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TR6 Suspension Rebuild and Drive Shaft Replacement - Lessons Learned


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Having spent several days over-hauling the rear suspension and replacing the drive shafts of my 1970 Six, I thought I’d write down a few notes of lessons learned.  Had I thought about writing this before I started work on the back end then I would have had some pictures to illustrate it.  Sadly, I didn’t have such foresight!

 

Trailing Arms:  These had probably been untouched since they were fitted to the new chassis in the early 90’s when the car was restored.  After removing springs and drive shafts I was surprised how much effort was needed to make them pivot around the mounting brackets; they were solid with the rubber bushings and bolts well seized. Long story short, stripped, cleaned, painted and poly bushes fitted with new hardware.  Note about the poly bushes – they are supposed to be a snug fit in the lugs of the trailing arms.  School boy error by me as I used silicone grease to aid the fitment of the bushes, such that once the lip was in the lug they pushed in very easily.  I discovered the consequence of that after I’d finished everything and took it for a drive.  The trailing arm on the off-side (OS) had moved hard inboard on the bushings such that inboard lug was against the mounting bracket because the bushing top hats had been forced into both lugs.  Took it off again, removed the bushings.  Noticed that the rebate in the lugs in which the bushing top hats was supposed to sit was rounded/smooth and not clearly defined such that it was making a very easy path for a greased bush to move in.   I carefully worked the ends of the lugs with files hand/rotary to get a sharp rebate.  Then refitted the bushings with StixAll (Hybrid PMS polymer technology adhesive/sealant from ToolStation) that provided lube for installation but also importantly fixed/bonded the bush to the lug.  The steel insert was fitted with silicone grease – as it needs to be free because that’s the pivot – and the hardware was installed with copious amounts of Copper Grease.  Torqued the pivot bolt/nuts when the wheels were on the ground.

Coil Springs:  Here lay a real surprise, in that near-side (NS) spring was 1/2” shorter than its opposite number and to make up for it the shorter spring had 5/8”red poly bush spacers and the longer OS spring had a very thin and frail black rubber insulators.  Springs were replaced with a pair of 450lb new ones complete with new poly bush spacers.

Lever Dampers:  I had toyed with the idea of replacing these with shocks and associated bracketry – but having read more on it I decided maybe they were just in want of a bit of attention; and it’s a relatively easy update if I decided to do it a future date. After removal from the chassis the top covers and the taper valves were dismantled, and the bodies were flushed out with paraffin and then clean oil.  Finally filled with Penrite No.2 Lever Oil which should give a slightly firmer effect.  I couldn’t get replacement gaskets for the top covers so had to make new ones from cork sheet. Note that the taper valve has a washer/spacer that sets the bump/force of the damper; make sure you have the same number of washers on both sides. On mine it was one/side but it’s possible to add additional spacers and that increases the force required to move the arm.  The links from trailing arms to lever arms were worn and so were replaced with new standard items.  

Drive Shafts:  One of the main reasons to undertake this backend rebuild was a clunk (not alarming but there nevertheless) from the back which I suspected was coming from one or both shafts. On removal it was apparent that the splines had not seen any grease for the best part of 25 years and although they still slid there was undue resistance/binding.  The bolts holding the inboard flange of the shaft to the flange on the diff were lose which I now understand is a very common issue; note to self to tighten them every year from now on.   The Universal Joints (UJ’s) seemed okay with no noticeable play in them.  Having gone this far I was left with a shaft decision; rebuild possibly with overhauled hubs – or replace outright with Constant Velocity (CV) jointed shafts.  After much forum reading and navel scratching, I bit the bullet and decided on CV’s.  Not to everyone’s taste – but looking at the pros and cons of both for me the CV’s came out on top.  Chose the Classic Driving Development (CDD) CV shafts and I am very pleased with the quality and fit and it was good to talk directly with Alasdair Southall at CDD;  he left me feeling very confident of the support available if at a future date there is an issue.   Note you need a hefty TQ wrench for the CDD CV shafts as they need to be tightened to 215 lbf ft.  

