Questions on the fit of the Roadster Body over the rear wheels...

[Slider]

I've fit the body onto the MK4. The front and rear body mount bolts fit perfectly, and everything seems to be right where it should be. The wheels have been aligned (by me here at home, so while not perfect, aren't too bad). The spacing around the wheel wells on all the tires looks really good, except for the drivers side rear. I can barely get my finger between the tire and the wheel well on that tire (from top of tire to the back of the car). I'm running 15" tires, (295s). I've adjusted the panhard bar so that the tires are straight and spaced evenly on each side. I cannot for the life of me figure out why the tire is tight on that one side, nor how to adjust it. (The rear suspension ride height is an even 4.5" at each corner). Any ideas on what I can check, or adjust?

[frankeeski]

This is really one of those issues that needs pictures. While the roadster body is NOT symmetrical, is is reasonably close from side to side. There have been a few instances in the past where the wheels just do not fit in the wheel wells but seeing exactly what you are experiencing will make it much easier for us to help you resolve the issue.

[Jeff Kleiner]

Like Frank said, pics or a better description of the issue would help. Are you saying the wheel is not centered in the body opening? If this is the case what is your pinion angle set at? We had a builder with a similar issue a year or so ago and after much discussion and measuring it turned out to be that his upper link (and consequently pinion angle) was way out of range. This allowed the axle to pivot from the lower control arm moving the wheels out of the center of the body openings. Simply adjusting the upper link to set the proper pinion angle brought it into place. Yeah I know, logic says if the axle is pivoted too far forward or rearward it would affect both sides and in the case mentioned above it did but it was much more visible on the driver's side.

Good luck,
Jeff

[Slider]

Thanks Guys. I'll get some pictures up shortly. I did set the pinion angle to the prescribed angle (or thought I did). I will re-check that as well. Pictures to come shortly.

[tcoon]

The chassis and body are not always symmetrical. Sometimes you have to use the panhard bar to adjust the axle so the wheels fit the opening. A small adjustment side to side makes a big difference in how the tires fit.

[Slider]

Here are the pictures. The side with the blue tape just above the wheel well is the drivers side, and the side in question. The other side is therefore the passenger side rear, and seems quite fine. On the drivers side I can barely get a finger between the tire and the body.

1663216633


Thanks Guys. I'll get some pictures up shortly. I did set the pinion angle to the prescribed angle (or thought I did). I will re-check that as well. Pictures to come shortly.

[CraigS]

Wow, that does seem off. Only thing I can think to to explain the difference side to side is how the adapter brackets are attached to the axle. As mentioned above, pinion angle has an effect, but that would move both sides equally. I guess it also wouldn't hurt to measure the L and R LCAs length to be sure one isn't longer than the other by some jig/welding error.

[Jeff Kleiner]

Very much like what mirose experienced (8 or more pages worth of reading on the other forum if you care to search for it but in a nutshell he could have saved himself a whole bunch of frustration by simply adjusting the pinion angle from the get-go). Sooo, just to be sure why don't you doublecheck that pinion angle---front of the pinion 1.5 to 2 degrees down relative to the trans output shaft/crankshaft.

Good luck,
Jeff

[Slider]

Jeff (and Craig), thanks for the replies. I went to the Mott Build school and in the course they noted a 2 degree UP adjustment on the pinion angle. I suspect that they are saying the same as you, but perhaps I've misinterpreted what "UP" means. Could you just define how you are defining "Down?" and how/where you are measuring. I had the gauge on the driveshaft. Thanks. I feel like I'm close to getting this solved, and will definitely double check the pinion angle.


Very much like what mirose experienced (8 or more pages worth of reading on the other forum if you care to search for it but in a nutshell he could have saved himself a whole bunch of frustration by simply adjusting the pinion angle from the get-go). Sooo, just to be sure why don't you doublecheck that pinion angle---front of the pinion 1.5 to 2 degrees down relative to the trans output shaft/crankshaft.

Good luck,
Jeff

[Jeff Kleiner]

I think we've found your problem!

It sounds like you have the front of the pinion pointed up which is backwards. When the upper link is adjusted to bring the front of the pinion up the rear axle pivots about the lower control arm mounting point and as it does so the center of the wheels move rearward---I believe this is what you are experiencing.

