Re: Unexpected disk brake - wheel problem
 

Stock 16 inch 4-1/2 inch wide wheels on a 53 had/have 0 offset. 15- 5.5 have 0 offset. That should give about a 2-1/4 inch backspace.

I've got what I think is a 15 inch AD wheel out here and if I can find it in the snow tomorrow I'll measure the backspacing.

This from page 155 of the GM Heritage 53 truck pfd https://www.gm.com/content/dam/compa...olet-Truck.pdf

Re: Unexpected disk brake - wheel problem
 

he is still gaining the 1/4 inch in offset, although you are technically correct that he will have more rim on the inside.

let me explain:

a 6 inch wide wheel is 7" lip to lip, a 0 offset would thereby be a 3.5" backspace. he has 3.75" backspace, which is 1/4" or 6mm offset.

a 7 inch wide wheel is 8 inches lip to lip, 0 offset is 4" backspace. he is still gaining the 1/4 inch in offset, and the width of the wheel on the barrel is 1/2 wider (half of the extra inch of width is added to the front side of the rim, half to the back).

at worst, the new wheel will fit exactly the same. at best, he will have gained the 1/4" offset he needs. it depends on where the wheel is hitting the caliper. my feeling is you are correct, the wheel is not different enough to make a difference.

my advice, grind the caliper slightly like other have said. no spacer, no new wheel, just a zip zip on the high spot, the caliper will never miss this small surface area.

actually i would probably switch back to drums :lol: there is very very very little gain to rear discs in 90% of driving. I have said before that you could probably disconnect the rear brakes in 90% of driving and never even notice. (do not disconnect your rear brakes!)

enough soapboxing, take the advice and just grind the high spot of the caliper. dont go crazy, just a little at a time and if it looks like you have to grind a big hunk off see where you are at then. you may order new wheels and find the same interference.

Re: Unexpected disk brake - wheel problem
 

Thanks Lee. I'm trying to salvage my investment in the 215/75/15 and 235/75/15 tires. Given that I'll need to sell the 15" chrome smoothies that I bought, I'm thinking of moving to a wider 7" Cragar wheel. It has -6 offset, which is a full 12 mm difference from the +6 I have now. Hopefully, that'd be enough to clear the calipers.

Attachment 2234998

Re: Unexpected disk brake - wheel problem
 

From under the car, I can see that the somewhat conical stepped shape of the inner wheel combined with how far out the caliper sticks out that unless I'm willing to live with about 1/16" in clearance, I'm going to need a better wheel fitment.

Last night I put the 1/4" spacer on, combined with one steel 1/2" washer. I was able to get the lugs on by a thread or two and from under the car and behind the wheel, see that I had about 1/16" clearance to the caliper. At that point, I was contemplating the longer studs that had been suggested earlier. When I saw how minimal clearance that produced, I wasn't happy.

When I consider the time it would take to disassemble the calipers, rotors, remove the axle shafts, press out the old lugs, press in new longer lugs, then reassemble only to get 1/16" clearance., getting new better shaped and offset wheels seems like a better idea.

Re: Unexpected disk brake - wheel problem
 

my bad. 8" rims with Tires BFGoodrich T/A P235/70 R15 all around
mustII w/ power steering

Re: Unexpected disk brake - wheel problem
 

1/16" clearance sounds like enough to me? As long as it does not rub I don't see any difference between 1/64" and 1/2". Just make sure there is no slop axle to spider pin that you might loose that clearance in corners

where does it hit the caliper? (picture?)
as suggested grinding can probably give you at least another 1/16

edit: but I do see your comment about the work to swap lugs!
Should be no need to remove axles to swap lugs though

I agree with joedoh, drums in the rear are fine for most of our trucks, simple, cheap, better e-brake.
For period correctness you could go drums on all 4, get some of those big finned aluminum '69 buick skylark drums for front. except those drums probably cost more than a disk conversion these days

