Sullii the 72 GMC 1500

[hewittca]

I've had a little set back with the truck this week. I drove the truck to work one day and upon walking out for the evening I was greeted with a puddle of coolant under the radiator. I was able to make it home, but the brand new Cold Case radiator was leaking from the core. Their customer service is actually quite good, however, and they are going to send me a new radiator thanks to their lifetime warranty.





While I wait on the new radiator, I figured it was a good time to clean up the garage a bit and get the truck up on stands to work on my wheels. My son was quite enthusiastic about helping me on this particular day.



The process is fairly simple for modifying the backspace of these wheels. Basically, I started by cutting the welds and knocking the centers out of the hoops so I could clean up all the old welds.





Next, I made a quick tool to press the centers in to the 5.25" backspace I wanted. When the horizontal bar reached the back of the hoop I knew I was at my desired backspace. I thought this would press in my centers squarely, but it actually wasn't as close as it needed to be. So, I made another tool for checking backspace all around the wheel mounting surface. A little tapping here and there with a hammer until this feeler gauge was even across all points on the center of the wheel.





Next, I needed to really fine tune the center of the wheel by actually measuring runout. Unfortunately, I did not have a way to spin up the wheel because I was doing all this at work. I ended up checking for variations across a flat plate set on top of the mounting surface with the wheel face down on a surface plate. Max allowable runout at the outer hoop is 0.030", so I figured under 0.010" would be good enough where I was measuring. This was achievable with a little patience and a few more taps of the hammer.





Once I was satisfied with the positioning of the center, it was simply a matter of welding them back in. All that work for 3/4" of difference!



In the end, they don't really look much different, but it bought me the extra clearance I needed so I could tuck tire on a 10" rim. My son helped me check clearance with my tire gauge stick.

[raggedjim]

Nice work on the wheels, I don't think I would ever try that!

You're son looks like he's a lot of help!

Rg

[PowerdbyChevy79]

Originally Posted by hewittca

I've had a little set back with the truck this week. I drove the truck to work one day and upon walking out for the evening I was greeted with a puddle of coolant under the radiator. I was able to make it home, but the brand new Cold Case radiator was leaking from the core. Their customer service is actually quite good, however, and they are going to send me a new radiator thanks to their lifetime warranty.





While I wait on the new radiator, I figured it was a good time to clean up the garage a bit and get the truck up on stands to work on my wheels. My son was quite enthusiastic about helping me on this particular day.



The process is fairly simple for modifying the backspace of these wheels. Basically, I started by cutting the welds and knocking the centers out of the hoops so I could clean up all the old welds.





Next, I made a quick tool to press the centers in to the 5.25" backspace I wanted. When the horizontal bar reached the back of the hoop I knew I was at my desired backspace. I thought this would press in my centers squarely, but it actually wasn't as close as it needed to be. So, I made another tool for checking backspace all around the wheel mounting surface. A little tapping here and there with a hammer until this feeler gauge was even across all points on the center of the wheel.





Next, I needed to really fine tune the center of the wheel by actually measuring runout. Unfortunately, I did not have a way to spin up the wheel because I was doing all this at work. I ended up checking for variations across a flat plate set on top of the mounting surface with the wheel face down on a surface plate. Max allowable runout at the outer hoop is 0.030", so I figured under 0.010" would be good enough where I was measuring. This was achievable with a little patience and a few more taps of the hammer.





Once I was satisfied with the positioning of the center, it was simply a matter of welding them back in. All that work for 3/4" of difference!



In the end, they don't really look much different, but it bought me the extra clearance I needed so I could tuck tire on a 10" rim. My son helped me check clearance with my tire gauge stick.

Very nice work...

[hewittca]

So I have a few items to add resolution to before we get to the good stuff. First, I was able to install the replacement Cold Case radiator. This resolved my leaky radiator problem with the best possible solution: a new radiator. Cold Case was awesome to work with on the warranty replacement, and super fast shipping. I'm just hoping the new radiator doesn't leak as well! While I was investigating the leak, I also noticed that my serpentine belt was bouncing around quite a bit. I checked the tensioner and it was at full extension... not good. I decided to go with a 1" shorter belt, PN K060785. It was also at this point that I noticed the alignment marks on the tensioner. This belt ends up with the tensioner at the ideal location.





Next up was my driveshaft vibration issue. After reviewing all my angles AGAIN, I decided to try adding a 2 degree shim to rotate the pinion downward. This put the pinion 1 degree below where I thought it should be in theory, but I was running out of adjustment at this point and wanted to try something. While I was checking angles, I also inspected the universal joints and noticed my front joint had radial play in both axes. Then I noticed that the cap faces were grinded down, I'm assuming in an attempt to get the retaining rings in. I was quite disappointed with this discovery since I specifically drove several towns over to go to a highly recommended drive shaft shop. I can only guess this is standard practice and someone just got a little over zealous on this particular u-joint. I decided to replace this ruined Moog joint with a Spicer that ended up fitting perfectly right out of the box. With the changes I made this time around, my driveshaft vibration is now gone!



