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Rear camber adjustment on IRS cars


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I recently noticed excessive inside shoulder wear on both rear tyres. I had the alignment and geometry checked with the car loaded as per manual and we found 2deg 13 min -ve on the near side and 2 deg 24 min -ve on the off side, the spec being 1 deg -ve +/- 30 mins. The rear toe-in was set a little over spec to try and even the wear across the tread.  I had two new rears fitted and within 2,500 miles can already see uneven wear. I was looking at adjustable trailing arm brackets but have been advised first to try raising the ride height by fitting spring spacers. Has anyone successfully reduced negative camber by this means and does anyone have an idea what total thickness of spacer I should try in order to give 1.5 degrees more +ve camber? I have standard size 165x80 R15 tyres. My car does not look to be riding low at the rear. I have about 60mm between top of each rear tyre and the wheel arch lip when the car is static laden (the tyres are well inside the wheel arches of course). An increase of 25mm or so in ride height would not look out of place and would even be of benefit in reducing instances of silencer scraping.  

Tim 

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Do I read that you increased toe in to reduce wear on the inside edges?  I’m not sure what you meant by over spec. If so that’s back to front. 

 

No, it’s not, I’m wrong here. 

Edited by peejay4A
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No, I meant toe-in. The advice of the fitter was that since the rear camber could not be adjusted as my car is fitted with the standard TA mounting brackets if toe-in were set a bit higher than spec it would even wear out a bit more across the tread. Specifically I have a total rear toe-in of 28'  against a spec of max 16'.

Tim

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Hi Tim,

There are three different brackets that hold the TA in place each can be fitted in two directions (up or down) the combinations are extensive (have alook at the Buckeye site for what to do)

If you have a lot of negative camber with the car correctly loaded then it is the camber that needs correcting.

Toe-in is not greatly affected  by the loading.  There are shims between the TA brackets and the chassis that correct Toe-In.

Indeed raising the chassis will reduce the camber.

Roger

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 A shim under the spring will raise the chassi ride height a bit more than the shim thickness Draw an imaginary line thorugh the t/a pivots and measure at right angles to the cnetre of the spring recess, and again at right angles out to the wheel cnetre, The ratio times the shim thickness gives the ride height gain.

The  chassis ride height increase will increase the angle of dangle of the t/a,  reduce the camber and increase toe-out. Geometry will give the answer. A vertcial line through the wheel centre has afixed relation with the t/a angle of dangle, giving the camber change. And a horixontla line the toe, which as Roger says wont change much at all. SO pick a shim thickness. measure the exisitn angle of dangle ( car loaded of course) and calcualte the rest.

Peter

 

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Thanks Peter. Can you tell me the direct relationship between ride height and camber, i.e Xmm increase in ride height = Y degrees decrease in negative camber? It's a long time since 'O' Level geometry!

Roger - I have struggled through the Buckeye item you mention in the past. Frankly life's too short and I can't be a**ed to try all brackets in all orientations to achieve desired result, I would rather go to the  expense of adjustable brackets if necessary but will try spring spacers first.

Tim

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Hi Tim,

there is no doubt that sorting out the TA brackets is not a quick job. But the process is quite do'able usng the Buckeye information.

Measure the ride height at the top of the wing through the vertical centreline of the wheel

See what brackets you already have

Check the existing camber

Select the new brackets

easy peasy  (dream on)

 

The adjustable brackets are for sissies

 

Roger

 

 

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Hi Tim, Is the rear spring bridge straight and solid,? Has it been reinforced at the ends, it could be bent or bending under load. Has the excessive camber always been there or has it developed over time, or suddenly happened? 

Chris

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Just to cap off the toe in aspect. If you give it too much you’ll wear the inside edges of the tyres even more (edit: no it doesn’t). I can’t see how increasing toe in can correct for excess negative camber (still true).

In spite of adjustable TA brackets being sissy I’ve fitted them and it saves no end of f@rting around swapping brackets, turning them upside down etc etc. 

 

Edited by peejay4A
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Don't shoot the messenger Pete, I was just passing on what the fitter told me. He is really into classics and seemed to know his stuff, he took great pains to get exactly the same toe in each side at the front.  I am talking about Discount Tyres at Hemel Hempstead, not the first place I would have thought about taking the TR but I went there on strong recommendation of Harry Dent.

Tim

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11 hours ago, tim hunt said:

Thanks Peter. Can you tell me the direct relationship between ride height and camber, i.e Xmm increase in ride height = Y degrees decrease in negative camber? It's a long time since 'O' Level geometry!

 

Tim

Tim, Very long time for me too.  The chnage in t/a angle does nto directly translate to a wheel ange, which I forgot eaarlier.  Easiest way is to fit a say 1cm shim and see. Or jack uo the rear to anew chassis height and measure the camber change, while ensuring the tyre can slide.

