GM ralley truck wheel measurements

[Beck]

I am running the GM truck Rally wheels (they have a lot of little square holes around them) from the 80s on my truck. Currently I have the 15x8 wheels on the rear. I have 255/70/15 tires. I need a taller tire to decrease engine rpm. I am considering cutting up a pair of the truck or van Rally wheels to take the centers out of them. I would like to install this center into a 16" outer rim. GM continued using a similar Rally wheel on it's 4x4 trucks that was a 16" wheel. Does anyone have one of these 16" wheels handy to measure the barrel size where the inner welds to the outer?
If I change to a 265/75/16 tire I will effectively get a 8 to 9% overdrive. The section width is close enough to the same to fit my fender opening.
I checked a Ford van and the barrel is much to big on it for the GM center to fit.

All of this follows discovering an out of round tire. That rim may be part of the problem. It is slightly out of round on the outer lip. Spinning the tire on the balancer it looks much worse. The tire store installed their last tire like mine on the rim. It was worse than the one I had. Cheap tires. I could find another rim that was true ( I have some that are worse) and then go somewhere else and buy another pair of tires the same size. This dealer no longer handles anything that size.
My truck needs overdrive. It really wants another gear. I am considering an OD for behind the transmission. These get expensive quickly! Then I had this brain storm about the larger diameter tires possibly helping the problem.
Everything gets expensive. 4 rims, 2 for the outers and 2 for the inners. More paint, I don't quite have enough. Two 16" trim rings. $400 worth of tires, they won't be the cheap ones this time. My savings would be the tire store will give me full credit for my 2 tires, which was only $120. Then I have to spend the hours getting the custom wheels true, welded, and painted.
The alternative is a used OD which will cost about $600. This is a divorced unit so I will need 2 drive shafts cut = $400. Then I need to make a mount for the OD, and cut a shift hole in the floor. For that I get an 18% OD which would suit the truck better. There are no guarantees with the OD. It could be all for nothing.
OR live with a little vibration and just slow down.

[wayne petty]

just curious....

i know those rims .. nice looking rims...

but...

how about updating to something else... or back dating....

http://www.4wheelparts.com/WheelFinder.aspx


i take it that you have 6 bolt rims.. not 8 bolt rims... since you mentioned 4 wheel drive...

[Beck]

My truck needs overdrive. It really wants another gear. I am considering an OD for behind the transmission. These get expensive quickly! Then I had this brain storm about the larger diameter tires possibly helping the problem.
The alternative is a used OD which will cost about $600. This is a divorced unit so I will need 2 drive shafts cut = $400. Then I need to make a mount for the OD, and cut a shift hole in the floor. For that I get an 18% OD which would suit the truck better. There are no guarantees with the OD. It could be all for nothing.
OR live with a little vibration and just slow down.

I didn't want to say to much on my previous post for fear someone would outbid me on the flea-bay overdrive auction.
I bought the overdrive. It is a Mitchell Gear Splitter. There is very little information available on the net about these units. I called the original mfg and talked to the wife of the deceased business owner and designer of the unit. It has an 8% under drive and a 18% overdrive in the box. There is no direct drive. The units are rated at 20,000 gvw and were often put into motor homes. Here is a link to the OD. The photos are big so it takes a while to load.
http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=150348921645&viewitem=&sspagename=STRK%3AMEWAX%3AIT
I bought it for $435 with shipping. From what I did find about the unit they are really tough. Previously I was looking at Doug Nash ODs. From surfing it appears they are failure prone and more expensive. The Gear Vendor units are the only ones I find currently available new. They are the most expensive used.
I have had some success in shortening my own drive shafts them having them balanced. I may try that again to try to cut some expenses. My major concern is ground clearance. My truck is low. This will be just about in the center of the wheelbase so will be susceptible to dragging. I may need to build a skid plate.
Now I just need to find a straight 15x8 2wd chevy truck rally wheel. Since I have road hazard on my tires I think the tire dealer will remount and balance my tire for free. Especially if it saves him replacing the pair of tires. I hope the tire runs true on a better rim.

[Beck]

I thought I would post a photo of what I was playing with. I know it is too new for this sight and I apologize.

[Beck]

Here is a little better door photo.

[enjenjo]

Not too new as fae as I am concerned. after all it will be NSRA eligible next year.

If you mount the OD unit close enough to the trans, you can use a CV cage for a double Cardan joint as a short driveshaft, and then just make up one shaft for the rear. You might get lucky and find one that fits.

If you can't find one local, I have some of those wheels.

[Beck]

Not too new as fae as I am concerned. after all it will be NSRA eligible next year.

