Would anybody have any ideas as to why I am having intermittent gear box jamming can't get into 1st, 3rd or 5th on my Peugeot 307 2006?

check the linkage on the gearbox, somethimes they come loose

have you checked the level of the transmission oil ?

. If the box has been performing as expected and this has just started ( manual box ) I would be checking the gear selector either on the side of the box -- in the selector levers or in the cable operation. As the movement for all three gears is in a forward direction and you may have a cable operation to select the gears check the cable for failure. It the selection is at the base of a steering column then check for failed bushes and if it is a top mounted lever directly into the gear box then check that the pin that pivots the gear lever is tight and not worn. I am reasonable confident that the problem is in the selection mechanism and not in the box proper.

If the clutch is a problem you will have difficulty selecting 1st only as the gears would be spinning from the engine revs.. I would say that the front input shaft (clutch shaft) bearing is failing allowing miss alignment of the synchros and not allowing proper engagement of the gears synchro rings. It means removal and repair to the gear box so the clutch can be inspected while the box is out.

Great to hear. Good Job!

how about the 4th gear?

if its fine in the 4th gear, its your transmission. if you have automatic I would try to replace the auto trany computer if you could find it at the wrecking yard.

im not telling you what to do because it could be a bad transmission and an easy fix but I cant tell without looking at it , but if its a hard fix just go to a reliable junkyard and get another

J1/S1 Found in: Integra XSI/RSI (DA6) Type: Cable 1st: 3.230 2nd: 2.105 3rd: 1.458 4th: 1.107 5th: 0.848 R: 3.000 FD: 4.400 Y1 Found in: CRX/Civic (optional LSD) Type: Cable 1st: 3.166 2nd: 2.052 3rd: 1.416 4th: 1.103 5th: 0.870 R: 3.000 FD: 4.266 YS1 Found in: Integra 92-93 XSI/RSI (DA6, DA9) Type: Cable 1st: 3.307 2nd: 2.105 3rd: 1.458 4th: 1.107 5th: 0.880 R: 3.000 FD: 4.400 S80 Found in: Integra Type R 98+ (LSD) Type: Hydraulic 1st: 3.230 2nd: 2.105 3rd: 1.458 4th: 1.034 5th: 0.787 R: 3.000 FD: 4.785 S80/Y80 Found in: JDM SiR-G (optional LSD) Type: Hydraulic 1st: 3.230 2nd: 1.900 3rd: 1.360 4th: 1.034 5th: 0.787 R: 3.000 FD: 4.400 Y21/Y80/S80/S4C Found in: JDM 96-97 Integra R(LSD) JDM Civic R [EK9](LSD) JDM Civic SiR [EK4, EG6] JDM CR-X DEL SOL SIR (EG2)(optional LSD) USDM DEL SOL VTEC (EG2)(OPTIONAL LSD) Type: Hydraulic 1st: 3.230 2nd: 2.105 3rd: 1.458 4th: 1.107 5th: 0.848 R: 3.000 FD: 4.400