Re: Unexpected disk brake - wheel problem
 

no, thats only going to be an additional 6mm. thats why i tried to explain the difference in offset and backspacing but i guess I did it poorly.


when you make the wheel wider, the extra width is spread equally over the front and back halves of the wheel. so a 7" vs a 6" will have an extra 1/2 inch on the front half of the wheel (wheel mounting surface to the front lip) and 1/2" on the back half of the wheel (wheel mounting surface to the rear).

so going from a +6 to -6 will be a 12mm (1/2") difference in the mounting surface to the center of the wheel, but the actual gain in backspace is only going to be:

8/2 -1/4 (-6mm) = 3.75 backspace
and

7/2 + 1/4 (+6mm) = 3.75 backspace

zero. there will be no difference in the backspace, all the extra inch of the wheel width change will be on the front side of the rim, 1/2 inch that was already on the front side + 1/2 inch in offset change.

also, and this is kind of important to put all the way down here at the bottom but cest la vie, if the caliper right now is hitting the CENTER of the wheel, a different offset will not fix it, only a spacer will. if the caliper is hitting the rim portion of the wheel, a different offset may fix it. a different style wheel with a different center shape may fix it too.

and finally its worth mentioning, if you have the room for the extra 1" wider wheel to have the extra width all the way on the front side.... just get some 1.25" spacers and dont worry about new studs, it will move the wheel center out away from the caliper for about $50.

Re: Unexpected disk brake - wheel problem
 

Here are some pics. BTW, I don't have a stock rear end, with the Hallibrand quick change diff the axle shafts need to come out to get to the lugs.


Attachment 2235037

Attachment 2235038

Attachment 2235039

You didn't do a bad job at explaining, I did a bad job at understanding...LOL I get it now.......I think.

When you say 1.25" spacers do you mean something like this?

Attachment 2235045

Re: Unexpected disk brake - wheel problem
 

Do you have the box and fenders on the truck?
I’d hate to see you finally figure out a rim/tire that fits your discs only to have the tire contact the fender.

Re: Unexpected disk brake - wheel problem
 

That is a really good question. The bed was on but not the fenders. To ensure that the spacer I purchased was going to work, I remounted one side and took measurements. There is another 2 inches from the current wheel/tire to the outside edge of the wheel well. The 1 1/4" spacer should work out fine. Also, the bottom edge of the wheel well is about an inch above the top of the tire, so I should be fine. Thanks for the heads up!

Re: Unexpected disk brake - wheel problem
 

why haven't you ground the interference off yet???
yeah a 1/4" less back space would have done it

and why did you mount tires on bare steel rims?
you need to dismount the tires to powder coat or paint rims
you can't tape it to keep the rust out of the crack

fyi i powder coated my steelies with an eastwood pc setup in an old oven
to avoid handling the powder, i dusted them right on the oven rack
and carefully slid the rack in
i made a rotisserie out of wood and a bearing to rotate the rim
yeah it smoked a bit but never affected the pc :lol:

Re: Unexpected disk brake - wheel problem
 

They are chrome rims, didn't think they needed powder coated. I'm reluctant to grind away at a brand new caliper, I'd rather fix the wheel issue.

Re: Unexpected disk brake - wheel problem
 

He won't have any trouble with fender clearance with 7 inch wheels unless his axle is way too wide as 64 inche wms to wms. His whole problem is that he hasn't quite figured out that more back spacing puts the rim closer to the caliper and less back spacing puts it further away to the caliper. We have explained the problem and have given him the fix but it takes him longer to figure it out.

He could have popped a lug stud out, run to the parts house and found some matching lug studs that were 1/4 or more longer and put the spacers on and done but he has to do everything the hard way and make old man Davison cringe. fiy Mr 48 = old man Davison or Rob Davison in some groups.

