Joined: Sep 2017 Posts: 21 Threads: 9
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A few months ago I obtained a late D-type rear axle and overhauled it prior to fitting it to my car. New bearings and seals all round. I set up the CWP adjustment according to Woodrow and everything else I could glean elsewhere.
During the overhaul I found that the pinion shaft had considerable end float and the crown wheel has run-out (sorry, I can't recall the figures for each).
After installing in the car the axle appeared to work well. The only negative thing is a droning noise at a steady 35/40 mph with light throttle. It doesn't happen when accelerating or on trailing throttle.
Can anyone suggest what may be causing this, and point me towards what I should be looking for before I tear it all to pieces again?
I had not driven the axle before I bought it, so I don't know if it made this noise before the overhaul. I suppose it is possible that, if it had previously been used for a long time with the pinion end float, the CWP gears might have worn unnaturally. Perhaps it is the effect of the crown wheel run-out and I shall just have to live with it.
My previous axle didn't make this noise, nor did any of the A7s I have owned before, so I know it is not right.
It would be great if I could adjust the mesh of the CWP and eliminate the noise, but I guess that would be a tricky operation with the axle on the car.
Any suggestions gratefully received!
Joined: Aug 2017 Posts: 497 Threads: 13
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From what you describe here is a complete guess you can try.
Try backing off the thrust of the crown wheel 2 notches and re tighten the other side.
My thinking is that you have run out on the crown wheel and it maybe meshed too tight.
Then drive the car, if that is no better then it all needs to come out and be done properly.
If that is the case, methinks you need to take it to an experienced seven engineer to avoid wasting the axle.
I really hope this helps you.
Joined: Aug 2017 Posts: 920 Threads: 6
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Location: Scottish Borders
I believe it's often difficult to get old CWPs to run quietly when readjusting them. They tend to have worn in such a way that the original mesh is lost.
Jack French's article in the Austin Seven Companion are very interesting.
Jim
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06-03-2018, 10:51 PM
(This post was last modified: 06-03-2018, 10:51 PM by Nick Lettington.)
I tried to reuse the diff carrier from an axle that had half the crown wheel teeth in the bottom of the casing. It was quite distorted... If the CWP pair was running out of true for a while and has worn unequally and the diff carrier is already distorted, you might as well try adusting it a little or simply drive until it goes pop (it may never). Other than the bearings, which you may struggle to re-use, the bits likely to be wrecked if it does die sound like they are already no good to re use.
Just my halfpennyworth..
Joined: Aug 2017 Posts: 2,748 Threads: 31
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Location: Auckland, NZ
If the runout is the problem the drone would oscillate. As above the cw can be adjusted in place but care necessary not to eliminate tooth backlash or introduce preload or the opposite. If the car can be raised high not too difficult to change shims but really need to withdraw the torque tube for pattern inspection and that is more work.
With used cwp the ideal pattern may never be obtainable and can spend days exploring a range of settings to prove this. Tedious at a bench and not something to do lying on your back. High mileage pinions in particular develops a wear step and unless removed limits pinion adjustment. Later pinions were shortened to avoid this. When reusing cwp any wear steps at end of teeth should be oilstoned away.
The fact that 42:8 does not hunt but runs in two engagement sets can confuse matters. Can espy the mesh pattern through the plug hole. Any gross error might show or be persuaded to. It is important that edges of cw not heavily engaged.
Unfortunately with Sevens and unlike cars with open prop shafts, diff noise is transmitted directly to the body. Carpet underlay felt under the back seat may work wonders.
I have doubts about Regent after market cws; one in my car seems barely hardened and a very distinct mesh pattern is formed and I have seen another similar.
I have seen original pinions worn 1/3 way through so the teeth must be robust!
Joined: Aug 2017 Posts: 1,666 Threads: 46
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Location: Auckland NZ
Car type: 36 Nippy, 31 RM, 38 Special, 24 Works Rep
Unless horribly mismatched or badly worn my experience is that with care a used CWP can be set up to run quietly or at least with virtually imperceptible hum.
Black Art Enthusiast
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I have successfully skimmed the mounting face on an A7 diff where there was axial run out caused by a previous pinion failure -that diff had about .005" TIR -The diff was running between centres in a lathe when I skimmed it. I think that having any run out there would make it difficult to get a consistent pattern when setting up the mesh and depth of engagement.
Did you check the pattern with engineers blue or chrome yellow when you built it up? With a well used CW & P I have found that getting a good pattern is the best way to get silent/quiet running; setting it up according to the book/numbers etched on the pinion etc. is going to lead to the CW & P pair running on high spots if that setting doesn't match what's been happening with the gear setup for thousands of miles previous.
