely would not be here to write this.

 

Having said that, catastrophic CV failures seem to be much less common nowadays than they once were, thanks in part to the MOT.

 

You may also find broken parts, of course, and any pitting on any of the running surfaces or balls means that a new CV is needed, but the usual problem is a worn cage.

[Stu.]

On that very helpful information tiger99, I will definately fully inspect both CV joints while replacing the gaiters. Ive ordered the tool to knock out the pot joints from the diff, so we will see soon. As far as cleaning out the old CV grease, whats the best solution to clean the joints and pots up to check for wear / damage etc, and can you recommend a good CV molygrease ?

[tiger99]

CVs must be greased with CV grease (surprise!). It was originally Duckhams Bentone Q5795, and the molybdenum disulphide and the bentonite which the name implies are both essential ingredients in this application, so a straight moly grease will not do. The reason is that the bentonite makes it sticky (which you will know only too well if you have ever dismantled a CV!), which prevents it centrifuguing out of the joint into the outer part of the boot. Remember that the whole CV is rotating, whereas in something like a wheel bearing one race is stationary, which helps to keep ordinary LM grease in place. There is also a very high contact pressure between balls and inner and outer members, as drive torque is being taken on six tiny contact points.

 

So ideally 30 cm² of Duckhams Bentone, if you can find it, which is unlikely, or pop into a modern car dealers parts department and ask for a tube of grease for a decent sized FWD car (Ford Focus for instance), which will be sufficient to do two joints on a Mini.

 

The grease for the inner pot joints was originally different, Shell S7274 Tivella A, and you can't get that either, so use 50cm³ of the same as for the CVs.

[Stu.]

The gaiters for the pot joint and outer CV joints seem to come with a sachet of grease in the kits.

 

Is it safe to assume this is the correct grease, or should I be getting a tub(s) of what you reccommend ?

 

You clearly know your stuff so please dont think I'm questioning you, but I want to be sure I use the correct grease and I'd just like some clarification if you dont mind.