10bolt and 9bolt brake compatability
 

Hi folks,

i'm considering changing over from my 10bolt drum in the '89 formula to a used cheap 9bolt setup that has discs ('87 style though) because my rear drums are always kinda shot and i need to pass the inspection each year (and also gain some peace of mind of course). also, i was assuming an auto-equipped L98 '87 GTA would have an LSD, right?

my plans are to upgrade to a T56 and my rebuilt and strenghened up 10bolt next winter the latest, so i would use this 3.27-geared 9bolt as an interim solution with the 700r4, and once i get the 10bolt built up the way i want it and got the T56 put in, use the 9bolts disc setup on the 10bolt until i have enough funds for some better brake setup :)

so, now my destilled questions are:
i'll get the whole axle with the brakes on it, speedo gears and the prop valve. what else do i need for this 10bolt drums to 9bolt discs kind of conversion, would i also need the brake lines or e-brake cables?
also, are the 9bolt and 10bolt brake setups different? speaking of the pre-89 setups here.

any comments are appreciated! Thanks in advance

greetz
ownor

Re: 10bolt and 9bolt brake compatability
 

The only way to verify what's in the car, where the LSD is concerned, is to look--who knows what may have happened over the years. Also, even if it has an LSD, does it function as designed?

If you're changing rear ratios, you'll need the drive and/or driven gears.
The combination valve may be a problem if your 89 has the second design valve. The threads would be different than the 87's.
No problem with brake lines.
You'll need the parking brake cables.
The 9-bolt is a direct swap.

BTW, you'll have to modify the axle flanges on the drum rear and get a 10-bolt backing plate if you expect to swap disc brakes to the drum rear end.

JamesC

Re: 10bolt and 9bolt brake compatability
 

James, thanks for your input. i was of course going to check for the existence/condition of an LSD , i was just wondering what would have come standard (it only has 80kmls).

the heads-up on the combination/prop valve is a good pointer, i'll have to check that. otherwise i can just use a 1LE comb valve and be good, right?

will the e-brake cables drop right in with the 9bolt?

also, just wondering one last time to be sure, are 9bolt disc brakes the same as would have come on any 82-88 10bolt rear?

Re: 10bolt and 9bolt brake compatability
 

The 1LE valve will have a different bias than the standard disc valve, but if you're going to upgrade to larger brakes in the future, you should be good to go--for that matter if you wish to keep the drum valve, the car would still stop, but again the bias is different.

Cables should be fine--at least I'd try them before purchasing new.

The iron Delco-Moraine calipers are the same for both 9- and 10-bolt

JamesC

Re: 10bolt and 9bolt brake compatability
 

There are two 1LE valves. You'll have to determine which you'll need.

1st design: M1.0 tube nut threads (For 1982 - early 1989 applications)
2nd design: M1.5 tube nut threads (Late 1989-92)

JamesC

Re: 10bolt and 9bolt brake compatability
 

very good information, thanks again James! seems i'll snatch that 9bolt :)

if my '89 has the smaller tube nut lines, i can use the disc combination valve from the '87 GTA, right? what's the difference between that (J65?) and a 1LE one anyways?

anyone on the e-brake setup? can i use the '87 disc e-brake cables?

Thanks!

Re: 10bolt and 9bolt brake compatability
 

Yes.

FYI: All four-wheel disc brake rear ends are J65. The difference is bias, as I mention above.

JamesC

Re: 10bolt and 9bolt brake compatability
 

i'm not sure i understand your statement about the J65 disc combination valve. i'm very well aware that J65 is discs on all 4 corners (my HO has them as well).
i'm guessing there is a drums, J65 and 1LE combination valve. i know that the one of a drums setup will have a very different bias, but what about J65 vs. 1LE?

Re: 10bolt and 9bolt brake compatability
 

Correct: There's a drum valve, a standard disc valve (82-88), and the so-called 1LE valve, "so-called" because all four-wheel disc cars from 89+ are equipped with them. What I mean about RPO J65 is that regardless of the rotor size and type of caliper, all four-wheel disc cars are J65, 82-92.

