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Trim Variation from Torsion Bar Adjustment Bolt

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jsrivard Avatar
jsrivard Joel Rivard
Riverview, FL, USA   USA
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1968 MG MGC GT "Maggie"
As many of you know I completed my front suspension re-build recently. When I lowered the car back to the ground the trim height was 15.25" (Manual spec is 14" +- 1/4" if I remember correctly). I used the under car adjustment bolt but was only able to get 1/2" of trim out of it. Now I'm faced with dismantling the torsion bar and rotating it a notch or two and then tightening it back down so I can get the trim within spec.

How much variation should I expect out of the torsion bar adjustment bolt?

Would I be inviting bigger problems if I were to leave it .75" out of spec for a few months?

Thanks,
Joel



Cheers,
Joel

MGC Life Blog: http://rivardweb.com/MGC/
MGC "how-to's" available on YouTube: https://www.youtube.com/channel/UCDMf5tRcUOG0ueyizruhv5w/


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kirks-auto Robert Kirk (RIP)
Davenport, IA, USA   USA
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Joel,
You may wish to drive the car a few miles to insure all has settled in before making adjustments. 3/4 inch should be addressed sooner than later but in the short while, as I am given to believe you won't be driving much, I'd flex the car and suspension a bit before taking on the more daunting task of torsion bar rotation. You didn't happen to check this out prior to scope of most recent parts and work?



Regards,
Robert Kirk

kirkbrit@yahoo.com
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Business phone 563 323 1017

http://kirks-auto.com/
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jsrivard Avatar
jsrivard Joel Rivard
Riverview, FL, USA   USA
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1968 MG MGC GT "Maggie"
Robert, no, I didn't check prior to starting the job. If I try to get a mental picture of what my ride height looked like prior to the job I think it was a bit lower up front but it's so close I can't really tell.

I'll give it a few more weekend drives and then get back in there an make the adjustment. It'll give me a good chance to check the lower trunnion bushing as was mentioned in a separate post to see if there is any binding with the bushing sleeve. It'll also allow me to re-check the hub spacers/bearing shims and re-torque.

Regards,
Joel

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Cincinnati, OH, USA   USA
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1969 MG MGC
Hi,
Just a thought..... have you compared your tire size and tire inflation to the manual/stock rim & tire? It might be that the OEM tires were actually taller than today's common replacements exemplifying the issue in a negative way.
Bob K

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Cincinnati, OH, USA   USA
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1969 MG MGC
OOps. Ok, stop. I get it. From the hub. My mind went back 30 yrs ago when a bunch of us walked around a parking lot of MG's measuring the chrome strip to the ground. Senior Cramp - sorry.

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ron neal Avatar
Coastal, SC, USA   USA
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1962 MG MGA MkII
1968 MG MGC
1969 MG MGC
1969 MG MGC GT    & more
Bob
I see you have been burning up cyberspace with 5 posts in 7 years.
Glad you are back online. Hope its not too cold up north.
Ron

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chuckmosher Gold Member Chuck Mosher
Minneapolis, MN, USA   USA
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1953 MG TD
1961 Ford Ranchero
1962 MG MGA MkII "Othello"
1968 MG MGC GT "Tordos"
I had this same problem. Apparently 48 years of stress leave a bit of "memory" on those old bones. I did the same as you, refit the bar with a twist to make up the difference, but will replace in the spring.

Chuck

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m.s.macrae Murray MacRae
Wellington, Wellington, New Zealand   NZL
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1968 MG MGC
1994 Subaru Impreza WRX
2000 Subaru Outback "A Bit Of A Dog"
2008 Mazda 6
interested to know how you go with setting up.
as this is a common problem after a rebuild ie how was that set up before?
sometimes you rear will affect the measurement at the front how is it at the back?

Ill be pissin around at xmas sorting this with my bars from MG Motorsport.

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jsrivard Avatar
jsrivard Joel Rivard
Riverview, FL, USA   USA
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1968 MG MGC GT "Maggie"
I probably will not take on this task for a week or so but in order to adjust the torsion bar you can't just pop off the adjustment piece and rotate it because the whole thing is under load. I'll have to first support the lower trunion with a jack, pop off the front half of the lower a-arm, pull out the lower trunion bolt, lower the jack which will release the tension on the torsion bar. Then remove the bolt holding the torsion bar adjustment piece together at the rear and slide the torsion bar to the rear. Rotate the torsion bar a notch or two counter-clockwise for the right side of the car and clockwise for the left side of the car and then put the whole thing back together.

