Grumbling rear end - UPDATE

[Lusso250]

Gentlemen I'm wondering if someone could assist.

I recently took the trip to the Le Mans Classic and covered 750 miles, just prior to the trip the car (series one 4.2 1966) was checked over by a local garage: the car was jacked up using a four point hydraulic lift (this could or could not be relevant). Ive been very fortunate to own a car that runs very smoothly and normally performs very well with out some of the normal problems of overheating etc.

I had covered circa 50 miles on the way to ferry, mostly motorway, when I stopped to meet up with some pals, however, when we pulled out of the service area on either lock there was a horrid grinding/rumbling noise from the rear end, when driving in a straight line nothing and drove as sweet as a nut!

On a simple inspection nothing was noted and decided to press on and in a straight line the car performed well, however, I was told by a follower that the car appeared to crab into corners. In addition when the car was cold at start off no grumbling noises on either right or left turns was noted.

Ive not had the car to the garage yet or tried to jack the rear end up but was wondering if the garage had possibly bent the radius arm when jacking but I have to say on visual inspection both sides look fine.

Any thoughts would be appreciated

Kind regards

Ian

[Heuer]

Have you checked the tightness of the spinners, particularly if they are repro ones (you can tell by the crap logo - compare it to the one on your oil filler cap).

[christopher storey]

I'm not really sure what "crab into corners " means. If a car is crabbing, it is usually most noticeable when the car is running straight . Certainly, a deformed radius arm could cause abnormal gait but because they are channel section it takes a fair force ( probably a dynamic rather than static force ) to deform one unless it is already weak from rust, or unless the mounting is corroded . As far as the noise is concerned, the first culprit I would look for is the hemispherical shields on the drive shafts touching something . This often happens if someone has taken hold of them with the car up in the air. Next to look at is the rear tyres rubbing on either bump stops or the wheel arch , or the front tyres rubbing on lock on the dirt shields . This is commonest where eg 205/70s have been fitted, but it is conceivable that if a radius arm had been distorted it could alter the rear suspension position sufficiently to cause a rub

[Lusso250]

Many thanks for your help, I will check out the hemispherical shields although I'm not quite sure what you are referring to but I'm sure ill find them with a little help from Google or the Forum.

Having now checked the Radius Arms in more detail they both look ok and the diff was refurbished about 3,000 miles ago so everything still looks fresh. Need to get the rear end in the air and see if there are any obvious signs of movement.

Appy daze

Ian

[mgcjag]

Hi Ian....thay are cup shaped shields fitted on the end of the rear driveshafts covering the universal joint....usually held onto the shaft with a jubilee type clip..but on many cars they are discarded

[44DHR]

Ian,

The Hemispherical shields that Chris is referring to are the tin covers that are on the drive shafts and cover the Universal Joints, (U/J) as Steve has just said. They are a two piece pressing and riveted together to form a cover which slides over the U/J and are held in place on the drive shafts by a hose clip. The larger outer diameter is a fairly tight tolerance into the outer alloy hub carrier and if someone has been inspecting the U/Js and slid the cover back away from the U/J to do so, they may not have replaced them correctly or pushed them in too far. You would tend to get this noise problem if the shields were touching the hub when driving straight or cornering.

The only other thing I could think regarding only happening on cornering is within the Differential. I would be interested what the local garage did when "servicing" the car. Did they change the oil - and if they did - did they refill with the correct Limited Slip oil ? The Salisbury 4HA Differential is "locked" in straight line motion by the end Belleville springs in the two clutch packs, but the friction plates are released on cornering to allow the inner wheel to travel less revolutions than the outer wheel. If there is dirt or damaged friction and clutch plates inside the differential, this could account for a rumbling noise after cornering when these re-lock - especially if the wrong oil is used. When starting from cold, the differential oil would be "thicker" and would change as it heats up after a decent run.

regards,

Dave

[Lusso250]

Many thanks for your detailed response; plant to think about!