If you had the gauge on the driveshaft you were looking at driveline angle, not pinion angle. The driveline angle is not part of the pinion angle equation. When we speak of pinion angle we are referring to the pinion shaft relative to the transmission's output shaft. When determining pinion angle you can leave the driveshaft on the workbench, and in fact if you follow my method described below it will be easier if you do just that :)

Don't get caught up or confused on any thoughts of horizontal. Think of it this way; when looking at the car from the side if you were to project one line from the transmission output forward and another line from the pinion shaft forward with your pinion angle at zero they would be parallel. If you put any angle to the pinion the two lines are not parallel and would get farther apart as they go forward. If the pinion were to be angled UP (relative to the trans) it's line would be above the output line; if it were angled DOWN the pinion line would be below. Below is what we're after. Clear as mud?

My method for ease of measurement:
Set ride height then put the car on jackstands so that the axle is loaded. We don't care if the frame is dead nuts level; we're only going to look at the difference between output shaft & pinion. We know that the crankshaft and trans output shaft are parallel therefore the face of the damper/ crank pulley is perpendicular to the output. We also know that the pinion flange face is perpendicular to the pinion. See where I'm heading? For me it is easier to get a good measurement with the magnetic angle finder by reading vertically on the crank pulley/ damper and pinion flange rather than trying to work with the horizontal shafts themselves. Once you can see the two angles you can then calculate the difference. Generally with these cars we want the pinion down ~1-2 degrees (once again, meaning the input is pointing down in relation to the transmission output shaft). Reason being is so that when the axle tries to rotate it's input upward under accelleration the pinion angle becomes less. This rotation is especially more pronounced on a 4 link car using the soft rubber bushings in OEM Mustang arms vs. a 4 link car with poly bushings or a 3 link with polys in the lowers and the solid upper link.

Three link adjustment is easy; simply alter the length of the upper link. If your pinion is pointing up as I suspect that would mean shortening it. Doing so will bring the wheels forward and I bet when you get to the proper pinion angle they will be more visually centered in the wheelwells.

Hope that all makes sense and good luck!

Jeff

[Ringo]

Jeff thanks for posting that, I had mine pointing up. I will fix it before the first start. It gets old going back and redoing stuff but easy to do it now.

[Slider]

BINGO! Set the pinion angle correctly and the problem is solved. Thanks so much. As someone else commented, it is getting old having to redo work, but I'm getting good at it. I think we've built this car about 3 times already. :-)


I think we've found your problem!

It sounds like you have the front of the pinion pointed up which is backwards. When the upper link is adjusted to bring the front of the pinion up the rear axle pivots about the lower control arm mounting point and as it does so the center of the wheels move rearward---I believe this is what you are experiencing.

If you had the gauge on the driveshaft you were looking at driveline angle, not pinion angle. The driveline angle is not part of the pinion angle equation. When we speak of pinion angle we are referring to the pinion shaft relative to the transmission's output shaft. When determining pinion angle you can leave the driveshaft on the workbench, and in fact if you follow my method described below it will be easier if you do just that :)

Don't get caught up or confused on any thoughts of horizontal. Think of it this way; when looking at the car from the side if you were to project one line from the transmission output forward and another line from the pinion shaft forward with your pinion angle at zero they would be parallel. If you put any angle to the pinion the two lines are not parallel and would get farther apart as they go forward. If the pinion were to be angled UP (relative to the trans) it's line would be above the output line; if it were angled DOWN the pinion line would be below. Below is what we're after. Clear as mud?

My method for ease of measurement:
Set ride height then put the car on jackstands so that the axle is loaded. We don't care if the frame is dead nuts level; we're only going to look at the difference between output shaft & pinion. We know that the crankshaft and trans output shaft are parallel therefore the face of the damper/ crank pulley is perpendicular to the output. We also know that the pinion flange face is perpendicular to the pinion. See where I'm heading? For me it is easier to get a good measurement with the magnetic angle finder by reading vertically on the crank pulley/ damper and pinion flange rather than trying to work with the horizontal shafts themselves. Once you can see the two angles you can then calculate the difference. Generally with these cars we want the pinion down ~1-2 degrees (once again, meaning the input is pointing down in relation to the transmission output shaft). Reason being is so that when the axle tries to rotate it's input upward under accelleration the pinion angle becomes less. This rotation is especially more pronounced on a 4 link car using the soft rubber bushings in OEM Mustang arms vs. a 4 link car with poly bushings or a 3 link with polys in the lowers and the solid upper link.

