That's only 500 revs, could still be the lock-up. If it kicks in and out of OD that much, it has problems.

 

It is a Chevrolet we're talking about here....:thatfunny

I remember an Oldsmobile I had that seemed like it was constantly engaging and disengaging the O/D. I talked to a GM guru friend of mine (always busy!) and he explained that that's how torque converter lockup worked and that it was normal. I didn't complain since I got about 32mpg on the highway with the AC running, but I hadn't been aware of torque converter lockup. This is not an issue in the A833 manual as there is no torque converter.

If the C1500 were shifting in and out of Overdrive like that, it could be speed or rev sensor issues or even a bad torque converter. I know that was an issue with mid nineties Suburbans.

Sounds like lockup to me, though...

 

833 is a manual trans. Also, I bet what you think is the OD on your grandpa's truck is actually the lock-up in the converter. Unless your grandpa drives at like 45mph all the time Then it will go in and out of OD.

Also, remember on an auto you have converter slippage, which raises the rpm by a couple-few hundred rpms.

 

Nah, he drives like a maniac some times, does donughts in the snow and that kinda stuff. says he's 78 going on 16.
It's actualy going out of OD, it will jump from 1400 to 1900 and back when a gust of wind hits it head on.

 

I see what the difference is now. The big difference b/w your truck and mine isn't the ring/pinion ratio, it's the transmission.

You've got a 3 speed auto. I've got an A833 overdrive. Your high gear ratio is 1:1. Mine will be 0.71:1. Take your tach @ any given speed in high gear and multiply by 0.71 (or 71%) and that's about what my tach will read.

55mph for me will not require overdrive unless I'm cruising on relatively flat ground and want to save gas. I won't really need the overdrive until 60mph or better.

-TJ

 

Is the a833 the later OD auto, or the OD 4 spd manual?

One thing i dont like about most newer OD autos( like my grandpa's chevy 1500) is thats it's allways shifting into or out of od, if your drive "uphill"( twords my house, 500ft elevation gain in 30 miles) it wont stay in OD, or if a wind gust hits you.

 

Those ratios are very close to the A833 from 2nd to 4th. Looks like they added a granny first to make it the 5 speed.

With the 33" tires, the 3.73 seems to be the way to go. I can expect to shift from 1st to 2nd at around 25mph and cruise around town in 3rd with good tach, highway speeds are within reasonable tach with passing gear sitting there in third. I think I've found the ratio! FINALLY...

 

I'm thinking 3.73 is the way to go. Here's what I can expect to be doing @ highway cruising speed:

Ring Gear and Pinion Ratio (3.08, 3.55, etc.) ---3.73
Tire Height (24.5, 26, 27.5, etc.) ----33
MPH --75
Transmission Final Gear Ratio (2.54, 1.43, 1.00, etc.) --0.71

Calculated Results
Engine RPM --2022

Shifting down to 3rd (1:1 ratio) will put me at around 2900 RPM which is right in the powerband for passing.

IMO, That's not bad RPM considering the speed. I don't have a point of reference in one of these Dodges, but my DD, a 1994 Nissan cruises at 75 and pushes around 2100 RPM or so.


Speed Dragon: What size tires do you have on your '93? I noticed you have a 3.55 pinion.

 

Damn, i dident think the diffenece between 3.55s and 3.73's would be that big.
Iirc the math says my truck cruses aruond 2000 at 60.

 

Preferable? Can't really say. More Fun? Yes! Seriously though I think there is an RPM calculator out there somewhere that you can figure out what your RPM at different cruise speeds, based on things like tire size, trans final drive ratio and rear end ratio.

 

Since I'm in there and changing it, would a 3.73 be preferrable?

I have to ask!:crazy:

 

Dude, go 3.55. You won't like the 3.23 w/ those big tires and the OD tranny.

 

I had 3.91s in my 79 D 100 with a 318 and an 833 OD; (235/75-15s abt 28" tall)
I had a 81 W 150 with a 318/727 (no OD) and 3.23s, 32" tires; seemed "perfect".
My current ride 83 D 250, 318/727/3.55s with 235/85R16 (10-ply, 32" tall) seems a lil "busy" on the hwy; For how I use the truck I would not mind either going up to a 3.23 or even a 3.08, considering no OD gear. But then again I just found a lo mileage 440 and 727 in a motorhome that's at a fairly nearby (45 mi) junk yard; I'm quite tempted to make that swap! in which case, I'd be looking even harder for something like a 3.08.

 

Now I'm a bit puzzled

Checked out a few tire radius calculators online and found this.


