General Transmission questions 4th gear

[SalF2]

Can't hold 4th gear on my 1981 spider. However, in cooler temps I can upshift into 4th and sometimes it will stay, though not downshifting. My friend thinks it may be a viscosity issue. Changing transmission fluid (higher viscosity) may be an answer or is it a parts issue? Thanks.

 

[paintdudeluke]

maybe it pops out easier when the oil is thinner, but it sounds lie a bent shift fork or maybe just the bushing at the bottom of the shifter is worn out and causing it. Any noise or difficulty engaging? A bad shift recently that whacked it a little? Does it push out even when you try to manually hold it in? Does it pop out when under acceleration or only when you let off?

 

[SalF2]

4th gear only works, briefly, upshifting, then starts to rattle so I shift to 5th. So I go 1st, 2nd, 3rd, 5th. Works fine. Will be working on trans. soon. Spoke with Csaba from Autoricambi. He thinks might be worth working on all gears since car has 114,000 miles. Thanks for your help.
S

 

[F123C]

In the past I worked on a lot of these type gearboxes fitted to the 124 Coupe model ( same g/box). There are a number of things that can cause the problem you describe, all require stripping the gearbox to correct . The only thing that might cause this problem that can be accessed with the transmission in the car is the detent mechanism,(i.e the ball bearing and spring arrangement). This is located on the side of the gearbox main (ribbed) casing just before the tailhousing, its under a metal plate about 2 inches long with rounded ends held on by 2, 8 mm nuts or bolts (13mm wrench size). You may need to drop the rear of the gearbox down for access. Under this plate there are 3 springs holding 3 ballbearings against notches in the selector shafts. When a gear is selected, a ball bearing is pushed into one of these notches to hold the gear in engagement until the gearlever is moved to select another gear.The ball for 3rd/4th gear could be sticking?
However this problem would probably also affect 3rd gear as well so its a long shot! Its likely that some damage has been caused by the jumping out of 4th gear anyway so as your contact Csaba has said a gearbox strip and overhaul is best.
Re: trying a different viscosity (thickness) of oil, I don't see this helping, if you go thinner, the gearbox will likely be noisier, if you go thicker, the synchromesh action may be adversly affected. I think you problem is a mechanical one not an oil one.

Al.