from what i remember from the '84 toronado parts car i had (wanted the engine ) the axles where lower then the pan

here is a pic from a toronado brochure

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2001 Grand Prix GT: supercharged L36, XP Hot cam, SSAC headers, 3.4 pulley. 12.99 @107 MPH

looking for a Fiero

quote Originally posted by jscott1: Does anyone have a picture of a THM-325 (with engine) mounted on a Fiero cradle? I'm having a hard time visualizing how the differential and axles clear the oil pan. All the pics I found in the archive don't show this clearly. The idea was very clever at the time, but GM (and everybody else) eventually decided to go transverse with FWD and this type of transmission disappeared. As a consequence, most of us have never seen a THM-325/THM-425

I was looking for the same thing I would love to see some pics of this setup as well.

I could go with the thm 325 just dont think it would hold the torque of a big block maybe i am wrong on that but i could cut the fire wall anr relocate the fuel tank to the front .

The 325-4L is the same as a th200-L4 which is used behind the Buick GN, can be built to withstand 800 to 1000 hp. I posted a link on your pontiac in a pontiac thread, also a GN guy spoke up on there. I think their spendy to beef up though which is a negative.

I talked to a tranny guy today and he said that the thm325 would not handle the torque of a big block remember torque is much different then HP

[This message has been edited by engine man (edited 12-03-2009).]

Stop trying to move the engine forwards.

Move the rear wheels back. Same effect, but you get a longer wheelbase for better stability. Probably the same amount of work in the long run.

Maybe less. Even if you don't flip the diff, you've got 2000 pounds of Fiero up front. Go se the Tubular Cradle thread. No, I don't know where. Just saw off everything aft of wherever and do a stretch. Throw away at least 250 pounds of sheetmetal. Push the rear wheel back to just clear the bumper, moving the wheel openings is just fiberglass.

Don't run down that "I'll just flip the diff" blind alley. PBJ found a brick wall at the end of his. Maybe you can make yours go somewhere, but think outside the box.

Think outside the BUILDING the box is in.

streching the car is not a option if i was going to do that i would rebodie and use a manual transaxle. yes I am going down a road of broken dreams that no one has seemed to be able to beat but i must try

If you have access to a tig welder, welding new ears on the trans like PBJ said is a great Idea, would eliminate the need for a plate and also keep all the strength. I bet a welding shop could do it for $100, you do the drilling.

welding ears on seems like a good idea but it is not du to there are open areas when you flip it i will sow you with some photos . i will be using 3/16 steel it will be pleanty strong i dont think it will bed when there is a bolt within 2 iches of each othere. thiis is some photos of the differential all apart you can see the retainer in the 1 gear that holds the short axle and it war just a matter of them swaping sides

cardealer's axles went through the oil pan.
engine faced the bumper

he reversed the drive by removing the rear plate and changing the gears around. He even looked into getting gears made, but never did...

ya i see carsealers thread and it looked like he had changed it from chain drive to gears to get the tranny to rotate in the directon he wanted . i dont know what he had to do to the tranny do to there are parts that are made to lock in one direction and freewheel in the othere

just added a gear inbetween the "chain gears" and that was it.
Maybe only certian years it did it that way???

quote Originally posted by engine man: ya i see carsealers thread and it looked like he had changed it from chain drive to gears to get the tranny to rotate in the directon he wanted . i dont know what he had to do to the tranny do to there are parts that are made to lock in one direction and freewheel in the othere

The internals of the TH425 rotate opposite of the TH400 due to the OEM chain drive. Using the gears make the HT425 rotate opposite, make it rotate like the TH400, so I would assume he used the TH400 internal parts.

The last issue will be the differential ring and pinion - they are designed with a "load" side and designed for seeing the highest load in a single direction. Spinning them backwards will be noisy and probably not near as strong. Any chance a typical RWD ring and pinion will fit within the TH425 diff?

the problem would be the pinion gear has a thraded shaft for a nut for preload and it is splined at the end for drive off the tranny

quote Originally posted by revin: cardealer's axles went through the oil pan. engine faced the bumper he reversed the drive by removing the rear plate and changing the gears around. He even looked into getting gears made, but never did...

