Tag: Jim O’Clair

What you need to know before buying a GM TH-200-4R Overdrive Transmission – Jim O’Clair @Hemmings

What you need to know before buying a GM TH-200-4R Overdrive Transmission – Jim O’Clair @Hemmings


The overdrive four-speed automatic is replacement for older three-speed Turbo Hydra-Matics or two-speed Powerglides

Many classic cars that used an original Powerglide two-speed or TH-350 three-speed can benefit from installing a TH-200-4R four-speed automatic without having to perform major modifications. The 200-4R can be used on many other GM passenger cars because it was manufactured with both a Chevrolet and a B-O-P bellhousing bolt pattern. The taller, fourth gear allows the engine it is installed behind to rotate at lower RPM than a three-speed transmission, and this not only will save on gas and engine wear, but it also allows you to change to larger rear axle ratios without severely impacting streetability.

TH-200-4R transmissions are very easy to locate from salvage yards, and most replacement parts are still available from transmission parts suppliers and auto parts stores. Heavy-duty parts for racing applications are available from transmission parts suppliers, as well.

Will a TH-200-4R fit in my car?

Your engine size should be a consideration; many muscle-car enthusiasts recommend using the TH-700-R4 or 4L80E overdrive units on large V-8 and higher performance engines. However, in many V-6 and small V-8 applications, a TH-200-4R will fit with fewer modifications.

The TH-200-4R, like the TH-350, uses a 27-spline output shaft, which is similar in length to the TH-350 and the TH-200, making it a natural for many overdrive conversions. The TH-200-4R is also similar in length to the Powerglide and the B-O-P Super-Turbine 300 (two-speed), which makes it a popular unit for converting from a two-speed to a four-speed automatic.

The TH-200-4R has a 2.74:1 first gear ratio, and overdrive is 0.67:1. Its odd-shaped 16-bolt pan has 13mm bolt heads. The TH-200-4R was used in GM rear-wheel-drive cars equipped with the 231 Buick, 301 Pontiac, and the Oldsmobile 307, 350 gas and 350 diesel engines from 1981-’90; however, many Chevrolet 267 and 305 V-8s also used the TH-200-4R because of the multi-fit bellhousing.

The transmission identification is on a plate on the right side of the case towards the tailshaft. This ID plate is attached by one rivet. The plate will have a two- or three-letter transmission code in large letters.

Which TH-200-4R should I get?

The most desirable TH-200-4Rs for performance enthusiasts are the units manufactured for Buick Grand National, Olds 4-4-2 and Chevy Monte Carlo SS in 1986-’87. These units used a special valve body. They also had a larger reverse boost valve, second to third intermediate servo, and a specially designed governor assembly. Their BQ, OZ, CZF, KZF or BRF transmission codes can identify these more desirable units.

This transmission is ideal for swapping with a TH-350 or a Powerglide, because the overall length and the bell housing bolt pattern of the TH-200-4R are the same, and your original driveshaft does not have to be shortened. The output shaft is 27-spline, the same as the TH-350’s. Moving the crossmember will be necessary, because the TH-200-4R crossmember is mounted on the extreme end of the tailshaft.

Read on

What type of battery should I choose? How lead-acid, gel, AGM, and other batteries compare – Jim O’Clair @Hemmings


With stay-at-home orders currently issued all over the country, people may have not considered the fact that many classic vehicles, boats, RVs, and motorcycles have been sitting dormant for even longer periods of time than normal this year and many will require a new battery, or at least some battery maintenance, before we fire them up again. These days, though, there’s more than just the standard parts store lead-acid battery to choose from, so let’s break down the differences between lead acid, gel, AGM, and other battery types now on the market to see which is best for your needs.
For almost 100 years, the lead-acid battery was the basis for any automotive electrical system to provide an energy boost for starting, as well as long-lasting amperage to power ignition systems and dozens of electrical accessories. Initially offered in 6-volt form, batteries used a series of lead-based plates (with other ingredients), bathed in 25-percent water and 75-percent sulfuric acid, encased in an acid-resistant rubber box. The acid (or electrolyte) allowed charged ions to move between the lead plates, which resulted in an electrical charge either being drawn from the battery or returned to the battery via the car’s charging system. These 6-volt batteries have three “cells,” and 12-volt batteries have six.

The Coker Tire Challenge 2019 is like a mini version of The Great Race – Jim O’Clair @Hemmings


The Coker Tire Challenge 2019

For anyone interested in speed, time, distance rally racing but aren’t quite ready for the  annual 10-day, 2,000-plus-mile Great Race, we suggest starting in one of the smaller regional rallies offered throughout the year. One such event is the Coker Tire Challenge, taking place a few days from now from September 19th-22nd. It’s a 3-day mini version of the Great Race, with similar rules and team directions, however, race teams start and finish each day back at Coker Tire world headquarters in Chattanooga on each of the three nights of the event. The Coker Tire Challenge runs through the beautiful Southeast Tennessee countryside with a few visits into northern Georgia and Alabama along the way. Scoring is identical to Great Race rules, with older cars receiving an adjustment factor to their scores based on the age of the vehicle (the older it is, the bigger the adjustment). For those unfamiliar with the format, two-person teams attempt to complete a route as close to a target time as possible, with no electronic aids to calculate speed and acceleration times. As always in this type of racing, the team with the closest score to perfect time wins.

The Coker Tire Challenge 2019

Read the article here

Related – West Coast route announced for 2019 Great Race

Tech 101: Fuel-line hose – what you should and should not use – Jim O’Clair @Hemmings


Most vehicle repair shops are encountering a lot of fuel-line-related issues since the introduction of ethanol into America’s pump gas. Because of ethanol’s effects on rubber, plastic and metals, they are finding themselves spending a lot more time fixing fuel delivery systems than they did in the days of leaded gas and carburetors.

Useful article by Jim at Hemmings to keep you safe!