F40 Transmission - Will It Work?

Desert Sasqwatch

Well-Known Member
So will these developments allow the use of an LS4 V8??? Just kidding... or am I????
That might be doable if there was more room between the engine and fuel tank location for the V configuration of the motor. Which subframe would you use, since the Cobalt/G5 frame is very tight for the I4 engine and trans. Granted, the Fiero guys are doing this, but with some pretty extensive modifications. I'm guessing some changes to more than the motor/trans mounts would be required. But why drop in a V8, with all of the extra weight penalty, when an Ecotec engine can be boosted into the 500hp (or more) range without the extra pork? Other than having a unique Goblin, not sure of the benefits? I am not trying to discount the idea and if someone does actually attempt to do this, it would a great build to follow. It's all good.
 

Tinkles

Active Member
Kyle, so the LNF axles are the correct axles for both the drivers and passengers side? That will simplify things greatly if others plan to use the F40 transmission in their build.
I'll say yes, but make sure they are ~24" long(overall) before you install them.
 

Desert Sasqwatch

Well-Known Member
Kyle, when I finally get the point of having my TC axles out of the donor, I will check for length and spline count. Between you and Ken, we may get his figured out an working. BTW, my donor showed up tonight from El Paso, got it unloaded and into the garage. I will have some new info tomorrow in my other 'new guy' post thread.
 

Adam

Administrator
Staff member
We test fit the F40 this morning (a day later than planned). We took the old frame that has been sitting in the barn for a couple of years and cut the old style engine and trans mounts off. We also had to cut the front radiator mount off because it interfered with the chassis jig (for those that aren't familiar with the early frames, the radiator mount used to be part of the frame instead of being a bolt on piece).

Once we got the frame on the jig, Ray welded on the current engine mount (passenger side) but did not weld on the transmission mount. We pulled the frame from the jig and lowered it down over the engine and transmission (our empty Ecotec and KLM's new F40).

We started to bolt the engine to the frame but immediately saw that the transmission end was way too low. We couldn't raise the transmission up high enough to level the engine because the transmission hit the chassis. We figured if we can't raise the transmission end, we should lower the engine end. So we added 5/8 spacers on the engine end to level the engine.

But then we saw that the transmission couldn't come far enough back so the driver side of the engine was further forward than the passenger side. The transmission hit the frame so it couldn't come further back. Since we couldn't move the transmission further back, we decided to take a shot at moving the engine forward to the bolt holes that are normally used with the automatic powertrain.

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With the engine in the forward holes and the 5/8 spacers installed, it looked like it would fit but would require a little bit of grinding on one of the transmission bosses to give a little bit of clearance.

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We then started to install the subframe. Even though the engine was 5/8 of an inch lower, the passenger side still cleared the subframe. However, the transmission did not. The subframe hit the transmission and raised it up until it touched the frame.

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This all means that the chassis is going to have to be modified to clear the F40.

Our first thought is to change the cage rail that is hitting the top/side of the transmission. We're thinking of adding a bend so that it ends up further away from the transmission. This will change a couple of other pieces but it seems doable.

With the test fit out of the way we are now thinking about all of the other things that will need to be adjusted or created. Things like the actual transmission mount, the front and rear trans mounts, shifter cable mount, linkages, etc. There is going to be a lot of drawing and CNC machining parts until we have mounts that we like. Then we'll send those models to the laser cutter to let them burn the parts our (CNC milling works alright for a prototype but is not okay for production pieces).

Hopefully by the end of the day we can have an idea of all of the steps involved to get the F40 to fit.
 

KLMOTORSPORTS

Active Member
Wow, thanks for all the work on this...pretty extensive fab work to do, but this will be awesome as an option to others as well as make one heck of a race car for me...much appreciate Lonny and Adam!!!
 

Desert Sasqwatch

Well-Known Member
Lonny, Adam, thanks for the update and photos. Appears you are putting a lot of engineering into this and many of us are greatly appreciative of this effort. This mod, if available, may prompt others to use the F40 transmission when it becomes available. Thank you so much for pulling this together.

Looks like getting the F40 squeezed into the frame will be a challenge but not undoable - which is good news. From the photos, the frame rail next to the transmission may need a slight reroute or cutout/reinforcement plate at that location. I was already planning this in my head when I first saw the build thread and photos from KJP and made the personal decision to use the F40 transmission in my build. Please keep us updated and I look forward to seeing the end result. I am still many weeks away from ordering my kit, I will wait until this mod is finalized and approved for ordering. Thanks, Tim
 

deuc224

Member
DS, what does the f40 tranny bring to the table that the F35 doesnt? I seriously have no idea besides an extra gear, but wouldnt that make them shorter ratios?
 

KLMOTORSPORTS

Active Member
DS, what does the f40 tranny bring to the table that the F35 doesnt? I seriously have no idea besides an extra gear, but wouldnt that make them shorter ratios?
Only speaking for myself and the research I performed, it is about the additional strength of the F40 and the availability (new) of the F40, not to mention the very reasonable cost of the F40 ($700 new) over getting a F35 repaired (very expensive). For me, just makes sense to move to a newer, more readily available component that is stronger, than staying status quo...just my thoughts and it works for me. If I shack a transmission, with the F40, I know I can have a new replacement the next couple days...not so much with the F35 (would either need rebuilt at a large expense...I was quoted over $2300 for the one I had..... OR buy a used one where I don’t know what I got).