Re: Unexpected disk brake - wheel problem
 

I looked up your smoothies on their website.
They certainly ain’t cheap.
A 16x7 would be the way to go but still not a gaurentee they’d fit either. Sometimes the wheel is designed different when you swap to larger sizes.
And if you changed to a different rim style like the cragars, still no gaurentee they’d fit.

Re: Unexpected disk brake - wheel problem
 

Despite your belief that I "could have popped a lug stud out" which sounds so incredibly easy which must be case on the factory axle. But as I've pointed out several times, I have an aftermarket axle that would require removal of the caliper, rotors, mounting brackets, and axle shaft. Then taking the 1/2 axle to my press to just pop out the lug stud. All of that just to see if that idea is workable.

Instead, I chose to purchase a wheel adapter to see if that remedies the problem. If it does, then I can continue with my build and decide at a later date if I change my wheels and tires.

By the way, I did try washers and the 1/4" spacer with the existing lugs and it just barely worked, which is why I purchased the 1 1/4" spacer/adapter that Lee suggested, which seemed like a more constructive suggestion than critical.

Re: Unexpected disk brake - wheel problem
 

Now you got it figured!
Do you have a link to the 1 1/4 spacers you bought?

Re: Unexpected disk brake - wheel problem
 

I bought them on eBay since I couldn't find 7/16-20 studs with a 6 by 5.5 bolt pattern (to match my lugs) on Speedway or Summit.....they may have them but they made it hard to find.

Here is a link to what I bought - https://www.ebay.com/itm/262252146185

Attachment 2235484

Yeah, #1 reason I was disappointed given what I spent for them and the tires. I'd prefer the ones I bought, so the spacer/adapter should allow me to save my current investment.

Thanks!

Re: Unexpected disk brake - wheel problem
 

Maybe!
Sorry to complicate things but best to be safe.
They’ll work to get you a roller for around the shop but possibly not safe to be driven on the road.
From your pic, your axles are lug centric. Your wheels are hub centric.
Your wheel adaptors are hub centric.
The wheel design is different for a lug versus hub centric rim.
Here’s a link to help with that.


https://lmr.com/products/hub-centric-vs-lug-centric

Re: Unexpected disk brake - wheel problem
 

You Buy longer studs at the local NAPA not through Summet or Speedway.

They have 16 pages of 7/16 lug studs listed. https://www.napaonline.com/en/search...%20&referer=v2

Re: Unexpected disk brake - wheel problem
 

geezer#99, How can you tell the spacers are hub centric? They look like they have tapered seats. The link does not appear to say specifically. Maybe there is a visual clue I am missing, but I have not had much to do with spacers.
I think I need hub rings for my wheels before I drive it so I want to learn more.

the wheels are not hub centric? - if this is the wheel in question https://www.summitracing.com/parts/usw-52-5660n

Mr48: he said he had trouble finding spacers with the right thread, not longer lugs

Re: Unexpected disk brake - wheel problem
 

Seems I got it backwards!
I assumed the conical style lug was used with hub centric wheels.
More research brings up a better link.
Seems his new spacers will work well with his wheels.
Apoligies for the confusement.


http://www.nissantechnicianinfo.mobi...g_Centric.html

Re: Unexpected disk brake - wheel problem
 

Gracias!

Re: Unexpected disk brake - wheel problem
 

Actually, if you filter the 16 pages down to just studs that are 7/16-20 there are sixteen choices of varying lengths and knurl sizings. If I decide to throw out the spacers/adapters that I just bought and remove the calipers, rotors, brackets, and axle shafts to use the press to punch out six studs (on each side), so that I can press in six new longer studs and then reassemble everything so that I can use a different spacer and/or washers, I'll head to Napa.

Re: Unexpected disk brake - wheel problem
 

That is indeed the wheel, luckily I must have bought them before the latest inflationary price increase/gouging. I've had them for several months and paid less than that price, thankfully.

Re: Unexpected disk brake - wheel problem
 

you got it figured out!