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Can the 2nd and 3rd and possibly the 4th gear ratios be changed for a T-19 transmission? My current 7.5L, T-19 transmission is geared 5.11, 3.03, 1.79, 1.00, bought new in the 1986 F250HD 4wd and spec'd it with 4.10 gear. I really don't like the 3-speed spread in the road section gearing but love the 5.11 first for creeping around in the woods. I wouldn't mind even having a slight overdrive in place of the 1.00, but probably no chance of that. I will just have to up my tire diameter from 35" to 36". 

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captain slow...To start, the T-19 was available in close and wide ratios.  Manufacturers that used this transmission include Ford and I-H.  Scout and I-H pickups used the T-19.  That increases the available gearset options.  Here are some insights for gear ratios used by I-H.  Note the I-H model designations at the left:

13427 or T-427 Warner Gear T-19, 4 Speed Wide Ratio, Synchro Low
1=6.32, 2=3.09, 3=1.68, 4=1.00, Rev=6.96
'75 & on
13428 or T-428 Warner Gear T-19A, 4 Speed Close Ratio Synchro Low,
1=4.02, 2=2.41, 3=1.41, 4=1.00, Rev=4.42
'75 & on

There may be a suitable ratio change with these I-H T-19 gearsets, though they each come with trade-offs.  You cannot "mix and match" what you want here, as the cluster gear tooth count governs these ratios.  This is it, pick a gearset you like or stick with your Ford ratios.

Given that you won't get overdrive from any of the T-19 transmissions, you do need to focus on tire diameter or axle ratio changes.  I've been through this with my Ram and its 48RE automatic/overdrive.  I have a wide (31%) overdrive that makes the split between 3rd (direct) and fourth overdrive excessive.  To save the transmission at more than 180,000 miles, I slow down for 6% and steeper grades, downshift into 3rd direct and hold it there.  Overdrive, in an automatic or manual transmission, is the weakest gear and subject to the worst punishment.  To save my transmission, I drop down a gear...Your 4th gear is direct 1:1 and quite strong.

For reasonable engine speeds on the highway at cruise, I'm running 4.56:1 gears with 37" diameter tires.  I may change to 4.10:1 in order to drop the tire size down to 35" or 36" diameter.  This would be my second axle ratio change.  I perform my own axle and transmission work, which is a plus and cost saver.

You have the option of a truck overdrive transmission like the Ford ZF.  I've juggled a more substantial approach for some time:  converting to a medium duty truck Spicer 7-speed with overdrive.  The 7-speed is a lot of work and fabrication;  however, there are positive examples across the internet.  That would be the ultimate up-and-down ratio spread, available as a 7th gear direct or overdrive. 

The 7-speed direct offers a stamina advantage, though you'd need to change the axle gears (ratios like 3.54:1 or even taller) to get the full benefit.  1st gear is ridiculously low.  Given the transmission's size and applications, overdrive would not be taxed in an F250 4x4 pickup—even if you pull hefty trailers.

Here is the Spicer ES066-7B that I've considered.  Lots of work with this conversion but perhaps the missing link in your quest?  If your truck is a 6.9L Navistar diesel or 460 (Series 385 design) V-8, you could start with a bellhousing from a medium duty Ford truck.  The transfer case would need to be a divorced type and not attached to the transmission.  Fabricated crossmembers, drivelines and other work are required:

 

Spicer ES56-7B and ES066-7B 7-Speed.pdf

Spicer ES066-7B Tremec Service and Operators Manual.pdf1.5 MB · 0 downloads

Here's a quick search example of a conversion involving a similar Eaton 7-speed into an F350 4x4.  The discussion covers the obstacles and gains:

https://www.4btswaps.com/threads/eaton-fuller-rto-6610-stuffed-behind-a-7-3-diesel-in-a-1997-f350.107959/

Moses

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Well, I thought that one couldn't just replace just the gear cog, but that there would be more to it. So If you had the two transmissions side by side, I'd think you could replace all the parts. But I suppose that there'd be an issue with the 1-2 synchronizer, a big jump. And I'd considered moving to medium duty transmissions, but the cost and complexity of manufacturing the adapters, crossmembers and divorced transfer case. After looking through your links and looking at the transmissions available for the medium trucks, I decided that I could get all the luxury I wanted with these: 

 https://www.fourwheeler.com/how-to/transmission-drivetrain/1906-junkyard-manual-transmission-spotters-guide/

NV5600
A heavy-duty six-speed transmission with a granny First found in Dodge trucks with the 24-valve 5.9L Cummins turbodiesel.
Found In: 1998-2005 Dodge Ram 2500 and 3500 trucks.
Identification: Huge with three main parts: the aluminum clutch housing, the main case made of cast iron, and a third extension housing also made of cast iron.
5.63:1 First, 3.38:1 Second, 2.04:1 Third, 1.39:1 Fourth, 1:1 Fifth, 0.73:1 Sixth, 5.36: 1 Reverse.

ZF6
Ford's six-speed truck transmission.
Found In: 1998 Ford Super Duty trucks.
Identification: All aluminum housing with an integral bellhousing. One unique feature is this big transmission uses an external transmission cooler so it should be just about the only manual you'll ever see with transmission fluid lines going in and out of the case.
5.79:1 First, 3.31:1 Second, 2.10:1 Third, 1.31:1 Fourth, 1:1 Fifth, 0.72:1 Sixth 5.23:1 Reverse.

https://en.wikipedia.org/wiki/ZF_S6-650_transmission

Or just live with the T-19 as is.

I am going to put on the straight up cam gear so that should improve the engines performance and do away with some of the limitations. Upon further reflection, the problem with that gear ratio only manifested itself with the stock tires, which I didn't use very long. And the bias ply tires until they started making taller radials.  I should stop this incessant quest for more gears and be satisfied with what I have. But the read with the fellow with the Jeep was an afternoons captive entertainment. Then I spent much of the evening into the night looking things up. And this morning with the links you sent in the email. Thank you very much. 

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captain slow...I would have mentioned the NV5600, however, it has several inherent issues, including synchronizer problems.  The OEM no longer supports these units.  They are expensive to rebuild.  I have installed the NV4500 in various applications with success, the HD version is stout and iron cased.  Only a five speed but ratio options are available.

The ZF is likely the easiest fit with OEM Ford parts bridging the conversion.  If driven properly with the correct lubricant, the ZF will hold up.  Any of these NV or ZF overdrives place a heavy load on the overdrive gear.  "Driven properly" in my view is shifting to direct drive when under severe load or on 6%-plus grades.

As for your consternation about a transmission change, don't feel alone.  I have batted the 7-speed idea back and forth, these units are heavy, and as you note, involve a great deal of downtime with the fabrication work.  Drivelines, crossmembers, floor pan changes, in my case clutch/brake pedals, a computer redo for the manual transmission, on and on.  It's more a novelty at that point, though amortizing cost would be possible if I keep the Ram for another 300,000 or more miles.  I'm at 180,000 miles now.

All of this points to sound decisions when we buy our trucks.  Often, the transmission ratios are limited, though as you suggest, Ford was not far off with your T-19.  Massaging the gearing, altering engine tune (camshaft and valve timing included) and selecting the right tire diameter can make a big difference.  Though the 48RE automatic has its limitations, the Cummins engine compensates.  Trade-offs.  My next Ram would definitely have the G56 Mercedes transmission—stock.  That means a 2018 or older chassis, which is fine with me.  The new models are ridiculously overpriced.

Your engine is a carbureted 351W or 460?  The Navistar 6.9L diesel?  Each very good engines.  1987 would have provided MPI in the gasoline engines.

Moses  

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