Vannin' Home Forums Chevy General Discussion Some questions about my new G30/G3500 Van

I just purchased this van recently. It's a 1990 GMC G3500 Rally STX. I bought it from a Catholic Monastery in a remote location from some nuns. It only has around 18,000 miles on it, and it was always garaged. As you can imagine it is in almost perfect condition. I'm not so thrilled about the color scheme, but I can't complain because I got a good deal on a barely used extended van. My plans are to make it into a cool camping van/bug out vehicle. For now it's my daily driver, and I am just kicking around a few Ideas on where I want to take this project.

This Van has a TBI 350, T400 tranny, and a 14 bolt rear end. It's a 1-ton with 16" wheels.

Here are my questions.. (I know it's a lot, all help is greatly appreciated!)

1. Does this van have a Posi-traction rear end? Does anybody know what the factory gear ratio is?

2. In an effort to get better gas mileage, I might be considering either putting in another transmission such as a 4L80E, or a gear vendors overdrive unit. Which would be easier and less expensive to have installed?

3. I might be considering doing a 4x4 conversion. I read some of the posts on this site about this topic, and I checked out the kit that boulderoffroadvans.com offers. I was wondering how easy it is to do this conversion, If I should just stick with my T400 transmission, what other parts I will need, and what other headaches I might run into like the steering etc.?

4. My 1991 Chevy G20 seems like it turns a lot sharper, like it can turn on a dime compared to this van. Is this just because this van is longer? Does it have a different gearbox than a G20? or did GM make some improvements to the steering in 1991?

5. Do the G30 vans sit higher than G20 vans from the factory due to the beefed up suspension? It seems like they do?

6. I am buying some new 16x8 wheels for this van. Does anybody know if I can run 265/75/16 tires without any clearance issues, or should I just stick with 265/70/16 tires? (There is a big price difference between the two.)

Thanks !!!

I wonder if I did something wrong because this thread doesn't seem to be showing up under 'General Discussion', and I haven't got any replies. Then again I'm just a newbie.

Its Memorial Day people are not home or are having a hard time with the weather....

Your RPO codes will answer what was put in factory... Compnine.com

A 4L60E is what they put on 350's but a 80 would be great ... I get 14mpg

A 4X conversion might well cost you in the end 12 grand to do right.

The long ones do need a little more room to turn.

I think 245/75/xx are the largest tires you can put on without any rubbing when turning.

Ok Thanks, that is true, there is bad weather these days etc. I wish everyone the best this weekend. I'm glad my thread is showing up.

Since you got the same type of van as mine, do you know where the RPO codes are located?

Is a 4L60E or 4L80E an easy swap out with a T-400?

With my 4x4 conversion money is not so much of an issue, I just want the job to be straight forward without any "surprises" that are going to leave me and my mechanic scratching our head. I'm going to call Boulderoffroadvans on Tuesday to get more info.

245/75/xx - Is that what you have on your white van? have you or anybody else tried anything wider?

Thanks again!

RPO codes will cost ya $5 ... https://www.compnine.com/vid.php

245 on white van ... dont know how easy of swap on the tranny... but they are a goooood tranny

Just an idea... You can put wheels from the newer Dodge Ram's on there as long as they are 8 lug. Might find a set cheap that someone has taken off of a new ruck for aftermarkets. Thats what I did. Got brand new wheels and tires off a 2019 Ram 2500. They are 17's and dont scrub at full lock. Makes the van look much better.

Check your RPOs. I want to say the sticker on a '90 is in the glovebox. It will answer both of those.



Gear vendors would probably be the 'easiest'...but a swap less expensive. check the final OD ratio and make sure it will be worth your while.



I have no answer to this.



Your van is a 146" Wheel base, so it needs space. My G30 is a 125" and can turn on a dime compared to the Econoline i have with a 138" wheelbase!



They sit about 2 inches higher.



I rub a little bit on slight turns with 265/70-16, but also only have 4.5? Back spacing. If you run like 6" BS, i don't think I would rub. that being said, a 75 series is about a full Inch taller, so i don't really know.

This information was a lot of help! I located all the codes in my glove box, and i'm going to be looking them all up to see exactly what I got. You have the same type of wheels that I ordered from U.S. Wheel. (you gotta love those 8 spokes!) I ordered 16x8's. Did you say that yours were Cragar's? I couldn't find any in a 16x8 because they only have 15" wheels in the Nomad style. So you're running the 265/70/16 tires and you're saying that when you turn even slightly they rub? Like when your pulling into a driveway while turning? do they rub when when you crank the wheels all the way? Thanks again.

yes, mine are Cragar Nomad II in a 16x8 and I ordered them from Summit. The rubbing I get is only at partial turn when I hit a bump, and I did have to gently roll the front fender in a bit in the back with a mallet as well.. I am sure that if I replaced my springs with fresh ones (less than 40 years old) the rubbing may go away. I don't have any rubbing at full lock.