Renault Un1-13 throwback through gear shift

Evening all,

After a bit of advice, I have just finished my car except for paint and have been trying to get the miles in to iron out any potential issues, unfortunately I have found one that now needs ironing out...

So far I’ve driven around 150 fairly sedate miles in the car and they have been largely problem free, mainly just small tweaks and tightening everything multiple times. However on my last drive I developed an issue I think is gearbox related, I have developed throwback through the gear shift, it is only noticeable under load so I can drive around at 25-30 mph with no real issue but as soon as I accelerate beyond that the gear shift noticeably throws forwards and backwards and the car surges, there is also a knocking sound from the read, something is not right. I have put the car up on ramps and checked all mountings between the gearbox and the engine and the engine and gearbox mounts to the car, all seem fine, next I’ve removed the driveshafts and checked them and the CV’s and again all seems fine so now I’m stumped.

The gearbox was reconditioned by Chris Cole about 6 years ago but has only done 150 miles since (yes I filled it with oil), I have asked Chris but he was not sure what it could be either, he did say he would take a look at it but as he’s so busy it would not be until after the summer and I’d really like to get this sorted before then as I have the paint booked!

I appreciate its not much to go on and I will try and get out with a passenger to assist in the diagnosis too.

Any suggestions as to what it could be will greatly appreciated, fingers crossed for an easy fix but I’m sure that’s wishful thinking...


Howard Jones

Do you have engine mounts that are rubber or some other material in between steel plates? If so take them off the car and check them for delamination. This is hard to see when the engine is setting on them. Also I had the Renault rear transaxle mounts crack on one side. That was a similar symptom as yours. Again had to find but it was there.
Hi Paul,
I’m presuming that you’ve got a rod operated gearshift on a standard Southern GT chassis if so, I’ve seen this issue before.

Basically there’s insufficient fore/aft stiffness in the standard engine & transmission mounting bushes and as you apply the load to the wheels the engine/transmission is reacting the load and moving around. The rod shifter mechanism will then show this movement.

You’ve a couple of options:
1 - fit stiffer mounting bushes, I presume that you’ve got standard Mustang engine mounts which are really soft
2 – Fit a fore/aft tie-bar between the transmission and the chassis to stop movement in this direction



Hi Paul
I have a different mounting bracket for my UN1 as mine did not have the fixing holes on the sides, mine bolts to the rear of the gearbox casing and it looked a lot sturdier than the side mountings, let me take a photo when I get back tomorrow, just working in a cold computer room in Chippenham living that dream :)

Ian Anderson

Lifetime Supporter
Left hand engine mount rubbers have come detached / or torn
Under acceleration the left side of the engine lifts and it then swivels around the compressed right hand engine mount.
This in turn moves the transaxle to the left and you get the movement on the gear stick

That would be my guess - I had the exact problem when i tore my engine mount at Santa Pod really quite alarming the amount of movement on the slow drive home from the Pod!

Thanks for the replies everyone, I also spoke to Mick today and he thought the same thing, so this evening I’ve spent a bit of time jacking up the car on both the gear box and the engine but unfortunately I can’t see anything wrong, mounts all look solid to me...
Mick also had the good idea of ratchet strapping the gear box to the chassis which I will be hopefully trying tomorrow night to see if they stops it, fingers crossed but failing that I’m gonna stick a GoPro under the rear clip at the weekend and see what I can see!