Unexpected disk brake - wheel problem
 

A month or so ago, I installed four disk brakes on my 1953 Chevy truck. The manufacturer of the rotors/calipers claimed that they worked with 15 inch wheels. I also purchased a set of chrome "Smoothie" wheels from US Wheels and installed them after the brakes were already done and on the old wheels.

While working on my leaf springs, I tried to rotate one of the rear wheels when the rear axle was off the ground. I found the rear wheels unable to rotate. Removal of the wheel/tire proved that the rotors and axle were able to rotate on their own. Further investigation showed that the wheels contacts the outer edge of the caliper, preventing it from rotating.

The chrome wheels are 15 inch by 6 inch wheels with an offset of 6 and backspace of 3.75. In contacting the brake manufacturer, they indicate that they designed the rotor/caliper to works with "factory stock wheels". which is not what I currently have.

Interestingly, the front wheels/tires have no issue with rotating. Which means at a minimum I'm stuck with two brand new wheels and new tires that don't work properly with the rear brakes. Even more confounding is, I don't know what size or backspace of wheel to use on the rears now. Any helpful suggestions will be appreciated.

Re: Unexpected disk brake - wheel problem
 

Put some washers onto the wheel studs to space the wheel out until it turns, then measure the washers?
You may just need a wheel spacer, or at least you will have some idea how much different offset you need.

Avoid the temptation to drive with the washers in there.

Re: Unexpected disk brake - wheel problem
 

In the stuff the previous owner had in a box were two wheel spacers of about 1/4 inch thickness. I did try those, but given the construction of the inner wheel, they forced the wheel to be pushed out nearly 1/2 inch and as a result the lug bolts were too short to even get one thread of the lug nuts on.

I will try washers tomorrow to see if that makes a difference. Thats a good plan, thanks.

Re: Unexpected disk brake - wheel problem
 

This used to be real common when putting non factory wheels on disk brake cars in the early 70's or after we started swapping disk brakes to our trucks in the late 70's early 80's.

I've taken a grinder to the high spots on the caliper and rounded them off more than once, I have a pair of those same spacers hanging in the garage that were on the disk brakes on my 48 when I had it subframed. That means those are 41 years old.

The good thing is that all you need to have is enough clearance that the wheel doesn't hit the caliper, As the pads wear the caliper will move away from the wheel.

First step is follow Leegreens's advice and figure out how much space you need.

Re: Unexpected disk brake - wheel problem
 

I have done both of the aforementioned things with new disc brakes or new wheels or both. the other thing I am curious about is whether you have the steering connected to the spindles. I ask because the next problem you may encounter is that the outer tie rods may rub the wheels on their back side. if the wheels are aluminum they tend to be thicker that the steel wheels, for strength, so those thicker wheels are sometimes just thick enough to interfere with the tie rod joint.
I usually try to set things up so I can use a wheel with some common size and back space, that way you can find some cheap wheels and tires to use when working on the vehicle. no worries about getting welding slag burnt in or oversprayed with paint or primer. since building doesn't usually happen in a week sometimes guys that buy new wheels and tires when they start the build find that by the time the project is complete those new wheels are out of vogue and the tires are outdated, so possibly need replacing. We all start with good intentions but then life gets in the way.

Re: Unexpected disk brake - wheel problem
 

some steel wheels are also made with a deeper "groove" or recessed are in the center of the donut. this smaller diameter area is sometimes what rubs the brakes.maybe you can find a wheel with a larger diameter center section?

Re: Unexpected disk brake - wheel problem
 

this. grind it

Re: Unexpected disk brake - wheel problem
 

Did you get the kit for 5 or 6 lug wheels? The 5 lug will have rotors off a 70's Camaro with a smaller diameter rotor than the 6 lug kit which uses parts originally for 16" wheels and a larger diameter rotor. Even though the 6 lug kit says can be used with 15" wheels it can be tight depending on the wheels like you have found out. I have a 6 lug kit and with the wheels I am going to use it will take some grinding on the calipers, a spacer and no wheel weights on the area where the caliper is near the wheel.

