1972 GMC Jimmy fact checking

[K5dreamer]

Well, I think I may have found my unicorn, 1972 GMC Jimmy, 350/sm465/np205 drivetrain, cant post pictures just yet, but its one of the best K5's ive found in my price range. solid body (only rust found was on the tailgate and rocker boxes, but both are still very solid) its a daily driver, hits 60+ mph with only a slight bob and weave but nothing I'd consider a death wobble, just worn springs and shocks. Its on 35's and has some bubba wiring done for the horn and some fog lights but other than that seems pretty unmolested. Fires right up, runs good. Brakes are a little underwhelming but they do work. (and i'm used to driving a 3000 lbs jetta with 4 wheel disks) wanted to fact check some info I wasn't sure on.

1. is there a trick to going into 4 hi on an NP205? The truck drove just fine in 2 hi, and I was able to push it forward into 4 lo, but could not for the life of me move the lever sideways in either direction, or towards the back of the truck to engage 4 hi.

2. Is 1st gear syncronized on the SM465? The shifts felt a bit clunky to me, but Im used to a 2000 VW jetta 5 speed. But it did shift well enough to easily drive, except 1st gear. I do realize its really a 3 speed with a granny first gear, but if the truck is moving at all, trying to shift into 1st gear is impossible. it grinds and makes all kinda awful noise. once the truck is stationary it will shift into 1st, and upshift to 2nd while in motion just fine.

3. How hard are parking brake pedal assemblies to find? and how expensive? I noticed it wasnt working and assumed the parking brakes were shot. he said the brakes work fine, but the pedal just wont ratchet and lock into position.

Aside from needing new tires stat due to dry rot, and a decent paint job, those are the only issues with it I could find.

Thanks for any and all advice.

 

[K5dreamer]

Also, I "think" it has 4.10 gears, the guy didn't know. It has a tach mounted to the dash. On 35's it was doing an indicated 40mph at 2000 rpm, which didnt add up using an rpm calculator. So I think at 2000rpm I'm actually doing about 50-55, which would add up to 4.10's in the axles.

 

[nvrenuf]

1st gear in a 465 is not synchronized, a little chatter is normal.

4hi in the 205 is straight back from 2hi (no side movement at all), no tricks to get there. If 4lo acts and sounds right I'd look at the linkage.

Sorry, that's all I've got...

 

[ekajkrats]

Parking brake assembly looks to be universal between trucks and blazers for first gen. Junk yards tend to have 69-72 trucks and infrequently a blazer. Ebay has used ones from $30 up to a new one (new, not new old stock) for $170.

I think mine switches into 4hi most easily when I am slow rolling and as nvrenuf said, it's straight back. This could also be because mine is not performing designed as well, but it's how it works.

Also on rust, really make sure the windshield frame is rust free on the inside all the way across the top.

-Jacob

 

[chulisohombre]

For normal driving don't use low on the tranny. It is 6:1 gear and only runs to about five mph tops. Use 123. Only use it with a load on a hill or wheeling. 4h is pull strait back torward you.it is a solid lever attatched to the side of the trans and pivots on one bolt. It is possible the sliders on the transfer case are worn and may take a lil force to drop it in. I have more trouble going into 4l. Sometimes have to bump the clutch a lil for it to drop in. I got my new ebrake lever from lmc truck under 200 bucks came with new cable as well. Othe than that welcome to the first gen club. And also.

 

[Greg72]

Also, I "think" it has 4.10 gears, the guy didn't know. It has a tach mounted to the dash. On 35's it was doing an indicated 40mph at 2000 rpm, which didnt add up using an rpm calculator. So I think at 2000rpm I'm actually doing about 50-55, which would add up to 4.10's in the axles.

With larger tires, there's very little chance that the speedometer is accurate. Use your smartphone GPS app to confirm your road speed and compare it to the speedo. Odds are good that it's WAY off.

BTW -> At that point, you can at least compare indicated RPM to the GPS speed and try again. Fair warning though.... stock factory tachs generally don't read very accurately either if the distributor has been swapped for an HEI unit.


-G

 

[Carcinogen]

You can check the gearing by jacking up the rear and turning the tires. Count revolutions of tire vs drive shaft.

 

[paratrooper307]

You can check the gearing by jacking up the rear and turning the tires. Count revolutions of tire vs drive shaft.

Yep. Of course, since you should be changing the diff fluid anyway, pull the cover and read the ratio off the ring gear.

 

[Carcinogen]

How do sellers take to people asking to pull the diff cover? Then again I'm assuming he was checking on these problems before he bought it too... so it may not even matter.

 

[paratrooper307]

I looked at a truck for a friend one time. We contacted the seller and explained what we wanted to do, and asked him what his brand of gear oil was. Picked up that and a gasket at the Autozone on the way over and he was fine with it. Given the amount of money potentially involved in a regear and the uncertainty when it comes to people knowing what gears or lockers they have, we considered it money well spent. I would think most people would be alright with it if you were a serious buyer.

 

[ashman]

if you were a serious buyer.

Thinking about it as if I was the buyer, I think that is the key. Basically I'd want some sort of assurance (maybe a deposit) that you plan on buying the truck unless you find something wrong. Maybe something along the lines of if it has 3.73 gears or higher we're good.

For what it's worth, from your description of the truck I'd bet on 3.73 gears myself. Regearing isn't something your average backyard mechanic can do, and judging by the state of the rest of the truck I'd say that is what you are looking at. 3.73 was as good as it got stock so if it doesn't feel like a dog with 35" tires that is probably what you have.