4th Gen Rearend
 

Greetings! This is my first post, so here goes nothin'! I am building a 1995 Firebird to Stock Eliminator specs. I have noticed when looking at cars that others have built, the rear wheels are nice and deep (shallow offset). To my understanding, the rearend has to be stock width, correct? How are they fitting those wheels in there with a stock width rearend? Thanks, everyone. There will be many more questions to come as I undertake this project :)

Re: 4th Gen Rearend
 

I have a complete 12 bolt rear done if you need one.

Re: 4th Gen Rearend
 

Take's a little measuring to get the correct offset wheel.

Re: 4th Gen Rearend
 

A few year old quote from a DTD, "my boss told me that he had better not see me climbing under cars and measuring rearends anymore". That would lead me to believe that as long as the springs are in the right place and the inner wheel housings aren't modified then you're OK to NOT have a "stock width" rear. Honestly, I don't have a problem with this. If anyone out there would know any different, then I would sure like to know. There IS a new Sheriff in town!

Re: 4th Gen Rearend
 

Here are some pics of what I am seeing. I'm not really interested in 'breaking the rules' so I am trying to figure out how everyone else is doing it. Glenn, I will definitely keep yours in mind. Right now my cash is going towards a trailer that I will pick up in a week or two.

Re: 4th Gen Rearend
 

Since one of those pics is my car I guess I will answer with what I know at the moment. The rear end is a 12 bolt with the stock width and coil spring mounting locations. It has the stock springs and I don't know offhand what the rear wheel offset is, but they are 10" width Weld Alumistars. I don't have any trouble with clearance.

Re: 4th Gen Rearend
 

I had a 4th gen Firebird and it had a KTRE 12 bolt and from what I knew it was stock width. All stock type mounting brackets for suspension and shocks. Pete Z traction bars and lower bars...

I replaced the springs and put stock ones in there to raise it a little.

10" rims and no clearance problems with any 9" tire....

I don't recall the offset but it was nothing unusual....

Hooked in a car wash....LOL

Re: 4th Gen Rearend
 

Thank you all for the input. I appreciate it. I will see what I can find out for offset on 10" wheels.

Re: 4th Gen Rearend
 

The rear ends under these cars are not stock width, a stock width rear end would be too wide. Most of the f body cars I've built had a 60" or so axle flange to axle flange rear end. As mentioned earlier if you have the wheels and tires that will be used on the car you can get a more accurate measurement.

Re: 4th Gen Rearend
 

This must be the norm!

Re: 4th Gen Rearend
 

Typically, one sources the wheels to be used with the desired BS that will be used, throws a set of the largest (or desired size) tires that will be used on them. With no rear in the car, position them under the car in the desired location, measure wheel flange to wheel flange and build the rear to that dimension taking into consideration the brake kit being used, pinion offset, etc. Build the rear to wheels - not the other way around. Typically.

Enough of those cars out there, the dimensions and specs should be standardized with little need to figure it all out yourself.

Re: 4th Gen Rearend
 

I was told it needed to be within 1/4" of stock.
Guess it depends on who you ask.
Pete

Re: 4th Gen Rearend
 

for some, asking forgiveness is easier than asking permission.

Re: 4th Gen Rearend
 

Thank you again for the help. I do not have the wheels and tires yet as I wanted to verify I was going to be legal on the width first. Will be running a 28x9 slick initially on a 9 or 10" wheel and possibly switch to a 30x9 down the road. From what I can gather (haven't measured mine, yet) the stock width is 64.72". It seems the general consensus is that rear end width is less important (within reason) than the the fact that the suspension and wheel housings are in their factory place. I really just want the mounting surface of the wheel as close to center as possible. Thanks again for all your input! So much to learn about class racing but enjoying it so far!

Re: 4th Gen Rearend
 

Deeper wheel = shorter rear = less unsprung weight. I realize there's not a lot to be gained with a 9 or 10 in. wheel, but every little bit counts. And they don't charge extra for deeper wheels or shorter axles.

Re: 4th Gen Rearend
 

Here's my question: The rule says it must be a stock width rear end with all of the details everyone has outlined. I've searched the classification guide high and low and I can't find anywhere that they note just what a stock width rear end should be for every car in competition. Anyone able to point me to that? If it's not documented in the NHRA classification guides at this point - it seems like a pretty unenforceable rule.

Re: 4th Gen Rearend
 

Classification guide won't have this info.


The rule book talks about wheel base. Since there are production line assembly tolerances, there is an allowable variation from factory specifications (I can't recall exactly...3/4 inch?). The rear axle width is not addressed, other than stock mounting points and stock width (between backing plates) must be used. I have factory rear housings that vary up to 5/16 inch for the same model of car.


In the spirit of the rules, it would seem that the factory tolerances should be factored in within reason. When asked, division tech would only say that they would not allow stock mounting points to be moved.

Re: 4th Gen Rearend
 

Since no one posted it. On a 4 gen F body. If you have a stock length rear end. Using a 10 inch wide wheel you need 7 1/2 inches of back space.

Re: 4th Gen Rearend
 

The trick is to use an 82-92 F-Body “STOCK WIDTH” rearend. It’s a complete bolt-in for a 93-02 F Body. The 82-92 is approximately 4” shorter than a 93-02 rearend. This is what u r seeing in the pics u posted. Now you can use a 15x10 wheel with a more common 5.5 backspace.

Re: 4th Gen Rearend
 

Where in the world is there a spec list or a source of published information regarding rear end housing widths? Nobody I know even mentions ever having been checked. Wheelbase, yes, but housing widths? If you put a 66 stock width Impala rear end in a Camaro with leaf spring perches installed, I'm sure that wouldn't fly with the extreme width differences, unless the big car rear end was narrowed, but I've never seen a spec for any car's mandated rear end width. With all the fourth gen F body cars out there, it should be no problem finding a good one all ready to go, in fact, don't the established rear end shops offer a complete ready to use rear end that's a bolt in?