Why Does Changing Peterbilt Shims Take So Long? (It's the Bolt Holes)
Changing Peterbilt Air Leaf shims shouldn't need a torch. Closed-slot shims trap seized bolts; Synergistic's 43-411 series is open-slotted — loosen the bolts, slide the shim, tighten down.
Chris Ludwig
10/22/20262 min read
Every alignment tech knows the job. A Peterbilt on the rack needs its thrust angle corrected, the shims between the spring hanger and the spring need to change — and a ten-minute adjustment turns into a fight. Nine times out of ten, the fight isn't the alignment. It's the design of the shim itself.
The problem: closed slots and seized bolts
Most Peterbilt Air Leaf tandem shims are built with closed slots — the bolt passes through the shim, which means the bolt has to come all the way out before the shim comes off.
That sounds fine on a new truck. On a truck that's been working for years, those bolts are seized, and the ends are gnarled up from road grime and old removals. They'll loosen — but they won't come out. In the shop, we watched the same scene play out over and over: the tech ends up with a torch, cutting bolts just to change a shim, then hunting down replacement bolts before the truck can go back together.
The shim costs a few dollars. The hour of labor and the bolt run cost real money — and the truck sits on your rack the whole time.
The fix: an open slot
Our Peterbilt Air Leaf adjusting shims (43-411, 43-412, 43-413) are slotted — open at the edge, not closed around the bolt.
Loosen the bolts — they don't have to come out.
Slide the old shim out (cut it off if it's stubborn) and drop the new shim in.
Tighten the bolts back down and finish the alignment.
No torch. No wrecked bolts. No parts run in the middle of an alignment.
Same shim, same job — built the way it should be
Thrust angle and toe adjustment on Peterbilt Air Leaf suspensions: 1/32" (43-411), 1/16" (43-412), 1/8" (43-413). Steel, zinc plated (0.008 mm), 12 per bag, starting at $9.60 a bag. Cross-reference: same part numbers as Stempf and Northstar; compare to SPC 35010 / 35011 / 35012.
How to order
We keep it old-school and simple: call or text 469-215-7730, or email customerservice@synergisticsupply.com. Most orders ship the same or next business day from Itasca, Texas, and shipping is free on orders of $1,000 or more. Pay by card from your invoice, or by Zelle.