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rear leaf spring troubles -- 2nd gen


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#1 fireforeffect

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Posted 14 May 2020 - 02:37 PM

In the process of installing a set of Detroit Speed 2" drop leaf springs in the back, appears to be the 1st time anyone has done anything to my '78 WS6. Installing Prothane spring buffers and shackle bushings, DSE shackles, new Calvert Racing 1/2" u-bolts (Grade 5?).

 

Driver side was discovery learning for me yesterday, cleaned and undercoated as I went, used new Grade 8 hardware. Got the leaf installed and the spring plate up, torqued the u-bolts to 65ft/lbs (based on Eaton Springs website and a post I found at NastyZ28 forums). But the spring plate was literally "U" shaped and left close to 1/2" gap between the plate and the upper spring mounts. Did the passenger side today and discovered the upper leaf buffer had to be trimmed down to fit the pocket upper pocket.

 

After trimming down 1/2 of the material, the buffer fit nicely into the pocket and the spring went in and spring plate went on. Torque to 65ft/lbs again, and despite the spring plate being up against the upper leaf mount, it was still "U" shaped and the u-bolts were splayed outward at the bottom. Decided to open up the driver side and trim the upper buffer, and the inboard u-bolt snapped off while removing the nuts. Other 3 nuts came off easily, but the spring plate remains "U" shaped. [Sorry, not smart enough to post pics, if someone will point me to a tutorial I will...]

 

1. WTF did I do wrong? Why did the plate stretch so much when reinstalling? Old steel that I should have replaced? Yeah, got that the urethane buffer pads don't compress like rubber ones. Did I waste my $$ on urethane buffers? Should I have used rubber?

 

2. WTF is wrong w/ Calvert 1/2" u-bolts? Or did I do something wrong? I'm not new to wrenching, been doing this for 25+ yrs (but on Harleys).

 

3. Recommendations on u-bolts and spring plates? I don't see a way around not replacing them...

 

So aggravated right now... this shouldn't be this difficult.



#2 NOT A TA

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Posted 14 May 2020 - 07:13 PM

You can flatten the plates back out in a press. If you don't have one any garage or machine shop will have one. It doesn't require a huge force, they're mild steel and straighten fairly easily.  I've done it many times with stock plates because folks get carried away tightening the stock U bolts and T bolts. Cause ya know, "goodntight".

 

That said, there are also stronger plates made by PTFB scroll down here http://pro-touringf-...nsion_kits.html

 

The torque should be 40 lb. ft.   Not sure why you found recommendations of 65 lb. ft.  Got a link to where you found it on Nasty?, I'm a member there.

 

Here's a link to info on tightening sequences, max torque specs, etc. for U bolts. https://www.scribd.c...lt-Torque-Chart


Edited by NOT A TA, 14 May 2020 - 07:26 PM.

John Paige

Lab-14.com


#3 fireforeffect

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Posted 15 May 2020 - 09:33 AM

Thx. Hadn't considered flattening them, but had to spend a fair bit of time cleaning them up before I was satisfied to paint/undercoat them before installing again. Mild steel... yup. Am I risking failure down the road (no pun intended) if I flatten them due to weakened steel?

 

Link to the NastyZ28 forum: http://nastyz28.com/...-torque.237261/

 

Typical of internet forums, the answers are all over the place. Google also got me to Eaton Springs webpage which showed 65ft/lbs for 1/2" grade 5 bolts (I'm guessing max, not recommended). Called a local "muscle car" restoration shop near B'more and asked same question, "Go ahead and torque the $hit out of them." Me: "Really? My spring plates are bent and the u-bolts are splayed." THEM: "Huh..." Won't be going to them for any specialty work soon. 

 

40-50ft/lbs sounds so much more practical... 


Edited by fireforeffect, 15 May 2020 - 11:02 AM.


#4 NOT A TA

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Posted 15 May 2020 - 05:45 PM

I follow the X pattern tightening in two steps 25 lb. ft. then 40 lb. ft.  Then drive the car and check them.

 

I've never seen any problems as a result of straightening plates.

 

Max torque on a grade 5 fine thread 1/2" bolt is 64 lb. ft. and course is only 57 lb. ft.  IIRC.  U bolts are typically a little lower and will bend/stretch a little so be sure to check after driving a little since it sounds like you ditched the T bolts for U bolts as well.

 

50 lbs will bend the plates.


John Paige

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#5 fireforeffect

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Posted 24 May 2020 - 03:49 AM

NOT A TA, quick note to say thx for advice above. Pulled the leaf spring insulators and trimmed to fit the pockets better and bought new bottom plates/shock mounts. Yes, knocked out the original inboard T-bolts and replaced w/ 1/2" grade 5 fine-thread U-bolts all around. Took my original plates to be pressed back flat by a local machine shop as suggested. Will keep on hand just in case. Put everything back together again and torqued to 40ft/lbs, which still bent the plates mildly but not nearly to extent the original ones were bent at 65ft/lbs. Were I to do it again this afternoon, I'd only go to 35ft/lbs, the U-bolts at 40ft/lbs look like they're ever so slightly distorted. But, everything is back together and looks correct. Also got the SpeedTech control arms, coil springs, new steering linkages, new axles, and new rear brakes installed (what a discovery learning experience...). Hoping to get the front calipers swapped today and the rest of what remains on the front end back together and get it down to the alignment shop. The tech at the local shop is an old GM guy and former 2nd gen T/A owner, will ask him to double-check my amateur shade-tree work. 


Edited by fireforeffect, 24 May 2020 - 03:53 AM.

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