Rivet in Rotors or no?

[Keith M.]

This is on a 69 L46 4spd vert. 100k miles. Planning to restore trailing arms and front rotors. Am presuming current rotors, which are riveted and presume to be original, are best to be replaced all around. I did some quick measurements with a caliper and pretty much every rotor I can get readings below tolerance. I am in dialogue with several of the places (many of you know would know them) about doing this work. This thread is primarily not about recommendations on where to go but I would gladly accept them...here or in a PM.

So my core question is this. To my knowledge some places will rivet in replacement rotors and some do not. Should I care which way and why? I am well aware of how times have changed and gone are the days or turning rotors which are now a disposable item. I can't imagine any performance or durability difference between riveted or not. Also, not a judging consideration that I know of. Non riveted would be bit easier to replace down the line...but that is an issue for the next owner as I will be long gone. My restoration philosophy is to strive for originality where it makes sense to me. Making sense can come from a lot of different angles. In and of itself originality would dictate rivet them in...but other than a purist interpretation does this really matter? Probably splitting hairs on this one ...but engineer types do that by nature.

[Richard M.]

Re: Rivet in Rotors or no?

Keith, Fellow member Gary R(expert rebuilder) recommends that the hub rivet holes should be threaded and rotor holes drilled and beveled to accept Allen flat head beveled bolts to attach the rotors. IIRC, 5/16"-18.

Then the hub/rotor assembly should be checked for runout and rotor turned as an assembly if needed.

Rich

[Keith M.]

Re: Rivet in Rotors or no?

Keith, Fellow member Gary R(expert rebuilder) recommends that the hub rivet holes should be threaded and rotor holes drilled and beveled to accept Allen flat head beveled bolts to attach the rotors. IIRC, 5/16"-18.

Then the hub/rotor assembly should be checked for runout and rotor turned as an assembly if needed.

Rich

And revelation of his process to me is what prompted this thread. Still seeking thoughts on whether I should care about bolts vs rivets. I know Gary does excellent work so I am not questioning from that dimension at all.
Keith

[Mark F.]

Re: Rivet in Rotors or no?

In addition to Rich's and Gary R's suggestions, Bair's Corvette in Linesville, PA is another option you could explore.
They did my trailing arm rebuilds (along with other tasks) almost 20 years ago...
Excellent work and reasonable pricing.
Dunno about the rivet - no rivet thingy, but just call and ask...

[Keith M.]

Re: Rivet in Rotors or no?

Thanks. And now we have revealed the two I am considering. So given that..I am sure Bairs does great work, but Gary has been phenomenal to communicate with and seems very high tech. An above and beyond kinda guy. But good to know you had good experience with Bairs..not surprisingly.

[Owen L.]

Re: Rivet in Rotors or no?

It's my understanding that the rivets were there only to keep the assembly together before installation on the chassis. My advice mirrors others that if rivets are drilled out, make sure to index-mark the rotor on the hub so that it goes back together as originally assembled as a sub-unit. If I ever need to have a rotor turned I hope to have it done on the car as a rotating assembly. Same goes for replacing a rotor: index-mark the new one to the hub and have the assembly trued on the car. I like the idea of threading the hub so that the rotor is firmly located on the hub - then turn to true.

I think the answer to rivet or not is completely up to you. Not necessary for a safety or longevity, but maintaining the hub to rotor orientation is important for run-out and some sort of mechanical fastener will keep this placement during maintenance operations.

[Keith M.]

Re: Rivet in Rotors or no?

It's my understanding that the rivets were there only to keep the assembly together before installation on the chassis. My advice mirrors others that if rivets are drilled out, make sure to index-mark the rotor on the hub so that it goes back together as originally assembled as a sub-unit. If I ever need to have a rotor turned I hope to have it done on the car as a rotating assembly. Same goes for replacing a rotor: index-mark the new one to the hub and have the assembly trued on the car. I like the idea of threading the hub so that the rotor is firmly located on the hub - then turn to true.

I think the answer to rivet or not is completely up to you. Not necessary for a safety or longevity, but maintaining the hub to rotor orientation is important for run-out and some sort of mechanical fastener will keep this placement during maintenance operations.

Thanks. Good points. But rotors in my case, and all eventually, need replaced...which makes the indexing point moot. Only reason I would be drilling the rivets out is to replace rotors...which then need tuned for runout etc. So question is...new rotors..rivet or bolt? I have have not yet heard a reason why bolting would be an issue..and keeps it simpler down the line vs riveting. Thx

[Owen L.]

Re: Rivet in Rotors or no?