If you mount the OD unit close enough to the trans, you can use a CV cage for a double Cardan joint as a short driveshaft, and then just make up one shaft for the rear. You might get lucky and find one that fits.

If you can't find one local, I have some of those wheels.

I was intentionally staying away from the NSRA situation. It makes this truck "legal" but I think it sucks.

Now I have to show my ignorance: I don't know what a CV cage for a double Cardan joint is. I am expecting it is similar to the double joints as found on some driveshafts. Is this a rebuildable part that new u-joints can be installed or is it purchased as a complete unit.
The manufacturing recomdations are for a minimum of 8" shaft from the trans to the OD.
I will need to go from the large 400 turbo output yolk through whatever shaft is used to another solid yolk on the OD. I expect the transmission joint will be a different size than that of the OD.
There is then the splined output from the OD just like a trans shaft except it isn't sealed and running in fluid. The OD output shaft is sealed before the splines.
Getting the shaft angles right will also be a challange. Currently my trans tailshaft points nearly at the rear axle. They are parallel and all that good stuff. It just worked out with the motor insalled it is level with the rear axle. I realize I need to keep a few degrees in the shaft/joint angle.

I have seen a lot of the wheels locally at swap meets. Unfortunately the swap meets are over here for the summer. I'll find one. Thanks.

[Crosley.In.AZ]

no vehicle age limits here to my knowledge.

Looks like a   nice truck. I like those years trucks with that design hood.

actually the chev trucks from the Advanced design style years  to 1972  year  are good looking body  designs  in my opinion.

one other item.. it is a drive shaft 'yoke'  not yolk  

[enjenjo]

Here is a picture of a yoke from a pickup truck that will fit that spline. The collar on the end is installed on the spline, then a splined washer, and a rubber or cork splined seal. you then screw the collar onto the yoke, capturing the seal between the washer and the yoke. It will then hold grease so it can slide. You can find these on the rear half of a GM truck driveshaft, from a two piece driveshaft.

The other picture is of a GM double Cardan cage. It uses a big GM Ujoint at each end, You can get an adapter joint to go to a Spicer 1300 series joint, which is what the yoke on the front of the OD unit appears to take.

[Beck]

Thanks for the spell check Crosley. The spell check on the forum missed that one. I spell so badly that the spell check often doesn't recognize the word.

Enjenjo, That is the piece I was thinking of, I just didn't know the name.

Do you think the GM double Cardan cage is long enough to work for the front "shaft"? It looks shorter than the 8" recommendation. Why would it have to be 8" anyway? The motor shouldn't move that much to cause alignment problems. That would sure make the front "shaft" easy.

Thanks for the help. You are always there when I need you.

[enjenjo]

The Ujoints are about 4" apart. I see no reason they have to be 8" apart. I ran a 4x4 with a divorced transfer case for many miles with a 4" shaft length.

[Crosley.In.AZ]

Thanks for the spell check Crosley. The spell check on the forum missed that one. I spell so badly that the spell check often doesn't recognize the word.

No problem...  

I use the spell check in my Firefox browser as I type. Plus yolk is a correct word

With my poor  spelling , I am glad my first and middle names only have 7 letters total.  

[Mac]

I like your truck and it should be perfectly acceptable here. Being no newer than `63 it's even acceptable over on The HAMB where they're hinky about that stuff.

I have the Fleetside version with rally wheels. Mine have fewer and bigger slots, which I always thought were the truck style while the ones on your truck I thought were Corvette/Camaro.
I like your spiders better than my caps too, which I think look 4x4ish.

Good luck on the OD install. A T-5 swap made my C-10 friendlier to drive, but it keeps my left leg busy.

[Beck]

I have the Fleetside version with rally wheels. Mine have fewer and bigger slots, which I always thought were the truck style while the ones on your truck I thought were Corvette/Camaro.
I like your spiders better than my caps too, which I think look 4x4ish.

My truck has had quite a few things swapped around. I am using the 5 lug wheels. I think these had the smaller holes. The 6 lug wheels were on the 4x4s. The 5 lug were on the 2x4 trucks. 2wd trucks used 15X8 wheels and the vans used matching 15X6.5. I have truck wheels on the back and van wheels on the front.
I have the stock caps on my wheels. I just painted the inside part to match the wheel. Then I added cones to the top of the cap. I don't know about the 6 lug caps but the 5 lug caps have a hole centered under the factory decal. The cones mount with a stud right through this hole. The cones are cheap and want to warp when the stud is tightened. They come loose if you grab them and give them a twist. The chrome is already getting rough on mine.

[Mac]

Your truck must have had  5 lug conversion. All 1/2 tons were 6 lug until like 73 or something. Anyway, I like the look you got and painting the base of the cap the same as the rim does half of the trick. Thanks for the tip.