This is what drove me to the F40...

Ken
 

Desert Sasqwatch

Well-Known Member
DS, what does the f40 tranny bring to the table that the F35 doesnt? I seriously have no idea besides an extra gear, but wouldnt that make them shorter ratios?
The first 3 gears in the F40 are nearly identical to the F35 with a 4.05:1 ratio and are closer ration than the F35 with the 3.84:1 ratio. The final 3 gears have closer ratios than the final 2 ratios in the F35. Overall, the F40 will allow the car to pull harder in all gears and still allow for a lower rpm at cruising speed on the highway. As Ken stated, these characteristics are desirable to many of us choosing to go with the F40 over the F35 - plus it is cheaper and easier to work on. That is why I am going the F40 route on my build.
 

George

Well-Known Member
I did not go with F40 (have every thing to do it) because of all the extra weight of the gears that have to be acclerated. The lighter the rotational mass the quicker the accleration. I went so far as to remove the balance shaft and long chain, only driving the water pump.It can beat all speed limits in the first 3 gears.
 
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deuc224

Member
Wow 2300 for a rebuild?!!!!! Yeah makes a ton of sense to just wait out if the frame will be tweaked for the F40 and get that. Damn the faster acceleration portion wont be hard to deal with cuz of the TC or SC models just drive a little more boost, which im sure most will do anyway.
 

Desert Sasqwatch

Well-Known Member
Examples of the F35 rebuild trans can be found at WERKS Racing:

performanceautowerks.com/catalog/product_info.php/werksracing-f35-stage-transmissions-p-2057

Plug in your requirements into the build options and hold onto your butt when you see how much it is to get a 'zero mile' F35.
 

KLMOTORSPORTS

Active Member
Wow 2300 for a rebuild?!!!!! Yeah makes a ton of sense to just wait out if the frame will be tweaked for the F40 and get that. Damn the faster acceleration portion wont be hard to deal with cuz of the TC or SC models just drive a little more boost, which im sure most will do anyway.
That was the cost for mine...they wouldn’t even touch the F35 at the shop in Dayton, Ohio...they sent it to a central place of repair in Louisville, Kentucky. I asked why so high for the repair and it was due to parts cost and availability of those parts. Shoot, I thought I was aiming real high at first when I told them “let me know if over $1,000...other than that, just do the work”...thought there is no way more than that. I was wrong...lol. The manager in Dayton first asked me if I was sitting down before he told me.

He asked me what I wanted to do with the transmission as it was all in parts now...they could send it back up and I could have it back ($50 transportation fee) or what did I want to do...I just told them to keep it and it was no cost for me.

This put me directly down the F40 path.

Ken
 

Tinkles

Active Member
Adam, What if the tube below the trans mount was notched to look like pac-man?



Would that allow enough room? Would it weaken that area too much?

Or cut that section of tube out and move it ~1" higher. Weld the trans bracket to the bottom of the tube and gusset it?
 
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George

Well-Known Member
The price of parts for the F35 are high but if you order them for a SAAB they are little less because that is a SAAB designed transmission. So GM has to buy the parts from SAAB and mark them up. They are still not cheap just maybe a little less.

Brad
 

Desert Sasqwatch

Well-Known Member
Technical information about the GM transverse manual transmissions:
The GM transmissions are usually numerically designated in newton metres that means F35 is rated at 350 Nm, the F25 at 250 Nm, F40 at 400 Nm, M32 at 320 Nm, and so on.

F35:
The F35 is a Saab-designed five-speed manual transmission. It weighs approximately 99 lb/45 kg with synchronized reverse, triple-cone synchronizers on 1st and 2nd gears, and single-cone synchronizers for 3rd, 4th, 5th and reverse gears. The gearbox is rated for 260 ft-lb (353 Nm) of engine torque.

F40:
The GM MR6/F40 six-speed manual transaxle built by Opel in Rüsselsheim am Main , Germany, was originally a design developed for Fiat, Opel and Saab applications, The F40 is cast in aluminum, and weighs 124 lb/56.2 kg. Triple-cone synchronizers are used on 1st and 2nd gears. The 3rd, 4th, and reverse synchronizers are double-cone, while the 5th and 6th gear synchronizers are single-cone. It has been certified for up to 295 ft-lb ( 400 Nm) of engine torque.

Bottom line: from the factory the F40 is capable of handling high torque (factory rating by 12%) than the F35, having more robust gears and better synchro design for more coordinated shifting under higher load.
 

Tinkles

Active Member
It looks like that in my chassis all that is needed to fit the F40 is to cut off and remake the trans mount. I could only get the engine and trans ~2.5" away from their mounts before the trans hit its bracket. So far it looks like everything will fit between the frame rails. It'll be tight, but I think it'll fit.









I wonder if there is a difference in case size in the F40s or (no offense Adam and Lonny) a slight different in the chassis? Or will the clearance that I think I have disappear once I get the engine and trans at the right height?
 
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