Re: Unexpected disk brake - wheel problem
 

6 lug axle with 15 inch wheels. As I mentioned, the fronts are free and clear. The rear are binding on the outside rear edge of the caliper.

I just tried the spacer again and managed to get the lugs to catch by a thread or two. With the spacer and the gap that exists between the spacer and the chrome wheel due to its configuration (looks stamped) it adds about 5/16 of an inch, the caliper just clears, but not by much.

I need a quick study of offset versus backspace to determine what is needed to make this work. I'm tempted to try a 16 inch wheel, but that has a big financial penalty given I already own new 15 inch wheels and tires.

Re: Unexpected disk brake - wheel problem
 

So I just did a quick study of offset versus backspace. It appears to me that my issue is related to offset. My current wheels are 15 inch by 6 inch wheel, with an offset of 6 and backspace of 3.75.

The wheel is set back to far on the axle, allowing the inside edge of the rim to rub against the outside edge of the caliper. If the offset were 0 or negative, the wheel would be moved outward and away from binding on the caliper.

I went to the US Wheel website where I purchased the Chrome "Smoothies" and see that there is a 15 inch by 7 inch wheel available that has a "0" offset and a 4.0 backspace. By moving the wheel 6 millimeters outward I think my binding issue would go away.

Thoughts?

Re: Unexpected disk brake - wheel problem
 

Sounds like you may have a somewhat easy solution. Just make sure you have fender clearance and sufficient thread engagement on the wheel studs for the lug nuts.

Re: Unexpected disk brake - wheel problem
 

Wrong way, you need a 3 to 3.5 inch back space. 4 puts the inside rim closer to the caliper yet. Most likely you won't even be able to get a 4 inch backspace wheel on the hub with the caliper on.

Re: Unexpected disk brake - wheel problem
 

This link that I snagged those images off does a fairly decent explanaiton.

https://www.roughcountry.com/blog/wh...explained.html


This may explain it a bit simpler Again 4x4 site but your problem now is too much backspacing and more backspacing will increase the problem. https://ok4wd.com/blog/the-differenc...d-backspacing/

Re: Unexpected disk brake - wheel problem
 

I get it now. I need a wheel with a negative offset.

As for the trick with the washers, I stacked three 1/2 washers on each stud after measuring their thickness with my caliper. They were 9/32 of an inch or about 7 mm. Which is darn close to measurement of the other 15 inch wheel that I mentioned. While it fit and the wheel turned, the caliper was only clear by the finest measurement known to man (as my Dad used to say). It's unfortunately clear, that simply buying a 15 by 7 inch wheel with 0 offset and 4 backspace will not work and as you mentioned, is moving in the wrong direction.

Should I just consider moving to a 16 inch wheel with -6 offset and 3.75 backspace?

Re: Unexpected disk brake - wheel problem
 

Maybe a good question for the group is, what size wheel and tires do you run on your truck? 15, 16, 17, 18 inch wheels? Tire size? Same tire size front and rear?

Re: Unexpected disk brake - wheel problem
 

15x9 rims from wheelvintiques 4 wheel disc brakes, 4" bs

Re: Unexpected disk brake - wheel problem
 

Power steering? How does it steer with 9 inches up front?

Re: Unexpected disk brake - wheel problem
 

I've run 14-7 on the front since around 1975 and used to run 14-8-1/4 Crager Mach 8's on the rear, Since around 1990 it has had Enkie 32's 14x7 on the front and 15x8 on the rear with 195-60 14 on the front and 255-60-15 on the rear. That for a staggered hot rod look with the percentage of sidewall to wheel on the fronts pretty close to the precentage of sidewall to wheel on the rear being fairly equial Per what Boyd Coddington suggested in the late 80's. Most of his earlier builds had a larger diameter wheel on the back than on the front and had that balance between front and rear.

