Spring Perch - Shock Plate Gap, Different Opinions? - Team Camaro Tech
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post #1 of 17 (permalink) Old Jan 16th, 17, 08:25 AM Thread Starter
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Spring Perch - Shock Plate Gap, Different Opinions?

This question is one of pure curiosity. Replies to a somewhat recent posting shown below suggested that a bit of a gap between the spring perch and shock plate was ok, in fact may even be desirable (see clipped in image). In another article posted in the Suspension Forum entitled "Good Article" the following statement is made:

"Some aftermarket leaf springs are thicker (height-wise) than stock springs and leave a gap between the perch and shock plate. This leaves you with the choice of removing the lower isolator pad to close the gap between the perch and shock plate or adding shims between them.With either solution, you should firmly lock the leaf spring in place between the perch and shock plate. If you have a gap between the shock plate and perch, the plate will start to bend and the hardware will start to bend and eventually fail."

So, which is correct? I'll assume we're not talking about a wide gap between the perch and plate, but should the perch and plate be in 100% contact when the bolts are torqued? If trying to accomodate angle shims to adjust pinon angle, this can be difficult without some form of spacers to close the gap. I have about a 1/8" - 3/16" gap with my U-bolts torqued to the recommended 40 lb-ft, thus my interest in this topic. I have a box of alignment shims and I may use a few of those to close the gap between the perch and plate allowing the proper U-bolt torque but limiting distortion of the lower shock plate. What are your thoughts on this?
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post #2 of 17 (permalink) Old Jan 16th, 17, 08:38 AM
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Re: Spring Perch - Shock Plate Gap, Different Opinions?

I would think the most important thing is that the leaf spring is locked in and snug in the perch. I'm not sure why there is a gap. I would think the pad would compress more as you torqued the nuts more . 40 lbs sure seems light to me. Just my thoughts here.

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post #3 of 17 (permalink) Old Jan 16th, 17, 08:48 AM
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Re: Spring Perch - Shock Plate Gap, Different Opinions?

The gap is correct. You do not want the shock plate tight to the perch.
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post #4 of 17 (permalink) Old Jan 16th, 17, 09:07 AM Thread Starter
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Re: Spring Perch - Shock Plate Gap, Different Opinions?

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Originally Posted by DT View Post
I would think the most important thing is that the leaf spring is locked in and snug in the perch. I'm not sure why there is a gap. I would think the pad would compress more as you torqued the nuts more . 40 lbs sure seems light to me. Just my thoughts here.
I'd have to double check, but I think the FAM shows 35-45 lb-ft, but probably for the T bolts. U-bolts could be torqued more, but it doesn't take much more to start really deforming the shock plate if there is a gap and I'd think that if I I'm using 2 U-bolts per side even at 40 lb-ft it's not going anywhere.

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post #5 of 17 (permalink) Old Jan 16th, 17, 09:10 AM
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Re: Spring Perch - Shock Plate Gap, Different Opinions?

Quote:
Originally Posted by ctcz28 View Post
I'd have to double check, but I think the FAM shows 35-45 lb-ft, but probably for the T bolts. U-bolts could be torqued more, but it doesn't take much more to start really deforming the shock plate if there is a gap and I'd think that if I I'm using 2 U-bolts per side even at 40 lb-ft it's not going anywhere.
I just checked and it appears that 40 lbs is Correct. I honestly would of guessed it was more.

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post #6 of 17 (permalink) Old Jan 16th, 17, 03:18 PM
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Re: Spring Perch - Shock Plate Gap, Different Opinions?

I would much rather torque and have a gap than no gap. With no gap, how can you be 100% you are clamping on the spring ?

I have a gap, removed the lower pad (and upper also...I think ?) but also installed a 1/2" spacer to make up for that and welded the spacer to the plate for alignment purposes.

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post #7 of 17 (permalink) Old Jan 16th, 17, 03:27 PM
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Re: Spring Perch - Shock Plate Gap, Different Opinions?

