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Gear Ratio Questions

C

Carmine

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Venice, CA
Gentlemen, I thought I had my ideal gear ratio figured out but now I'm not so sure. Here's the background: Just rebuilt the 350 in my 1986 K5. Recently installed a semi-float 14 Bolt with a Detroit True Track. I'm running 32 x 11.50 BFG Mud Terrains so I thought I'd be happy with 4.10 gears (truck has the auto-overdrive tranny). But the transmission seems to hunt for a lower gear more than I thought. Anyone running 4.56's with 32's? Truck will see some highway time. Also, just picked up a Dana 60 front housing. Now if I go with a Detroit True Track up front, from what I understand, one is available for 4.10's and lower numerically, and a different one is required for 4.56's and higher. Any suggestions would be welcome.
 
Are you sure the 700R4 is working correctly? 4.10's are low geared for 32's. 4.56's are good for 35's.
 
700r4 trans. have a deeper 1rst gear than th350 or 400, which is good. I agree with ajmblazer, 4.10 with 32's, that's not a bad combo.
 
What kind of gear hunting are you talking about? Is it shifting between 3rd and 4th too much?. The first thing to do is to make sure the TV cable is set correctly. Changing gears is expensive and your ratio is a good one, so you should try to make it work.

Assuming that the tranny is OK, here's a couple of things you could do:
-modify the governor to change (all) the shift points
-modify the valve body to hold the desired gear(s) longer.
-Of course the quick fix is to select 3 in town and move to D when your speed is higher.
 
Thanks for the responses. The down shifting occurs on the highway from overdrive to third. Truck seems to be a bit challenged by this gear ratio. Maybe I'm expecting too much from the rebuilt engine. The new engine only has about 400 miles on it but it was built rather well. I have Edelbrock performer heads and intake, re-jetted Quadrajet, Crower Baja Cam, Edelbrock Headers, and 9:1 compression. Previously with my 10 Bolt rear I had 4.88 and 35's.
 
Ya I'm surprised it's hunting for OD, I'd check issues with the shifting first.

My '96 5.7L vortech (around ~255hp factory) has 180k miles on it and I live at 4500' elevation. It will hunt slightly under acceleration when I'm driving up to Donner Pass (around ~8000' I believe) with my 34" LTBs (heavy bastards). When I had 235/85/16s it would dance past people while it was in 4th.

I have the stock 3.73s and the 4l60e, which is basically the same tranny you have but electronically shifted.

I'd say you probably have a vacuum leak or something (think that how yours shifts). I've never fiddled with the shifting on my K5 cuz I just always leave it in 1st, so I don't know much about how to fix that. You could always convert it to reverse-manual cuz it's nifty and would solve any shift-timing issues you'd ever have. That's my plan in my wheeler when the shifting starts to bug me. I'd kinda like this feature in my DD also, as sometimes based on the TPS it thinks I want to accelerate faster than I need to. When I'm just cruising past someone on the flats, I'd rather lock it in OD than have it downshift to 3rd only to go back in 5 seconds when I release the throttle.

I think I'm one of those guys that would be happier with an NV4500 in everything I buy :). You just can't deny the benefits to a good auto though. Mine has treated me really, really well for the last 13 years.
 
I have 350 with a700r4 running 4.10 gears with 35's and dont seen to have any problems with it hunting for gears. It seems to me that your problem is not in your gears as some others have said
 
Everybodys perspective on what too much gear hunting is can be different, so hard to tell if what you are experiencing is normal or not. Overdrive in a 700r4 is extremely high and was only designed for the purpose of being able to maintain highway speeds under minimal loads (i.e. only small to moderate grades). I've found the hunting is really bad if on slower speed secondary roads where it wants to be in OD at only 35-40 mph and it takes hardly any additional load and/or throttle to make it downshift.

While you may have a built engine I really don't have the details. If it has a "big" cam which makes power at higher RPM then engine just may not be well suited to rather low-rpm cruising as the engine doesn't make a ton of power down low.

There may still be a problem, and my first suspicion would be the adjustment of the TV cable since you mention just rebuilding the engine.
 
Thanks for the comments. I continue to put miles on the new engine. I agree 100% with the comments regarding the 700r4 being "exremely high". This coupled with the fact that my new engine does seem to have quite a bit of power on the highway (maybe it's too fast since it pulls to 85 with power to spare), at some point I think I'm going to re-gear to the 4.56s. I say this because of my front dana 60 (acquiring parts now). I'd like to go with the Detroit TruTrac which means I'll need to commit to either a 4.10 set up or a 4.56 plus set up. So, considering that the K5 will see offroad use and probably pull a trailer at some point, I'm favoring the 4.56s. Any body thing I'm nuts? I also think that my 700r4 will have to be rebuilt. That's another project in itself. Also, I currently have the Detroit TruTrac in the rear (14 bolt). I love it. It's invisible until you need it.
 
Personally I think going from 4.10 to 4.56 is a lot of time and money for minimal change in overall gearing.
 
Yeah, I know. The problem I'm facing is the front Dana 60. Apparently there is a difference in the Detroit TruTrac depending on the gear ratio. One TruTrac is for 4.56 and higher, the other for 4.10 and lower. So, I'd rather go with the 4.56 and build my matching Dana 60. If anyone is aware of another solution I'd be interested.
 
If you are also wanting to rebuild your tranny i would seriously think ab going to a 350turbo even though the 700r4 has a lower forst gear if you are going to be doing much highway driving then the 350 turbo will hold up much longer
 
roughstockcowboy4 said:
If you are also wanting to rebuild your tranny i would seriously think ab going to a 350turbo even though the 700r4 has a lower forst gear if you are going to be doing much highway driving then the 350 turbo will hold up much longer
Click to expand...

It's just not the first gear, but you also lose overdrive when going to the TH350. With 4.10 or 4.56 tires and 32" tires that engine would be screaming on the freeway.
 
My 700r4 does just fine. I have 35" tires and recently switched to 5.13 to get more towing power. If your wanting to tow with the stock motor I would go with a lower set of gears. If your just looking to daily drive then go with the 4.10s.
 
are you sure your plug wires are good? a few years ago i thought i had a problem w/ my 700r4. it cropped up after i rebuilt the top end w/ edelbrock intake, cam etc. the truck started shifting badly, sometimes refused to down shift. this usually occurred on the streets around town (40 mph) and cruising on the highway (55-65) when the engine wasn't working hard. i thought the newly unleashed power might be messing w/ the tired trans so i took it to the trans shop. i spent a good bit of coin to have the trans rebuilt and even put a shift kit in it. problem didn't stop. turns out 2 of the new spark plug wires were bad.
 
Very interesting. I did just have the engine rebuilt. Funny, I had a lot of problems with the distributor. I purchased a new Accel distributor specifically for the computer controlled Quadrajet. Engine ran really bad. Replaced the old factory distributor and engine ran much better. Never figured out the cause beyond that... I assumed that the Accel was defective (?).
 
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