Have you ever talked to him again?
https://www.fiero.nl/forum/A...070315-1-062225.html

this is a photo of cardealers gear drive

i think it is cool and could work but like some one said now the ring and pinion are spining backward and load is on the wrong gear face

I thought about some things I know that some are saying the plate will be to thin but i will try it . My othere thought would be to go 3 inches thick then have a itnermediate shaft made to conect the tranny to the differential . another thing is rotate it so the long shaft is going down hill just a bit to help with the clearance problem under the engine

You will quickly run out of room between the firewall and the axle centerline moving the diff back... might want to consider a stock body wheel base stretch that moves the rear wheels back but keep the body stock length... something like this:


Doing this would get the entire diff out from under the engine (no oil pan or interferance issues) and allows you to use a dana44 corvette rear diff with a wide range of available gearsets. Plus, it puts the entire engine/tranny weight in front of the rear axle centerline.

the strech would work but then you have to mod the bodie and with the wheels that far back i dont know if it will look that great. if I moved the differetnial back 3 inches i t would be out of the sump part of the pan and angle the shaft down that passes under the pan . i can get a posi unit for this rearend and 4.10 gears

quote Originally posted by fieroguru: You will quickly run out of room between the firewall and the axle centerline moving the diff back... might want to consider a stock body wheel base stretch that moves the rear wheels back but keep the body stock length... something like this: Doing this would get the entire diff out from under the engine (no oil pan or interferance issues) and allows you to use a dana44 corvette rear diff with a wide range of available gearsets. Plus, it puts the entire engine/tranny weight in front of the rear axle centerline.

do you or anybody else have pics of that setup with the exterior finished? ie wheels body panels and etcetera? kind of interesting to say the least.

this is a build thread the guy did a big block on the cheap
https://www.fiero.nl/forum/A...090219-1-062869.html

quote Originally posted by ghost187x: do you or anybody else have pics of that setup with the exterior finished? ie wheels body panels and etcetera? kind of interesting to say the least.

Nope, that project is in idle mode... too many other projects infront of it - belongs to the Russ Fiero.

Ok thought i would do some math that is more than likely not ritght.
Ok if 510 lbs of torque can be handled by 5/8 of shaft spline on a 5000 lbs + car then how much will 7/16 of spline do in a 2600 lbs car. I took 5/8 and made it in to sixtenths so there are 10 in 5/8. so torque devided by 10 times 7 the seven is how many sixteenths due to the 3/16 plate 510 divded by 10 = 51 X 7 = 357 X 1.88 = 707lbs torque . the 1.88 is the weight factor due to the fiero is about 1/2 the weight of the cadillac and this assumes that it was on the raged edge with the 510 foot lbs of torque in the 5000 pound car and i know that they built in some room to play and was stronger than that. of course there maybe othere factors such as gear ratio and othere things that will efect this

quote Originally posted by engine man: Ok thought i would do some math that is more than likely not ritght. Ok if 510 lbs of torque can be handled by 5/8 of shaft spline on a 5000 lbs + car then how much will 7/16 of spline do in a 2600 lbs car. I took 5/8 and made it in to sixtenths so there are 10 in 5/8. so torque devided by 10 times 7 the seven is how many sixteenths due to the 3/16 plate 510 divded by 10 = 51 X 7 = 357 X 1.88 = 707lbs torque . the 1.88 is the weight factor due to the fiero is about 1/2 the weight of the cadillac and this assumes that it was on the raged edge with the 510 foot lbs of torque in the 5000 pound car and i know that they built in some room to play and was stronger than that. of course there maybe othere factors such as gear ratio and othere things that will efect this

The relation ship of shear strength through torque isn't only linear with respect to section diameter.

The polar moment of inertia is an nominal measurement used to calculate shear strength in torsion.
J=polar moment of inertia
c=radius
tau=shear stress
T=torque applied to shaft
tau=T*c/J
Not only does it make it a 4th order relationship to diameter (J=pi/2*(d/2)^4), surface heat treatments to the axle affect the strength as well, which makes an analytical solution of ultimate strength more difficult to approximate. A more acceptable calculation that follows closer to ACCEPTED materials science theory would be to determine the static resistance of a 4500lb car subject to 500lb-ft of torque through a ~26in tire, and that of a (more accurate) 3000lb car subject to the 500lb-ft of torque through a 25" tire. But not only is it 500lb-ft of torque at the crank, it is 500lb-ft of torque through a gear reduction that adds a torque multiplier probably close to 14:1. Then since this system is a dynamic one, where the components are in motion, it is common practice to apply a dynamic load factor to all external forces.
So perhaps doubling the torque by a factor of 2 will provide some more insight. Also, the ultimate shear strength could be as high SAE 4340 heat-treated steal (95ksi), or as low as a standard wrought iron (25ksi). Keeping the shear stress lower than the ultimate shear strength by a determined factor of safety (depends of component life and load cycle, maybe around 12?) of tau(ultimate)/tau=n is common engineering practice.
Just some insight to a simple method of mechanic strength theory.
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1986GT 4-speed DOHC and 1987GT Auto

[This message has been edited by FieroWannaBe (edited 12-06-2009).]