The issue I'm trying to work through in my head is how many notches to adjust the torsion bar to equate to .75" in trim height adjustment... I only want to do this once.

-Joel



Cheers,
Joel

MGC Life Blog: http://rivardweb.com/MGC/
MGC "how-to's" available on YouTube: https://www.youtube.com/channel/UCDMf5tRcUOG0ueyizruhv5w/

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m.s.macrae Murray MacRae
Wellington, Wellington, New Zealand   NZL
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1968 MG MGC
1994 Subaru Impreza WRX
2000 Subaru Outback "A Bit Of A Dog"
2008 Mazda 6
Joel,
You are so correct have done that many times on the old MM. when I rebuilt the rear springs...
But in answer to how to sort the amount of change to make.
Get the degrees per spline by dividing 360 by the number of splines. Then to get the lift per spline given the circumference of a circle drawn around the front pivot (lower arm) you have the distance in total. Divide that by 360 then multiply by the degrees associated with each spline calculated earlier. That will give you the lift or drop per spline.

IIRR the manual procedure should have worked though...ie to give you a suitable positioning of the rear lever.
Am travelling at the moment so wont be back home to check for a few more days yet. someone else that has done this with a better memory might chip in...

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blurtheline Platinum Member Art Jones
San Diego, CA, USA   USA
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1969 MG MGC
1969 MG MGC GT "My "C"
Hi Joel;

I'm actually at the point where I need to re-setup the torsion bars, and I didn't write measurements down before-hand either sad smiley

I'll be following comments to your post closely!

Regards, Art



Art Jones
San Diego, CA
69 MGC-GT - Maniflow headers and exhaust, triple Weber 40DCOEs, Alloy flywheel, Alloy wheels

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m.s.macrae Murray MacRae
Wellington, Wellington, New Zealand   NZL
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1968 MG MGC
1994 Subaru Impreza WRX
2000 Subaru Outback "A Bit Of A Dog"
2008 Mazda 6
One issue is if you have not got them both the same to start with you will potentially be "jacking" the car in one corner (racers worry about this issue a lot).

Perhaps we will end up doing it at about the same time I will start in 10 days approx.

Best wishes Joel.

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jsrivard Avatar
jsrivard Joel Rivard
Riverview, FL, USA   USA
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1968 MG MGC GT "Maggie"
Both the left and right sides are equal, but they are both .75" too much. I'm going to work through the calculations mentioned a few posts back tomorrow. I think I have worked out that there are 60 splines around the bar, although I may be off by a spline or two. It is hard to count with all the bits installed. Does anyone know for sure how many splines there are?

Regards,
Joel

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kirks-auto Robert Kirk (RIP)
Davenport, IA, USA   USA
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Email me Joel and I'll count them. I won't remember without an email.



Regards,
Robert Kirk

kirkbrit@yahoo.com
E-mail PLEASE for quote/questions/orders

Business phone 563 323 1017

http://kirks-auto.com/
Moss distributor/UK importer
Beat or match most retail/delivered quote

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jsrivard Avatar
jsrivard Joel Rivard
Riverview, FL, USA   USA
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1968 MG MGC GT "Maggie"
Disclaimer - all of the calculations here are based on 60 splines around the torsion bar. I tried to count them with the torsion bar in place which was quite difficult so I'm not sure my number is completely accurate.

I made the picture below to explain the math that Murray described above. Isn't trigonometry fun? The radius is the length of the lower a-arm from pivot point to the center of the lower trunion bolt, which happens to be 12" based on my tape measure and eyeball. If the 60 splines turns out to be true (Mr. Kirk has kindly agreed to count them for me) then adjusting the torsion bar by one spline should equate to a 1.25" adjustment in trim height.

This is where I get confused. The adjustment bolt should have plenty of adjustability to allow several splines worth of adjustment, however I was only able to get about .5" of adjustement turning the adjustment bold all the way to it's max from center. What I'm now thinking, based on a separate forum post, is that since I torqued all of the bolts before the suspension was under load, could the friction on the bushings be preventing the entire system from lowering the car any further? What I'm going to do to test this theory is jack up the car, loosen all of the pivot point nuts, then put the system under load and check the trim height again. I'm hoping that will solve my problem. I'll report back...

Regards,
Joel



Edited 2 time(s). Last edit at 2016-12-14 03:06 AM by jsrivard.


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