Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing 1975 Plus 8 Diff noise?

Hi Andy, thanks for clarifying this. No a BTR diff won't fit a Salisbury axle.

Andy, you mention about the danger of fitting a wider axle to an 'early' car. There are a couple of erroneous articles in magazines and books that say this. A number of 'library/bar room' experts merely restate this nonsense.

1976 4 speeders were fitted with the wider five speed chassis. My car was fitted with one and I am almost definite 1975 cars were as well.

There are two ways of determining the type of chassis fitted to a Plus 8:
1). Measure the width of the chassis and the axle;
2). look under the car, if the chassis has a cross member that sweeps below the clutch bell-housing then the chassis will be an early narrow chassis; if there is a straight U section cross member it will be a wide chassis.

My apologies Andy if this comes across terse but I hear this nonsense repeatedly stated and it is wrong. Even the factory has probably forgotten this fact.

Would any 1975 and 1976 four speed Plus 8 owners like to look underneath their cars and verify?

David

I am very pleased you have cleared that up, and I take your information as positive and constructive.

I was really referring to the Moss Box cars , which I am certain were built on the narrower chassis, which you confirm. If Neil has one of these , then he would have an issue with the wider BTR axle, but looking back through the thread I don't think we know what year of construction his car was.

I did not know the Rover 4 Speeders had the wider 5 speed chassis, but that is another useful piece of information.

Having talked with other Australian owners they try very hard to source parts locally rather than import from Europe, as the freight, import duty and other charges make this a very expensive choice. Thus I was looking for a "home made" solution for him. The BTR axle is pretty bombproof as it was used in the high power version of the Holden Monaro with the 5.7 litre V8. I agree that it would also involve some other changes , all of which would add up, but it still might be his cheapest option, and would almost certainly be the quickest.

Hi Andy, I absolutely agree, shipping for an axle would be eye-wateringly expensive!

Its getting worse. Do I even have a differential that was originally installed?

Upon perusing the GoMog Salisbury Diff images, I see a few serious differences.

1) No top filling hole. (I only have bottom drain and a fill hole halfway up the rear right side)

2) Casting number is 7NA-004-15 (hard to be sure with some numbers, but is definitely 7NA.

If I can figure out how to post photos, I will do so, just so someone here can confirm that I am now dealing with a mutant diff.

Was on the phone to a diff. guru in Brisbane who seems to think that I should change the wheel bearings first to exclude them as a culprit.

I'll order a complete set of bearings and seals and get to it in the next 2 weeks or so.

Will advise the outcome of the bearing/seals change in a couple of weeks.. or however long it takes for me to receive them.

Photos are here.

http://www.talkmorgan.com/ubbthreads.php/galleries/304491#Post304491

Let me know if you need other angles.

Hi Niels. Deep deep down under is NZ(if you have not guessed already). Your photo certainly looks like a Salisbury 7HA. Just drain whole in bottom and filler part way up the rear casing. Your car has the four speed rover box? Mine is a 77 with the LT77 gb. Yes the BTR may be too wide for your car but as I said hopefully won't be needed. To check bearings before ordering same just pull the axles (may need a slide hammer to do, one of mine was exceedingly tight.) then rotate the bearings with your finger to see if you can pick up roughness.
Replacing your lever arm shocks with telescopic is a massive improvement.
Just thought also to check if your tyres are not rubbing on the exhaust pipe because of lateral movement if the spring eye bolts are warn or loose. if happening you should be able to see the rub marks on the tyres.
Doug
from deep deep down under

Worth a quick check of the u-bolts, if loose (or worse still sheared) they can cause knocking/other noises. Long shot but....

First off everybody, - I passed on duff gen.. the diff is indeed a 7HA, with all the underbody sealant goop stuck in there, the H looked like an N.

Sorry.

Richard Aus - The U bolts look o.k. No movement and all intact.

I'm ordering a complete set of bearings and seals for all 4 wheels from Chris van Wyk - at least this will exclude one possible source of noise.

One further question - where is the diff ratio stamped? The supplier of the bearings needs to know whether its 3.31 or 3.58 apparently the bearings are different.

Hi Niels. The ratio should be on a small metal tag fastened to one of the bolts holding the back rear casing on.
Doug
from deep deep down under

As your car is 1977 the ratio should be 3:31, if in doubt count the teeth on the CWP and do the maths. The 3:31 axle was introduced in October 1973 Ch R7659 [source Ken Hill]
Do not loose any of the assembly bolts as [some/all?] 3:31 Salisbury axles used 'semi' metricated fixings, i.e metric threads but SAE heads, you can do a quick check with the bolts holding the diff cover - 9/16 AF spanner but M8 thread. Likewise the CW bolts are M10x1.5 and not 3/8 UNC but still have an SAE bolt head!
The 3:31 axle is in effect the next series on from the 3:58 axles, visually similar but different. The 3:58 axles were fully imperial, a different overall length of nose, a smaller diameter pinion shaft and a set [thankfully] without a crush washer. Later 3:31 7HAs may be fully metricated - I don't know.
Were you to find a Reliant Sabre/Scimitar with a 7HA it would be of the earlier 3:58 style of construction.