As I understand it, the following valves increase in bias from first to last:

Disc/drum
Disc/disc (10.5" rotors with Delco-Moraine calipers)
Disc/disc (11.7" rotor with PBR's)

JamesC

Re: 10bolt and 9bolt brake compatability
 

Thanks for the info. So basically, the 89-up J65 valve is called "late 1LE" and 82-88 J65 valve is called "early 1LE" valve? That's kinda misleading lol.
Can you help me out with specific numbers on all these valves? I remember reading the drum was like 2 psi in front and 10 psi out back or so, or say just "proportioning" the line pressure in a 1:5 ratio? Guessing the disc valves would increase front bias (or put it how you like, decrease rear bias :D).

Re: 10bolt and 9bolt brake compatability
 

There are two 1LE valves, an early 89, whose threads should match earlier models, and a late 89 whose threads differ and which goes through 92.

Sorry, no help on specific numbers.

JamesC

Re: 10bolt and 9bolt brake compatability
 

Aah i see, that explains a lot :) Thanks again. I'll research some about the different valves, that detail got me interested now.

Hoping to arrange a pick'n'pull appointment with the 9bolt soon hehe. :)

Re: 10bolt and 9bolt brake compatability
 

urgent question: will my 10bolt sway bar mounts fit the 9bolt? i bought new zinc-plated and PU-fitted mounts from TDS last year and i'd hate to be unable to put them back in with the 9bolt.
thanks!

Re: 10bolt and 9bolt brake compatability
 

Yes.

JamesC

Re: 10bolt and 9bolt brake compatability
 

finally got that 9bolt hauled into my garage. damn that was a messy job. almost every bolt broke, i cut off the rubber brake hose with the T on it because the fittings wouldn't open either. oh and i forgot about the 3 weeks of rain we have been having here before i jacked this GTA up in a muddy backyard...
btw, i know this has been covered countless times here already, but which speedo gears do i need exactly to upgrade from my 2.73? whole gearset as in driver and driven gear, or just one of those?
thanks again for the info!

Re: 10bolt and 9bolt brake compatability
 

For a T-5, swapping from 2.73's to 3.27's, you'd need both drive and driven gears. I'm clueless about the 700R4. The stickies in the "Transmission and Drivetrai"n forums should provide the info you need for either trans.

JamesC

Re: 10bolt and 9bolt brake compatability
 

thanks for the pointer, i found out which gears i need from those great stickies. the trans from the GTA is in a million parts on that *******'s basement floor so i'm not sure whether i want to dig through all that filth or just install new ones ;) (11$ each according to transmissioncenter.net). when i'm swapping out my 2.73 speedo gears, can i just re-use all the retainers or do i need some kind of new seals or retainers for them, too?
i know this is not really 100% on topic although it's involved in this whole swap. tia again!

Re: 10bolt and 9bolt brake compatability
 

You can reuse, but I'd probably replace the driven gear housing, which has an internal and external seal--at least on the T-5--I 'believe' the 700R4 housing does as well.

PM.

JamesC

Re: 10bolt and 9bolt brake compatability
 

ok. another idea that just crossed my mind: since i'm up for a T56 change this winter the latest, i guess i could also leave my current speedo gears in there and opt in for a speedometer manipulation box like the dakota digital sgi-5 most are using here? i'm going to change to 4.10's later down the road as well. looks like it would be the right point to get one now? :)
thanks again, greetz

Re: 10bolt and 9bolt brake compatability
 

ok i'm gonna bite the bullet and ask the stupid question: which part do i need to swing my caliper around to determine which one i have?
I started unbolting the lines from the 87 GTA's prop valve but had to stop because it was getting to dark and rainy to go on - iirc there were two different sizes of tube nuts on that valve, i don't remember exactly but i think i used like 11 or 12mm and a 14mm wrench for them.
very much appreciated if you guys have any pointers for me - thanks! need to know if i should order a late model valve or not.

Re: 10bolt and 9bolt brake compatability
 

finally got the swap done after about 4 days of hard work! here's some pics :)

bottom: nasty old stock goddamn open 2.73 drums 10 bolt; top: my 'new' 3.27 posi discs 9 bolt from the '87 GTA
Attachment 411577

9 bolt after some stripping, cleaning, de-rusting and new hammerite paint, gasket, fluid, and brake lines
Attachment 411578
Attachment 411579

first contact of formula and 9bolt
Attachment 411580

FINALLY GOT A WORKING POSI - YEEHAW!
Attachment 411581
Attachment 411582

thanks for your help :)
actually i still need to do some readjustment on the e-brake, speedo gears and prop valve. but for now it's working pretty good!
greetz
ownor