Chadeux Dork
5/15/17 4:04 p.m.

So I was measuring for transmission mount on the Bravada and I now have a couple questions.

Question the first: How big of an issue is if the tail of the trans isn't centered in the chassis?

Question the other, it's a long one :

So I don't have a driveshaft for it yet, but I took the now incredibly too short driveshaft that was in it before, slide it into the back of the trans, aimed it at the yoke on the rear axle and found a problem. The truck is sitting on the rear tires. The driveshaft is going to have to run over the top of the torsion bar cross member. With the driveshaft where I think it's going to land. I can barely fit my hand between it and the cross member. This leads me to believe they're going to touch if the rear suspension droops any at all.

I've got 3 ideas that might fix this.

1" lowering blocks in the rear to raise the yoke relative to the transmission output, in theory gaining more clearance. This is the simplest answer, but unfortunately I don't think it's a total solution.

Next idea is to notch the cross member. I really would like to avoid this if possible

The last idea is to put a carrier bearing on top of the cross member and run a 2 piece driveshaft with a really short front section. I'm not currently sure how feasible this option really is.

Keith Tanner
Keith Tanner MegaDork
5/15/17 4:31 p.m.

Work on your driveshaft angles as well. Ideally you want 3 degrees at each end to keep vibrations at a minimum. That'll help you decide which of your three ideas will work best.

I don't THINK having the diff and trans offset is that big a deal, it'll factor in to your 3 degrees.

NOHOME PowerDork
5/15/17 4:37 p.m.

The gearbox output and the differential input should be parallel but offset. The offset forces the needle bearings to rotate and maximize bearing life. The equal but opposite angles of the driving and driven shafts cance the difference in velocities that are a side effect of a u-joint drive.

If the engine and gearbox are angled in respect to the chassis center line, then it will not be parallel with the pinion. So, it might induce a vibration.

Knurled MegaDork
5/15/17 4:56 p.m.

Every 1st-generation RX-7 made had the engine/trans cockeyed sideways in the chassis for exhaust-steering clearance on RHD cars. But the left side of the tub had more room than the right.

Anyway the 1-2 degrees of gink didn't seem to matter much.

A 2 piece driveshaft sounds like your best bet. Be tricky to get those angles right, but not hitting things with the driveshaft is even more important.

Chadeux Dork
5/16/17 12:25 a.m.

So, if I'm getting this right, I need as close to 3 degrees of total angle on the u-joints, transmission tail shaft and pinion need to be parallel but offset. tail shaft not being centered won't matter as long as those first 2 criteria are met. I need to do more research on how to properly put a 2 piece drive shaft in place, and decide if that route makes more or less sense than cutting a notch in the cross member and then adding bracing to make up for what I cut out.

Thanks for the input.

Streetwiseguy UltimaDork
5/16/17 8:04 a.m.

Two wheel drive S pickups used a two piece shaft. I'd look for a shaft from an early one of them, and shorten the front section. I say early, because the later ones used a double joint at both end, weigh about a ton, and are impossible to balance.

Chadeux Dork
5/16/17 8:49 p.m.

So the 2 piece shaft may be the way I go. I'm also going to try to see what I can do to get the engine/trans closer to center. I don't like how far the mounts I got move the engine over to the passenger side. I would not recommend these mounts to anybody else who's silly enough to want to put a gen 1 SBC into a 4wd S10. I may end up cutting them up and trying to roll my own.

classicJackets HalfDork
6/25/17 8:26 p.m.

So I know this was a little while ago, but to follow up (for my own purposes): Centered (to the frame line) transmission output with a differential that's off centered should still be okay. For vertical angles, they should look sorta like the sketch below? In my case, differential surface is ~ angled upward at 6 , so the transmission output should be angled "Downward" at 6 too, and the U-Joints at each end will allow the operating angles to be the 3* mentioned above?

Knurled MegaDork
6/26/17 12:10 p.m.

What you want is the angle from the trans to the driveshaft, and the driveshaft to the rearend, to be identical. Sometimes they have to flip signs if you want to keep U-joint angles under 3 degrees. Which you do.

3 is a MAXIMUM not something to shoot for. I've had drivelines with zero angle and they lived just fine, things move around enough that the needles don't stay in one spot.

classicJackets HalfDork
6/26/17 8:24 p.m.

In reply to Knurled:

That's exactly the feedback I was looking for - Thank you!!

JBasham Reader
6/28/17 12:06 p.m.

I'm going to be running 0 degrees transmission, 4.2 degrees downward shaft, and 0.7 degrees downslope differential. And changing my U joints every 150 hours, religiously. Keep me in your prayers.

Chadeux Dork
6/28/17 12:38 p.m.

Thanks for bumping this, I've changed to a 700r4 and am thinking a stock 2wd 4 door blazer drive shaft might work for me. Still need to decide where things need to live though.

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