Did chevy really put wholes in the 3100 frame for wheel base ?

[Mains52]

I have a temporary straight axle on my frame right now and I am waiting on my 4 link to get here. I noticed there are wholes in the frame right about where the wheel centers should be. I measured it with a loose tape and it was around 116 ish. Does anyone know if they meant to do that.

[b-mac]

No clue on this as I have an S10 frame. But when I was building my 4-link, I welded my axle to the frame using square tubing, before I removed the springs. Removed the springs; built the 4 link, then removed that square tubing. That way it was exactly where the spring would have put it.

[Mains52]

Originally Posted by b-mac

No clue on this as I have an S10 frame. But when I was building my 4-link, I welded my axle to the frame using square tubing, before I removed the springs. Removed the springs; built the 4 link, then removed that square tubing. That way it was exactly where the spring would have put it.

That's my plan for the rear for sure I just need to figure out how to get perfect MII crossmember placement when I take the straight axle off.

[dsraven]

if you look at the assembly manual it will show you the different holes they used for frame measuring etc. an assembly manual is always a good thing to have for stuff like that. I wish I wouldda got one waaay back.

anyways, heres a few pointers from my mII install.

before you install the MII cross member be sure to check the frame for straight, sag and square. it is easy enough but a bit time consuming. a good thing to do while waiting for the parts to show up though. my frame looked great but was bent. better to find out before than after the MII install.

do a corner to corner check and compare the findings. 1/8" is allowable. be sure to hold the tape the same on both sides. explain that to the dude helping.

mark each cross member at it's center (masking tape works great), side to side, then run a laser or a string down the middle from the front to the rear. all the center points should be in line with the string/laser.

do a sag check with the string/laser from front to rear

set the frame up on stands and get it level side to side and at the rake angle you want fore to aft. block it well so it won't move when you add or take away weight. place the stands where they won't be in your way when doing the work.

use some scrap metal, or whatever, tacked to the frame in an X pattern once the frame is set up level and square. that way it won't move on you when the cross members are cut out.

I used some modified jack stands to level the frame for working on it. I removed the sliding part of the stands, tack welded a piece of square tube on top with some holes drilled in it and some nuts welded on top for the threaded rod to go down into. then used some large threaded rod from there to a hole in the frame. I used some 1/2" rod with a 3/8 bolt welded on the one end (top) so it would fit through an existing hole in the truck frame. use a couple of nuts on each end and move them to get the adjustment you need to level the frame and get the rake angle correct, then jam the one nut against the other to lock them in place. it sure makes leveling easier. I used a couple of flat washers between the nut and the frame so the frame wouldn't move when the nut was done up tight. I has a couple of sets of the threaded rod because I needed the frame to be up high at first when filling holes and boxing, but then down low later, when installing the MII.
you can use threaded rod

I used a 4 ft level as much as possible to get things close and get the bigger picture but used a shorter digital level on top of the longer one for more accuracy when doing the final small steps. always use the level orientated the same way in case it isn't quite calibrated correctly or has been dropped or whatever. you can check it periodically by setting it on something and getting a reading, then spin it around and get another reading with it at 180 degrees from where it was. the readings should be the same.the digital levels have come down a lot in price now so a 4 ft digital level is probably less than the shorty I bought 10 yrs ago. harbor freight is a great place for that stuff. we don't have them in Canada unfortunately. a magnetic digital level really comes in handy when installing the MII stuff because the bubble levels are close but not really great when you need to be dead on to a decimal point. the magnetic style will stick to the control arms so you can adjust things while watching the level. remember the alignment shops are gonna be using a decimal point in their alignment and it would suck to get it there on the rack and find out they could only get the alignment "close" because they ran out of adjustment before it was dead on.

the pics may be helpful for you to understand what I am talking about. the one pic shows the axle center line 1" ahead of the stock location (on a 57, single headlight truck) with a 215/70r15 tire. the tire is basically 27" tall.
there is another that shows how I set up the frame for working on it (filling holes and boxing) and then another with the frame set lower for stability and ease of installing the cab. I suggest to have the cab bolted on before the cross member job starts. also have the front clip ready to hang when you have the member tacked in and assembled for mock up of the tire in the wheel opening. have a set of wheels with tires of the size you want to end up with (diameter).

if you are thinking the frame is too long you are right. it is a 58 frame. they are longer out front because the fenders are longer and there is also a filler behind the front bumper. the rad support is also a bit further away from the firewall. found that out the hard way.

sorry for the long post. hope it helps somebody

[dsraven]

before you tack weld the cross member in you need to know the tire diameter you will end up and how much drop you will be putting into the package. this is because the front fender has an angle on the rear of the wheel opening and as the body is lowered over the wheels it makes the tires look like they are being stuffed into the rear of the opening with a stock axle center line. this effect is reduced with a smaller tire and less drop but is something to think about.

the pic in my last post is a TCI kit with 2" drop spindles. it is an older kit so it has the old style of upper control arm mounts that use the T bolts instead of the GM style of mounting that uses shims for adjustment. my cross member location, for height, is at an unknown location compared to their normal kit for the task force. this is because I was shipped the wrong cross member so it didn't fit the curve of my frame. I got the run around asking for specs from the supplier and from TCI (they both said just weld it in except I had a 3/8 gap on the rear side of the member) so I trimmed the cross member to fit the frame and then adjusted the upper mounts to achieve the correct measurement between the control arm upper and lower pivots. I also had to adjust the top mount to get the antidive angle correct. there is a good article on the heidts site (or call and ask them to send you a copy) called understanding independent front suspension. it explains a bunch of stuff that is good to know before you start your install. I would attach a copy but the file is too large. sorry.

