I am looking for 3.56 Ring and Pinion gear set and .846 4th gear for my 25-1 trans. It seems 3rd and 4th gears are very close together and need more rpm drop when shifting. does anyone have this problem with the -2 trans?
thanks Larry
Original Post

On the ZF data, it seems to me that this is a pure calculation on the RPM.

For example, when you hit 45 miles an hour in 1st gear (at 5500 RPM), when you shift to second, you have to be doing 3600 RPM (at that gear ratio) to stay at 45 mph.

As the gear ratios get "taller", the RPM drop required between gears is less than needed at the lower gears to achieve the same speed in MPH.

I want to show that I sometimes use my scientific thought process. Now everyone is free to poke holes in my hypothesis!

on paper, tyler's selection looks pretty good to me for a interstate cruiser.
the taller 4th will drop the rpm after shift, but it does raise make 4 to 5 narrower.

then given the axle change, 5th becomes an overdrive, and lowers the "speed limit" cruise rpms

Finding the parts would be my question
(and if I hadn't hesitated last month on that "buy it now", I would be looking similar gears)


Photos (1)
Thanks for the input guys. yes I have used the RBT calculator. it is great! Please note my stock -1 trans has 1st,2.42 2nd,1.47 3rd,1.09 4th,.96 and 5th.705 4.22:1 final
so take a moment and put this into the calculator. You will see 3rd to 4th is very short. in fact rpm drops faster than I can shift unless way up in the rpms. 6500 to 7000.
is the ratios you show from a stock -2 trans?
the green is the "stock" that RBT calculator provided.
the red is with change to 4th and axle

If you desire, I can use the ratios you just provided and do a cut and past overlay from the RBT?

Originally posted by tyler5:
Please note my stock -1 trans has
4th,.96 and
4.22:1 final

MAN! that is a horrible LOOKING shift layout!

It might be GREAT if the track was such all you used was 4th and 5th...


Photos (1)
Tyler, your "dash-1 ZF", if its in a Pantera, is in fact a Mangusta transmission rotated 180 degrees & attached to a sand-cast differential housing, with the ring gear swapped to the other side. The transition bellhousing has two small cooling holes up on top and only 4 bolts. The first 500-or so '71 Panteras got these transition ZF assemblies that Lloyd Butfoy of RBT Transmissions calls a 'dash-1.5' ZF. They were used while ZF got their assembly line up & running for DeTomaso/Ford. A true dash-1 ZF only fits a Mangusta or GT-40, has a different access cover facing up and the shifter assembly on the lower right.

There's nothing intrinsically wrong with that unit - it was used in pro racing in the '60s & '70s- except that spare parts for them are virtually nonexistent and quite a few things inside do not cross to the 5DS-25/2 ZF used in most other Panteras: mainshaft, synchro assemblies, gears, differential etc. Contact Lloyd Butfoy at www.RBTTransmissions.com and see if the gearing you think you need even exists anymore. I advise not spending much effort/money on that early ZF and buy a later dash-2 assembly to play with; at least the very high-priced spare gears will be available from Lloyd. You are working with a rare museum piece. Even the GT-40 guys use dash-2 ZFs these days.
Hey Bosswrench. yes you are correct about the bellhousing and it seems to be a sandcast. the dif housing is very smooth and clean so don't think it is. My #1387 must be a rare one indeed. Anyway Lloyd offered me a 1.09 or 1.05 4th. didn't make sense to change to a same gear as my 3rd?? maybe he was busy. I didn't know the Mangusta was set up with the ZF right side up. thanks
Still looking for ring and pinion gear set. I now have a 4th gear same as a -2 trans. Just want to do it all at the same time. does anyone sell parts other than Lloyd? Maybe in Europe. He just is too difficult to deal with. waiting months for a reply is unacceptable.
Tyler, you have a problem. Lloyd has official title for ALL new ZF parts, due to the rights, tooling and spares his late father Roy bought from ZF in the mid '70s. Lloyd gets occasional gears made to very high standards from a few pro gear makers. ALL other 'ZF' gears f/s on the planet are either cannibalized but usable parts from hopelessly broken transaxles, or an occasional NOS part found on a dusty shelf somewhere in the world. I have heard rumors that one or more U.S. shops have made undersized bronze synchro rings to fit our always-worn ZF gear-cones in place of stock steel ones, but I have never seen one. Some bearings are ZF-specific and some gaskets and shims are critical in thickness. The OEM gear steel was spec'ed by Ford. No one has ever duplicated any ZF stuff in any quantity.