Ring Gear/Pinion Ratio: 3.23
Tire Height: 33"
MPH: 15
Tranny Final Gear Ratio: 3.09 (first gear in the A833od)

Calculated RPM: 1524

--------------------------------------------------------------------------

Ring Gear/Pinion Ratio: 3.23
Tire Height: 33"
MPH: 25
Tranny Final Gear Ratio: 3.09 (first gear in the A833od)

Calculated RPM: 2541

--------------------------------------------------------------------------

Ring Gear/Pinion Ratio: 3.23
Tire Height: 33"
MPH: 35
Tranny Final Gear Ratio: 1.00(third gear in the A833od)

Calculated RPM: 1151 (seems a bit low to me, may have to top out second gear in town)

--------------------------------------------------------------------------

Ring Gear/Pinion Ratio: 3.23
Tire Height: 33"
MPH: 50
Tranny Final Gear Ratio: 1.00 (third gear in the A833od)

Calculated RPM: 1644

--------------------------------------------------------------------------

Ring Gear/Pinion Ratio: 3.23
Tire Height: 33"
MPH: 75
Tranny Final Gear Ratio: 0.71 (fourth gear (overdrive) in the A833od)

Calculated RPM: 1751



Now, I imagine that these calculators assume level ground, non-towing, perfect world conditions, but those RPM figures don't look that bad to me. Does anyone have any expertise that would prove otherwise? Wouldn't the weight of the vehicle or the resistance to motion associated with that weight have an affect on these numbers?

I also have found that the 3.23 ratio with the 33" tires changes the ratio to 2.86. simple cross multiplication shows that if I installed a 3.55 gear, I'd end up with a 3.14 ratio with 33" tires.

I probably need to consult a physics professor now!!:teacher:

 

3:55 might be better with the bigger tires. What are you planning on doing with this truck? The reason I ask is those are hefty tires for a 2WD. Other than looking good they won't offer much in the way of fuel economy. I assume you don't plan on doing much off road with a 2WD? Just asking not judging..................

 

No offense taken at all! I want the truck to have the stance and appearance of a 4wd, but it's a 2wd. Think of the Prerunner package on Toyota trucks. No plans on making it 4wd. It's a budget body off restoration and it's down to the cab now, but I'm beginning to put everything together. Driveline is in except new rear end and propshaft. Fuel system and brakes, then wheels, then front fenders and bed go on. I'm not looking for 25mpg, but if I can maintain 13-15, I'm happy. The A/T tires may negate this, but it's a weekender, so I'm not overly concerned.

As far as offroading, I don't plan on any serious offroading, but I'd like to be able to drive it into a cow pasture or near a fish pond and get out easily. Ground clearance and tire tread are the biggest factors there.

My goal is to accomodate the tires and the overdrive gear in the tranny. I read about Jeeps with the same tire size with 4.11 diff ratios, but they're 4wd. If I'm getting into something that drastic, I'll go with smaller tires.

If anyone knows of a formula to calculate the effect the tire's outside diameter has on rear end gear ratio, that would be helpful to me. I'm a civil engineer by trade, so the math doesn't scare me..

 

After a little digging, I believe I'm going to go with 32x12.5 BFG All Terrains on 15" Mickey Thompson Rims.

318 V8 and A833 OD Tranny

Does the 3.23 seem wrong for this application?

BTW, this is a 2WD truck....

 

Thanks for the info, Ron. My fear is that using larger tires will exagerate the already lower gear ratio. I'd like to do better than 8mph in 1st gear!

3.55 was normally the matched rear end to the A833 OD. That's what I've been told by someone smarter than me, anyway.

 

Well, I have a stock 318 with a 833 OD and a 3.23 rear with stock 15 inch wheels. It pulls well but not anything spectacular. The 1 st gear in the 833 is low so it winds out pretty quick. With a 3:55 you would be working the gearbox, but second gear is tall so it may equal out. So, problems? No, but I have toyed with the idea about a 3:55 for myself. Keep in mind my 318 is stock and the only mods are a true dual exhaust, plus my engine has 163,000 miles on it. Your engine is probably much stronger.

 

I'd go 3.55 at least. I like the 3.55's in my '93, great street gear.

 

This one from Summit

http://www.summitracing.com/parts/SUM-BK1329/?rtype=10

 

what disk brake set up are you planning to use with the 8 3/4?

 

Probably a 285 ?? 16" All Terrain. Haven't decided on tire size yet, but something beefy with aggressive tread. Somewhere between Goodyear Wrangler and Mickey Thompson.

 

What tire size?