Now that those issues are resolved, it's on to the fun stuff. I debated on which tires to get for my new wheel setup and was stuck between a 275/60 or a 295/50 rear tire. I liked the height of the 275, but did not like that it would be a bit stretched like my 235 on the 8" wheel. The 295 fits a 10" wheel perfectly, but the 50 aspect ratio results in a very short tire for a truck at 26.6". Ultimately, I ended up going with the 295/50 rear and a 245/60 front to match. Coincidentally, this wheel/tire combo is the so-called "Squarebody Syndicate Formula" but I'm about to make it fit on a 67-72.

The first photo is the old 215/75 (left) and the 245/60 (right) that will replace it on the front. Second photo is the old 235/75 (left) and the meaty 295/50 (right) replacement! This tire definitely adds some depth to the rear of the truck compared to the skinny 235.







I went with Cooper Cobra Radial G/T tires because they were the only decent tires in these sizes that I could find. BFG no longer makes the 295/50. You can get a BFG copy from Coker but I didn't want to drop that much change on tires. Besides, the Coopers are pretty darn nice tires anyway. The only thing I don't like about them is the ridiculous cobra emblazoned on the blackwall side of the tire, so white letters out it is.

[zicc1835]

nice catch on the tensioner and U joints ...and look forward to seeing the new tires installed

[hewittca]

With the tires mounted the only thing left to do was put them back on the truck. I may have mentioned already, but on the front I have to run a 1/4" spacer since the wheel hits the tierod arm. This was an easier solution instead of cutting these wheels up to reduce the backspace by one quarter inch. On the rear, it's a bit of a process to get the wheels on. I have to put the rear end on jackstands, then jack up the frame on one side to articulate the rear suspension, and then squeeze the tire inside the fender. I was worried I added too much backspacing to the wheel, but after installing them I am glad I went with 5.25". Another 1/4" less backspace and it would not have fit! With the shorter tires, I also had to double the height of my blocks that I use for getting the jack under the truck. Here it is after lowering it down for the first time.



The rear fitment is exactly what I was hoping for. It's very aggressive but it fits without rubbing after all the clearancing work I did at an earlier stage.







The front is close to where I want it, but it still needs some work. I had to remove 1/8" of camber shims to tuck the wheels in more because they were too close to the fenders. Even after this, my turning radius isn't very good. My limiter is tire rub on the outer fender. If I could narrow the control arms about 1/2" I think it would be perfect. For now, I will just have to be cognizant that anything resembling parking is going to take a wide arc or two attempts.





Ground clearance has been reduced by 1" compared to where I was with the other tires. It is almost to the point of "stupid low", however, it is still higher than my R32 and I never have any issues driving that car. I realize I have crippled this trucks ability to do anything other than cruising around, but I knew that going in. I wanted to get the truck as low as I could static, and I think this is the absolute limit within my means. My goal was gringoloco levels of low. His photo of a can in front of his bumper was my reference for what low is He still has me beat by about 1/2" but I can live with that.









Out on the road, I can definitely tell I have shorter sidewalls. The tires translate more road content, but in a good way. The ride is still very comfortable. I did not have any tire rub issues while driving with my other tires, and this remains the same with the new tires. Steering feels about the same. I was very happy with everything... until I hit 55 mph. Then the whole front of the truck got a case of the shimmies. If I went +/- 5 mph beyond 55 the shimmy went away. It was not tied to engine load since I could drop it in neutral and it would make no change to the shake.



After this first ride I was a bit disheartened because these wheels/tires were fresh off the balancer. My intention at this point is to put the original front wheels back on and see if the shake goes away. If so, I will promptly pay a visit to the tire shop and demand in the nicest way possible that they recheck the balance of my tires. It will be a few days before I can get to this, so for now I stuck the caps on and will just enjoy looking at the truck.

[72 tigger]

Nice work!
Hopefully you’ll get the shake figured out
At least you corrected the driveline vibration!

[raggedjim]

Dude, I love how that truck sits. In the end how much lower are you? 7-9? I think I will end up at 5-1/2 front and 7 rear.

[raggedjim]

I'm guessing the trailing arm mounting flip raises the nose of the rearend up? I have always mounted my shims fat end forward but have never flipped the trailing arm mounts.

[hewittca]

Nominally, the truck is dropped 8/10 but with the short tires it's even lower. My rocker to ground clearance is 3.25".