Ok so I went from mono to multi. I bought the kit to do the swap and there is no gap, the spring is firmly held in place only the rubber spacers are crushed. Is that a bad thing?
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post #8 of 17 (permalink) Old Jan 16th, 17, 04:18 PM
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Re: Spring Perch - Shock Plate Gap, Different Opinions?

Quote:
Originally Posted by bigblockragtop View Post
Ok so I went from mono to multi. I bought the kit to do the swap and there is no gap, the spring is firmly held in place only the rubber spacers are crushed. Is that a bad thing?
if the spring is FIRMLY in place and the rubber is compressed you should be ok.
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post #9 of 17 (permalink) Old Jan 16th, 17, 04:48 PM
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Re: Spring Perch - Shock Plate Gap, Different Opinions?

Thanks!
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post #10 of 17 (permalink) Old Jan 16th, 17, 04:55 PM
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Re: Spring Perch - Shock Plate Gap, Different Opinions?

That picture is of my car - I feel famous.

If you DON't use rubber pads, there should be a gap unless you are certain that the thickness of the spring is exactly equal to the depth of the perch - not easy to do. That is so you can be certain the springs are securely clamped between the lower plate and the upper perch.

The factory setup used rubber pads and engineered it so that when the lower plate is touching the perch the pads are compressed the correct amt to hold everything together.

Probably 99.99% of all leaf spring cars and trucks did NOT use the rubber pads. They used a flat perch - not U-shaped - and it was ALL gap. Go look under virtually any pickup.


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post #11 of 17 (permalink) Old Jan 16th, 17, 06:28 PM Thread Starter
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Re: Spring Perch - Shock Plate Gap, Different Opinions?

Al,
Yes, I really like those beefy DSE shock plates. Your original picture prompted my question about the gap. I've been changing out my pinion angle shims to adjust for the new T56 angle and got to thinking about it and found conflicting opinions about the spring perch/shock plate gap. I've also ditched the rubber pads and still have a small gap. With the 40 lb-ft torque the shock plate doesn't bend too much so I'll probably go with it.

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post #12 of 17 (permalink) Old Jan 16th, 17, 08:37 PM
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Re: Spring Perch - Shock Plate Gap, Different Opinions?

It's important to have a beefy shock plate so it can maintain torque. My Jeep for example has an axle perch that sits on top of the spring only and nothing above the shock plate so having or not having a gap is not an issue, the shock plates are thick enough to easily maintain 80 ft lbs.

I think the article you read was using a thinner stock shock plate as an example.

What size u-bolts are you using?

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post #13 of 17 (permalink) Old Jan 17th, 17, 06:24 AM Thread Starter
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Re: Spring Perch - Shock Plate Gap, Different Opinions?

I'm using 1/2" U-bolts, but stock OEM shock plates so torquing to 80+ lb-ft deforms the plate if not contacting the perch. I think that the 80# number is more in line with what the 1/2" bolts can handle, but it's too much for the plates if there is a gap. I had 7/16" U-bolts before and torquing them to the 70-80# zone caused slight deformation of the bolts and damage to the threads so I'm staying with the 35-45 recommendation in the FAM. I agree that GM engineered the original setup such that the spring with the rubber pads top and bottom were an exact fit with the specified torque with the perch contacting the shock plate. I think that without any rubber pads, only metal against metal, I can use less torque since I don't have to worry about things moving around on the deformable rubber pads.

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post #14 of 17 (permalink) Old Jan 17th, 17, 06:59 AM
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Re: Spring Perch - Shock Plate Gap, Different Opinions?

Just to clarify the DSE shock plates, Aren't they for mini tub installations only ?? Relocated shock mounting points ??

Update: It appears they make several shock plates for diff applications.
http://detroitspeed.com/1967-1969-F-...ck-plates.html

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post #15 of 17 (permalink) Old Jan 17th, 17, 07:06 AM
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Re: Spring Perch - Shock Plate Gap, Different Opinions?

DSE shock plates are available for both stock and mini tubbed applications

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