I need to know how hard it is to swap an LSD diff into a '79-'80 drum brake rearend (small flange, early thread pitch).

 

The other thread was about the driveshaft and I never got a clear answer when I asked some questions about the rearend stuff, specifically my question above (drum, LSD etc). I'd like to keep this thread on topic.

peejay?

 

Never tried it Jeff.

I've heard reports that the Series 1 axleshafts are a tad too long for the LSD diff, or something of that nature. I did have an S2 open diff in my '80 for a whopping month before the engine tried to auto-disassemble. Fit with no problems.

 

What did you do about the the brake line thread pitch change? Also, was it a drum brake rearend?

 

jeff
you can swap up to 83 GSL 3rd member to a SA. thats how I did my 2 prior SA.


the only time that the tread pitch will matter is when it comes to a complete change out. say 81-83 to a SA.

mel

 

Thanks for the info, but did yours have a drum brake rearend?

Sorry to sound like a moron, but when it comes to this rearend stuff, I don't fill smart.

 

yes, i retained the drums to avoid the hazzle of re-doing the flex brake line. Be sure to soak the brake line fittings over night and USE the proper 10" flare wrench to avoid rounding off the fittings.

I've done several complete disk brake conversion on customers cars. To avoid downtime, be sure to have a custom flex line (SA fitting on one end and FB on the other) pre-made. Im referring to the flex line located in the center of the rear end. Its pretty difficult to find an 1.00 - 1.10 (i think thats what FB is) adapter here in Socal.

 

So are you saying it might be best for me to look for an '81-'83 small flange drum rear end and located an LSD and do the swap in it instead of the SA style to avoid the wrong type of axel shafts (as peejay mentioned)?

It's going into a GLC, so it's got the the old style thread pitch and needs drum brakes so I won't have to change out the brake master and/or proportioning valve. It also will need to be narrowed and recieve the GLC's mounting hardware.

In other words, I'm looking for suggestions and opinions.

 

[QUOTE]Originally posted by Jeff20B
[B]So are you saying it might be best for me to look for an '81-'83 small flange drum rear end and located an LSD and do the swap in it instead of the SA style to avoid the wrong type of axel shafts (as peejay mentioned)?


The 81-83 3rd member is a direct swap to a SA. I never had any problem with any of my installs. In fact, in my RX-3, Im using an 3rd member from a 83 GSL with auto tranny.



It's going into a GLC, so it's got the the old style thread pitch and needs drum brakes so I won't have to change out the brake master and/or proportioning valve. It also will need to be narrowed and recieve the GLC's mounting hardware.

Im not quite familar on the GLC's brake set up. But, if I were you, I will do the complete disk-to-disk swap to make it unique. To eliminate the brake line issues or to make the install simple, just get a custom made soft line as I mentioned in my prior post. Its cheaper than flaring/install new hard lines with old thread pitch

 

I wanted to do disk brakes at first, but then I thought of all the other swaps required to make them work (master cyl. etc). I also thought of all the times I've read about racers whom liked their drum rears, but wished they came with an LSD option. Our own peejay is kinda sorta one of them (or does he like open diffs with disks better?).

I know some parts of the GLC came from the RX-3, but not the rear end. peejay says it's around a 6" and 1st gens are 7". It's going to cost at least $500 to do the swap, but probably a lot more.

What if the axle shafts are the same thickness and spline count as 1st gens? That would be great because I could just poke them into the narrowed 7 rear end and not have to have the 7's shortened and resplined.

 

I only changed the centersection, since my diff decided to die after doing a redline burnout (one wheel only) in 3rd gear while travelling about 50mph. Had to drive 120 miles home without letting off, since letting off allowed stuff to shift around and cause the diff pin (which broke free in the one wheel burnout) to smack into the pinion gear. (Picture traffic slowing down, having to brake and hold throttle at the same time) As I was getting home I had to drive in city traffic, and trying to shift resulted in the rear wheels locking up. Fun times.

 

Ah yes, the 50MPH difference between wheels.

Hey, do you know if the 6ish" axles are the same diameter and spline count as early 1st gen stuff?

 

Closer to 100. If the driveshaft is going about 95, and one tire is going about 50, then the other tire is going (95 - 50 + 95) 140mph.

No I don't.