I'm asking in here because many of you have had first hand experience with 1st gen driveshafts.

My early (small flange) '79-'82 (replaceable U joint) driveshaft is 10mm longer than the old one in my GLC. Will this cause any problems under normal rear suspension travel?

In case you're wondering, yes, the early shaft's small flange is compatible with the GLC's diff. Mazda loves that parts bin.

The reason why I need to swap shafts is because GLC's universal joints are very tiny and will probably snap if I look at them funny.

 

i think it will be fine
i always have at least 20mm between the end of the yoke and the outputshaft

 

Cool! Yep, 20mm is what I was aiming for when I upgraded to a '74 and up tranny and a 13B in my MG Midget. The '73 and older trannies were 40mm shorter, and the 12A is 20mm shorter than a 13B. I had to have my custom driveshaft shortened by 60mm and was looking for that 20mm of slack, as you mentioned (I could not allow the front of the 13B to go forward in that car due to limited space).

Another funny thing I noticed was after I put the 13B in the GLC, the GLC's stock driveshaft looked a little too short. Since I didn't have any RX-7s handy to compare, I just decided to drive on it. No problems of any kind. I then found out later that it was nearly the perfect length (d'oh!). That's why I'm concerned about upgrading to a driveshaft that is 10mm longer.

I'll just try the RX-7 driveshaft and see if it'll bottom out on the rear tranny seal.

Hmm, I should have measured the distance from the outer sleeve to the edge of the tranny casting before pulling everything out. FWICR, it looked like 20mm.

 

i would measure for sure
if its too close you could always get a little thicker bump stops on the back

 

Jeff, just load the rear of the car down until the pinion flange is as close as possible to the transmission, then see how much end-motion you have.

Worse comes to worst you *could* always just shift the engine/tranny forwards a bit by ovalling mount holes.

Bear in mind this: This is third-part info, but I knew someone who would destroy a tranny on every launch in his Mustang. Each time he'd launch at the dragstrip, he'd frag a tranny. After the fourth or fifth tranny, he noticed his torque boxes were distorted... under launch conditions it was slamming the driveshaft HARD into the tranny output shaft.

Something to bear in mind!

 

Yeah, I think I could get away with 5mm on the motormounts without a problem. It'll be enough. Thanks guys.

 

One more question. Can I remove the '79-'83 flange from my differential and swap in an '84-'85 flange? I'm only asking because the '84-'85 driveshaft has thicker U joint brackets and should handle more power. I also have access to an '84 rearend that I could have shortened to fit in the GLC.

Hmm, I wonder what I'd do about brakes. Maybe it'd be better to get a drum brake rear and swap in an LSD 3rd member? What years can allow a swap like that?

 

for the rear you have to keep in series and non se (ie 84gs with gsl pumkin)

im sure a good machinist could make the flanges fit

 

That '84 GSL rear has disc brakes obviously. Do you know if earlier drum brake rears can hold an LSD 3rd member? I'd like to keep the drum brakes if I can (no swapping master cylinders).

 

Come back when you actually know what the hell you're talking about.

 

peejay, do you know if I can keep the small flange and drum brakes with LSD?

 

Absolutely.

For the Mazda 7" rears, the flanges are interchangeable. The diffs are interchangeable as long as the side gears are the correct size (large axle or small axle). It was a dealer fix back in the day, when people would complain about the rear end chattering around corners, to bolt in an open diff centersection.

 

Cool! I'll just drive on the stock GLC's open diff as long as it can withstand the power. Then once it breaks, do you know if an RX-7 LSD 3rd member will bolt in? Or do I need an early complete rearend and just swap my attatchments over and have it narrowed?

Which model RX-7 should I look for in the junkyard? I'm eager to learn how to do this swap.

 

Woah Nellie. This is for the GLC...

I am fairly sure that the GLC has the 6-ish inch diff, *not* the 7". (The tiny diff was also found under the rear of 323GTX's) I do not think that cross-swapping will be possible in this manner.

In which case, yeah, you get to play with custom length crap, or fender flares, or something.

 

Hmm, I was thinking about getting steve84gs' narrowed '82 rear out of his GLC, if he chooses to part it out (I think he'd rather sell the whole car sans engine, trans, seats, guages). But since I believe he went with disc brakes, I'd probably be better off finding a small flange drum brake rear and installing an LSD 3rd member in it after having it narrowed. Does that sound like a workable plan?

What is your opinion of rear discs vs drums (need I ask? hehe)?

 

Rear discs are OK as long as you keep up on them and don't mind having a nearly-worthless handbrake.

Drums are great if you don't mind the possibiliy of them locking up sometimes (if you have servo-type brakes).

 

I like having a healthy handbrake. The drums are incredibly narrow on the GLC though. I'm curious if I could find an '80 with drums (same brake line thread pitch) and install an LSD 3rd member into it. Then I wonder if the GLC's brake master would function correctly with the 7's wheel cylinders.

My friend used to have a '79 with an LSD disc brake rearend. The rear brakes wouldn't disengage fully which caused them to always ride, thus heating the rotors and making life difficult. It felt like driving with the E brake on. He eventually sold the car after the problem seemed to work itself out. I have no idea what year the disc rear was out of, but I assumed the stock drum master cylinder was never swapped out for a disc unit.

I certainly don't want to run into that problem here. I asked Steve if his has discs or drums.

 

i had to fit one on my car
s2 GSL will fit in a s2 drum
s3 will fit in s3and so on
but no s4 in s3,s2,s1

 

as long as the LSD is from a 82,82 GSL is should fit right in
the different axle size on the 84-85 is the inly prob

 

S4 diffs will fit in a S3. The only difference between an S4 and S3 centersection is the pinion shaft length, the diffs themselves can be interchanged. (Hmm, well the S3 diffs might not work in a IRS car, stub axle retention?)

 

woops counted too high.. you get he poitn

 

If I could find an '80 rearend with drums, can I install an LSD 3rd member into it? Do you think the GLC's brake master cylinder would function correctly with the RX-7's wheel cylinders? What about the handbrake? Thanks in advance.

 

jeff20B....you suck. feel privilaged that you don't have an 84 or 85. my u-joints went and i had to replace the whole shaft. just joking hope your project goes smoothly

 

I hope you didn't spend too much on it. I got mine with aftermarket GMB U-joints already in it for $25. It just needs a paint job and it'll look beautiful. (some surface rust)

 

man you suck. i ordered the aftermarket mazdatrix one. easy install but it rubbed on the exhaust heat shield thing. if this one goes bad again all i have to replace is the u-joints