Rear End Alignment with Driveshaft Opening in Frame (Gen2)

[Higgi56]

I installed the rear end using the lower bolt holes for the upper and lower control arms as suggested by the manual.

After the installation was complete I noticed the pinion flange on the differential was lined up such that it appears the driveshaft would hit the frame.

I am wondering once i set it on the ground on wheels will the flange align properly with the opening in the frame or should a move the control arms to the upper bolt holes on the frame to lift the rear end.

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[michael everson]

Is the pinion really pointing down that much? try jacking up the rear to simulate ride height and see what it looks like. It should be parallel to the drive line center line.
Mike

[NAZ]

The pinion is angled down quite a bit so it's going to be hard to say if the driveshaft will hit the chassis. Once the pinion angle is set correctly you can determine how close it will come to the chassis and make adjustments as necessary for sufficient clearance.

The driveshaft should never hit the chassis under full rear axle articulation -- never!

[Higgi56]

The pinion is angled down quite a bit so it's going to be hard to say if the driveshaft will hit the chassis. Once the pinion angle is set correctly you can determine how close it will come to the chassis and make adjustments as necessary for sufficient clearance.

The driveshaft should never hit the chassis under full rear axle articulation -- never!

Would raising the lower control arms to the upper holes on the frame tilt the rear end to raise the pinion angle?

any other ideas?

thanks!

[Higgi56]

Is the pinion really pointing down that much? try jacking up the rear to simulate ride height and see what it looks like. It should be parallel to the drive line center line.
Mike

i tried jacking up the rear end but it lifted the whole frame off the jack stands. I agree with your assessment, I am used to seeing the flange parallel or even a slight upwards angle when the frame is jacked up. thats what instantly told me somehting was wrong. the new gen 2 frames have 2 to 4 holes per flange with no explanation of which hole is for which configuration or rear end type. They're trying to build univeral frames for 4 link, 3 link and IRS set ups.

[NAZ]

This appears to be a Mustang four-link system. And the new revision chassis which I'm not familiar with so I can only give you some general advise that is applicable to suspension systems in general.

Using the LCAs to adjust pinion angle is not the correct way even if it would work. Using adjustable UCAs would be the correct way to set your pinion angle. I don't see adjustable UCAs in you photos so that would be the first thing I would change. You need to be able to adjust pinion angle or you will be bumping other areas to try and establish a correct relationship between the pinion angle and the trans output shaft angle. Using adjustable UCAs would give you that ability while leaving your LCAs for establishing your wheelbase. I suspect that the various holes for your LCAs can be used to adjust anti-squat -- not sure why else they would be there and that is an adjustment used to help with traction.

Never liked the FFR rear suspension design for the solid axle. Not nearly enough adjustment, and the angled LCAs are inefficient at transferring energy to the chassis which is why I designed my own for my car.

[Higgi56]

This appears to be a Mustang four-link system. And the new revision chassis which I'm not familiar with so I can only give you some general advise that is applicable to suspension systems in general.

Using the LCAs to adjust pinion angle is not the correct way even if it would work. Using adjustable UCAs would be the correct way to set your pinion angle. I don't see adjustable UCAs in you photos so that would be the first thing I would change. You need to be able to adjust pinion angle or you will be bumping other areas to try and establish a correct relationship between the pinion angle and the trans output shaft angle. Using adjustable UCAs would give you that ability while leaving your LCAs for establishing your wheelbase. I suspect that the various holes for your LCAs can be used to adjust anti-squat -- not sure why else they would be there and that is an adjustment used to help with traction.

Never liked the FFR rear suspension design for the solid axle. Not nearly enough adjustment, and the angled LCAs are inefficient at transferring energy to the chassis which is why I designed my own for my car.

so i think i found a problem. it appears when i built the shocks they were fully extended and I put the sleeves on the upper snap ring to make it a tight fit. it appears they should be built on the lower snap ring to make them shorter. however, i am befuddled why they would use such a long shock with such a short spring.

