G.T. Fieros

In this thread, I will document my design of the F23 transaxle mounts. I'm doing this because I enjoy building things and I'm helping out a friend as well. This will be my take on making a set of mounts and it's aimed at the 88 but may work with other years. The only stipulation that I have is to use any existing holes in the cradle and use the mounting points that GM used. I want to keep this cradle stock.

Since I have the 88 cradle here, it'll need some attention before I start. There are a few weak points in the 88 cradle. The one that I'll be addressing, is the front crossmember. These are known to crack with anything more powerful then stock. Since we'll be putting the SC3800 on top of this, let's beef it up.





Here's the solution. A formed brace that will help to spread the load in the weak area.










It's a little narrower than the inside channel so I'll clamp it after I center it up. What's difficult to see is that I've already taken the die grinder and cleaned up the area's to be welded.


Note: It doesn't have to be fully welded 100% around the perimeter.






Now that the cradle has been beefed up, I can start on reverse engineering the engine mounts. There's no need to redesign the wheel here so lets take a known working mount and use that.

Here's my model of the lower 88 mount.


Now this will attach to this engine mount.


Thus making this assembly.


Which looks like this.




I think it'll be nice to use round mounts on the transaxle. Since I have some poly bushings here, I'll need some sleeves. After a few minutes, I have what I need.




I will need to make a little stand to get the cradle off the floor. This will make things easier to measure and work on. I also need to get some metric fasteners to hold the engine to the trans.

Hey Shayne

that cradle looks familiar....

Can you please do me a favour and get the thing sandblasted and powder coated before continuing? (I will pay for this obviously), If this ends up going into a car, I don't want any of the rust being on it, and this is the time to clean it up before too much more stuff gets attached to it. Looks good so far!

For future brackets you might want to consider expanding the lower bracket sheet metal to cover all of the outside diameter of the poly bushing. This will reduce wear and stress on the bushing. Just a suggestion. The only axle (side) stress exerted on this type of bushing is transferred via the exposed lip.

.

That engine mount looks a lot like the west coast Fiero one with more metal removed but is still a decent way to go for mounting

Hey Pete.

I will get this blasted and coated for you, no problem. Ideally, I'd like to do all the fab work first, then send the cradle and mounts out together. This way I don't risk damaging the nice finish.

After leveling the cradle in both directions, I just bolted the block to the trans and set the assembly in place. The elevation of the block is good at this point.




While the engine mounts visually look okay, they will need to be modified. This set up will probably work well for the 3800 and Getrag but we're using the F23. I "think" the axle centerline's changed between the Getrag and F23. If anyone has a spare Getrag on the shelf, perhaps they can confirm this.

Right now, the engine is square in the cradle. You can clearly see the axle is not in the right location.


Note: According to my measurements, the distance between the inside edges of the fore and aft control arm brackets is 98 mm. The stock axle centerline doesn't fall exactly between them. It's 33 mm behind the rearmost edge of the forward control arm bracket. It's very clear, the entire assembly has to move rearward. Without actually measuring, it looks like I'll have to move it back around 50-60mm.

The F23 and F40 have the axles coming out the tranny approx 1 inch closer to the block so yes drive train needs to move rearward slightly making it a snug fit mount wise on the rear side

I can confirm that the F23 transmission is has the differential pushed over to the right 10.5 mm. To compensate you must mount the engine 10.5 mm over to the left (move towards the drivers side). You can also move the engine back to compensate for the driveline being aligned further inboard on the F23 transmission, but that is also what CV joints are for so that choice is up to you.

Cheers,

.

Thanks for the input guys, I appreciate it.

I decided to take the driveline off the stand. I wanted to re-position everything and tack weld the I beams to the cradle.


I also marked the axle centerline and the outer edge of the CV joint.


Here's the lower engine mount that I need to modify. I need some movement here.


Cut the sides off as they're the only thing I'll be using.


Here's a piece of 1/4" steel that I'll use as the base for the lower mount. It's a little longer and wider, which is what I want.


A slight radius.


This is better.




I'll probably use these holes for the rear bracket. I drilled them to 8.5mm and tapped them to M10x1.5


Now the driveline is square in all three planes, just like I want it.


Here you can see the tripot flange lines up with my mark.


At this point I tacked the engine mount in place to keep things where I want them.


I'll start on the rear mount and bracket assembly first.


Using a cardboard template, I came up with the angles that I needed.


Then to the press brake and transfer the angles to the steel.






Drilled two holes so I can bolt to the stock holes in the cradle.


I need to get some supplies before I continue...

I chose to use this style of poly mounts for the transaxle. Right now, I like them and I'll make use of them.
I tapped the holes on the steel plate for the mount to 3/8"-16. I will weld a stud in there but for now some short bolts went in.


I ground them flush.


Completed heavy duty mount assembly. This is 1/4" plate and a fail-proof positive lock poly mount.








Now on to the rear trans mount. I have a few idea's for this but I'd like to try this one first.
Using cardboard, I made the basic shape. This is the easiest way to visualize what might work.


Then I transferred to some 16 gauge steel that I have here. Piece by piece, it takes shape.
Here's the starting point.


Remember the holes I tapped earlier? I'll use two of them.




The end result will have an opening for the fill hole. I took it out for the mock up.


I was trying hard to not cut anything off the transaxle. Well, this offending area has to go.


Moving on.






I'll add some gussets here.


It looks like the rear mount will clear the sway bar.


I might just add a little tab from the rusted bolt(s) to the rear upright part.


Now that I have this tacked up, I'll take it off and create this is Solidworks. I want to have a design that I can cut on the laser and bend on the brake. Yes I'm taking my time here. I want the final result to look good, be strong and fit well. I'll cut this on the laser using 1/8" aluminum since we have a lot of it. Then I'll form it and put it back on the transaxle and see how I like it. Only then, I'll cut it one more time but using heavier steel and bolt in place.

Looks good, one thing to keep in mind is accessing the bolts once installed or to even be able to tighten the bolts when installing.

Here's a 3D model to see how it will look. I'll try to get this cut this week and see how I like it, with proper bends, hole locations, etc.
I might leave out the top hole so it doesn't get distorted during forming. I'll also give all the sharp corners a little radius too.

You do realize when these are done and work nice and strong there is a market for making them for others as the 3800SC F23 swap is becoming quite popular.

Hey Shayne

Any update on this? I see you started working on a Northstar to F23 project. Does this mean you ended up getting the rear mount figured out and built for the 3800? would be great to see some pictures. I do know of a couple of other guys interested in proper F23 to 3800 mounts and are eagerly awaiting the results here. Let me know if you need anything waterjet/laser cut. I would be glad to help to get these mounts finalized. The Solidworks models look great