Yeah, that is one of the benefits of flipping the trailing arm mounts. It was actually a negative for me since my rear is dropped so much, which is why my pinion shim is mounted large end to the rear. My driveshaft runs up hill on its way to the rearend, so my pinion needed to point down.

[clay68c10]

Originally Posted by raggedjim

I'm guessing the trailing arm mounting flip raises the nose of the rearend up? I have always mounted my shims fat end forward but have never flipped the trailing arm mounts.

I made my mounts removable but didn't end up keeping them flipped. It made the rear pinion angle 9-10 degrees up.
https://67-72chevytrucks.com/vboard/...&postcount=280


I really like the new wheel/tire combo.
A re-balance will probably get you fixed up.

[raggedjim]

Originally Posted by clay68c10

I made my mounts removable but didn't end up keeping them flipped. It made the rear pinion angle 9-10 degrees up.
https://67-72chevytrucks.com/vboard/...&postcount=280

Thanks!

Sorry for the thread-jack! Rg

[gringoloco]

Duuuuuuuude. I fricken love this truck. I just read the whole thread and had a few “totally relate to that” moments.

If I can help you spend some money: Mike Losh just released an OE-style front wheel tub that might fit the bill.

Excellent read, great detail. Keep up the great work and updates, please.

[cornerstone]

Good golly miss molly! If it's ever possible I hope you and Gringo can do a photo shoot of the 2 coolest C10 rides in the world. The both of you fellas went to ridiculous effort to get EXACTLY what you envisioned and clearly ya'll have 20/20. Both trucks are just perfect in my humble opinion.

[hewittca]

Thanks you guys!

gringoloco, I will definitely look into those wheel tubs. No inners is creating a mess under my hood.

cornerstone, you are too nice!

Here's a little before and after now that I am 3 years and 10 pages into this build. When I first got the truck I hated the white letter tires. Well look at me now. I guess grandpa was right!

[Kronald_70GMC]

Great looking truck! Loving this build.

[PowerdbyChevy79]

Originally Posted by hewittca

With the tires mounted the only thing left to do was put them back on the truck. I may have mentioned already, but on the front I have to run a 1/4" spacer since the wheel hits the tierod arm. This was an easier solution instead of cutting these wheels up to reduce the backspace by one quarter inch. On the rear, it's a bit of a process to get the wheels on. I have to put the rear end on jackstands, then jack up the frame on one side to articulate the rear suspension, and then squeeze the tire inside the fender. I was worried I added too much backspacing to the wheel, but after installing them I am glad I went with 5.25". Another 1/4" less backspace and it would not have fit! With the shorter tires, I also had to double the height of my blocks that I use for getting the jack under the truck. Here it is after lowering it down for the first time.



The rear fitment is exactly what I was hoping for. It's very aggressive but it fits without rubbing after all the clearancing work I did at an earlier stage.







The front is close to where I want it, but it still needs some work. I had to remove 1/8" of camber shims to tuck the wheels in more because they were too close to the fenders. Even after this, my turning radius isn't very good. My limiter is tire rub on the outer fender. If I could narrow the control arms about 1/2" I think it would be perfect. For now, I will just have to be cognizant that anything resembling parking is going to take a wide arc or two attempts.





Ground clearance has been reduced by 1" compared to where I was with the other tires. It is almost to the point of "stupid low", however, it is still higher than my R32 and I never have any issues driving that car. I realize I have crippled this trucks ability to do anything other than cruising around, but I knew that going in. I wanted to get the truck as low as I could static, and I think this is the absolute limit within my means. My goal was gringoloco levels of low. His photo of a can in front of his bumper was my reference for what low is He still has me beat by about 1/2" but I can live with that.









Out on the road, I can definitely tell I have shorter sidewalls. The tires translate more road content, but in a good way. The ride is still very comfortable. I did not have any tire rub issues while driving with my other tires, and this remains the same with the new tires. Steering feels about the same. I was very happy with everything... until I hit 55 mph. Then the whole front of the truck got a case of the shimmies. If I went +/- 5 mph beyond 55 the shimmy went away. It was not tied to engine load since I could drop it in neutral and it would make no change to the shake.



After this first ride I was a bit disheartened because these wheels/tires were fresh off the balancer. My intention at this point is to put the original front wheels back on and see if the shake goes away. If so, I will promptly pay a visit to the tire shop and demand in the nicest way possible that they recheck the balance of my tires. It will be a few days before I can get to this, so for now I stuck the caps on and will just enjoy looking at the truck.

The stance on this truck is perfect.. What crazy is that its static... Love it!

[YBNORML]

Originally Posted by hewittca

Thanks you guys!

gringoloco, I will definitely look into those wheel tubs. No inners is creating a mess under my hood.

cornerstone, you are too nice!

Here's a little before and after now that I am 3 years and 10 pages into this build. When I first got the truck I hated the white letter tires. Well look at me now. I guess grandpa was right!