FieroWannaBe
I have read what you said but not sure if you are saying i will not have a problem or will.

I dont know if you will either, I didnt loko very much into it, but just letting you know some calculations you could try to gauge the strength the axles.

not trying to find the axle strength but the drive of the pinion that fits in the end of the tranny output due to there will be 3/16 less engagment it is going from 5/8 to 7/16

Oh, there's me paying attention. Sorry about that. Well, in that case, everything after the torque through a shaft applies, the torque will still have a multiplication of the chain drive, and the transmission. The torque is then equally divided into the number of splines. So the force, F (Torque/radius), is divided by the area (created by the total spline length engaged times the width of each spline.) This can give you an approximation of the shear stress seen in a spline. Keep it under the ultimate shear strength (0.577*Ultimate), you should be OK for a while, negating fatigue.
(FYI I am treating each spline as a key-way failing in shear)
So
F=T*Ratio/(r*N)
N=number of splines
F=force on spline
T=Torque
r=shaft radius=diameter*.5 (assume the radius from shaft center to lower spline dimension)
tau=F/(t*l)
t=spline width
l=length engaged
You want to keep tau under 0.577*UltimateStrength/n (safe to assume 65ksi?), where n=factor of safety (I would say higher better maybe 10 or 12)
maybe this will help you.

[This message has been edited by FieroWannaBe (edited 12-06-2009).]

well i think it is cool all the math and knew mine was gona be wrong so i will go by the do it if it works great if not oh well

[This message has been edited by engine man (edited 12-06-2009).]

Thes fellow has an interesting concept, he could box in the tubes with steel plate to make a nice solid torque tube, solid mount the diff and add an intermediate shaft.
https://www.fiero.nl/forum/Forum2/HTML/095676.html

[This message has been edited by AmericanMuscle (edited 12-08-2009).]

intressting that is cool looking he just needs to weld a pice of aluminum tubing in there

I got a ? on the THM 325 differential is the output shaft to the differential male or female if male do any of you know what spline it is? did they just go with the 27 spline thm350 ? .
What i am thinking is if it is male on the transmission side and female in the differential and 27 spline why not adapt the thm 325 differential to the thm425 tranny it would solve alot of problems.

I do not know about the 325, but on the 425 the spline on the short axle shaft matches the output shaft spline. I had mocked it up to use that short axle flange to be the output flange.

[This message has been edited by fieroguru (edited 12-11-2009).]

well it is my day off so to the bone yard to see how the differential is on a thm 325 if it is female and 27 spline i will buy it due to i think that it will be the same as the thm 350 output shaft that you can get for a thm 400/425

What! Hey EM I told you that a month ago here https://www.fiero.nl/forum/Forum2/HTML/104650.html . might have to start a new thread now called THM 325-4L reverse rotation. while your on the phone with Art Carr, ask him about the thm 325 3 speed, if it can be built the same, just 1 less gear.

I ask them out there and they said they dont build front wheel drive trannys but what i did get for inf on the thm 200-4r is that the forward drum needs to be replaced i think he said there like $199 . I think there are more things like line pressure and a wider 2nd gear band . I am sure that the thm 200c can be built it just dosent have the over drive setup in it . the othere thing is the differential how strong is it i have read there was problems with it but was it due to bad spider gears and some one spining one tire on snow or somthing making the spiders come apart. i think the only good gear is the 3.15 but not sure if that came in the 6 cyl turbo riviera . thing i do know is the way 2nd gear is set up in a thm200 & 200-4r is better than the thm400 all in all i will pull the 325-4l out of the 84 it will only run me a $81 like the thm425 then i can decide weather to go with it or the thm425 or a mix thm425 tranny & 325 differential

Get as much of that drive train you can, axles brackets etc, I think some guys used Ciera steering knuckles that fit the axles. but research it to make sure.