Brakes:  One of the cylinders had been weeping – nothing major – but nevertheless time to reseal.  That’s when I found a mismatch on the size of cylinders fitted; on the NS I had a 0.875” (22.25mm) Girling cylinder and on the OS a 0.7” (17.8mm) Delph cylinder.  I assume this would have resulted in a mismatch in braking efficiency so not sure why it never got picked up by MoT’s.   New TRW GWC1154 cylinders have now been fitted and the old tendency of pulling to the NS on heavy braking is now but a memory!

Conclusion:  The ride is significantly improved (no chattering of teeth) and it handles much better than before which shouldn’t be a surprise as the trailing arms were effectively acting as dampers, so the back end was pretty solid.  Not sure if the poly bushes are better for ride than rubber, but they should outlast rubber and save me having to do them again.

With a combination of solid trailing arms, odd springs, dry splines and different size brake cylinders I’m amazed I have put 8K miles on it in the last 5-years without incident.

Looking forward to some COVID free touring in 2021 as 2020 has been a disaster.

 

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Good write up about your experience doing this rear end rebuild. 

Hope it's not long before you/ we can all enjoy driving our TR's properly again. 

Gareth

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I have just been completing a rear end update, new blue bushes, need to rebuild one rear hub with new bearings, I have welded up the grooves in the brake back plates as well.

I would be very interested to know what positions the trailing arm brackets have been set to on cars that people have just rebuilt the rear. Is there a typical starting point and what have they finished up with having done some alignment.

I know about the Buckeye article, but interested to know where abouts the brackets are set, if there is a common trend.

John

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Thanks Mikael,  It looks outside 1up and inner 2 up or is it three? Its the bracket positions I'm after.

One comment I may make,  I think its better to put the long bolts in from the inside, when the body is on you wont be able to get the long bolts out as they are now.

John

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Brackets on my Six are one notch "up" innner and two notches "up" outer.  I understand that later cars may be three notches "up" inner and one notch "up" outer.  That said, you can have multiple options of notches and brackets fitted "up" or "down" to play with camber. 

Re tracking shims, mine had two under each bracket.  Changed Off Side(OS) to correct previous toe-out to 2 shims inner and 1 shim outer, and changed Near Side(NS) to correct previous toe-in to 2 shims inner and 3 shims outer.

I still need to get alignment and camber garage checked, but string and iPhone with Mk1 eye-ball tell me its close enough for the time being.

Re mounting bolts, I assembled with both bolt heads inboard.

Adrian

Edited by Adrian Steele
Correction to bolt orientation
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The hub nut gets torqued to 215 lbf ft.  On CDD shafts its not a nyloc, but the nut has a collar on the nut that is peened in three places to grip the exposed threads on the shaft so its effectively a metal locking nut; see rubbish sketch!

I had to remove the OS shaft so ended up refusing the locknut - may not be best practice but I re-peened the original three lock marks and there was good resistance on refitting so happy that it locks.  I'll check re-torque everything next week (about 100 mile since fit) and I don't anticipate any movement.

2C621CCD-669D-4CBB-853C-5AFBE0528D01.heic

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On 12/22/2020 at 5:05 PM, John L said:

I have just been completing a rear end update, new blue bushes, need to rebuild one rear hub with new bearings, I have welded up the grooves in the brake back plates as well.

I would be very interested to know what positions the trailing arm brackets have been set to on cars that people have just rebuilt the rear. Is there a typical starting point and what have they finished up with having done some alignment.

I know about the Buckeye article, but interested to know where abouts the brackets are set, if there is a common trend.

John

all our chassis can be different over the years and trailing arms a little twisted/ bent so no standard notches or shims for us .

Use the buckeye article and you can overcome these and obtain your required settings.

Roy

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