Three link adjustment is easy; simply alter the length of the upper link. If your pinion is pointing up as I suspect that would mean shortening it. Doing so will bring the wheels forward and I bet when you get to the proper pinion angle they will be more visually centered in the wheelwells.

Hope that all makes sense and good luck!

Jeff

[Jester]

BINGO! Set the pinion angle correctly and the problem is solved. Thanks so much. As someone else commented, it is getting old having to redo work, but I'm getting good at it. I think we've built this car about 3 times already. :-)

Very good post - I will be checking and tweaking my adjustment accordingly. This should be copied to the tech update section for future reference.

Thanks and good luck with the rest of your build

[CraigS]

Can you post a couple of pics of the "after" result for us please?

[Ringo]

I have a question. What down angle do you like to see on the motor transmission, and do you pull the back of the transmission over so it lines up with the rear?

[FFinisher]

I think we've found your problem!

It sounds like you have the front of the pinion pointed up which is backwards. When the upper link is adjusted to bring the front of the pinion up the rear axle pivots about the lower control arm mounting point and as it does so the center of the wheels move rearward---I believe this is what you are experiencing.

If you had the gauge on the driveshaft you were looking at driveline angle, not pinion angle. The driveline angle is not part of the pinion angle equation. When we speak of pinion angle we are referring to the pinion shaft relative to the transmission's output shaft. When determining pinion angle you can leave the driveshaft on the workbench, and in fact if you follow my method described below it will be easier if you do just that :)

Don't get caught up or confused on any thoughts of horizontal. Think of it this way; when looking at the car from the side if you were to project one line from the transmission output forward and another line from the pinion shaft forward with your pinion angle at zero they would be parallel. If you put any angle to the pinion the two lines are not parallel and would get farther apart as they go forward. If the pinion were to be angled UP (relative to the trans) it's line would be above the output line; if it were angled DOWN the pinion line would be below. Below is what we're after. Clear as mud?

My method for ease of measurement:
Set ride height then put the car on jackstands so that the axle is loaded. We don't care if the frame is dead nuts level; we're only going to look at the difference between output shaft & pinion. We know that the crankshaft and trans output shaft are parallel therefore the face of the damper/ crank pulley is perpendicular to the output. We also know that the pinion flange face is perpendicular to the pinion. See where I'm heading? For me it is easier to get a good measurement with the magnetic angle finder by reading vertically on the crank pulley/ damper and pinion flange rather than trying to work with the horizontal shafts themselves. Once you can see the two angles you can then calculate the difference. Generally with these cars we want the pinion down ~1-2 degrees (once again, meaning the input is pointing down in relation to the transmission output shaft). Reason being is so that when the axle tries to rotate it's input upward under accelleration the pinion angle becomes less. This rotation is especially more pronounced on a 4 link car using the soft rubber bushings in OEM Mustang arms vs. a 4 link car with poly bushings or a 3 link with polys in the lowers and the solid upper link.

Three link adjustment is easy; simply alter the length of the upper link. If your pinion is pointing up as I suspect that would mean shortening it. Doing so will bring the wheels forward and I bet when you get to the proper pinion angle they will be more visually centered in the wheelwells.

Hope that all makes sense and good luck!

Jeff



Wow. ..............


Nice Job Professor Howell.!!!!!

Very impressive.

[Slider]

Here are the "After" pictures. Big Difference.

1665016651
Can you post a couple of pics of the "after" result for us please?

[CraigS]

Ringo, to add to the above w/ respect to your question about the trans. Don't get too worried about the left/right location of the trans. It would be real difficult to measure the left/right angle relative to the diff and i have never read anything about this being an issue.RE: up/down trans position. This has more to do w/ suspension (3 or 4 link)up/down travel and making sure the driveshaft doesn't bind when the axle moves. Don't worry about it too much either until you have finalized rear ride height. A general comment about diveshaft alignment. The diff and the trans ideally should be parallel. They can be offset to the left/right or up/down but should always be parallel. The reason that we in the FFR community use the diff 2 deg. down angle is that, as you accelerate, the front of the diff rises. W/ rubber bushings it rises the most, w/ rodends it rises the least, but it always rises somewhat. None of this matters much when the car is just cruising w/ little load, but gets important when accelerating hard.The 2 deg down, is a good guess so that, as the diff rises during hard acceleration, the angle will become the ideal zero.HTH

[Ringo]

Thank You for the help?