overdrive units for manual trans.....

How they work, how they don't work, and how to fix them

Moderators: Greenleaf, BC847, Richie O

overdrive units for manual trans.....

Postby jethro » Tue Nov 01, 2016 6:53 pm

Getting to know my fummins with the zf-6. 5 forward gears---- is really nice for around town situations. I can ooze
around town and most of the time never get 200 RPM above idle. (seeking MPG- not Big HP or smoke-)

I got to test it out a couple weeks ago on the expressway. In 5-th it seems to hit a nice RPM sweet spot somewhere
between 50 and 55 mph. But by 55- I am wanting to shift again. (this is ALL empty with no load)

I have seen lots of trucks use really tall tires- maybe to help this . But really tall tires are hard on the front end and brakes.

On the street--- in 2 wheel -high range-- 1-st gear is a granny gear just to get the truck rolling a little (it appears maybe for
when hauling a big load) But when empty it is all most wasted. Im only in 1-st for about 1.5 seconds.

Im thinking about devices which might be grafted into the drive line somewhere to raise the road speed about 1 more gear.

Looked at the gear vendor units--- like the overall way it mounts in and its compactness--- don't like the price and the fact
that it has a friction clutch for shifting on the fly. I don't believe I will want to shift on the fly (like a splitting situation)
I would just as well have something I could shift while sitting still. Probably want to leave it in OD except when in mountains
or in off road conditions. If it could raise my granny 1-st up about 2/3 of the way to regular 2-nd - that would effectively
make my current 5-th act like a 6-th I don't have. just shift every gear up about 3/4 of a gear.

So if that's not a gear vendors unit - then what brand ? New or old unit ?
Found one brand that bolts directly to the front of the pumpkin---- but it appears they don't make it for the 9+1/2 sterling
diff.

There are ones made by browning and spicer- appear to be made for medium and heavy trucks. anyone tried these ?
These seem to be 3 or 4 speed boxes......

Any opinions on what might work ?

Thanks-
Tim

PS--- embarrassingly--- I just noticed that the gear I thought was the lowest gear (called "first" on the knob-)
is not the lowest gear. The REAL lowest gear is called "low". I have been starting out from stop lights in "1" ---
letting the clutch out without having to add pedal.... it just goes ! :lol: Now I realize there is a lower gear yet -
just when you thought it couldn't possibly go any slower--- and that's in HIGH RANGE ! :hs:
Its slower than my tractor in low/high range.......
jethro
fuel screw!!!!
 
Posts: 412
Joined: Sat Mar 08, 2014 12:32 am

Re: overdrive units for manual trans.....

Postby dazedandconfused » Wed Nov 02, 2016 4:40 am

What gear ratio is in your truck? What size tires are you running and what is your rpm at highway speeds?
1983 Dodge D150 that has been repowered with a 93 Cummins/518 running gear AKA The Ugly Duck! I would much rather build them then buy them.[
User avatar
dazedandconfused
14mm rotor
 
Posts: 6066
Joined: Thu Apr 05, 2007 6:25 pm
Location: Walton, Kentucky

Re: overdrive units for manual trans.....

Postby PToombs » Wed Nov 02, 2016 4:44 pm

From the sounds of it regearing the diffs is the proper answer, just not the one you want to hear. Larger tires work, but you already stated the problems with them. A gearvendors works very well, but they are really pricey, I was looking at them years ago.
pete

Just enough power to break everything behind the crankshaft.
User avatar
PToombs
14mm rotor
 
Posts: 11193
Joined: Sun Jan 07, 2007 6:13 pm
Location: Syracuse NY. Snow central!
Top

Re: overdrive units for manual trans.....

Postby classiccarjack » Wed Nov 02, 2016 10:16 pm

jethro wrote:Getting to know my fummins with the zf-6. 5 forward gears---- is really nice for around town situations. I can ooze
around town and most of the time never get 200 RPM above idle. (seeking MPG- not Big HP or smoke-)

I got to test it out a couple weeks ago on the expressway. In 5-th it seems to hit a nice RPM sweet spot somewhere
between 50 and 55 mph. But by 55- I am wanting to shift again. (this is ALL empty with no load)

I have seen lots of trucks use really tall tires- maybe to help this . But really tall tires are hard on the front end and brakes.

On the street--- in 2 wheel -high range-- 1-st gear is a granny gear just to get the truck rolling a little (it appears maybe for
when hauling a big load) But when empty it is all most wasted. Im only in 1-st for about 1.5 seconds.

Im thinking about devices which might be grafted into the drive line somewhere to raise the road speed about 1 more gear.