[whitedog76]

When looking at my assembly manual, it says 36.5 (I believe) to the end of the rear frame stub.

On the front it’s 20.59 from the front of the frame to the front axle centerline.

3100 trucks have a 116 wheelbase. Most opt for moving the rear axle 1.5-2” further back to center it in the wheel well better.

Chris

[b-mac]

DSRAVEN, I've seen your picture before with the jack stands and the threaded rod. What a great idea. Wish I had seen it sooner.

Mains52, my apologies. When you said 4-link, I incorrectly assumed "rear".

[mr48chev]

Most MII aftermarket manufactures set the front axle center line at 18-1/2 inches from the center of the front spring shackle bolt hole. I've never figured out why but the first thing a lot of guys do "cleaning up the frame" is get rid of the piece that is riveted in that the shackle bolt and bumper bracket bolts bolt to.

As for the exact fore/aft location of the wheels in the wheel wells I'd say that is personal preference. It has to look right to you when you are done.

DsRaven gave a pretty good tutorial on setting the frame up to work on it and that is well worth following. Getting the frame level and square and well supported before you start fabbing on it is a must. The only thing that would top that would be having a frame table to hook it to.

[Mains52]

Originally Posted by b-mac

DSRAVEN, I've seen your picture before with the jack stands and the threaded rod. What a great idea. Wish I had seen it sooner.

Mains52, my apologies. When you said 4-link, I incorrectly assumed "rear".

I am putting in a 4 link in the rear and doing the MII up front. You're good no worries. Thanks everyone for the info.

[mr48chev]

If you haven't pulled the truck apart you can find some reference points for rear axle location if the one in there now sits where you want it.

[Jesse Z]

A stock frame has so darn many holes, I can't even imagine what most of them are for! Wheelbase location - good a theory as any.

[duramax55]

the wheel base on a 3100 short box is 114 not 116 those are the numbers from gm site

[Mains52]

Originally Posted by whitedog76

When looking at my assembly manual, it says 36.5 (I believe) to the end of the rear frame stub.

On the front it’s 20.59 from the front of the frame to the front axle centerline.

3100 trucks have a 116 wheelbase. Most opt for moving the rear axle 1.5-2” further back to center it in the wheel well better.

Chris

This actually seems pretty accurate. I measured these last night and just eyeballing it. Its seems pretty legit. Where did you get those measurements WhiteDog?

[dsraven]

maybe you can get something from these. google frame dimensions for your year o chevy and see what comes up. one of these is a 58-59 frame so it will be a bit longer out front and the rad support bracket will be further forward.

[whitedog76]

Originally Posted by duramax55

the wheel base on a 3100 short box is 114 not 116 those are the numbers from gm site

The numbers I gave are out of my 47-54 Assembly Manual.

BTW, hes’s working on a 52, not a 55-59.

On my 54, when dropping a string line the front axle is 18” on one side, and 17 7/8 on the order from the front shackle mount. Of course, that’s with 60+ year old leaf springs.

[dsraven]

good to know the year. if the urge comes over to get a task force then the diagrams will REALLY be useful, lol.
sorry, I will try to keep up.....

[PDW HOTRODS]

On my 1950 117" wheelbase look just right. I moved the rear back to fit the fender cut out.

[mr48chev]

Originally Posted by duramax55

the wheel base on a 3100 short box is 114 not 116 those are the numbers from gm site

TF 3100 trucks show to be 114. AD 3100 trucks are 116.

It's more common to move the front wheels forward a bit on a TF to center the wheel than it is on an AD.

[OrrieG]

Probably jigging holes for frame assembly. When I pulled my body off I found my frame was 3/4" out of square.

[dsraven]

orrie, that is why I always suggest to get the frame out from under and do some hands on checking for square, sag and out of round. it would suck to spend $2500 on a new front end and find out after that the frame was in need of a pull one way or the other.
some of the items I posted can be ideas used for any vehicle getting restored or hot-rodded. I always say take lots of pics as you take stuff apart so you can reference them in a couple of years when you are putting the stuff back together. remove things, put the bolts back in where they came from. box it and tag it. same reason.

[OrrieG]

Originally Posted by dsraven

orrie, that is why I always suggest to get the frame out from under and do some hands on checking for square, sag and out of round. it would suck to spend $2500 on a new front end and find out after that the frame was in need of a pull one way or the other.
some of the items I posted can be ideas used for any vehicle getting restored or hot-rodded. I always say take lots of pics as you take stuff apart so you can reference them in a couple of years when you are putting the stuff back together. remove things, put the bolts back in where they came from. box it and tag it. same reason.

Yep! Especially when you are opening the coffee cans and bags for the first time in 14 years like me. Also kept a note book with lots of notes and sketches on how stuff came apart. I also like to clean up the parts as I take it apart so when reassembly time comes you can just grab and go.