SFI 29.1 chromoly 168-tooth flexplate for internally balanced 1957-85 small block Chevy engines backed by a TH400, 700R4 or big-bell TH350.
Hearing a knock at idle that changes when you drop it into gear, or a starter that grinds after you added a higher stall converter? On a small block Chevy with an automatic, a cracked flexplate is one of the first things to rule out. PRW part 1835001 is a Sportsman Series SFI 29.1 replacement with a 168-tooth ring gear, made for internally balanced small blocks backed by a TH400, and by a 700R4 or TH350 that runs the large-diameter flexplate and its matching starter.
The flexplate bolts to the crankshaft flange and the torque converter bolts to the flexplate, so every bit of engine torque headed into the transmission passes through it. It also carries the ring gear the starter engages. A stock stamped plate flexes slightly every revolution, which is fine at factory power, but behind a higher-output engine and a stall converter those stresses concentrate around the crank bolt circle and at the spot welds that hold the ring gear on. PRW builds this plate from cold-rolled chromoly steel 0.035 inch thicker than stock, with a forged one-piece ring gear that is double welded to the center, and it is certified to SFI 29.1, which drag strip tech inspection requires on many combinations.
Pull the inspection cover and turn the engine by hand with a socket on the balancer bolt. Look at every crank bolt hole and converter pad for cracks and check the ring gear for broken teeth. Do not confuse a cracked plate with a bad pump bushing or converter noise; our 700R4 pump failure guide covers the transmission-side noises. While the cover is off, count the ring gear teeth on the old plate. That number, not the transmission name, decides which plate you order.
PRW lists the 1835001 for Chevrolet small block engines with an internally balanced crankshaft and the two-piece rear main seal, which covers 1957-1985 blocks, plus the 90-degree Chevy V6, with the TH400 as the main transmission. It has a 168-tooth ring gear and neutral balance with no counterweight, and is drilled for both the 10.75 inch and 11.50 inch GM three-bolt converter patterns. A 700R4 or TH350 can use this plate only if the bellhousing, starter and block are set up for the 168-tooth pattern; many run the 153-tooth plate instead, which we stock as the PRW 153-tooth SFI flexplate. This is not the plate for a 400 small block or a 1986-and-later one-piece rear main engine, which need an externally balanced plate. Send us the engine, transmission and tooth count if you are unsure, or browse our TH400 parts and 700R4 parts pages.
If the plate failed behind a worn transmission, this is the right moment to go through it with a 700R4 master rebuild kit, and to fix a slipping 3-4 clutch at the source with our 700R4 common problems guide.
| Fits | Small block Chevy 1957-1985, internally balanced (two-piece rear main); Chevy 90-degree V6 |
| Main transmission | GM TH400 (also 700R4, big-bell TH350) |
| Ring gear | 168 tooth, double welded |
| Balance | Internal (neutral) |
| Certification | SFI 29.1 |
| Material | Chromoly steel, iridite finish |
| Thickness | 0.035 in thicker than stock |
| Part number | PRW 1835001 |
Doing this repair right usually means replacing these at the same time. Same transmission, ships together.
Only if your 700R4 uses the 168-tooth flexplate and matching starter. Many small block 700R4 installs use the 153-tooth plate. Count the teeth on your old plate and order the same count.
No. One-piece rear main engines use a different crank flange and external balance. This plate is for 1957-1985 two-piece rear main, internally balanced small blocks and the 90-degree V6.
No. The 400 is externally balanced and needs a weighted flexplate. This plate is neutral, and on an external-balance engine it will cause vibration.
PRW lists it for the GM three-bolt 10.75 inch and 11.50 inch patterns. Measure your converter's bolt circle before ordering.
Yes. PRW certifies the 1835001 to SFI 29.1, the specification tech inspectors check for flexplates on automatic transmission cars.
