I just had a local import shop turn my front drums to get rid of all the ridges and grooves before I install new cylinders and shoes. Now they tell me they don't know if the drums are safe to use because they don't know what the maximum allowable oversize is for the 544 drum. My Volvo factory manual isn't much help. It mentions only a maximum "radial throw" of 0.006". Does anyone have an explaanation of "radial throw" - I assume it is a measure of out-of-round. The factory manual does list a maximum oversize of 0.015" for the 120 and P1800 rear drums. Does anyone have a source for an acceptable limit on the 544 drums? Are the 120/P1800 drums the same? Many thanks.

Well, from the info I've gathered here, most,if not all, of my drums are too worn to use. The only source I've found so far for a 122 front disc setup wants $300 for used parts. I emailed John Parker about his Ford rear brake conversion; it's not as simple as I had remembered. It involves cutting and welding the axle housing as well as re-machining the half-shafts. Also too expensive at this time. I think I'll hit the salvage yard and take a look at those Ford Ranger drums. As far as that goes, my Jeep also has a 9" drum with the same bolt pattern..... I'll keep you all posted. Thanks for your help and support.

Ken

Whenever drums are machined your shoes should be fitted with oversize bonded linings and radius ground to suit diameter of drum. This will bring your adjustment back to specs and lessen bed in time. I dont think fade would be an issue with normal driving unless they are obviously thin. With cars of that vintage drum limits would be advisory not legal.

I don't have any information on what the original diameter and the max allowed limit is on the drums but can help as to "why it is".
First off, When a drum is turned out too far enough metal is gone that it effects the heat dissipating capabilitys of the drum itself and you can get some serious brake fade due to the heat. Second because Volvo uses the cam type adjustment you can get to a point where the cam will not push the shoe out far enough to get a good adjustment as the cam will go over center. You might have 1/2 to 3/4 shoe left but it will give you the same as worn out brakes.
At one time I looked into using a Ford Ranger rear brake drum as the Volvo replacement was so much. The bolt pattern is the same but I never got as far as having the inside diameter of the drum checked with a mike to see if it was close enough. The Volvo is in metric and the ford is in dec. measurement. If it has enough meat to work it is a matter of finding a machine shop that can cut the center of the drum so it will fit over the hub of the Volvo ( the large center hole is slightly smaller than the one on the volvo) and press new lug bolts in. The Ford drum costs around $ 18.00 each and the Volvo is $ 150.00 and up plus exchange each. Exchange tells me they are getting a bare drum somewhere and pressing it on to a hub then charging an arm and a leg for it because they are the only game in town.
Good luck and let everyone know what you find out as we all can use this.
Dennis

I also forgot to mention that the ford drum has a little more meat on the inside outer diameter and small cooling fins that can help on brake fade a little also.
Dennis

I put a tape measure to some drums at the wrecking yard today. The Ford Ranger drum is about 3/8" too narrow to replace the Volvo drum. The Chevy S10 and Jeep Cherokee also have 9" drums with the same bolt battern, but they are about 5/8" too wide. The guy at the wrecking yard was running out of patience, so I didn't look at anything else.

Dennis, I notice from your profile that you've got the whole Ranger rear end in your car. Did you have to get it narrowed? What did you have to do to attach the Ford axle to that upper link in the Volvo suspension? I've been eye-balling a Jeep rear axle, but it seems like the suspension could be tough to hook up, plus the driveshaft would have to be modified. That's why John Parker's conversion uses most of the Volvo axle except the ends of the housing and the half shafts. I don't think I'm up to such a big project at this time, so I guess I may be looking for a pair of used drums after all.

Ken

Can't speak to the legality of this, but there's a rule of thumb... there's a 45-degree chamfer on the inner edge of the circumference of the drum. If there's some chamfer left, it's good to go.

Phil,

Thanks for the insight. Looks like one of my four drums might be usable. I'm not sure I want to pay the price for new drums, and I suspect most used drums are not much better than mine. I'm considering going for the 120 front disc conversion as it sounds relatively simple. I'm wondering about the Ford rear brake conversion that John Parker wrote about on your vclassics web site. As I recall from talking to John some years back, I would have to get the half shafts re-machined, but otherwise it's pretty straightforward. Do you know anything more about that conversion, or would you just advise looking for 544 drums? Many thanks.

Ken

Ken,

I think discs up front are a big improvement. You already know more about the rear Ford drum conversion than I do -- I have a long-range plan to do that to my 1800, but it's too spendy for me at the moment. If you plan to keep the car, I'd say both conversions are worth the investment.

--Phil

Phil,

By your criteria for measuring the life left in a drum, both of my rear drums came back from the lathe good to go back on. And they only charged me for turning one pair because they hadn't checked the limits before turning the front drums too far. So I'm going to set aside the notion of Ford rear brakes for now, though I'm still not getting off real easy - looks like I need to replace the rear axle seals to keep my new shoes from getting oily. And the front disc setup should be arriving soon. Thanks again to everybody for their help.

Ken

For what it's worth, the 122 and 544 rear drums are interchangeable if not
identical. It would seem to me for something that size that 0.015" over
as a max pretty much means that if you have to machine them, they are already
too far gone, considering the grooves, etc that I have seen on them.

I believe "radial throw" = travel of the brake shoe from rest to full braking.
--
George Downs, Bartlesville, Oklahoma, Central US

I don't know what the spec is, but did you look all over the outsice of the drum tosee if it is stamped on there anywhere? Some manufacturers stamp the max dia on the drum .
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-------Robert, '93 940t, '90 240 wagon, '84 240 diesel (she's sick) , '80 245 diesel