Volvo Amazon and PV Brake Drums
 

Having got to a rear axle refurbishment on my 544 restoration I noticed the rear drums were a bit scored. Having discovered how expensive these are to replace I thought I would skim them out on a lathe. Well they cleaned up after machining about 0.020” out of the diameter. There is absolutely no information in any of the Volvo manuals I have regarding the maximum diameter the drum can be (either through wear or machining). But having spoken to Amazon Cars,Rob uses a gauge to check the diameter, which measures 230mm (9.055”). If the gauge goes in the drum he scraps it. I am wondering if machining the drum bore to no more than 9.030”diameter is in order. Does anybody know please?

Drums
 

I have also seen the info regarding the drum maximum diameter being 229mm.My amazon has been idle through I'll health followed by the dreaded covid lockdown. The rear brakes were stripped, cleaned, checked. The drums were both 227 mm diameter. I also have 2 spare drums which are 227mm diameter. I have no official info or diameter detail for new drums, maybe some kind person will tell us the new drum internal diameter. I am hoping mine last a few years more.
Chris

According to the official Volvo manual the drums when new are 228.6mm (9”) internal diameter. My query is what is the maximum oversize that is acceptable. Thinking about it the drum starts to wear from day one of the cars life and presuming there is no scoring how did Volvo technicians know when to replace them?

Drums
 

The Volvo mechanics possibly removed the drums, if there was no "step" in them to be ground off, they were re fitted.

The Green Book says that maximum radial throw allowed is 0.006" (0.15mm). The problem with grinding the drums is that new shoes won't match the radius. Volvo has very specific instructions about grinding the shoes to match the drums. Pre disc brakes that procedure was common but finding someone with facilities to do that now may be difficult. Not doing this may mean that the full surface of the lining may never contact the drum even after many thousands of miles. This is also one of the reasons that the PV brakes are notorious for pulling to one side or the other when braking. Quick hard breaking can have you off the road or or into the opposite lane. Not good!
Rob's rationale, shown I think in one of his videos, is that if you reduce the thickness of the drum, it greatly reduces its ability to dissipate heat. Being rally orientated this is very important but perhaps normal quiet motoring on normal roads would stress them too much.
Green Book -Brake Drum - Check the friction surfaces of the brake drums and radial throw. The radial throw shouldn't exceed 0.15mm (0.006"). If the surface is hollow, scratched or cracked the drum should be replaced. Rust spots or small scratches can, however, be polished or ground off."

Hi Derek thanks for that detailed reply. I have done the front disc brake conversion to my PV so when I actually get it on the road it will be interesting to see how the brakes perform. Any issues at all will make me bite the bullet and purchase new rear drums. Am also considering fitting a servo into the system. Any body done this on 544 and was it a big plus? Thanks.

Something isn't right here, if the official new diameter stated by Volvo is 228.6mm how can V133 have some at 227mm? And for Rob to dismiss them at 230mm would mean bearly 0.5mm thickness of wear, surely Volvo in the 60's would have allowed for more durability than that plus they were notorious for over-engineering. Maybe 228.6mm is actually Volvo's max diameter.

Sorry cannot answer your question.According to the official green Volvo section on brakes the drum diameter when new is 9” which equates to 228.6 mm.I have machined my rear drums to 229.1 to get them to clean up. Will try them out with my front disc conversion and see how it goes.

You may have over-done it (if only a little).

The direct link to the page I want to refer does not seem to work, but you can get to it by going to the index at:

http://www.networksvolvoniacs.org/in...rie:How_To%27s

and then go to section B and click on:

Bremse. Arbeiten an 1 – 2 und 2 mal 3 Kreisanlagen ..mit entlüften.,

It then takes you to the relevant page. About halfway down the page, for Daten Bremssysteme PV544 (Buckel), it says:

max permitted diameter 229 mm – if it is above that, replace.

Re grinding the profile on the brake shoes, shouldn't they wear to the correct profile fairly quickly?