GaryJ

I have a 79 with a 5 speed. I am planning on doing some engine upgrades this winter and have been doing some work along the way. I recently replaced the clutch and everything was done, master cylinder, slave, discs, intermediate plate, pivot ball and arm, and fly wheel resurfaced. The transaxle has had the fluid changed and is running Mobil 1.

Once the car is warmed up the up shifts go pretty well but down shifts are another matter, unless I am stopped or practically stopped I can’t seem to downshift into second I just get a horrendous grind it doesn’t even sound like it is close to getting me in. Down shifting is important to me since we have so many nice mountain roads around here and a road course race track right down town.

What should be my next move?

Thanks,

Gary

Andre Hedrick

Try floating your RPMS and see if that makes it easier, first.

AO

I'm not 100% sure, but I believe even the 79's are subject to the weak 2-3 synchro problem. I think the only known remedy is to open the gear-box and rebuild.

GaryJ

Hi Andre:

Thanks for the response but what is RPMS?

Thanks,

GaryJ

Hi Andrew:

I was kind of afraid of that. If I have to do a whole rebuild I was thinking about putting in a later model transaxle with the better synchros. Is this advisable and or is it preferable to keep my 2.7 rear end?

Thanks,

AO

RPMs=Revolutions per minute (engine speed)

What he means is you should try matching the engine speed by "blipping" the throttle and then down shift. For example if you are at 2500 RPMs in 3rd gear, you'd want to step on the clutch, hit the gas so the engine is now at about 3100 RPMs while sliding it into 2nd. If you do it perfectly, you wouldn't even a clutch.

GaryJ

Thanks Andrew:

I guess Andre threw me with the term float your RPMS I though it was a part I wasn’t aware of or some different way of mounting the transaxle.

My daily driver is a Land Rover Defender and I always blip the throttle before I down shift so it is a habit I bring to everything I drive.

I even tried to step on the gas and slowly build the revs to see if I could get second gear to slip in but I never got it to work then I was too deep in the corner and just used 3rd. Thank goodness the 928 has good torque.

Any thought on the Cost/ Benefit of having my current transaxle rebuilt or putting in one from a newer car.

Thanks again.

checkmate1996

From the research I read, the later boxes which have the better synchros have different length torque tube which would cause some issues. Plus, finding a later model manaul gearbox is often hard to find and very expensive $3-4K or more depending.

Your best bet, if mechanically inclined, is to drop the box yourself and replace the synchros and dogteeth. Another gentlemen on this forum, (jyoon, I think??) just did this for about $600 in parts. Or take the box to a shop. Probably about a $1000 in labor. Or do a swap out with 928 intl. You give them your box + $3k for a rebuilt unit.

Good luck...

Tom. M

Even after the new clutch stuff...your intermediate plate may be just a bit off....not sure why it wouldn't affect upshift as well as downshift...but might be worth looking in there again and adjusting the Int. plate..

Good luck...

Tom
89GT

marton

I bought an 89/90 928 GT box for circa 600US$ & put it straight into my euro 81s.
No issues

Marton

GaryJ

Thanks guys:

Brad,
Thanks for the input, if those are the numbers I will probably pull the box and have it rebuilt.

Tom,
Thanks, I took it to a Porsche mechanic and he said everything looked like it was adjusted properly.

Marton,
Thanks that sounds very encouraging.

Does anyone know if Marton is correct? OR if Euro’s are so different that this swap will work Euro to Euro but not US to US.

Thanks for you input guys.

Gary

Jim bailey - 928 International

In order for reving the engine between shfits to enable you to match gear speeds you MUST let out the clutch in neutral to get the clutch discs, driveshaft ,and interal gears of the transmision turning the higher speed for the lower gear. Called double clutching it was neccesary before syncronizers were invented or you could not downshift. I spent hours learning how to get a 47 Plymouth into first gear on the fly.... Reving the engine after it is in gear and BEFORE you let out the clutch does keep you from chirping the tires from too much engine braking easy to spin out that way if you are in a corner BUTdoes nothing to help the syncros or shifting. Basic fact is syncronizers work by using friction and like brake pads and clutches they wear and the harder they are driven the faster they wear. Second gear gets worn because people downshift into it so much rarely does one downshift into 4th agressively. And almost you never go to first unless you have stopped.

GaryJ

Thanks Jim,

I will try that correct double clutching technique but it sounds like the syncros are gone, I just have to decide if it is better to rebuild mine or put in a new style transaxle.

Gary

Jim bailey - 928 International

My wife's 79 was much like your's when cold it did not like upshifting into second and warm it was not to happy she drove it that way for years ( it was OK for her purposes ) it went through two other drivers before the latest owner decided to get a rebuilt trans from us. As was mentioned the 78-79 and early 1980 has a different length torque tube and I believe rear suspension cross member so installing a 1985 or newer trans (Borg Warner style syncro) requires additional parts. The early trans is a good trans the later ones just take more abuse. I have lost track of how many track hours I have on the Very Brown 1980 but it is a BUNCH and I use 2nd gear a LOT at the Streets of Willow and it down shifts just fine......

GaryJ

Thanks for the encouragement Jim.