Kind regards

[JagWaugh]

Ian,

The "Crabbing" into the corners would make me would make me take a very close look at the IRS mounts and the trailing arm mounts and bushings. If the car crabs in a turn but not in a straight line then something is loose and shifts around under cornering loads. A bend trailing arm would not change geometry just while cornering, but a forward mount disconnected from the floor would. The noise could be the driveshaft rubbing on the tunnel, tires rubbing. A loose wheel, or a pair of them would probably wobble in a straight line more than in a corner, but check that as well.

Did they service anything while the car was up on the lift?

[mgcjag]

If the car had been up on a 2 post lift it was very likely tbat the irs was left unsupported and one of the mounts could have seperated

[Moeregaard]

I'm with Steve regarding a separated IRS mount. I've mentioned it elsewhere, but the IRS unit should never be allowed to hang unsupported when the car is raised. It can damage new mounts, and the results can be catastrophic if the mounts have seen better days.

[Lusso250]

Once again thank for your help ill get the IRS mounts checked out, would it be quite evident from a visual inspection that there is movement or separation on the mounts?

Ian

[1954Etype]

Very easy to check if they are delaminating by either a visual check or raising the car so the rear suspension is hanging from the mounts. Dont have the car high in the air. Note that the mounts are not designed to work in this way but if they let go, they have had it. Good practice to change all of them if one is worn.

[JagWaugh]

Ian,

If the IRS is loose enough to cause the car to visibly crab as seen from a car following it then it should be simple to spot. A donut mount will be free from the floorpan, or the large bushing will be visibly degraded, or as you lift the body the wheels will clear the ground differently and/or a mount will allow one corner/side of the cage to hang farther away from the chassis leg.

[JagWaugh]

And if that didn't sicken you enough there is also the chance of the inner wishbone mount, the wishbone itself, or the hub carrier being damaged.

[PeterCrespin]

I'd bet wrong diff oil without LSD additive, judging by symptoms described. Ask them did they change it and if so to replace with correct oil or extract enough to leave room for supplementing with LSD additive.

On a worn diff with weak clutches it might not show so markedly, but with the recent rebuild and fresh bellevilles it's typically jerky without the correct lube.

[Lusso250]

If I may post an update on this on going saga:

I think the crabbing originally mentioned is a friend with dreadful eye sight, Ive followed my own car and it looks ok to me, however, the intermittent grinding noise when i turn into a drive or junction is still there but only intermittently!
Its now been through two garages but the difficulty is asking someone to cure a noise which is not apparent at the time.
There is little to no play in the hub bearings, we have drained the diff old and as clean as a whistle with not filings on the magnet or floating.
Everything else is tight and looks and feels ok.
Ive just driven the car for at least one hour including motorway work and no noise, I arrive home and in turning into drive the noise is apparent! The cars drives beautifully and both mechanics confirm same "its one of the nicest e types we have driven"
So any further thoughts or suggestions would be most welcome.
N.B. I can assure you I'm not imagining this noise although I can understand why I'm beginning to have a few doubters

[PeterCrespin]

Nothing you have written rules out my last post suggestion. Sticking ckutches sfter rebuild, helped but sometimes never totally fixed by LSD additive.

Pete

[nefematic]

Peter,

other than relying on the workshop's say they used the correct LSD fluid, would it hurt to drain a bit and add the additive - maybe twice? A second question is how to test a LSD on a lift?

Martin

[JagWaugh]

Martin,

Jack the car up with both wheels in the air, GB in N. Turn one wheel, if the wheel on the other side turns the same direction you have an LSD, if it goes the opposite direction, then you have a open diff.

The tag will always have two numbers which indicate the ratio, and "PL" if it is an LSD ("PL"=PowrLock).

Andrew

[nefematic]

Andrew,

my question was more aimed at testing the "rumbling factor" on a lift, not if a LSD is fitted. I'm with Peter, the malfunctioning LSD hasn't been ruled out. But how to test this on lift?