Control arm length

9

90FoxLX

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Dec 12, 2023

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Dec 27, 2023

#1

• Dec 27, 2023

• #1

Hi all, I am assembling a 1.5” & 1” lowering kit and BMR UCAs and LCAs on my 1990 LX Convertible. On LMR, where I get all my parts, they say to basically match up control arm lengths and use the lock nut to set it at that length. My UCAs were able to match up fine but the new BMR LCAs are about 1.5”-2” longer than the ones that were on it. This will drastically change the pinion angle I would assume. I have the car up on stands and I’m waiting for a few more parts before completely assembling everything, but my question is, how am I supposed to counter the difference in the lengths of the LCAs? I think I will have to lengthen my UCAs but I also have to consider it being lowered. Is there a way of getting a rough estimate of how much I will need to adjust the UCAs to get the ~2 degree pinion angle? Also if my adjustments were off could it possibly push on my driveshaft putting lots of load on the trans/yolk? Would I be better off taking the driveshaft completely off and using rope or something similar to try and find angles first? Before lowering to the floor and putting everything under load. Hopefully my explanations make sense and sorry for the lengthy post.

 

AeroCoupe

lube between the nut and the face. I know my lubes

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#2

• Dec 29, 2023

• #2

You posted in the wrong section (94/95 cars vs the 79-93 cars) so hopefully on of the mods can move it. Ca you be more specific as to which BMR’s you ordered? Seems they have several adjustable control arms.

 

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90FoxLX

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Dec 29, 2023

#3

• Dec 29, 2023

• #3

You’re right, my bad I was looking for some 94-95 spindle info. I’m terrible with Forums. The UCAs are BMR part #UTCA040 on car adjustable control arms and the LCAs are BMR part #TCA049 single adjustable. On LMR where I buy my parts they didn’t say that they were on car adjustable but on the BMR website I see they say they are. Makes sense they would be. I may have to get some Race Ramps to be able to get under the car and make adjustments after it’s lowered.

 

AeroCoupe

lube between the nut and the face. I know my lubes

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#4

• Dec 29, 2023

• #4

Okay, 79-04 control arms are all the same length but the rear bolt diameter in the LCA’s changed in 1999.

The rear stock control arms measure 17 5/8 lower and 9 1/4 upper center to center. Will yours get to that length?

 

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90FoxLX

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#5

• Dec 29, 2023

• #5

I did what LMR said on their install video and tried to match the control arms to what was on the car using bolts through the bearing and bushing holes. The measurements I just got were:
Before new Control arms:
UCA-9 1/4”
LCA-16 1/2”
New control arms:
UCA-9 1/4”
LCA-17 1/4” (bottomed out)
I had the transmission put in and driveshaft cut professionally so I’m assuming he had the 2 degree angle. If the LCA is going to go from 16 1/2” to 17 5/8” is there a way to calculate the difference needed to make up for it on the UCA? Hopefully I’m explaining it right.

 

AeroCoupe

lube between the nut and the face. I know my lubes

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#6

• Dec 30, 2023

• #6

So in a true four link lengthening the LCA”s will drive the nose of the pinion down. To counter this the UCA’s will need to be lengthened.

Do you have a way to measure pinion angle? Was the tire centered in the wheel well with the old control arms?

 

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90FoxLX

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#7

• Dec 30, 2023

• #7

AeroCoupe said:

So in a true four link lengthening the LCA”s will drive the nose of the pinion down. To counter this the UCA’s will need to be lengthened.

Do you have a way to measure pinion angle? Was the tire centered in the wheel well with the old control arms?

Click to expand...

I do have an angle finder. It looked centered when I started this. The last time anyone touched the driveshaft would have been the transmission shop. The only problem I’m seeing now is that I have it on stands, so what angle would I be looking for that’s not under load? I took all control arms off yesterday to remeasure and try to figure out a way of getting close then go from there.

I measured the distance (with the BMRs how they were) between front of wheel well to axle then axle to rear of well and it was and it was about 13 1/2” and 16”. I know that needs correcting too.

Also I have 94-95 sn95 spindles I took in yesterday that won’t be back from sandblasting for another 4 weeks so I won’t be able to lower it and check angles under load for a bit.

 

KRUISR

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Apr 16, 2015

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#8

• Dec 30, 2023

• #8

To put the rear under load and check your angles, with everything in the rear assembled jack up the rear and move the jack stands to under the axle tubes. All the rear weight will be on the suspension. To have the weight on the front in the right location, move the axle stands to between the front control arm mounts on the k-member. This way everything should sag the way it would be on the ground. Check/adjust your LCA/UCA as needed. Then check the driveshaft length (as I would expect they didn't adjust pinion angle before measuring for length).

By doing this you can also put your tires on and see how they fit in the wheel well.

 

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90FoxLX

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#9

• Dec 30, 2023

• #9

I was trying to figure out a way of doing that but wasn’t sure if it would be accurate. I will give it a shot. At least it will be half assembled when I get my spindles back.

I have an issue with my K Member also. I had my motor remounted a few years back by a very reputable shop but the 6 quart oil pan is touching the K Member. I haven’t driven it because of this. I plan on going BMR everything and getting a tubular K Member but I’m not sure if I can tackle that myself. It will at least need to be able to be trailered to the shop.

 

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2000xp8

SN Certified Technician

Aug 8, 2003

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NJ

Dec 30, 2023

#10

• Dec 30, 2023

• #10

Any particular reason why you purchased this set?
Probably good for a drag race car, but otherwise they just add complication to an uncomplicated situation.
I'm definitely not about heim joints on regular street cars either.
For the same or close to the same price you could have simply just used maximum motorsports control arms and just slapped them in and been done with it with no metal on metal connections or worrying about pinion angles or adjustments.
Are they still returnable?

 

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90FoxLX

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#11

• Dec 30, 2023

• #11

No definitely past the return date. I honestly didn’t know MM had a set that would just go on without adjusting. It started out as a drag car project but now I was just thinking rebuilding what I haven’t gotten to yet. I’ve been going with all BMR suspension products. I know spherical bearings cause more NVH but will it be so bad that I’d be better off getting new control arms? I have BMR front control arms too, so I pretty much went with all BMR products.

 

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90FoxLX

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#12

• Dec 30, 2023

• #12

I’ll admit I didn’t have previous experience with car suspension but I have rebuilt my dirt bikes engines and suspension for years so I felt like I could get it figured out.

 

AeroCoupe

lube between the nut and the face. I know my lubes

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#13

• Dec 30, 2023

• #13

So with all of that I would put the BMR’s at the stock lengths I have you, install them, load the suspension like KRUISR suggested, see what your angles are and post that up. You should be able to use just the UCA’s to adjust the angle and in all honesty I seriously doubt your DS will have any issues. Most shops say you want about 3/4” of yoke sticking out of the rear of the trans with the suspension loaded.

 

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90FoxLX

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Dec 30, 2023

#14

• Dec 30, 2023

• #14

Alright I’ll set them to stock length now and see where it’s at under load and go from there.