Thee are a few shops that build custom ZFs for customers (GT-40s et al) and most get their parts, at retail price, from Lloyd. The rest do as above. Next bad-news: hundreds of potential replacement ZF dash-2s for Panteras were stocked by Ford who never quite trusted them. They were shipped and stored in open crates with no oil inside. So many of these BRAND NEW, never used but still 40-year-old NOS ZFs have rusted bearings, pitted gear teeth, and dried out seals from moisture- depending how & where they were stored. They need careful rebuilding with much hand work before they are usable. So paying extra for NOS may not be the answer for most owners.

Over years and decades, we've all found the ZF transaxle to be THE most durable part of the DeTomaso GTs, with the exception of the synchro assemblies and the "racing" sprag-type LSD used in GT-40s, some Mangustas and a very few pushbutton Panteras. GT-40s were delivered with cast aluminum bearing side-plates that are identical to the early iron ones but 6 lbs lighter. Ford managed to break a ZF during their 24 hr durability tests with a LeMans-spec 7-liter engine, so ZF 'upgraded' to cast iron side and end plates and added two cross-bolts to restrain case growth under high temperature, high horsepower/high torque use. On the street, the early cast aluminum side plates have worked fine on my lightweight dash-2 with a hot-rod Cleveland for 20 years. But OEM dash-1 or dash-1.5 parts are museum pieces. Be patient.
Thanks as always for the reply. I am fully aware of the history on these -1 or -1.5s as you put it. They may not be as rare as you think my friend has a matching number -1 in his 72 pre L. My #1387 is early yes but not a push button as some have stated the -1 only came in. I also have another -1 for parts with the same close 4th gear set up. #1973 stamped on it. This is 208 units more than My #1765. so apparently there are quite a few out there. With all this said, I fail to understand why so many state that these are complicated units. yes the -1 has the funky individual spring and detent for the gear collar. But this is no different than many transmissions of the day. Clearances and Pinion setting is quite simple done from the rear. maybe in just too old school. lol I will enjoy my 720Hp 410 highly modified Cleveland without the boat anchor 4V cast heads until she breaks.
Bossman, Just curious how much does your lightweight Pantera weigh? Im at 2850lbs 1/2 tank of fuel which is 17-1/2 gal. 35 total. obviously not stock. I have dual tanks. I was running E-85 and needed the extra. Full frame integrated in the Monique frame, carbon hood and deck I made. stock 40Lb radiator ha ha. So, added some and took some away.
Our street licensed '72-1/2 L model with full (fiberglas) bumpers weighs 2690 lbs with 1/2 tank of fuel, 8" & 10" Campys, A/C, stereo and leather upholstering. Just to demonstrate what's possible at home. Body is stock appearing from 5 ft away except for a Revson front spoiler. My goal when I started this project was 2650 lbs, street legal & ready to drive.

That's with a stock iron 351-C block & alloy heads- I haven't found the money to complete my Fontana alloy block that will remove 52 more lbs. I've spend 30 yrs shaving weight off almost everything else, more or less as a hobby since we don't club-race anymore. For instance, our dash-2 ZF weighs 135 lbs while a stock ZF weighs 155 lbs, and our 351-C engine now weighs 425 lbs while a stock engine weighs over 550 (Ford's number), ready to drive. When I do a mod', I write an article for the POCA Newsletter detailing what happened, how, and members make the call as to whether it's worth the effort.

Incidently, the 'dash-1.5' designation is Lloyd's label, from the combination of a rotated Mangusta tranny and a Pantera diff case on a transition bellhousing. A true dash-1 ZF is upside-down for Panteras and causes some confusion.
2690 very nice indeed. I believe I have added just over 100lbs with the additional internal frame and 14 gauge floor metal. As you, I will continue to shave. Thought about flipping my ZF (upside right). Of course that's some work again. My axles are at too much upward angle and I believe it is causing a vibration under full load from the U Joints. Let up slightly and it goes away.
Tyler, I accidentally found some years ago that a vibration on acceleration CAN come from a single slightly loose halfshaft bolt (out of 16). This can also happen from stock lock-washers, which are prone to crack and eventually fall out, leaving that bolt(s) woefully loose. I do not recommend using lock washers on the halfshafts at all, and I play around with the ZF until I can get the halfshaft bolts in from the ZF side. Then, an open-end wrench can hold the bolt head and a proper torque wrench can be used on the nut.
thanks Boss. no lock washers used only nyloc nuts and none loose as I have had these out numerous times for eng rebuild and double checking axles and u joints. again only vibrates under 1/2 throttle and up. tends to minimize as speed increases. not noticed at 130mph light load.
Tyler, From the chassis drawings I've seen it appears that the Pantera rear suspension geometry has little or no anti-squat built into it. Depending on your spring/shock combo you may be increasing the angularity of the halfshafts and aggravating things from increased camber because the rear is squatting under acceleration. Just something to think about.

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