Hey guys, I just swapped 98 Trans Am rotors/disc brakes into my '88 this past weekend. It was a simple straight forward swap. The only problem I've got is the same as before the swap: poor brake bias. The rears barely operate at all. I've got an adjustable proportioning valve that I'm looking to put in but I'm hoping that someone knows the sizes of the fittings and lines that come out of the M/C, the size of the fittings that go into the stock prop valve, and then the size of the lines and fittings that come out of the stock prop valve. I'm hoping I can find some adapters so it's a fairly simple process. If not, I'll have to cut and flare the lines with the fittings. Hopefully someone has this info squirreled away somewhere so I don't have to spend the day at AutoZone going through all of their fittings.

Of course, if you've got a better answer than all that please post!

Thanks,
Steve

 

Hey Steve, when you find out let me know.
I jsut installed my brothers 4th gen rear from his car onto mine with his brakes as well. We used my stock lines and just attached them to the 4th gen calipers since his car has 2 lines on the rear, one for each brake since he has traction control and ABS and mine only had one line split to two.

Doesn't look like it's leaking, gonna bleed the brakes tomorrow since we were cold and tired after dropping his rear, my rear, and installing his rear on my car.

I'll talk to you later,

 

Do you have the correct factory proportioning valve for a disk/disk car? If not, I would recommend that first. If so, I would recommend adjusting your brake pad compounds to even out the bias. An adjustable proportioning valve is a band-aid for a bad brake set-up and can be very dangerous. IMHO, I would not use it.

Just my $0.02

-Matt

 

If you are replying to me, I already had disc/disc on my car, just put on the 4th gen discs that were on my brothers rear end.

 

I duuno! But I must not have mentioned it before. I have the full 1LE (or whatever ya wanna call it) four wheel disc brake package. Am using the stock J-50 (disc/drum( master cylinder and proportioning valve. My brake bias is perfect.

I suggest that the very first thing to replace in any situation like this, is the master cylinder. It's a long and dry technical story. But basicly: The rear portion (that controls the front brakes) must have NO LEAK DOWN in order for the rear brakes to work correctly. Even a little leak down will cause you to have front brakes only. It is a safety feature of the master cylinder.

I have (if you will search under my user name) road tested nerly every conceivable combination of components. The stock J-50 setup of master cylinder and proportioning valve works best for me. Several other board members have found the same thing.

Besides the master cyl is cheap insurance.

Thanx,ANDYZ28