[michael everson]

In picture 9, I wonder if your front lower control arm bolts should be in one of the other holes in the mounting tab. That would bring the pinion up.
Mike

[GoDadGo]

If you need adjustable UPPERS and perhaps LOWERS then this may be a possible option:

https://www.spohn.net/shop/Factory-Five-Racing-MK3-MK4-Roadster/

I actually had SPOHN build shorter fixed lowers (16 7/8") for my MK-4 to bring the pinion up and to better center the wheels within the wheel arches.

https://youtu.be/CaRlqMmKIzk

Just understand that I'm running the 3 Link so I'm not sure how the adjustable uppers would impact and/or cure your issues.

Good Luck!

[Higgi56]

I compared the installed set up on the website versus mine and it appears i have shocks that are too long. this is pushing the entire rear end down. as can be seen in the pictures from the FFR web site the drivers side shock connection to the traction lok bracket is higher than the bolt holes in the bracket for the cross bar. in my set up the shock connection is below this location. Additionally you can see there is more shock body exposed. I double checked the bolt hole center to bolt hole center and it is 17.75", which agrees with the manual. I am wondering if there was a change between the Gen1 and gen2 design that has not been captured in the manual.

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[michael everson]

Keep in mind that your ride height is adjusted by turning the spring seat collar up and down. If you have it all the way up and tight against the spring, this might not be the proper ride height. the spring may even be loose when its jacked up. I would disconnect both shocks and then raise the rear until the lower control arms are approximately level and then check your pinion angle. This must be inline with the drive line within a couple of degrees. You need to solve that first. I suspect the front of the lower control arms need to be in the other set of holes further forward on the mounting plate.
Mike

[colsen23153]

I compared the installed set up on the website versus mine and it appears i have shocks that are too long. this is pushing the entire rear end down. as can be seen in the pictures from the FFR web site the drivers side shock connection to the traction lok bracket is higher than the bolt holes in the bracket for the cross bar. in my set up the shock connection is below this location. Additionally you can see there is more shock body exposed. I double checked the bolt hole center to bolt hole center and it is 17.75", which agrees with the manual. I am wondering if there was a change between the Gen1 and gen2 design that has not been captured in the manual.

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Have you solved your problem? I had this. I also have a axle with the calipers on the back of the axle. You need to mount the shock in the outside mount with thicker spacers.

[Higgi56]

yes, still have the problem.

Can you share pictures of your set up?

[sread]

Looking at your pics, it looks like your jack stands are under the frame and the rear end is hanging at full droop. You need to check it with the weight on the wheels. Move your stands under the rear axle and see how it looks.

[Higgi56]

Looking at your pics, it looks like your jack stands are under the frame and the rear end is hanging at full droop. You need to check it with the weight on the wheels. Move your stands under the rear axle and see how it looks.

I did that after moving the shocks to the rear mounts and loosening the springs. My wife and I sat on the frame with only stands under the rear axle and the driveshaft would still be hard of the frame by at least 2-3”.

[sread]

Yea , I see what you mean now - not even close. I agree with somebody earlier that said it looks like you need to try the other set of holes for the fwd end of the LCA. I am afraid you can't put too much faith in some of the specs in the manual - especially with the revisions on going and the transition to Gen 2 - may not be accurate.

[Jim Schenck]

Shoot me an email at jim(at)factoryfive(dot)com, I have a couple measurements I want you to take off of the axle. Have you talked to anyone here already?

[sethmark]

I have the same problem. It looks like a combination of a shorter rear shock and an adjustable upper arm would solve this issue.

[Higgi56]

Shoot me an email at jim(at)factoryfive(dot)com, I have a couple measurements I want you to take off of the axle. Have you talked to anyone here already?

Just sent you an email.

[Higgi56]

So it looks like I am getting adjustable UCA from FFR. Apparently there was a geometry change with the GEN 2 frame, but they had shipped out the older version of UCA.

Will update the thread after they are installed.