3500S reverse issues

[Bunji]

Hi all. Relatively new to owning a 3500S down here in NZ within the last few months.

Purchased knowing the gearbox was tired and noisy in the forward gears bar top, which I understand is fairly common for the standard box.

Shifting up in the forward gears is fine, as is top down to 3rd, and 2nd to 1st. Down across the gate from 3rd to 2nd is ok perhaps half the time, and difficult to engage 2nd the other half.

Reverse is noisy also, but has recently started to jump out of gear.

From reading previous posts on the forum, I understand this could be caused by a number of things from simple(ish) fixes to internal issues.

The plan is to get the car up on a hoist to look underneath with my mechanic to try and identify if it's a selector issue vs internal.

Any advice on the best way to proceed with troubleshooting is appreciated.

The longer term plan is to get this box rebuilt, but id like to be able to use the car over the next 6 months of our summer and autumn.

 

[jp928]

BTDT....mine was caused by a sagged rear gearbox mount preventing full selection. If the acorn on the bottom of the lever is worn or gone that could also prevent full selection travel. I did manage to install a new rear mount without pulling the box, but its not easy. Check my project for pics.

 

[JoshW]

I’ve had issues with mine since I’ve had it, used to always pop out of reverse (always happened reversing into my garage which is uphill) and would struggle to get into 3rd.
I replaced the acorn and spherical bush which made a minor difference (maybe a placebo). The selector housing already had some bushes/blocks machined in for the selector rod, but the selector finger looked worn down and had some brittle plastic on the end which was destroyed. I’m not sure if this was for an earlier car and mines a later car as I know there’s 2 types.
I haven’t had chance to take the car for a spin since putting it all back together but I can select every gear while stationary and I’ve reversed the car into the garage without it popping out of gear.

 

[harveyp6]

Difficulty engaging second on the 3-2 downshift can be the rear flange nut loose. Does the Speedo needle waver?
Check all the remote bushes, and the gearlever, and the selector striker lever. After that the reverse light switch, and the reverse selector rod stop bolt can cause it to jump out of reverse, as can incorrect positioning of the reverse selector fork inside the box.

 

[Bunji]

Difficulty engaging second on the 3-2 downshift can be the rear flange nut loose. Does the Speedo needle waver?
Check all the remote bushes, and the gearlever, and the selector striker lever. After that the reverse light switch, and the reverse selector rod stop bolt can cause it to jump out of reverse, as can incorrect positioning of the reverse selector fork inside the box.

Can all of these be checked underneath?

I would say the speedo needle wavers slightly but not overly so.

 

[Bunji]

I’ve had issues with mine since I’ve had it, used to always pop out of reverse (always happened reversing into my garage which is uphill) and would struggle to get into 3rd.
I replaced the acorn and spherical bush which made a minor difference (maybe a placebo). The selector housing already had some bushes/blocks machined in for the selector rod, but the selector finger looked worn down and had some brittle plastic on the end which was destroyed. I’m not sure if this was for an earlier car and mines a later car as I know there’s 2 types.
I haven’t had chance to take the car for a spin since putting it all back together but I can select every gear while stationary and I’ve reversed the car into the garage without it popping out of gear.View attachment 27682

Did you have to drop the box down to replace the selector finger?

 

[harveyp6]

Box has to be dropped down to fit the selector striker lever. Don't drop it too far otherwise the RH rocker cover will break the petrol reserve tap. The only thing that I listed that needs the box to be removed is the internal reverse selector fork adjustment. When you get the top off the box, a lot of the time you find the gears are worn.

 

[JoshW]

Did you have to drop the box down to replace the selector finger?

Followed this post by Harveyp6:

Exhaust front pipes and propshaft off, disconnect speedo cable and reverse light wires, remove air cleaner and horizontal throttle rod, disconnect top hose at rad, then turn the fan so that the widest gap between two blades is at the bottom, that way the fan will clear the rad there, and the top blade will hit the fan shroud as you lower the engine back so you don't tilt the engine too far. If you do go too far back it will break the petrol reserve tap. Then support the back of the box, remove the gearbox mounting and lower it down. Then reach over the top of the box from the back to remove the remote. And if I haven't forgotten anything, that's it.

 

[Bunji]

Thanks all for your replies. Regarding visibility from underneath to try and diagnose the cause(s), I'm struggling to picture how one can see the selector striker and remote bushes. Wouldn't the view be blocked by the box itself ?

 

[JoshW]

Thanks all for your replies. Regarding visibility from underneath to try and diagnose the cause(s), I'm struggling to picture how one can see the selector striker and remote bushes. Wouldn't the view be blocked by the box itself ?

Selector finger can be seen through the transmission tunnel under the drivers side carpet big rubber bung/inspection hole, think it can be seen best when the gear lever is selecting reverse as it’ll be closer to the hole. I’m sure you’d be able to see the selector bushes underneath, as soon as I was under mine I could tell it had been modified with some poly blocks

 

[harveyp6]

The selector mechanism is mounted to the top of the box, but all the important bits to look at are behind the box itself. If you know what you're looking at you can diagnose everything from underneath.

 

[Bunji]

With the help of a friend I've investigated the selector striker and underneath the car.

It appears there are a few issues

1) lots of slop with the selector striker. I'll try and upload a video, here is a still shot as best as I could get from the video.



2) It appears both bushes 591353 are missing from the selector arm:



3) Rear box mount gap is only around 5mm, I understand from a previous thread of jp928's that it should be closer to 20mm.



4) The acorn and spherical bush still need investigation.

 

[jp928]

In my experience the rear mount that low will inhibit full travel of the lever when going for reverse, as it did for me. I changed the mount in place without box removal, but it took quite a while to finish. The mount is the same as a P5 rear spring rear mount, and for a P6 BW 65 . These days they are made by drilling the steel triangle and bolting double studded bobbins to it, rather than welding a special bobbin. If you can get 2 bobbins you might repair your old mount?

 

[Bunji]

In my experience the rear mount that low will inhibit full travel of the lever when going for reverse, as it did for me. I changed the mount in place without box removal, but it took quite a while to finish. The mount is the same as a P5 rear spring rear mount, and for a P6 BW 65 . These days they are made by drilling the steel triangle and bolting double studded bobbins to it, rather than welding a special bobbin. If you can get 2 bobbins you might repair your old mount?

I was planning to purchase the whole triangle and bobbins from Wadhams as below. Unless there are quality issues with that? I'm down in NZ so parts supply is somewhat harder. If it's the same as the auto box P6 I might be able to find a good used or NOS one locally.

 

[harveyp6]

It's the same shape as the P5B rear spring mounting, but I'm sure the gearbox mounting is smaller