Rear drum brake torque

[hairyapple]

I've just replaced the rear brakes on my 67 estate. All new parts including the wheel cylinders. The drums were so good that the local brake experts only pummeled them with grit to clean off the rust so I could paint them. That said, on my test drive I noticed a significant and rhythmic "whumping" when the brakes were applied at speed, say 15 miles an hour or greater. The pedal seemed firm with no pulsation. Took it all apart and found nothing amiss. My suspicion is that it's either an axle or drive shaft bearing, although there is no noise when foot is off brake or perhaps I've torqued the castellated nut improperly. Does anyone know what that torque ought to be??? Once the recommended torque is reached which way do I go to line up the cotter pin???
Cannot find any reference to the torque on those particular nuts in my reprint of the entire Volvo Shop Manual.

Any ideas out there????????????????????????????

[tdz840]

I had exactly the same noise. Replaced everything including the bearing and shimmed the half shaft accurately.The only thing I didnt replace was the wheel cylinders as they looked brand new. However my thought now is that are sticking.
The other thought is the handbrake. The rear drums require the action of the brakes to have most of the movement at the fulcrum taken out by setting up the handbrake first. With the adjusters fully off set up the handbrake to 4 clicks and then set up the adjuster.
I have done all that but still the noise, therefore my reasoning the cylinder(s) are sticking. Its the only thing left!!
However I can save you a bit of grief by not touching the bearings!
Hope this helps
Russ

[tdz840]

Oh and the torque question!
When doing up axles I believe the normal approach is up tight until the wheel binds, then quarter of a turn back until the castellated nut meets the split pin hole.
I believe that is correct - but there are more knowledgable people than me on this forum.
Russ

[mike gilbert]

I have just replaced my back axle with a reconditioned unit and new wheel bearings professionally fitted, new springs, new bushes all round, new shockers, new wheel cylinders - you name it. And yes I am getting the same symptoms as yourself when I brake, a kind of rythmic scraping noise and some vibration though not much. I think it is the drums going oval, I cant think it can be anything else. As for torque on the drum nut - I've seen it written down somewhere and it is substantial. My torque wrench is busted so I do the nuts up untill my own start to hurt and hopefully it lines up with a pin hole. You cannot slacken off the nut to find a convenient hole like the front stub assembly because the bearings are completely different at the back. I think I'm going to get mine machined to perfectly round and see if that helps.
I'm also getting a scraping noise and a banging from underneath at low speed which the new axle has not cured. I'm thinking its the prop shaft but the centre bearing on that seems OK. If its not the prop I'm stuffed.

[hairyapple]

Okay, I've jacked up the car and am waiting for a friend to come by to give a listen while the drums go round. Also my cousin, a retired tool maker (don't call him a machinist if you know what's good for you) is coming over with a set of micrometers to check the drums for roundness. So we'll see.

I already checked the wheel cylinders by removing the drums and using a carpenter's hand screw (a big one, sometimes called parallel clamps) to contain the brake shoes and as an assistant (my begrudging wife) stepped on and off the brake I could see the shoes move in and out nicely, so it's probably not that. The bearings don't seem to be noisy when the drums are turning under power but I haven't eliminated that yet.

[wellshj]

Three answers from the workshop manual:

If it is any comfort the Volvo workshop manual says: "Tighten the castle nut well and lock it with a split pin."

The manual also says there should be no more than 0.15mm or 0.006" of radial throw on the drums.

The only mention of vibrating brake drums (other than for out of true drums) in the falt tracing section suggests "Fit damping springs to the outside of the drums."

Hope this gets you back on the road.

Harvey

[tdz840]

Woops - thanks Mike muddling up the fronts with the rears.
Like you I used an iffing great breaker bar and worked on the logic of three white knuckles.
Russ

[amazondean]

The rear drums are held on the half shaft by a taper so as long as it's tight there is no need to torque it up. Then back it off until the split pin fits. If it looks like you need to back it off so much that the nut feels a bit too loose, fit a slightly thicker washer behind the nut.

I had a similar noise once and after a lot of head scratching it turned out to be the drum was not tight on the half shaft. But that made a noise all the time. the noise sounded like there was a spring clicking inside the drum. I thought it was the handbrake spring.

Regarding the rear drum brake set up. I believe you should slacken the hand brake off first on both sides then with the car jacked up at the back apply the foot brake hard on and off a few times. Then adjust the adjusting screw for the shoes until the brakes bind then apply the foot brake a few times again and keep repeating the procedure. Every time you apply the brake on and then off again, the drum feels slacker and alows you to adjust the adjuster a bit more. Eventualy the shoes will start to grab and not slacken off once the brake pedal has been pressed and released. Then back the adjuster off a small amount so that the shoes are just touching. Then set the hand brake adjuster for a perfect setting. I will gaurantee a perfect rear brake set up with this method.

[mike gilbert]

Yeah I've checked my manuals today and there is no mention of a torque setting for the rear drum nut - just 'do it up tight' - don't know where I read it before. I will have another go at my brake adjustment this weekend using the recommended technique - maybe the shoes are now too loose.

[amazondean]

By the way I am also tool room trained and your cuisin is absolutely right. We are engineers and not operatives as most people think. By the way, the drum could be round within limits, but could still be out of true to the centre taper. A bit more difficult to check!!