Looked at the gear vendor units--- like the overall way it mounts in and its compactness--- don't like the price and the fact
that it has a friction clutch for shifting on the fly. I don't believe I will want to shift on the fly (like a splitting situation)
I would just as well have something I could shift while sitting still. Probably want to leave it in OD except when in mountains
or in off road conditions. If it could raise my granny 1-st up about 2/3 of the way to regular 2-nd - that would effectively
make my current 5-th act like a 6-th I don't have. just shift every gear up about 3/4 of a gear.

So if that's not a gear vendors unit - then what brand ? New or old unit ?
Found one brand that bolts directly to the front of the pumpkin---- but it appears they don't make it for the 9+1/2 sterling
diff.

There are ones made by browning and spicer- appear to be made for medium and heavy trucks. anyone tried these ?
These seem to be 3 or 4 speed boxes......

Any opinions on what might work ?

Thanks-
Tim

PS--- embarrassingly--- I just noticed that the gear I thought was the lowest gear (called "first" on the knob-)
is not the lowest gear. The REAL lowest gear is called "low". I have been starting out from stop lights in "1" ---
letting the clutch out without having to add pedal.... it just goes ! :lol: Now I realize there is a lower gear yet -
just when you thought it couldn't possibly go any slower--- and that's in HIGH RANGE ! :hs:
Its slower than my tractor in low/high range.......


I have a couple of Brownie Units. I am not sure what I am going to do with them just yet. They are called Auxiliary Transmissions and offer a range of gears "after" your transmission. They fit where the Drive shaft carrier bearing normally resides. One of the units drops me to a 2.44:1 then its 1:1 and the OD is .73:1. The other one I have is 2:1, 1:1, and .73:1(OD). If you are in First gear, it can really lower your truck to a crawl. And then you can Overdrive over your Overdrive, that may not be a good choice and hard on the gears, but the possibilities are there.

One is rated for 580 FtLbs of Torque and the other is rated for over 600 FtLbs.... These units come with an extra shifter assy. I may put one in my 1937 Dodge ME32, but I will need to take some time to figure out where to put the second shifter.... I got one out of an GMC that hauled Elephants, and the other came from a Dodge COE. They weren't cheap, but I see a lot of potential in which I can put them to good use.
classiccarjack
fuel screw!!!!
 
Posts: 72
Joined: Sun Feb 08, 2015 12:46 pm
Location: JAMUL, CA
Top

Re: overdrive units for manual trans.....

Postby jethro » Thu Nov 03, 2016 7:07 pm

my truck (2004 f-350) is running stock tire size 235-85-16. My rear end is a 3.73. I am not considering changing it- as it is the 2-nd
fastest I believe.... ( I think there is a 3 ) ---- and not least-- I just spent about 2000$ doing a complete overhaul of all parts in the
rear end. New Ring and pinion, bearings, outer axle bearings, new oil seals .... overhauled the rear brake calipers. So Im not really
anxious to replace all that..... and the same on the front pumpkin.

I don't have a working tack yet but I used the on-line calculator----- which shows.....

in 5-th------ 40 mph=1617 rpm
in 6-th gear (zf-6 overdrive) 50=1455 55=1601 60=1747

I am wanting to shift into a non-existing 7-th gear at about 1500 rpm in 6-th.

Tim
jethro
fuel screw!!!!
 
Posts: 412
Joined: Sat Mar 08, 2014 12:32 am
Top

Re: overdrive units for manual trans.....

Postby jethro » Thu Nov 03, 2016 7:35 pm

clasiccarjack-----

How big are these gear boxes ? I have heard some off the bigger trucks can weigh 250-350 lbs.
Can you give me a rough idea of height and width ? I have looked at pictures but cant tell the scale .......

Tim
jethro
fuel screw!!!!
 
Posts: 412
Joined: Sat Mar 08, 2014 12:32 am
Top

Re: overdrive units for manual trans.....

Postby dazedandconfused » Fri Nov 04, 2016 3:35 am

Why are you lugging it down so low? In all my manual trucks they got the best mileage running 1800-2000 rpm and shifting around 2500
1983 Dodge D150 that has been repowered with a 93 Cummins/518 running gear AKA The Ugly Duck! I would much rather build them then buy them.[
User avatar
dazedandconfused
14mm rotor
 
Posts: 6066
Joined: Thu Apr 05, 2007 6:25 pm
Location: Walton, Kentucky
Top

Re: overdrive units for manual trans.....