Thanks. Good points. But rotors in my case, and all eventually, need replaced...which makes the indexing point moot. Only reason I would be drilling the rivets out is to replace rotors...which then need tuned for runout etc. So question is...new rotors..rivet or bolt? I have have not yet heard a reason why bolting would be an issue..and keeps it simpler down the line vs riveting. Thx

I guess I wasn't clear in my attempt to address multiple scenarios. New rotors should be trued on the car if there is excessive run-out after installation. This ensures that the imperfections in the mating surfaces of the rotor and hub are machined out in the disc's planes. To index-mark the new rotors, mechanically fasten them, or not, just depends on your desire to ensure the new rotor is kept in the orientation in which it was installed. Also, you may get a more accurate and consistent run-out measurement (and truing, if needed) if you rivet or otherwise fasten the rotor to the hub rather than truing it while secured by lug nuts but I'm not certain of that.

[Joe L.]

Re: Rivet in Rotors or no?

This is on a 69 L46 4spd vert. 100k miles. Planning to restore trailing arms and front rotors. Am presuming current rotors, which are riveted and presume to be original, are best to be replaced all around. I did some quick measurements with a caliper and pretty much every rotor I can get readings below tolerance. I am in dialogue with several of the places (many of you know would know them) about doing this work. This thread is primarily not about recommendations on where to go but I would gladly accept them...here or in a PM.

So my core question is this. To my knowledge some places will rivet in replacement rotors and some do not. Should I care which way and why? I am well aware of how times have changed and gone are the days or turning rotors which are now a disposable item. I can't imagine any performance or durability difference between riveted or not. Also, not a judging consideration that I know of. Non riveted would be bit easier to replace down the line...but that is an issue for the next owner as I will be long gone. My restoration philosophy is to strive for originality where it makes sense to me. Making sense can come from a lot of different angles. In and of itself originality would dictate rivet them in...but other than a purist interpretation does this really matter? Probably splitting hairs on this one ...but engineer types do that by nature.

Keith-------


Keep this in mind: the original unfinished rotor castings, front and rear, were riveted to the hubs/spindles and machined to finished thickness as an assembly. If a rotor is replaced, it has to be replaced with a finished rotor. If this assembly has significant runout, the amount of machining necessary to correct the assembly could result in a rotor that's below minimum thickness. To avoid this the hub or spindle must first be machined to correct any runout and a finished rotor then installed. This involves quite a lot of work.

Unfinished rotors, such as used when the assemblies were originally riveted together and finish machined, were never available from GM or, as far as I know, anywhere else. GM once sold in SERVICE front rotors that were complete with riveted-on hubs. Unfortunately, the rear rotors were never sold with attached spindles.

[Keith M.]

Re: Rivet in Rotors or no?

Keith-------


Keep this in mind: the original unfinished rotor castings, front and rear, were riveted to the hubs/spindles and machined to finished thickness as an assembly. If a rotor is replaced, it has to be replaced with a finished rotor. If this assembly has significant runout, the amount of machining necessary to correct the assembly could result in a rotor that's below minimum thickness. To avoid this the hub or spindle must first be machined to correct any runout and a finished rotor then installed. This involves quite a lot of work.

Unfinished rotors, such as used when the assemblies were originally riveted together and finish machined, were never available from GM or, as far as I know, anywhere else. GM once sold in SERVICE front rotors that were complete with riveted-on hubs. Unfortunately, the rear rotors were never sold with attached spindles.

Joe,
I bow in reverence to your depth of knowledge on this topic and want to be clear I am grateful for your response. That said, as I look up into the air I see about half of what you posted going over my head, even as an engineer. Though I always welcome the opportunity to be further educated.

This has all gone a bit sideways so lemme take another run at it. My front rotor and trailing arm assemblies are 53 years old and need complete servicing and restoration to a reasonably high standard. My question is simply...Gary or Bairs for front rotor and trailing arm work?? When Gary said he bolted rotors vs riveting that started down this rabbit hole. Seems it really is a non-issue from what I can tell so far. I live about 2 hours south of Bair's and get back home to New England occassionally (Gary) and have already decided Gary is doing my steering box. So at this point am figuring bring Gary everything. "Everything" means front rotors on the knuckles as an assembly as taken off the car. Ditto trailing arms to be taken off and brought to him. The rest technically I leave in his capable hands and am fully confident he is a "do it right" kinda guy. Maybe bring him my half shafts whilst torn down anyway. Dunno I can handle (financially in part) doing the diff yet but when I get to that...Gary or Bairs. Will bring A-arms to Bairs...wasn't planning to do those just yet but the usual.."while I am in there"...might as well do with front end apart.

Thanks to all and appreciated any continued guidance/suggestions.
Keith