I have a 1988 IROC disk brake rear in my 1939 Oldsmobile. I would like to know if the 4th gen rear disk brakes will fit on the 3rd gen rearend. I need to have a working emergency brake for the state inspection.

 

Welcome roket. Nine or ten-bolt?

The 9- and 10-bolt axle flanges have different bolt patterns. The company below fabs both 9- and 10-bolt backing plates, so you can mount 89-92 and/or 93-97 (LT1) rotors/calipers, which are nearly identical, without difficulty. I don't believe that anyone fabs anything that would allow the LS1 (98+) system to be used on a 9-bolt, but a search on site might provide a better answer. With a 10-bolt, the LS1 system will be a simple swap on (much better parking brake than the 89-97 set-up). I assume you'll have to fab parking brake cables regardless of the system you choose.

Various kits for both the above can be found at the following site:

http://www.flynbye.com/index.html

Here's what the 89-97 swap (to my 85 IROC) looks like, along with part numbers, etc.:

https://www.thirdgen.org/forums/faq-...iscs-89-a.html

BTW, new OE calipers for the 88 might be the ticket.

JamesC

 

I aleardy replaced the calipers and still have no emergency brakes. I am going to try adjusting them one more time before I give up.

 

Q: Do my rear disc brakes need to be adjusted?

A: A technical service bulletin described this for early-mid '80s rear disk brakes. It seems that the rear disks in these cars would be adjusted by applying the emergency brake. When you pull the emergency brake lever up, the lever turns this little device called an actuator screw. This little screw type device is also on a ratchet, so that pulling the e-brake up, turns the screw. But letting go allows the ratchet part to function and set the pads at that time. So, using the emergency brake is mandatory for maintaining the rear disk setting on early model rear disk units.

But, here's the problem with them. There's a little spring on the actuator screw assembly that allows the pads to back-off from the disk a little bit before the ratchet mechanism is engaged. This must be done, otherwise full brake pressure would be left on the pads when the e-brake is released. Well, that little return spring K-factor was not correctly chosen from the factory, and the result is that the ratchet NEVER functions after the actuator screw gets a little dirty. Hence, the pads simply work their way out all the way when the e-brake is used. Using the e-brake all the time seems to keep the actuator free for a longer period of time, but even with the correct spring weight and screw, the e-brake is required to adjust the parking brake actuator.

The TSB states that cars with a manual tranny are eligible for a free fix as the e-brake is required to park the car, but the auto is not eligible. Why? Only GM knows. However, fixing it yourself should be relatively easy. The rear wheels are removed, and there is a nut on the back side of the brake caliper that holds the parking brake lever. Remove the nut, lever, and soft grommets. Put a large washer over the shaft to act as a spacer, and then put a wrench on the hex of the shaft, and tie it down with the nut. Turn the wrench to back the brakes off. After a while, this will over travel, as if there was a one way clutch. Tighten the shaft to see where the hex is when the pads are tight agains the rotor. If it is in a spot that the parking brake lever will fit, and turn about 1/3 of its travel to tighten apply the brake, then it is good. If not, try again.

This will remove some of the brake pedal slop also. It's supposed to be self-adjusting (apply parking brake thirty times), but it is common for it not to work.

Perhaps the above will prove useful.

JamesC