Postby PToombs » Fri Nov 04, 2016 3:56 pm

You need to get a tach in it so you know for sure how fast you are turning. Based on your guess about rpm at speed, that's not far off from my D350 with the Getrag and 3.54's. Based on what I have read, the most torque is made about 1600 rpm, and best fuel mileage is also in that range. Now from real world experience, at 15-1600 rpm, the Cummins is lugging and can destroy a manual trans because it surges. I thought yours was winding like 23-2400 rpm at 60-65 mph when you were talking about how low it was geared. If you can run along at 70 and be turning 1800 or so, that's a good place for mileage and power. I understand why you don't want to regear. ;) I think I would go play with an online tire calculator and find what size tire will bring the rpms down a little. You don't need to go to 37's or 44's, maybe a 33 or 35 inch diameter tire will be just right for you.
pete

Just enough power to break everything behind the crankshaft.
User avatar
PToombs
14mm rotor
 
Posts: 11193
Joined: Sun Jan 07, 2007 6:13 pm
Location: Syracuse NY. Snow central!
Top

Re: overdrive units for manual trans.....

Postby DodgeFreak » Fri Nov 04, 2016 8:24 pm

I think mine likes around 1700-1800 anything over 2k the mileage starts dropping.
92 D350 Cab and Chassis. Auto stock, wiring gremlins. 330k miles
92 W250 Ext cab rotted completely out. Auto, pump maxed, 215 ppump nozzles, Denny T2 pin.
85 D350 single wheel, converted to cummins, getrag, turned up 2 turns and afc screw flush.
User avatar
DodgeFreak
14mm rotor
 
Posts: 1701
Joined: Sat May 15, 2010 8:14 pm
Location: Iowa
Top

Re: overdrive units for manual trans.....

Postby jethro » Fri Nov 04, 2016 10:11 pm

I had it to the land fill the other day- it weighed about 8300 empty. -which it what it will weigh most of the time.
I am in flat-land here. Most of the time I don't need a lot of acceleration- just enough to keep it rolling along.

I have a set of 35 inch toyo wild country on big alloy wheels. I may stick them back on and see how that feels.
(they are getting some age on them looks like- maybe OK for around town) If I had to do over I would have gone taller-
but the coopers are brand new. Have to wear them out first.

I am guessing/estimating my rpm's from an on-line calculator using tire size and diff ratio. (235-85-16 and 3.73 front
and rear) One of the next things is to put in a tach unit. I have an idea how to make one that will be driven off the
serpentine belt up top somewhere -maybe near the gen or idler. Have to fab up a mechanism for that.

I have a 3200 gov spring so I CAN rev up------ just seems like I shouldn't need to (to a certain point)
when I am in first (NOT LOW) at a light--- I don't have to touch the gas...... just let the clutch out as normal---hardly
any perceptible rpm drop---- the about 1 sec later I am going into 2-nd. I can definitely break loose the rear end in
2-nd and third. By 4-th Im up about 40-45 and have moved away from the monster torque--- about like a gasser there.

Will give another report after the tach is working so I can give reliable numbers.

By the way---- is there an RPM for idle that is some agreed upon number ? maybe dictated by water pump minimum flow
or maybe generator output ? (or power steering flow)

Tim
jethro
fuel screw!!!!
 
Posts: 412
Joined: Sat Mar 08, 2014 12:32 am
Top

Re: overdrive units for manual trans.....

Postby spencerdiesel » Sat Nov 05, 2016 7:24 pm

I like my idle kind of on the high side, about 850 rpm at full engine temp and 60 degree ambient temp (my idle can be + or - about 25 rpm depending on outside temp). Your AC will keep being reasonably cool (with truck idling) in the summer, and the truck will be idling at a decent "slow speed" when its first started in really cold weather, meaning it wont need to be idled up. Plus it feels like a monster idling off in 3rd gear with no throttle applied :lol:
1992 W250, 5 speed, 4.10, Ext. cab Ext. bed, 12.5k winch, 75 gal. fuel tank

Fuel: THD 12 psi piston pump, THD fuel pin, 366 spring, fuel screw bottomed @ 3 turns, timing bumped 3/16"
Muffler delete
spencerdiesel
14mm rotor
 
Posts: 1015
Joined: Tue Oct 27, 2015 4:02 pm
Location: Brevard, NC
Top

Re: overdrive units for manual trans.....

Postby classiccarjack » Tue Apr 24, 2018 1:09 am

jethro wrote:clasiccarjack-----

How big are these gear boxes ? I have heard some off the bigger trucks can weigh 250-350 lbs.
Can you give me a rough idea of height and width ? I have looked at pictures but cant tell the scale .......

Tim


They are large and heavy, if I get some free time, I will see if I can help you out with this request.
classiccarjack
fuel screw!!!!
 
Posts: 72
Joined: Sun Feb 08, 2015 12:46 pm
Location: JAMUL, CA
Top


Return to Transmission

Who is online

Users browsing this forum: No registered users and 1 guest

cron