Hi! I got a 69 riviera GS, which has the 3.42 posi rear end i believe. I cant figure out the stamp whether it's "PY" or "PX" but counting the turns it was pretty close 3.5 turns in drive shaft with one turn on tires. But the problem is that my car is screaming! It has 215/70R15 tires and it's less than 30 mph speed when i got the third gear so it feels absolutely terrible to drive on a highway... what options do i have? i got one 8.2/8.5 BOP rear with 2.73 gears from 67 pontiac and i planned on putting that instead. looking that rear next to my current rear there is a lot of fab that needs to be done and i am not sure will my riv's brakes even fit to that rear. riv's rear is a lot tougher in every way (9 3/8"??) and it's a three link with panhard. Pontiac rear is a triangular 4 link... i live in finland, so i cant get the rear from junkyard. Taller tires (235/75R15) wont be long enough for my cruising riviera. it's got fully overhauled stock 430 with ez-efi, so i am not planning on hitting the 1/4 mile Is the 3.07 longest gear for my rear? will some other rear got longer gears and almost direct fit? Propably 3.07 + taller tires would do the trick. about 20% longer gears total (8% tires, 11% rear) Cheers EDIT: Tranny is th400 will any over drive tranny fit directly? that could be option too and it doesn't need to hold up too much power.
People are always looking for 3.42 gears with the 9 3/8" ring gear. You can trade someone for a lower number gear, but be careful with used gear sets. There was some talk about having some 9 3/8 sets remade, but I never heard that it took place. Check with Brian Trick or Jim at JD Race on this Board. Also be careful because there are 9 3/8 BOP gear sets which are not the same as yours. They were used in post 70 Riviera's. Your gears are Buick only.
And to add, you can't just trade the 3.42:1 gears for a 3.07:1 or 2.78:1 set (often found in '67-'70 Electra) because the carriers are different in regards to ring gear spacing. To make that big of a numerical jump, you're going to need gears+carrier from a donor car. Devon
The missing third gear was the thing i thought first but with selecting 1 and 2 gears from shifter they both exist. And i have had a vacuum leak because of the turning head lights, that causes me to drive 40 mph with 2nd gear. A lot of rpm going in that way also feeling the gear shifts is easy because it shifts pretty hard. I can the gears for a second time and i can also check the rpm on driving 60 mph so that you can tell me is it normal or messed up. So if i want longer gears get the whole rear? which cars have bolt on or almost bolt on rear swap? is my posi stuck on my 3.42 or can it be swapped to 3.07 or 2.78? What about the transmission? OD trannys like th700r4 or th200r4 bolt on swaps? or should i forged that also?
Stock they may last for a little while. But stock they were never designed to handle so much torque in a heavy vehicle. They can be built with heavy duty parts that will allow these transmissions to last. Adding a Gear Vendors overdrive to your existing TH400 is another option. http://www.gearvendors.com/
The shorter tires (26.85") are part of the problem. The right tires should be 2" taller (28.88") and drop the RPM at 60 MPH by 200 RPM. Right now, you should be at about 2700 RPM at 60 MPH. As mentioned, no one makes new gear sets for the rear in your car. Swapping an entire rear into your car is not a good option and certainly the most difficult. You should be able to trade someone your 3.42 gears for a lower gear set as many desire the 3.42's here in the states. I would put up a thread in "Parts Wanted", or contact Monzaz here on V8. He may have a gear set for you, not sure. Ordinarily, I would recommend a Gear Vendors Overdrive, https://www.gearvendors.com/ The problem is, the Riviera has an X frame, and I don't think you have enough room for the Gear Vendors unit. Swapping in a 200 or 700R4 will not be the answer as these units in stock form will not live long in a heavy car like the Riviera. They will need modification to last.
If you need higher gears it should not be too hard to find someone with a RIV that wil ltrade with you ... That should not be a problem. Jim
Ok thanks for everybody for helping me. Trading the 3.42 is not an option for me because of the distance. I'll open a thread to parts wanted section for set of gear and carrier. See if someone will send to Finland or wait for a container to float in here. first aid will be the tires. I wonder how funny it wil look if i get only new rear tires
I did the test and my rpm was 1900 to 1950 when i drove 40 mph on gps. so its going to be around 3000 on 60 mph.
I'm not really understanding why you feel you have to drive with a vacuum leak and why that would limit you to 40 MPH. If there is a vacuum leak in the headlight system, then block it off at the source so you can drive without the leak. Is the transmission shifting through all 3 gears. You should be able to feel the 1-2 shift and the 2-3 if you pay careful attention. With 26.85" tall tires and 3.42 gears, you should be at around 1800 RPM at 40 MPH, and 2700 RPM at 60 MPH unless the transmission isn't shifting into 3rd gear, or the transmission is slipping.
I quess i was unclear. Sorry i dont speak english as my native language. But i was trying to say that i have driven my car once with vacuum leak and then it didnt change to third gear. That was for like 5 miles. I have all three gears dont worry about that. I will hunt the 2.78 gears + carrier and be happy.
There is something else going on with your transmission. The final gear of a TH-400 is 1:1, even with a 3:42 rear axle you should have less RPM at 96 KPH. You say the transmission is shifting into 3rd gear and stays in 3rd gear, so the only thing I can think of is a slipping torque converter. Instead of changing the rear axle (or just the gears), replace the torque converter.
might be the tc but i don't think so. at least i dont hope so I'll check that there is right amount of fluid and hit the 60 mph next time. i think that the wrong tire size is enough. atleast i dont feel like i have loss in acceleration and my tranny fluid looks like new... smokes both tires when i need