Peter

Edited by Peter Cobbold
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2 hours ago, tim hunt said:

Don't shoot the messenger Pete, I was just passing on what the fitter told me. He is really into classics and seemed to know his stuff, he took great pains to get exactly the same toe in each side at the front.  I am talking about Discount Tyres at Hemel Hempstead, not the first place I would have thought about taking the TR but I went there on strong recommendation of Harry Dent.

Tim

Not shooting at you Tim so I’m sorry if it came across like that. In fact I’m wrong and excess toe in causes wear on the outer edges, brain fade. That said I wouldn’t be happy correcting one fault by effectively applying another. 

Edited by peejay4A
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Hi Tim,

For rear wheel TA camber correction, I would use the not so scientific method:

1) Measure the camber with a straight edge (in mm, which you can calculate back to degrees). Make sure the rim is true. If not, take a 2nd measurement with the car rolled exactly  “half a wheel” further.

2) Fit an additional spacer under the spring, roll the car couple of meters back and forth  so it is in the same spot, and bump the rear so the suspension settles.

3) Measure the effect on camber with a straight edge vertical on the rim and calculate the required spacer.

Make sure the wheel is in the same position on the floor (mark it with a dot at 12 ‘o clock and mark the floor), and also mounted on the same position on the drum when removing/installing the wheel.

It’s not easy, but doable.

Regards,

Waldi

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I reckon that's a bit strong. What makes you think my suspension is worn out? At last  MOT two weeks ago tester gave no advisories and actually mentioned he found no play anywhere and commented on the polybushing all round. OK maybe rear springs have settled a bit but that's remediable.

Tim

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Interesting. Went through this very process last weekend. While on the 10CR (alongside Tim Hunt).  We noticed that a lot of the TRs seemed to be running excessive camber. My own 6 didn't look to bad. However I had to take the rear suspension appart when I got back to fit CV axles and helicoil (had bought the jig when I was in the US) the studs in the trailing arms (mountain passes + supercharger stresses the system somewhat). I also measured camber and it was 2.5 degrees.  I had some adjustable trialing arm mounts in stock so I fitted them.  Adjustment back to spec was super simple.very much recommended. 

Cheers Tim

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Interesting Tim. Did you fit the all singing all dancing brackets that handle toe and camber or those that allow camber adjustment only, still relying on shimming to adjust the toe? You don't have a second set of adjustable brackets in stock for sale do you? Good call to helicoil the TA brackets for the hub mounting. I did mine 45+ years ago, drilling and tapping for 5/16 BSF studs and they are still taking the specified 14lbs ft torque no problem. On acquiring the car inn 1970 we found that several of these threads had been stripped and one hub was hanging on by a wing and prayer!

Tim

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Hi Tim,

Sorry my terminology was a bit misleading. When I said "stock"  meant my one personal stash of spares.  Fitted the camber only brackets.  Think the shims are easy to change for toe in. When I went to fit helicoils is discovered that 1/4 of them had already been done!

Tim

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Found this on the Goodparts website:

"TR6 Rear Camber Adjustment

Lowering the rear ride height of a TR6 will increase the negative camber. This may be corrected by changing the “U” brackets mounting the semi-trailing arms. Three different brackets were used to adjust the height of the pivot bolt in relation to the mounting bolts to the frame. The brackets are marked by one, two, and three notches cut into the edge. When the brackets are mounted with the notches turned up, the pivot bolt will be offset from center approximately as follows: one notch: down 1/8”, two notch: up 5/16”, three notch: down 9/16”. Early cars used an inner bracket with one notch turned up and an outer bracket with two notches turned up. Turning the inner bracket to locate the notches on the bottom will raise the inner pivot bolt ¼” and reduce negative camber by approximately 1 degree. Further correction can be made by replacing the inner bracket with a two notch on top to raise the inner pivot or by replacing the outer bracket with a one notch on the bottom to lower the outer pivot. Later cars mounted the whole trailing arm a bit lower on the frame by using an outer bracket with one notch on top and an inner bracket with three notches on top. Again, negative camber can by reduced by lowering the outer pivot bolt or by raising the inner one. Keep in mind that your ride height will be effected by the average height of the pivot bolts in relation to the frame. Raising the pivot bolts brings them closer to the upper spring seat and increases the ride height.

When the rear ride height of a TR6 is lowered it is recommended that the bump stops on the semi-trailing arms be shortened. Thread the rubber bump stop out of the raised post on the semi-trailing arm then carefully draw a line around the post and ribs at the level where it is to be cut. Up to one inch may be removed. Saw the post off with a hacksaw taking care to cut on the line to maintain a level pad. Drill 21/64 and tap 3/8-24 deeper if necessary then install the rubber bump stop" .

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Strange comment.. machanisms that allow continuous adjustment are always superior to discontinuous. Or would you rather a torque wrench that only did 10, 20 and 40 ftlbs rather than 10-40 continuous

Tim

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