Looks perfect. Those Coopers with 295’s sure take me back to high school. Same tire setup i ran on my 67’ longbed.

[raggedjim]

If you feel like working at it Frizzle Fry has a great thread on inner fender modification

https://67-72chevytrucks.com/vboard/...d.php?t=258732

[hewittca]

Originally Posted by raggedjim

If you feel like working at it Frizzle Fry has a great thread on inner fender modification

https://67-72chevytrucks.com/vboard/...d.php?t=258732

I have read through that thread before and gathered many ideas. The inner fenders are definitely something I'd like to build if I can find the patience!

[hewittca]

Over the last few weeks I've gone through a number of tests to try and determine where this vibration is coming from. First I started with my original 15x6 wheels/tires on the front with the 15x10s on the rear. Same vibration, so I redirected attention to the rear tires/wheels.



Next, I ran the new 15x8 245/60 setup on the front with the original 15x6 on the rear. It looks goofy, but the truck ran smooth without the 15x10s on it. With the 15x8s on the front the steering has a weird point where it feels like the tires grab more and turn in if I hit any kind of bump in the road. For the current experiment, this is an aside and something I will think about later.



Last test was to run the original 15x6 on the front with the 15x8 and 245/60 on the rear. This configuration gave me a very slight wobble/vibration at the same RPM as the 15x10 295/50 combo. At this point I was really fed up with these tires. It was also at this point that my daughter figured out she could turn the garage into a skating rink! This was a good reminder to look at the positives.





One thing that concerned me was the insane amount of weights they had to add to my 15x10s to get them balanced. They had 6 oz of stick on weights on one side and 2.5 oz on the other. This, combined with my tests, got me thinking that I may have screwed up these wheels when I changed the backspace. I rechecked the runout and got 0.034" radially and 0.055" laterally. From what I can find this is still within the upper limits of spec, but it's still more than my original 15x6 wheel which was less than 0.030" in both measurements.





I also measured runout on the tires which was about 0.060". Again, the tire shop told me the runout was within spec when they checked it. After all this investigation, I decided I needed to abandon this setup for now and go back to what I know was working. Problem was, I now had these Cooper tires that I didn't want anymore and I didn't feel right selling them to someone else when I knew they might be out of spec. Luckily, I purchased these from Summit and they were more than willing to honor Coopers 45 day satisfaction guarantee exchange policy. All I had to do was send these tires back and they would let me exchange them for another tire within Cooper's catalogue. So, the truck went up on stands for a few weeks while I waited on new tires.

[zicc1835]

Interesting calculations and diagnosis and will be waiting-patiently for the next update good news with the Summit return����

[hewittca]

Originally Posted by zicc1835

Interesting calculations and diagnosis and will be waiting-patiently for the next update good news with the Summit return����

You don't have to wait long, update incoming...

[hewittca]

Fast forward after two weeks of waiting for my replacement tires. I'm not complaining though. Summit took the old tires back no questions asked, paid for shipping both ways, and refunded me the cost difference between the new and old tires. Can't beat that. The only catch was I had to get Coopers to replace the old set. They do not have many options left that fit 15" wheels these days, so I had to go with a tried and true setup: 225/70 fronts and 275/60 rears. I have now had 275/60s on the rear of all my vehicles. You'd think I would know by now that this size is what I like.

I was able to get these tires mounted up by the shop that mounted my last set the same day they were delivered. The 225/70 replaces the 215/75 Hankook that I had on the front originally. The new tire is a bit shorter and wider than the 215/75. The 275/60 on the rear is much wider and a little shorter than the 235/75 I had on the rear originally. This new rear tire fills out the wheel well much better and doesn't look stretched like the 235/75 did.



Seeing the truck back on the ground was like seeing it come together for the first time again. The white letter tires were fun to try, but ultimately this wheel/tire setup is much more my style. After seeing the truck with this setup I'm not sure I even want to revisit the 15x10s again. For now, I will keep them in the corner until I run this setup for a while and then make a decision.









All that was left at this point was to finish it off with some caps and go for a test drive. Overall, the truck felt significantly better with this new setup. The vibration at 2300 RPM was gone and the weird grabby steering issue was resolved. I should make note that going back to these wheels allowed me to go back to my original camber adjustment. The other tires forced me to remove 1/8" of shim and add 2 degrees of camber. It was also nice to have my steering radius back. It is a much more pleasant driving experience with this setup and with everything working properly. The truck just floats down the road so smoothly now and requires very little correctional steering input. It took me quite a bit of experimentation to get here, but I think it was worth it now that I know what does and doesn't work. I think for now I will focus on driving the truck and enjoying it while it is in such a fine tuned state.

[zicc1835]

love the stance looks great