Back when it still had the Crager Mach 8s on it.
https://hosting.photobucket.com/albu...720&fit=bounds

Still and I know that some might get tired of me saying it, Wheel and tire choice have to match your total build theme and have to be a working and contributiting component of the total look. They shouldn't overpower the truck and turn it into a background for a wheel add but on the other hand they shouldn't look settled for as most white spoke wheels scream on old trucks. When you look at a vehicle your eyes should not pick out one specific component before they take in the whole vehicle as a total package. That is any part of the rig unless you are specifically looking for that part. If you scroll down the page or flip pages or are walking though a show and your eye picks out a component before you see the whole rig as a unit that component is wrong for that truck.

Re: Unexpected disk brake - wheel problem
 

I pretty much agree with you. Given the pedigree of this truck (was a pusher truck on the Bonneville salt flats), a 1959 261cu/in inline six engine with a McCulloch supercharger, a vertex magneto, and a Hallibrand quick change diff. I'm definitely going for more of a hot rod look than a low rider.

While I have 15 inch wheels, I did have slightly different sizes 215/75/15 front and 235/75/15 rear. I'm really torn on what to do to correct my disk/caliper issue. It seems that when I find a wheel size that has the appropriate offset (negative) it seems too wide for the brand spanking new tires I already own.

Re: Unexpected disk brake - wheel problem
 

I pretty much agree with you. Given the pedigree of this truck (was a pusher truck on the Bonneville salt flats), a 1959 261cu/in inline six engine with a McCulloch supercharger, a vertex magneto, and a Hallibrand quick change diff. I'm definitely going for more of a hot rod look than a low rider.

While I have 15 inch wheels, I did have slightly different sizes 215/75/15 front and 235/75/15 rear. I'm really torn on what to do to correct my disk/caliper issue. It seems that when I find a wheel size that has the appropriate offset (negative) it seems too wide for the brand spanking new tires I already own.

Re: Unexpected disk brake - wheel problem
 

Use your spacers, grind a tiny bit more clearance on the calliper and install some longer wheel studs.
For those who think the spacers are the weak point, I’ve used them for years on trucks/cars with way more power and torque than your set up produces.
JMHO

Re: Unexpected disk brake - wheel problem
 

When I took that photo in 1982 At the Chevy-GMC Truckin Nationals in Ogden I had a 68 Camaro Subframe with 72 Monte Carlo disk brakes on the front and a 66 Impala 12 bolt posi under the rear. That is after I did have to use spacers and had to grind on one corner of the caliper for clearance.

Still I have to believe that you can get by with just a bit of a spacer. get a hand full of flat washers and go one layer at a time until you have clearance and the measure the stack. Don't forget that it isn't very hard or expensive to swap out the lug bolts for longer lug bolts. That is under 20 bucks a side if you do it yourself.

I'd add that I think your choice of simple chrome wheels and those tires do give it that all business push truck look. I might go as far as actually build a push bar for it. If you drove it to Bonneville for speed week that sure would one up those posers who paint drag car classes on their rust buckets and pretend that they are old land speed cars hoping someone will take a photo of it.

Re: Unexpected disk brake - wheel problem
 

My reply from Post #14 above -

As for the trick with the washers, I stacked three 1/2 washers on each stud after measuring their thickness with my caliper. They were 9/32 of an inch or about 7 mm. Which is darn close to measurement of the other 15 inch wheel that I mentioned. While it fit and the wheel turned, the caliper was only clear by the finest measurement known to man (as my Dad used to say).

Re: Unexpected disk brake - wheel problem
 

Two question.

1) Does anyone know the backspace/offset dimensions of the stock factory 15 inch rims?

2) For those of you without power steering, what is the size of the tires you are running up front?

Re: Unexpected disk brake - wheel problem
 

I could measure a factory 16 in a day or so if that helps.
I seen online sources saying the base tire for 1/2 tons was 15 and 16. At least around here all the trucks I found back in the day were 16s.....I wanted 15s with the factory shape to the centre and cap clips and never found any.

I have 15x8 aluminum slots, 235/70 on rear and 215/60 front, I like that look.

I've driven other trucks with 235/75/ front and no power steering and it was not a problem.

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.